Methods of formulating a cement composition
A method of cementing a wellbore in a subterranean formation comprising formulating a non-Portland base cement composition that may be suitable for long-term zonal isolation, preparing the non-Portland base cement composition, determining a density of the non-Portland base cement composition and adjusting the density as needed to within an optimized density range to form a first optimized cement composition, determining the percentage of tensile strength relative to compressive strength of the cement composition, and placing the optimized cement composition in the wellbore.
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BACKGROUND1. Technical Field
The present disclosure generally relates to well cementing. More specifically, this disclosure relates to a methodology for formulating a rapid-setting non-Portland cement composition to achieve long-term zonal isolation.
2. Background
Zonal isolation refers to the isolation of a subterranean formation or zone, which serves as a source of a natural resource such as gas, oil, or water, from other subterranean formations. To achieve isolation of a subterranean formation, a well bore is typically drilled down to the subterranean formation while circulating a drilling fluid through the wellbore. After the drilling is terminated, a string of pipe, e.g., casing, is run in the wellbore. Next, primary cementing is typically performed whereby a cement slurry is placed in the annulus and permitted to set into a hard mass, thereby attaching the string of pipe to the walls of the wellbore and sealing the annulus. Subsequent secondary cementing operations such as squeeze cementing may also be performed.
Conventional Portland cement based slurries have been used to prepare cement sheaths employed in wellbore servicing operations such as long term zonal isolation. However, there are often challenges to the use of Portland cement for long term zonal isolation. For example, one challenge to the use of Portland cement includes long wait on cement (WOC) times. WOC time is usually defined as the time for which a drilling rig may have to suspend active wellbore construction operations while waiting for a cement slurry that has been placed in the wellbore to develop sufficient compressive strength to allow operations to recommence. With well designs becoming more complex and the environments in which they are constructed becoming more challenging, long WOC times may increase the costs of well construction. Additionally, long WOC times may also increase the possibility of allowing the undesirable influx of fluids prior to the transition of the cement from slurry to solid form. Such fluid influx may compromise zonal isolation which may lead to increased operating cost and potentially negatively impact other factors such as health, safety and the environment. Other design criteria to be considered include the thermal stability of the cement sheath formed and the slurry rheology.
Thus, it would be desirable to develop a methodology for designing a cement composition that overcomes some of the challenges associated with the use of Portland based cement slurries in wellbore servicing operations.
SUMMARYDisclosed herein is a method of cementing a wellbore in a subterranean formation, comprising formulating a non-Portland base cement composition that may be suitable for long-term zonal isolation, preparing the non-Portland base cement composition, determining a density of the non-Portland base cement composition and adjusting the density as needed to within an optimized density range to form a first optimized cement composition, determining the percentage of tensile strength relative to compressive strength of the cement composition, and placing the optimized cement composition in the wellbore.
For a more complete understanding of the present disclosure and the advantages thereof, reference is now made to the following brief description, taken in connection with the accompanying drawings and detailed description:
It should be understood at the outset that although an illustrative implementation of one or more embodiments are provided below, the disclosed systems and/or methods may be implemented using any number of techniques, whether currently known or in existence. The disclosure should in no way be limited to the illustrative implementations, drawings, and techniques illustrated below, including the exemplary designs and implementations illustrated and described herein, but may be modified within the scope of the appended claims along with their full scope of equivalents.
An embodiment of a method 100 for formulating a non-Portland cement composition that may be suitable for long-term zonal isolation of a subterranean formation is shown in
It is to be understood that herein references made to adjusting a cement property refer to adjustments made to a wet cement or cement slurry composition. Herein references made to determining the mechanical properties of a cement composition refer to evaluating the properties of the set cement composition. For example, a portion of the cement slurry may be used to prepare at least one specimen of the set cement which is in turn used to determine one or more mechanical properties. Herein an “optimizing range” refers to a range of acceptable values a particular parameter may assume. The “optimizing range” may be a particular range of numerical values the parameter may adopt or may be a value relative to that of another cement composition (e.g., Portland cement) as indicated. In cases wherein the value is relative to that of a Portland cement, it is to be understood that the parameter being discussed was measured for the Portland cement in accordance with the referred to ASTM method.
Referring now to
The method 100 may then proceed to block 110 where a non-Portland base cement composition (NPBC) is formulated. The NPBC may be formulated so as to impart a baseline set of physical properties determined by evaluation of the subterranean formation as previously described, block 105. Such NPBCs may be formulated so as to function in support of a casing in a wellbore, to isolate a subterranean formation, or both and shall neither exceed the fracture gradient of the formation nor allow influx of formation fluids during the cementing phase.
In an embodiment, the NPBC comprises a Sorel cement. In various embodiments, Sorel cements comprise a metal oxide such as magnesium oxide, and a soluble salt such as a chloride or phosphate salt. In an embodiment, the NPBC comprises a Sorel cement wherein the Sorel cement comprises a magnesia based cement. A discussion of various magnesia-based cements can be found in Lea's Chemistry of Cement and Concrete by Peter Hewlett: Fourth Edition, pages 813-820: 1998: Elsevier Publishing which is incorporated by reference herein.
The Sorel cement may comprise a metal oxide, alternatively an alkaline earth metal oxide, alternatively magnesium oxide. In an embodiment, the Sorel cement comprises MgO. MgO may be prepared by calcination of Mg(OH)2 as depicted in Reaction 1:
The calcination of Mg(OH)2 results in what is commonly referred to as “burned” MgO. Three basic grades of burned MgO are typically produced with the differences between each grade related to the degree of reactivity remaining after being exposed to a range of high temperatures. The original magnesium hydroxide particle is usually a large and loosely bonded particle. Exposure to thermal degradation by calcination causes the Mg(OH)2 to alter its structure so that the surface pores are slowly filled in while the particle edges become more rounded. This results in MgO with varying degrees of crystallinity and consequently varying degrees of reactivity. When the MgO is produced by calcining to temperatures ranging between 1500° C. to 2000° C., the MgO is referred to as “dead-burned” since the majority of the reactivity has been eliminated. Dead-burned MgO has the highest degree of crystallinity of the three grades of burned MgO. An example of a dead-burned MgO includes without limitation THERMATEK™ HT additive, which is commercially available from Halliburton Energy Services, Inc. A second type of MgO produced by calcining at temperatures ranging from 1000° C. to 1500° C. is termed “hard-burned” and displays an intermediate crystallinity and reactivity when compared to the other two grades of burned MgO. An example of a hard-burned MgO includes without limitation THERMATEK™ LT additive, which is commercially available from Halliburton Energy Services, Inc. The third grade of MgO is produced by calcining at temperatures ranging from 700° C. to 1000° C. and is termed “light-burned” or “caustic” magnesia. Light-burned MgO is characterized by a high surface area, a low crystallinity and a high degree of reactivity when compared to the other grades of burned MgO.
In an embodiment, the MgO for use in the Sorel cement comprises 100% dead-burned MgO (e.g., THERMATEK™ HT additive), 100% hard-burned MgO (e.g., THERMATEK™ LT additive), 100% light-burned MgO, or a combinations thereof. In other embodiments, the MgO for use in the Sorel cement comprises combinations of hard-burned MgO, light-burned MgO and/or dead-burned MgO. One of ordinary skill in the art with the aid of this disclosure may select the ratio of hard-burned MgO, light-burned MgO, and/or dead-burned MgO to achieve one or more user desired properties. For example, the MgO may comprise a combination of 90% to 80% dead-burned MgO and 10% to 20% light-burned MgO, alternatively the MgO may comprise a combination of 90% to 80% hard-burned MgO and 10% to 20% light-burned MgO.
In an embodiment, the Sorel cement comprises a soluble salt. The soluble salt may include a chloride salt, a phosphate salt, or combinations thereof. In an embodiment, the Sorel cement comprises a phosphate salt such as for example potassium dihydrogen phosphate, sodium dihydrogen phosphate, ammonium dihydrogen phosphate, or combinations thereof. In such embodiments, the ratio of MgO: phosphate salt may be from about 1:4 alternatively from about 1:3, alternatively from about 1:2, alternatively from about 1:1.
In an embodiment, the Sorel cement comprises a chloride salt. In such an embodiment, the Sorel cement may comprise an alkaline earth metal chloride, for example a magnesium chloride (MgCl2) such as magnesium chloride hexahydrate, MgCl2.6H2O. MgCl2.6H2O is well known and available from a wide variety of sources. A MgCl2.6H2O suitable for use in this disclosure includes without limitation C-TEK magnesium chloride salt, which is MgCl2.6H2O commercially available from Halliburton Energy Services, Inc. In an embodiment, the soluble salt may be incorporated into the Sorel cement as the solid material (e.g., C-TEK). Alternatively, the soluble salt may be dissolved in an aqueous solution to form a salt solution at least a portion of which may be used to prepare the Sorel cement. The concentration of the salt solution may be selected by one of ordinary skill in the art with the aid of this disclosure to meet the needs of the process. For example, the C-TEK may be dissolved in the aqueous solution to its saturation point. In an embodiment, the soluble salt may be dissolved in an aqueous solution and may have a concentration of from about 10 wt. % to about 70 wt. % by total weight of the aqueous solution, alternatively from about 20 wt. % to about 70 wt. %, alternatively from about 40 wt. % to about 67 wt. %.
In an embodiment, the Sorel cement is formed through contacting MgO of the type described previously herein with MgCl2.6H2O in the presence of other components to be described in more detail later herein. In such an embodiment, the Sorel cement may comprise metal oxide (e.g., MgO) and soluble salt (e.g., MgCl2.6H2O) present in a ratio of from about 2:1 to about 1:1 MgO:MgCl2.6H2O, alternatively from about 1.5:1 to about 1:1 MgO:MgCl2.6H2O, alternatively about 1:1 MgO:MgCl2.6H2O. Examples of Sorel cements comprising MgO and MgCl2.6H2O (e.g., C-TEK) include without limitation THERMATEK™ fluid invasion control treatment, which is commercially available from Halliburton Energy Services Inc.
In an embodiment, the NPBC comprises a retarder. The retarder may be a solid retarder or it may be dissolved in an aqueous solution (i.e., a liquid retarder). Retarders, also referred to as inhibitors, may be used to adjust the time required for setting of the slurry. Retarders suitable for use in this disclosure include without limitation polyphosphate salts such as sodium hexametaphosphate (technical grade granular), potassium magnesium phosphate hexahydrate, potassium magnesium hexametaphosphate, or combinations thereof. Other examples of set retarders suitable for use in this disclosure include boric acid and salts of boric acid such as sodium borate. An example of a retarder suitable for use in this disclosure includes without limitation R-TEK retarder, which is sodium hexametaphosphate commercially available from Deepearth Solutions. The sodium hexametaphosphate may be dissolved in an aqueous solution to form a liquid retarder. Liquid retarders and methods of making and using same are further described in U.S. patent application Ser. No. 12/217,950 filed Jul. 10, 2008, which is incorporated by reference herein in its entirety.
The NPBC may include a sufficient amount of water to form a pumpable slurry. The water may be fresh water or salt water, e.g., an unsaturated aqueous salt solution or a saturated aqueous salt solution such as brine or seawater. The water may be present in the amount from about 10 wt. % to about 200 wt. % by weight of cement (bwoc) wherein the cement comprises both the MgO and the soluble salt, alternatively from about 50 wt. % to about 200 wt. %, alternatively from about 50 wt. % to about 180 wt. %, alternatively from about 20 wt. % to about 60 wt. %, alternatively from about 30 wt. % to about 70 wt. % by weight of MgO.
Referring again to
Referring to block 125, the density may be adjusted by any means suitable for adjusting the density of a cement composition. One drawback to the use of Sorel cements is that the incorporation of additives is challenging due to the relatively low density of the slurry. In an embodiment, the density of the NPBC is adjusted using density-modifying additives (DMAs) such as weighting agents. Examples of DMAs suitable for use in this disclosure include without limitation barite, hematite, hausmannite, calcium carbonate, siderite, ilmenite, or combinations thereof. Barite is a nonmetallic mineral of barium sulfate (BaSO4) with a specific gravity range of from about 4.3 to about 5. Examples of barites include without limitation BAROID 41 and SWEEP-WATE, which are commercially available from Halliburton Energy Services, Inc. Hematite is a mineral form of iron (III) oxide (Fe2O3) with a specific gravity range of from about 4.9 to about 5.3. Examples of hematites include without limitation HI DENSE #3 weighting agent and HI DENSE #4 weighting agent, which are commercially available from Halliburton Energy Services, Inc. Hausmannite is a complex oxide of manganese containing both di- and tri-valent manganese (Mn2+Mn3+2O4) with a specific gravity of about 4.8. An example of hausmannites includes without limitation MICROMAX FF which is a weighting agent commercially available from Halliburton Energy Services, Inc.
Alternatively, the DMA comprises a quaternary amide, a quaternary amide ester or combinations thereof. In an embodiment, the DMA comprises an amidopropalkonium chloride with a chain length of greater than about C12, alternatively greater than about C13, alternatively greater than about C14. An example of a DMA suitable for use in this disclosure includes without limitation stearamidopropalkonium chloride. In an embodiment, the DMA is present in an amount of from about 0.05 wt. % to about 5 wt. % based on the total weight of the MgO, alternatively from about 0.05 wt. % to about 0.5 wt. %, alternatively from about 0.05 wt. % to about 0.4 wt. %. DMAs and methods of using same are disclosed in U.S. patent application Ser. No. 11/622,356 filed Jan. 11, 2007 and entitled “Methods of Servicing a Wellbore with Compositions Comprising Quaternary Material and Sorel Cements” which is incorporated by reference herein in its entirety.
Following adjustment of the density, the method 100 returns to block 115 where the density is again determined. Following determination of the density, the method 100 again proceeds to block 120 and the density is evaluated as to whether it falls in or out of spec. In an embodiment, the density of the NPBC is out of spec, and the method 100 proceeds to block 125 wherein the density is adjusted as previously described. The density adjustment, determination-evaluation loop represented by blocks 125, 115, and 120 continues iteratively as necessary to prepare an NPBC having a density in spec. Once the NPBC is found to be in spec at block 120, the method 100 proceeds to block 130, and the NPBC is hereinafter referred to as a first optimized cement composition (CC-1). Without wishing to be limited by theory, a CC-1 may have sufficient density that is able to suspend additives that may be included later herein to adjust the mechanical properties (e.g., Young's Modulus, Poisson's Ratio, etc.) of the NPBC.
At block 130, Young's modulus (YM) of the NPBC is determined. The YM, also termed elastic modulus, λ, is indicative of the elasticity of a material or the tendency of the material to reversibly or resiliently deform under an applied force. Young's modulus is represented by Equation (1)
λ=(F/A)/(x/1) (1)
where F is the applied force, A is the area to which the force is applied, x is the extension of the material when the force is applied and 1 is the original length of the material. In an embodiment, the elastic modulus of the CC-1 is determined in accordance with ASTM D 3148-02.
Following determination of the YM, the method 100 proceeds to block 135 and YM of the CC-1 is evaluated as to whether it is in an optimizing range. In an embodiment, the optimizing range for YM is from about 1,000 psi to about 3,000,000 psi, alternatively from about 1,500 psi to about 1,500,000 psi, alternatively from about 5,000 psi to about 1,000,000 psi, alternatively less than about 1,000,000 psi. When YM of the CC-1 is out of spec, the method 100 proceeds to block 140 wherein YM is adjusted. Alternatively, when YM of the CC-1 is in spec, the method 100 proceeds to block 145.
Referring to block 140, YM may be adjusted by any means suitable for adjusting the YM of a cement composition. Methods of adjusting the YM of a cement composition are known to one skilled in the art with the aid of this disclosure. For example, YM may be adjusted using modulus-modifying additives (MMA) such as elastomers and rubbers.
In an embodiment, the MMA is any polymer that is normally regarded as elastomeric such as for example and without limitation polyisoprene, polybutadiene, polyisobutylene, polyethers, polyesters, etc. Alternatively, the MMA is any polymer that is normally regarded as thermoplastic as for example and without limitation polystyrene, poly(methacrylate), isotactic polypropylene, polyurethane, dienes such as butadiene, isoprene and hexadiene, and/or monoolefins such as ethylene, butenes, and 1-hexene, or combinations thereof. Alternatively, the MMA may be a copolymer formed by combinations of monomers used in production of the aforementioned materials.
The MMA may also include polymers comprising aromatic hydrocarbon monomers and aliphatic dienes. Examples of suitable aromatic hydrocarbon monomers include without limitation styrene, alpha-methyl styrene, and vinyltoluene. The MMA may be a crosslinked or partially crosslinked material such as a styrene butadiene block copolymer, alternatively a styrene butadiene styrene (SBS) block copolymer, alternatively a hydrogenated form of an SBS having radial or linear polymer chain architecture.
In an embodiment, the MMA is a thermoplastic elastomer having a tensile strength by itself in the range of from about 500 psi to about 4000 psi, recoverable elongation of from about 200% to about 1000% and thermostability in the temperature range of from about 30° F. to about 500° F. In an embodiment, the thermoplastic elastomers may be added to CC-1 in an amount effective to adjust the YM of CC-1 to within the optimizing range. Such thermoplastic elastomers may be present in an amount of from about 5% to about 50%, alternatively from about 5% to about 30%, alternatively from about 5% to about 20%, all based on percentage by weight of the cement (% bwoc). Examples of MMAs suitable for use in this disclosure include the thermoplastic elastomers sold as WELLLIFE 665, FINAPRENE 411, FINAPRENE 435, FINAPRENE 401, and FINACLEAR by Total Petrochemical USA, Inc. or as KRATON products by Kraton Polymers. In an embodiment, the MMA (e.g., WELLLIFE 665) has about the physical properties set forth in Table 1.
In an alternative embodiment, the MMA is a rubber present in an amount effective to adjust the YM of CC-1 to within the optimizing range. Examples of suitable rubbers include, the natural rubber (cis-1,4-polyisoprene) and most of its modified types; synthetic polymers including styrene/butadiene rubber; cis-1,4-polybutadiene rubber, or blends thereof with natural rubber or styrene/butadiene rubber; high styrene resin; butyl rubber; ethylene/propylene rubbers; neoprene rubber; nitrile rubber; cis-1,4-polyisoprene rubber; silicone rubber; chlorosulfonated rubber; polyethylene rubber; epichlorohydrin rubber; fluorocarbon rubber; fluorosilicone rubber; polyurethane rubber; polyacrylic rubber and polysulfide rubber. Such rubbers may be used either in the vulcanized or unvulcanized form.
Other copolymers that can be employed as MMAs include without limitation block copolymers of various olefins as for example ethylene/propylene copolymers wherein the ethylene block segments are generally considered elastomeric in nature and the polypropylene segments are generally considered semi-crystalline. Various elastomers and rubber compositions suitable for use as MMAs are disclosed in U.S. Pat. Nos. 5,688,844 and 5,293,938, each of which is incorporated by reference herein in its entirety.
Following adjustment of the YM at block 140, the method 100 returns to block 130 and the YM of the CC-1 is again determined. Following determination of the YM, the method 100 again proceeds to block 135 and the YM is evaluated as to whether it falls in or out of spec. In an embodiment YM of the CC-1 is out of spec, and the method 100 proceeds to block 140 wherein the YM is adjusted as previously described. This YM adjustment-determination-evaluation loop represented by blocks 140, 130, and 135 continues iteratively as necessary to prepare a cement composition having an YM in spec. Once the YM is found to be in spec at block 135, the method 100 proceeds to block 145.
At block 145, it is determined whether the CC-1 has been adjusted at block 140 as described previously. If so, such would indicate that the composition of the CC-1 has been altered (referred to as the adjusted CC-1), and therefore the method 100 returns to block 115 to determine the density of the adjusted CC-1 and subsequently to block 120 to evaluate whether the density of the adjusted CC-1 remains in spec. Where the density of the adjusted CC-1 is not in spec, the method 100 proceeds through blocks 125, 115, and 120 wherein the density is readjusted, redetermined, and reevaluated until the density falls within spec, as described previously. The method 100 then proceeds through blocks 130 and 135 wherein the YM of the adjusted CC-1 is determined and evaluated as previously described. In an embodiment, the YM of the adjusted CC-1 is not in spec and the method 100 proceeds through blocks 140, 130 and 135 wherein the YM is readjusted, redetermined, and reevaluated until the YM of the adjusted CC-1 again falls within spec, as described previously. In some embodiments, adjustments, determinations and evaluations of the density and/or YM of adjusted CC-1 continue iteratively as described until both values are in spec and no further adjustments are made, allowing the method 100 to proceed from block 145 to block 150. The cement composition at block 150 having the density and YM in spec is hereafter referred to as a second optimized cement composition (CC-2). Without wishing to be limited by theory, a CC-2 having a YM in the optimizing range may be sufficiently resistant to deformation such that the cement composition is able to withstand the cyclic stresses experienced over the life of the structure to which the composition provides support.
Following preparation of the CC-2, the method 100 proceeds to block 150 wherein Poisson's ratio (PR) is determined PR refers to the ratio of transverse contraction strain to longitudinal strain in the direction of stretching force and is represented by Equation (2):
v=εtransverse/εlongitudinal (2)
where v represents PR and ε represents strain as defined by the change in length divided by the original length. In an embodiment, Poisson's ratio (PR) of the CC-2 is determined in accordance with ASTM D 3148-02 (Standard Test Method for Elastic Moduli of Intact Rock Core Specimens in Uniaxial Compression).
Following determination of PR, the method 100 proceeds to block 155 wherein the PR of the CC-2 is evaluated as to whether it falls within an optimizing range. In an embodiment, the optimizing range for the PR is from about 0.05 to about 0.40, alternatively from about 0.08 to about 0.25, alternatively from about 0.1 to about 0.2, alternatively greater than about 0.2. When the PR of the CC-2 is out of spec, the method 100 proceeds to block 160 wherein the PR is adjusted. Alternatively, when the PR of the CC-2 is in spec, the method 100 proceeds to block 165.
Referring to block 160, the PR may be adjusted by any means suitable for adjusting the PR of a cement composition. Without wishing to be limited by theory, cement compositions having a PR in the optimizing range may have the ability to sustain cyclic stresses without significant volume changes and thus are suitable for long-term zonal isolation. Methods of adjusting the PR of a cement composition are known to one skilled in the art with the aid of this disclosure. For example, the PR may be adjusted using Poisson's ratio modifying additives (PRMA). Examples of suitable PRMAs are known to one skilled in the art with the aid of this disclosure and include without limitation flexible, compressible beads and resilient materials such as graphite carbon, liquids, non-aqueous fluids, solids, gases and the like. The resilient material may have a thermal expansion coefficient equal to or greater than about 1×10−4 K−1.
In an embodiment, a CC-2 having a PR in the optimizing range is formed by the inclusion of an effective amount of flexible, compressible beads. Flexible, compressible beads as used herein refer to beads that may expand and contract without adverse effect to the structure of the bead in response to changes in pressure and/or temperature. Any suitable flexible, compressible bead that may expand and contract and that is compatible with a cement (i.e., chemically stable over time upon incorporation into the cement) may be combined with the cement to adjust its PR. In an embodiment, the flexible, compressible beads may be substantially hollow objects filled with fluid, such as gas. Alternatively, the fluid inside the flexible, compressible beads is air, carbon dioxide, an inert gas such as nitrogen, or an organic liquid with a low boiling point such as n-butane, isobutane or pentane. In an embodiment, the flexible, compressible beads have a diameter of about 6 to 150 micrometers at 25° C. and atmospheric pressure.
In an embodiment, the flexible, compressible beads have a substantially uniform, flexible outer wall comprising of one or more elastomeric materials or polymers. The temperature at which the elastomeric material melts or becomes so soft that it loses its ability to contain the fluid and/or expand and contract may be higher than the temperature in the well bore, which may range from about 120° F. to about 400° F. In an embodiment, the elastomeric material may be a styrenic polymer, alternatively, a copolymer of methylmethacrylate and acrylonitrile or a terpolymer of methylmethacrylate, acrylonitrile, and vinylidene dichloride. Without limitation, a suitable flexible, compressible bead composed of this copolymer and this terpolymer is sold as EXPANCEL by Akzo Nobel, Inc. Several grades of EXPANCEL beads are available and may be selected depending upon the degree of expansion, the physical state, and the temperature range for a given application by one skilled in the art. Without limitation, other examples of materials that may be used to form the flexible wall include a styrene-divinylbenzene copolymer and polystyrene. Hollow polystyrene beads are available from many polystyrene suppliers, such as Huntsman Corporation of Houston, Tex. (sold as Expandable Polystyrene Grade GRADE 27, GRADE 51, or GRADE 55) and BASF Corporation of North Mount Olive, N.J. (sold under the tradename STYROPOR). The flexible, compressible beads may be incorporated into the cement in a concentration of from about 1% to about 200% by weight of the cement (bwoc), alternatively from about 2% to about 100%, and alternatively from about 5% to about 50%.
In an embodiment, the PRMA is a resilient material. Herein resilient materials refer to materials that are able to reduce in volume when exposed to a compressive force and return back to about their normal volume (e.g., pre-compressive force volume) when the compressive force subsides. In an embodiment, the resilient material returns to about the normal volume (e.g., to about 100% of the normal volume) when the compressive force subsides. In an alternative embodiment, the resilient material returns to a high percentage of the normal volume when the compressive force subsides. A high percentage refers to a portion of the normal volume that may be from about 70% to about 99% of the normal volume, alternatively from about 70% to about 85% of the normal volume, and further alternatively from about 85% to about 99% of the normal volume. Such materials may be solids, liquids or gases. An example of such a material is a gas, such as nitrogen, air or hydrogen present in the form of foam bubbles. The volume of the gas phase needed to make a cement composition resilient may be in the range of from about 0.01% to about 40% by volume of the cement composition under downhole conditions. The gas phase may be incorporated in the cement composition by any means known to one skilled in the art with the aid of this disclosure. Alternatively, the gas phase may be incorporated by injecting appropriate volume of the gas. Alternately, the gas phase may be generated by the use of solid materials incorporated in the cement slurry that generate gases upon exposure to the cement slurry or under downhole conditions. An example of a suitable gas generating material includes the cement additive sold as SUPER CBL by Halliburton Energy Services. This material generates hydrogen gas upon exposure to cement slurries under downhole conditions. Other gas generating material compositions suitable for incorporation into cement slurries are described in U.S. Pat. Nos. 6,715,553; 6,722,434; and 6,858,566, each of which is incorporated by reference herein in its entirety.
Solid materials or particles which undergo reversible volume changes with changes in stress may also be used as a PRMA. Such resilient solids may have thermal expansion coefficients greater than about 1×10−4 K−1. Without limitation, examples of suitable resilient solids include natural rubber, elastomeric materials, styrofoam beads, polymeric beads, or combinations thereof. Natural rubber includes rubber and/or latex materials derived from a plant. Elastomeric materials include thermoplastic polymers that have expansion and contraction properties from heat variances. Examples of suitable elastomeric materials include without limitation a styrene-butadiene copolymer, neoprene, synthetic rubbers, vinyl plastisol thermoplastics, or combinations thereof. Without limitation, examples of suitable synthetic rubbers include nitrile rubber, butyl rubber, polysulfide rubber, EPDM rubber, silicone rubber, polyurethane rubber, or combinations thereof. In some embodiments, the synthetic rubber comprises rubber particles from processed rubber tires (e.g., car tires, truck tires, and the like). The rubber particles may be of any suitable size for use in a wellbore fluid. In an embodiment, the rubber particles are of a size from about 10 microns to about 20 microns. Without limitation, processing the rubber tires may include mechanically removing metal such as steel surrounding the inner core of the tire and thereafter shredding and grinding the tire into the desired particle size. In some embodiments, the PRMA and the MMA may be the same or different, and may be selected from any PRMA or MMA described herein.
In an embodiment, the PRMA is resilient graphite. Graphite has a laminar structure. Without being limited by theory, it is believed that the layers in such a laminar structure provide the graphite with the ability to reduce in volume upon exposure to a compressive force and thereby provide expansion volume in the annulus. For instance, as the compressive force is applied and increased, the layers become correspondingly closer together, which may result in a reduction in volume of the graphite. Upon alleviating such an applied compressive force, the layers may spread apart, which may result in an increase in volume of the graphite. In some embodiments, the graphite may return to about the volume it occupied before exposure to the compressive force.
Graphitic carbon-based materials generally are considered resilient if they have a resiliency of at least about 20% after compression at 10,000 psi. As used herein, the term “resiliency” refers to the percentage increase in sample volume after release of a compaction pressure and is defined by the following formula:
wherein ho is the height of a column of the material being tested under the compaction pressure and hr is the height of the column of the material being tested after the compaction pressure is released. A resiliency test procedure is described in U.S. Pat. No. 5,826,669, which is incorporated by reference herein in its entirety.
An example of a suitable resilient carbon-based material includes without limitation a carbon additive having a particle size distribution d50 of less than about 20 microns sold as DESULCO 9090 RGC by Superior Graphite. Other examples of suitable graphites include without limitation the loss circulation additives, sold as STEELSEAL and STEELSEAL FINE by Baroid Drilling Fluids. An example of suitable particles comprising elastomeric styrene butadiene block or random copolymers is a styrene-butadiene random block copolymer sold as FINAPRENE 411 by Total Petrochemicals Elastomers USA, Inc. The resilient material used as a PRMA may be present in the range of from about 0.5% to about 30% by weight of the total cement composition. In an embodiment, any non-aqueous fluid with a thermal expansion coefficient higher than 2×10−4 K−1 may be used as the PRMA. Such fluids may be liquids or gases under ambient conditions. These fluids may be used as aqueous emulsions. The volume fraction of such fluids in total cement slurry volume may be in the range of from about 0.002 to about 0.3.
In an embodiment, an effective amount of a resilient material is added to the cement composition such that the PR of the CC-2 is adjusted to an optimizing range. For example, graphite carbon may be added to an amount of from about 1 vol. % to about 50 vol. %, alternatively from about 10 vol. % to about 40 vol. % resilient material, further alternatively from about 20 vol. % to about 30 vol. % resilient material, and alternatively from about 22 vol. % to about 26 vol. % resilient material.
Following adjustment of the PR at block 160, the method 100 proceeds to block 150 and PR of the CC-2 is again determined. Following determination of the PR, the method 100 again proceeds to block 155 and PR is evaluated as to whether it falls in or out of spec. In an embodiment, PR of the CC-2 is out of spec, and the method 100 proceeds to block 160 wherein the PR adjusted as previously described. This PR adjustment-determination-evaluation loop represented by blocks 160, 150, and 155 continues iteratively as necessary to prepare a cement composition having a PR in the optimizing range. Once the PR is found to be in spec at block 155, the method 100 proceeds to block 165.
At block 165, it is determined whether the CC-2 has been adjusted at block 160 as described previously. If so, such would indicate that the composition of the CC-2 has been altered (referred to as the adjusted CC-2) and the density and YM of the adjusted CC-2 need to be rechecked and readjusted as needed to be in spec, as described previously. Where the CC-2 has been adjusted, the method 100 returns to block 115 to determine the density of the adjusted CC-2 and subsequently to block 120 to evaluate whether the density of the adjusted CC-2 remains in spec. Where the density of the adjusted CC-2 is not in spec, the method 100 proceeds through blocks 125, 115, and 120 wherein the density is readjusted, redetermined, and reevaluated until the density falls within spec, as described previously. The method 100 then proceeds through blocks 130 and 135 wherein the YM of the adjusted CC-2 is determined and evaluated as previously described. In an embodiment, the YM of the adjusted CC-2 is not in spec and the method 100 proceeds through blocks 140, 130, and 135 wherein the YM is readjusted, redetermined, and reevaluated until the YM of the CC-2 again falls within spec, as described previously. The method 100 then proceeds through blocks 145, 150, and 155 wherein the PR of the CC-2 is determined and evaluated as previously described. In an embodiment, the PR of the CC-2 is not in spec and the method 100 proceeds through blocks 160, 150, and 155 wherein the PR is readjusted, redetermined, and reevaluated until the PR of the CC-2 again falls within spec, as described previously. In some embodiments, adjustments, determinations and evaluations of the density, YM, and/or PR of the CC-2 continue iteratively as described until all three values are in spec and no further adjustments are made to the CC-2, allowing the method 100 to proceed from block 165 to block 170. The cement composition provided at block 170 and having the density, YM, and PR in spec is hereafter referred to as a third optimized cement composition (CC-3).
Without wishing to be limited by theory, a CC-3 having a PR in the optimizing range may be sufficiently ability to sustain cyclic stresses without significant volume changes such that the cement composition is able to withstand the cyclic stresses experienced over the life of the structure to which the composition provides support.
Following preparation of the CC-3, the method 100 proceeds to block 170 wherein percentage of tensile strength relative to compressive strength (TRC) of the CC-3 is determined by dividing the tensile strength (e.g., determined using a Brazilian Tensile Strength test) by the compressive strength of an unconfined sample and multiplying by 100%. Generally, the tensile strength of an unmodified Portland cement (e.g., base) is about 10% of its compressive strength, while the tensile strength of an unmodified Sorel cement (e.g., base) is from about 10% to about 15% of its compressive strength.
Herein the tensile strength is defined as the maximum longitudinal stress a material can withstand before tearing. Typically the tensile strength is envisioned as the forces required to pull apart the cement composition while the compressive strength can be envisioned as the force required to crush the cement composition. Cements typically have a low tensile strength when compared to the compressive strength and this may have important implications for the long-term zonal isolation since the stresses induced in a cement sheath by increased wellbore pressures are predominantly tensile in nature. For example, when processes such as stimulation treatments or fracturing are undertaken the cement sheath can have tensile stresses, which can occur indirectly through contact with the casing or directly through contact between the cement sheath and a fracturing fluid. The tensile strength of the CC-3 may be measured on a cylindrical sample having a 1″ width×2″ diameter or on a dog-bone shaped briquettes using a Brazilian Tensile Strength test in accordance with ASTM D3967-05.
Herein the compressive strength is defined as the maximum resistance of a material to an axial force. Within the limit of the compressive strength, the material becomes irreversibly deformed and no longer provides structural support and/or zonal isolation. The compressive strength of cement is recognized as a standard measure of cement quality and durability with high compressive strengths being an indicator of high quality. The compressive strength a cement formation attains is a function of both the cement maturity and the temperature at which setting occurs where the cement maturity specifically refers to the time the cement formulation is allowed to set. The compressive strength of the CC-3 may be determined in accordance with ASTM D 2938-95.
Following determination of the TRC, the method 100 proceeds to block 175 where the TRC of the CC-3 is evaluated as to whether it falls in an optimizing range. In an embodiment, the optimizing range for the TRC is from about 2% to about 20%, alternatively from about 4% to about 15%, alternatively from about 5% to about 12%, alternatively greater than about 10%, alternatively from about 15% to about 20%. When the TRC of the CC-3 is out of spec, the method 100 proceeds to block 180 wherein the TRC is adjusted. Alternatively, when the TRC of the CC-3 is in spec, the method 100 proceeds to block 185.
Referring to block 180, the TRC may be adjusted by any means suitable for adjusting the tensile and compressive strengths of a cement composition. For example, the TRC may be adjusted by the inclusion of strength modifying additives (SMA). SMAs are known to one skilled in the art with the aid of this disclosure. Without limitation, examples of SMAs are strength enhancing additives and fibers such as plastic, carbon or glass fibers.
In an embodiment, the SMA is a plastic fiber. Fine monofilaments of plastic fibers have been used to improve the tensile strength of cement while reducing plastic shrinkage cracking. Plastic shrinkage cracking occurs from constraints on the shrinkage of a cementious composition as it sets. The constraints arise, for example, from the cement being cast on in a subterranean formation to make a wellbore. Examples of plastic fibers include polypropylene (PP), polyethylene (PE), polyethylene terephthalate (PET), aramids (e.g., KEVLAR) and polyvinyl alcohol fibers. Methods of incorporating fibers into cement compositions to modify the compressive and tensile strength are known to one skilled in the art.
An effective amount of an SMA may be included with the CC-3 so as to produce a composition with a TRC in the optimizing range. Various SMAs are disclosed in U.S. Pat. Nos. 5,049,288, 6,793,730 and 5,358,047 each of which is incorporated by reference herein in its entirety.
Following adjustment of the TRC at block 180, the method 100 returns to block 170 and the TRC of the CC-3 is again determined. Following determination of the TRC, the method 100 again proceeds to block 175 and the TRC of the CC-3 is evaluated as to whether it falls in or out of spec. In an embodiment, the TRC of the CC-3 is out of spec, and the method 100 proceeds to block 180 wherein the TRC is adjusted as previously described. The TRC adjustment-determination-evaluation loop represented by blocks 180, 170, and 175 continues iteratively as necessary to prepare a CC-3 having a TRC in spec. Once the TRC is found to be in spec at block 175, the method 100 proceeds to block 185.
At block 185, the method 100 determines whether the CC-3 has been adjusted at block 180 as described previously. If so, such would indicate that the composition of the CC-3 has been altered (referred to as adjusted CC-3), and therefore the method 100 returns to block 115 to determine the density of the adjusted CC-3 and subsequently to block 120 to evaluate whether the density of the adjusted CC-3 remains in spec. Where the density of the adjusted CC-3 is not in spec, the method 100 proceeds through blocks 125, 115, and 120 wherein the density is readjusted, redetermined, and reevaluated until the density falls within spec, as described previously. The method 100 then proceeds to blocks 130 and 135 wherein the YM of the adjusted CC-3 is determined and evaluated as previously described. In an embodiment, the YM of the CC-3 is not in spec, and the method 100 proceeds through blocks 140, 130, and 135 wherein the YM is readjusted, redetermined, and reevaluated until the YM of the CC-3 again falls within spec, as described previously. The method 100 then proceeds to blocks 145, 150, and 155 wherein the PR of the adjusted CC-3 is determined and evaluated as previously described. In an embodiment, the PR of the adjusted CC-3 is not in spec, and the method 100 proceeds through blocks 160, 150, and 155 wherein the PR is readjusted, redetermined, and reevaluated until the PR of the adjusted CC-3 again falls within spec, as described previously. The method 100 then proceeds to blocks 165, 170, and 175 wherein the TRC of the adjusted CC-3 is determined and evaluated as previously described. In an embodiment, the TRC of the adjusted CC-3 is not in spec, and the method 100 proceeds through blocks 180, 170, and 175 wherein the TRC of the adjusted CC-3 is readjusted, redetermined, and reevaluated until the TRC of the adjusted CC-3 again falls within spec, as described previously. In some embodiments, adjustments, determinations, and evaluations of the density, YM, PR, and/or TRC of the CC-3 continue iteratively as described until all four values are in spec and no further adjustments are made to the CC-3, allowing the method 100 to proceed from block 185 to block 190. The cement composition provided at block 190, and having the density, YM, PR, and TRC in spec is hereinafter referred to as a forth optimized cement composition (CC-4). In an embodiment, the method 100 may conclude at block 195 with placement of CC-4 downhole.
In an addition or in the alternative, the composition's ratio of Young's modulus relative to compressive strength (YRC) may be determined. In such an embodiment, the YRC may be determined for an unconfined sample by dividing Young's Modulus by the compressive strength which was multiplied by 10 (i.e. Young's modulus/(compressive strength *10). Generally, the YRC of an unmodified Portland cement (e.g., base) is from about 35 to about 70, while the YRC of a mechanically modified Portland cement is from about 1 to about 35. Without wishing to be limited by theory, cements having a lower YRC are less prone to cracking because the tangential (circumferential) stress is more compressive. In an embodiment, the optimizing range for the YRC is from about 1 to about 70, alternatively from about 2 to about 45, alternatively from about 2.5 to about 40, alternatively from about 3 to about 35, alternatively from about 3 to about 30, alternatively less than about 30. A composition of the type described herein may have the YRC adjusted using the methodologies described herein for adjustments of the YM and/or compressive strength until the value falls within the optimizing range.
In various embodiments, the method 100 may proceed after block 120 to block 195 and a CC-1 is placed downhole. Alternatively, the method 100 may proceed after block 135 to block 195 and a CC-2 is placed downhole. Alternatively, the method 100 may proceed after block 155 to block 195 and a CC-3 is placed downhole. Hereinafter, a NPBC having at least one of the density, YM, PR, or TRC falling within an optimizing range is termed an optimized non-Portland cement composition (ONCC).
As deemed appropriate by one skilled in the art with the benefits of the this disclosure, additional additives may be included with CC-1, CC-2, CC-3, or CC-4 for adjusting the values of the density, YM, PR, and TRC into their optimizing ranges and/or for imparting other desired properties. Such additives may, or may not, simultaneously affect the density, YM, PR, and/or TRC of the CC-4. Examples of such additives include, but are not limited to, set retarders such as lignosulfonates, fluid loss control additives, defoamers, dispersing agents, set accelerators, and formation conditioning agents. Examples of suitable fluid loss control additives include without limitation HALAD 344 and HALAD 567 fluid loss additives, which are commercially available cement additives available from Halliburton Energy Services, Inc. An example of a suitable defoamer includes without limitation D-AIR 3000L defoamer, which is commercially available from Halliburton Energy Services, Inc. Other additives that may be introduced to the cement composition to prevent cement particles from settling to the bottom of the fluid are, for example, bentonite and silica fume, which is commercially available from Halliburton Energy Services Inc. under the tradename SILICALITE. Further, a salt such as sodium chloride may be added to the cement composition when the drilling zone has a high salt content.
In addition, modifications such as changes to the water-to-cement ratio and the addition of non-cementitious materials such as flyash may be carried out as deemed appropriate by one skilled in the art to adjust the values of density, YM, PR, and/or TRC into the disclosed optimizing ranges. An example of flyash includes without limitation POZMIX A flyash, which is commercially available from Halliburton Energy Services Inc. Following inclusion of any additional additives, the of density, YM, PR, and/or TRC of the cement composition may be determined, evaluated, and adjusted as disclosed herein.
In an embodiment, an ONCC suitable for long term zonal isolation has a density of from about 5 ppg to about 22 ppg, a YM of from about 1,000 psi to about 3,000,000 psi, a PR of from about 0.05 to about 0.40, and a TRC of from about 2% to about 20%. Alternatively, an ONCC suitable for long term zonal isolation has a density of from about 5 ppg to about 22 ppg, a YM of from about 1,000 psi to about 3,000,000 psi, and a PR of from about 0.05 to about 0.40. Alternatively, an ONCC suitable for long term zonal isolation has a density of from about 5 ppg to about 22 ppg, and a YM of from about 1,000 psi to about 3,000,000 psi. Alternatively, an ONCC suitable for long term zonal isolation has a density of from about 5 ppg to about 22 ppg.
In an embodiment, the methods disclosed may be carried out manually or may be automated in whole or part. For example, the calculations and determination of the mechanical properties of the disclosed cement compositions may be carried out using software and or equipment designed to evaluate and adjust the described parameters. Likewise, any or all of the determining, evaluating, and adjusting steps may be automated and/or computer controlled.
In an embodiment, the ONCCs of this disclosure (e.g., CC-1, CC-2, CC-3, and CC-4) may display a number of desirable physical and/or mechanical properties that in conjunction with the aforementioned properties enhance the suitability of these compositions for use in long term zonal isolation.
An ONCC of this disclosure may exhibit a relatively constant viscosity for a period of time after they are initially prepared and while they are being placed in their intended locations in the wellbore, i.e., during the period when the slurry is in motion. Eventually, the ONCCs quickly set such that the viscosity of the placed slurry increases from about 35 Bearden units of Consistency (Bc) to equal to or higher than 70 Bc in equal to or less than about 20 minutes, alternatively equal to or less than about 15 minutes, alternatively equal to or less than about 10 minutes. In an embodiment, the set time corresponds to the exothermic hydration of the ONCC after which the strength development is faster than when the composition sets or becomes unpumpable due to gelation. This sudden jump in viscosity (i.e., from 35 Bc to 70 Bc after placement of the slurry) may be very desirable in preventing unwanted events such as gas or water migration into the slurry because it indicates the quick formation of an impermeable mass from a gelled state after placement. This behavior is often referred to as “Right Angle Set” and such cement compositions are termed “Right Angle Set Cement Compositions” in reference to the near right angle increase shown in a plot of viscosity over time.
In an embodiment, the ONCCs of this disclosure may display a more rapid onset of compressive strength development, hereinafter is referred to as waiting on cement (WOC) time, when compared to an otherwise similar composition comprising a Portland cement. WOC time refers to the amount of time for cement to develop compressive strength after placement as the cement transitions from a slurry to a solid form. Typically, the time for the cement to reach a compressive strength of 50 psi after placement as measured by a non destructive compressive strength testing device is referred to as WOC50. At WOC50, certain drilling rig operations may recommence. Typically, the time to reach 500 psi compressive strength after placement is also measured and recorded, and hereinafter is referred to as WOC500. At WOC500, the cement exhibits a compressive strength where the majority of drilling rig operations can recommence. In an embodiment, the ONCCs of this disclosure may develop a compressive strength of 50 psi (WOC50) within a time period of equal to or less than about 4 hour, alternatively equal to or less than about 2 hours, alternatively equal to or less than about 1 hour. In an embodiment, the ONCCs of this disclosure may develop a compressive strength of 500 psi (WOC500) within a time period of equal to or less than about 12 hours, alternatively equal to or less than about 8 hours, alternatively equal to or less than about 6 hours.
The ONCCs of this disclosure may display a desirable thickening time that allows the composition to remain pumpable without gelling during downhole placement before setting. The thickening time refers to the time required after contacting of the slurry components for the composition to achieve 70 Bc. At about 70 Bc, the slurry undergoes a conversion from a pumpable fluid state to a non-pumpable paste. In an embodiment, the ONCCs of this disclosure may have a thickening time of from about 30 minutes to about 10 hours, alternatively from about 30 minutes to about 5 hours, alternatively from about 30 minutes to about 3 hours at temperatures of from about 40° F. to about 400° F., alternatively from about 230° F to about 400° F.
The ONCCs of this disclosure may display an increased Zero Gel Time (ZGT) when compared to an otherwise similar composition comprising a Portland cement. The ZGT refers to the time required for the ONCC to reach a static gel strength of 100 pound force per hundred square foot (lbf/100 ft2) after the slurry has been allowed to stay static, in the downhole situation. In an embodiment, the ONCCs of this disclosure may have a ZGT of from about 5 minutes to about 110 minutes, alternatively from about 20 minutes to about 80 minutes, alternatively from about 30 minutes to about 60 minutes. The zero gel time of the disclosed compositions may be decreased by from about 15 minutes to about 90 minutes when compared to an otherwise similar composition prepared using a Portland cement, alternatively from about 20 minutes to about 70 minutes, alternatively from about 30 minutes to about 50 minutes.
The ONCCs of this disclosure may display an increased transition time when compared to an otherwise similar composition comprising a Portland cement. The transition time refers to the period of time during which gas migration into the slurry can occur, which is typically the time ranging from when the static gel strength of the slurry is about 100 lbf/100 ft2 to when it is about 500 lbf/100 ft2. The transition time reflects the ability of the ONCC to minimize gas influx. During this transition time, the hydrostatic pressure applied from fluids above will be decreased and can allow gas influx through the cement. When the static gel strength reaches 500 lbf/100 ft2, the fluid has sufficient static gel strength to block the gas influx through the slurry and no longer transfers full hydrostatic pressure from the fluid. In an embodiment, the ONCC of this disclosure may have a transition time of from about 2 minutes to about 30 minutes, alternatively from about 6 minutes to about 20 minutes, alternatively from about 10 minutes to about 15 minutes.
In an embodiment, the ONCCs of this disclosure may have a linear expansion of from about 1% to about 10%, alternatively from about 1.5% to about 6%, alternatively from about 2% to about 5%. The expansion of the disclosed compositions may be increased by about 0.3% to about 10% when compared to an otherwise similar composition prepared using a Portland cement, alternatively from about 0.5% to about 1.5%, alternatively from about 0.5% to about 1%.
In an embodiment, the ability of the set cement sheath to withstand cyclical stresses associated occurring during the life of the wellbore may be enhanced by the ability of cement composition to expand upon hydration. The expansion test may be carried out using Ring Molds where linear expansion percentage of the ring molds may be determined before and after setting.
In an embodiment the ONCCs of this disclosure may have a density variation allowance (DVA) of from about 0.01 pound per gallon (ppg) to about 1 ppg, alternatively from about 0.1 ppg to about 0.8 ppg, alternatively from about 0.2 ppg to about 0.5 ppg as determined in accordance with the BP settling test standard procedure set forth in the Halliburton Global Standard Manual dated May 1997, which is incorporated by reference herein in its entirety. Herein the DVA refers to the extent to which the density may vary over a column of cement slurry. Generally, solid particles, such as weighting agents, have a tendency to settle in slurries over a period of time thereby causing a non-uniform density distribution (i.e., density variation) which in turn may further decrease the mechanical properties of the ONCC. The settling in ONCCs may be measured using BP settling test where a column of set cement, cured under controlled pressure and temperature, is cut into sections and the density of each cylindrical section is measured.
In an embodiment, the ONCCs form set cements having a thermal stability so that they do not undergo strength retrogression below 700° F. when compared to an otherwise similar composition comprising a Portland cement. The thermal stability with respect to mechanical properties may be evidenced by measuring the mechanical properties (e.g., compressive strength) as function of treatment time temperatures up to 700° F. or higher. Herein a cement having a thermal stability refers to a cement that does not loose its mechanical integrity such that it provides zonal isolation at these temperatures.
In an embodiment, the ONCCs may be employed in well completion operations such as primary and secondary cementing operations. Primary and secondary cementing operations refer to wellbore completion processes as known to those skilled in the art, and ONCCs for use in such cementing operations may or may not contain cement. The ONCC may be placed into an annulus of the wellbore and allowed to set such that it isolates the subterranean formation from a different portion of the wellbore. The ONCC thus forms a barrier that prevents fluids in that subterranean formation from migrating into other subterranean formations. Within the annulus, the ONCC also serves to support a conduit, e.g., casing, in the wellbore. In an embodiment, the wellbore in which the ONCC is positioned belongs to a multilateral wellbore configuration. It is to be understood that a multilateral wellbore configuration includes at least two principal wellbores connected by one or more ancillary wellbores.
In secondary cementing, often referred to as squeeze cementing, the sealant composition may be strategically positioned in the wellbore to plug a void or crack in the conduit, to plug a void or crack in the hardened ONCC (e.g., cement sheath) residing in the annulus, to plug a relatively small opening known as a microannulus between the hardened sealant and the conduit, and so forth. Various procedures that may be followed to use a sealant composition in a wellbore are described in U.S. Pat. Nos. 5,346,012 and 5,588,488, which are incorporated by reference herein in their entirety.
In an embodiment, the ONCC is used in a wellbore that is arranged in any configuration suitable for injecting or recovering material from the wellbore, such as a steam-assisted gravity drainage (SAGD) configuration, a multilateral wellbore configuration, or a common wellbore configuration. A SAGD configuration comprises two independent wellbores with horizontal sections arranged one above the other. The upper wellbore is used primarily to convey steam downhole, and the lower wellbore is used primarily to produce oil. The wells are positioned close enough together to allow for heat flux from one to the other. Oil in a reservoir adjacent to the upper wellbore becomes less viscous in response to being heated by the steam such that gravity pulls the oil down to the lower wellbore where it can be produced. In an embodiment, the ONCCs of this disclosure provide set cement compositions that are thermally stable when subjected to high temperature environments.
The methods described herein may be carried out manually, may be automated, or may be combinations of manual and automated processes. In an embodiment, the method is implemented via a computerized apparatus, wherein the method described herein is implemented in software on a general purpose computer or other computerized component having a processor, user interface, microprocessor, memory, and other associated hardware and operating software. Software implementing the method may be stored in tangible media and/or may be resident in memory on the computer. Likewise, input and/or output from the software, for example ratios, comparisons, and results, may be stored in a tangible media, computer memory, hardcopy such a paper printout, or other storage device.
EXAMPLESThe disclosure having been generally described, the following examples are given as particular embodiments of the disclosure and to demonstrate the practice and advantages thereof. It is understood that the examples are given by way of illustration and are not intended to limit the specification or the claims in any manner.
Slurry PreparationIn the following examples, cement slurries were prepared according to API Recommended Practices 10B, Procedure 9, Twenty-Second Edition, December 1997. When fibers are used, the fibers were mixed using a Waring blender at a blender speed of up to 4000 rpm.
Example 1The viscosity, fluid loss, and expansion of an NPBC of the type described herein were investigated. A Sorel cement slurry whose composition is shown in Table 2 was prepared and designated Sample 1. Sample 1 has a density of 14.7 pounds per gallon (ppg). The viscosity of Sample 1 was determined to be about 25-30 Bc. Fluid loss test was performed on a 45 cc cylinder for 4 minutes and 45 seconds and determined to be 211 cc.
Next, a ring mold expansion test was carried out. Two ring molds having two opposite splits and steel balls attached to each side of the split were prepared from Sample 1. The distances between the outside of the steel balls attached to each side of the split in the expandable ring were measured at 0.46760 inches and 0.45335 inches. The rings were allowed to set. After 16 hours, the distances between the outside of the steel balls attached to each side of the split in the expandable ring were measured again at 0.76400 inches and 0.79900 inches. From the expansion test, the average linear expansion was 3.78%. The results demonstrated that the NPBC sample expanded after placement and did not shrink.
Example 2The thickening time and mechanical properties of an NPBC were investigated. A Sorel cement (i.e., an NPBC) cement slurry whose composition is shown in Table 3 was prepared and designated Sample 2. POZMIX A flyash, WELLLIFE 665 elastomer, WELLLIFE 734 fiber, Bentonite, HALAD-344 fluid loss control additive, D-AIR 3000L defoamer were first dry mixed. Next, water, R-TEK, C-TEK, T-TEK-HT and the dry mixture were sequentially mixed. The density and total volume of Sample 2 was 14.6 ppg and 725 cc respectively.
The viscosity of slurry Sample 2 was then determined at various RPM using a Fann viscometer. The Fann readings from the Fann viscometer are shown in Table 4.
The thickening time and viscosity of Sample 2 was determined at a temperature of 176° F., a pressure of 8000 psi, with a 35 minutes ramp time.
Next, the slurries Sample 2 were poured into dog-bone briquette molds for mechanical properties testing and designated Samples 2A-2F. Compressive strengths, Young's modulus, Poisson's ratio, and Tensile strengths were determined and the results are tabulated in Table 5.
The average Compressive strength, Young's Modulus, Poisson's Ratio, and Tensile strengths were 1664.5 psi, 7.49×105 psi, 0.305, and 256 psi respectively. Thermal conductivity test was also carried out for Sample 2 and was determined to be about 0.6-0.7 W/m° K.
Example 3The rheology and fluid loss of another NPBC having a density of 16.4 ppg were investigated. A Sorel cement slurry of compositions shown in Table 6 was prepared and designated Sample 3. T-TEK HT, POZMIX A flyash, MICROMAX FF weighting agent, WELLLIFE 665 elastomer, WELLLIFE 734 fiber, and HALAD-344 fluid loss control additive were first dry mixed. Next, water, D-AIR 3000L, R-TEK, and C-TEK were sequentially mixed. The density of Sample 3 was determined to be 16.4 ppg. After 30 minutes conditioning at 172° F., fluid loss was determined to be 50 cc. The results demonstrate that a fluid loss control additive (e.g., HALAD-344) can aid in controlling fluid loss in an NPBC.
The mechanical properties of an NPBC having a density of 16.5 lb/gal were compared to Portland cements (Class G DYCKERHOFF CEMENTS) having a similar density. Two Portland cement slurries, designated Samples 4 and 5, and a Sorel cement, designated Sample 6, having the compositions shown in Tables 7-9 were prepared. Sample 4 was ECLX1655 Portland cement, which is an ELASTICEM cement, Sample 5 was ECWL1654 Portland cement, which is a LIFECEM™ cement, and Sample 6 was THERMATEK cement which is a Sorel cement, all of which are commercially available from Halliburton Energy Services, Inc.
The free water, settling, fluid loss, thickening time, and compressive strength were determined for Samples 4-6. The tests were performed at a bottom hole circulating temperature (BHCT) of 172° F., the bottom hole static temperature (BHST) at the top of the liner was 189° F., and the BHST at a measure depth (MD) of 11,448 ft was 208° F. The results are tabulated in Table 10.
Free water is an indication of settling and the static stability of the slurry. Zero to trace free water indicates a stable slurry. Fluid loss is a measure of the amount of water that may be lost to the formation. It is desirable to limit fluid loss so as to not alter the desired hydration of the cement. Additionally, a loss of fluid will result in a more viscous slurry which in turn may affect the ability to properly place the slurry in the well bore. Settling data is collected to investigate the rheological behavior of the slurry. Generally, solid particles in slurry tend to settle towards the lower portion over time. No settling indicates that the slurry is able to suspend those solid particles over time. The results demonstrate the Sorel cement slurry (Sample 6) shows zero free water and settling which is identical to the behavior observed with the Portland cements (Samples 4 and 5). Further, the Sorel cement displays less fluid loss and thickening time than the Portland cement compositions. The compressive strength of the Sorel cement was found to lie between that of the two Portland cements tested.
Static gel strength (SGS) and transition time tests were performed using a mini multiple analysis cement system (mini MACS) with a variable speed stepper motor drive and a precision force transducer. The motor speed was controlled at 0.2 deg/min for SGS test and 150 rev/min for thickening time test with pressures up to 20,000 psi and temperatures up to 500° F. The results of the tests are shown in
From the results, Sample 6 has shorter transition time and much higher ZGT value when compared to Samples 4 and 5.
The amount of time for Samples 4-6 to develop compressive strength (e.g., WOC50, WOC500) was measured using a non destructive ultrasonic compressive strength testing device (UCA). The results of the tests are shown in FIGS. 6-8, which are plots of compressive strength as a function of time. The WOC50 and WOC500 are tabulated in Table 12.
The results demonstrated that the WOC50 and WOC500 of Sample 6 were more rapid than Samples 4 and 5.
Next, the mechanical properties of Samples 4-6 were investigated. The samples were cured for 7 days at temperatures of up to 208° F. and pressures of up to 2,000 psi. Compressive strengths, cohesions, friction angles, Brazilian Tensile strengths, percentage of Brazilian Tensile strength relative to Compressive strength (TRC), Young's modulus, percentage of Young's modulus relative to compressive strength (YRC), and Poisson's ratios were determined. Cohesion tests may be determined by the uniaxial compressive strength, fc, and the angle of internal friction, f0. The cohesion of materials with a zero friction angle is equal to one-half the compressive strength for, while the cohesion of material with a positive friction angle is less than one-half the ultimate compressive strength. Friction angle tests may be determined by using the unconfined tests and considering the Mohr-Coulomb shear failure criteria. The results are tabulated in Table 13. Plots of Young's modulus, Poisson's ratio, and TRC are also shown in
The results demonstrated that Young's modulus of all samples were less than 1,000,000 psi and the Young's modulus of Sample 6 was lower than Sample 4 and comparable to Sample 5. The Poisson's ratio of Sample 6 was above 0.2, and higher than Samples 4 and 5, which were below 0.2. The TRC of Sample 6 was higher than 10% and also higher than both Samples 4 and 5. The compressive strength of Sample 6 was about 40% higher than that of Sample 5, however, the Young's modulus for both Samples 5 and 6 were similar.
While embodiments of the disclosure have been shown and described, modifications thereof can be made by one skilled in the art without departing from the spirit and teachings of the disclosure. The embodiments described herein are exemplary only, and are not intended to be limiting. Many variations and modifications of the disclosure disclosed herein are possible and are within the scope of the disclosure. Where numerical ranges or limitations are expressly stated, such express ranges or limitations should be understood to include iterative ranges or limitations of like magnitude falling within the expressly stated ranges or limitations (e.g., from about 1 to about 10 includes, 2, 3, 4, etc.; greater than 0.10 includes 0.11, 0.12, 0.13, etc.). For example, whenever a numerical range with a lower limit, RL, and an upper limit, RU, is disclosed, any number falling within the range is specifically disclosed. In particular, the following numbers within the range are specifically disclosed: R=RL+k*(RU−RL), wherein k is a variable ranging from 1 percent to 100 percent with a 1 percent increment, i.e., k is 1 percent, 2 percent, 3 percent, 4 percent, 5 percent, . . . , 50 percent, 51 percent, 52 percent, . . . , 95 percent, 96 percent, 97 percent, 98 percent, 99 percent, or 100 percent. Moreover, any numerical range defined by two R numbers as defined in the above is also specifically disclosed. Use of the term “optionally” with respect to any element of a claim is intended to mean that the subject element is required, or alternatively, is not required. Both alternatives are intended to be within the scope of the claim. Use of broader terms such as comprises, includes, having, etc. should be understood to provide support for narrower terms such as consisting of, consisting essentially of, comprised substantially of, etc.
Accordingly, the scope of protection is not limited by the description set out above but is only limited by the claims which follow, that scope including all equivalents of the subject matter of the claims. Each and every claim is incorporated into the specification as an embodiment of the present disclosure. Thus, the claims are a further description and are an addition to the embodiments of the present disclosure. The discussion of a reference herein is not an admission that it is prior art to the present disclosure, especially any reference that may have a publication date after the priority date of this application. The disclosures of all patents, patent applications, and publications cited herein are hereby incorporated by reference, to the extent that they provide exemplary, procedural, or other details supplementary to those set forth herein.
Claims
1. A method of cementing a wellbore in a subterranean formation, comprising:
- formulating a non-Portland base cement composition that may be suitable for long-term zonal isolation;
- preparing the non-Portland base cement composition;
- determining a density of the non-Portland base cement composition and adjusting the density as needed to within an optimized density range to form a first optimized cement composition;
- determining the percentage of tensile strength relative to compressive strength of the first optimized cement composition;
- adjusting the percentage of tensile strength relative to compressive strength of the first optimized cement composition as needed to within an optimized percentage of tensile strength relative to compressive strength range to produce an optimized cement composition; and
- placing the optimized cement composition in the wellbore.
2. The method of claim 1 wherein the optimized density range is from about 5 ppg to about 22 ppg.
3. The method of claim 1 wherein the adjusting the density comprises adding weighting agent, barite, hematite, hausmannite, calcium carbonate, siderite, ilmenite, or combinations thereof.
4. The method of claim 1 further comprising:
- determining a Young's modulus of the non-Portland base cement composition; and
- adjusting the Young's modulus as needed to within an optimized Young's modulus range to form an adjusted first optimized cement composition.
5. The method of claim 4 wherein the optimized Young's modulus range is from about 1,000 psi to about 3,000,000 psi.
6. The method of claim 4 wherein the adjusting the Young's modulus comprises adding an elastomer, a rubber, or combinations thereof.
7. The method of claim 4 wherein the adjusting the Young's modulus comprises adding polyisoprene; polybutadiene; polyisobutylene; polyether; polyester; polystyrene; poly(methacrylate); isotactic polypropylene; polyurethane; natural rubber; styrene/butadiene rubber; cis-1,4-polybutadiene rubber; high styrene resin; butyl rubber; ethylene/propylene rubbers; neoprene rubber; nitrile rubber; cis-1,4-polyisoprene rubber; silicone rubber; chlorosulfonated rubber; polyethylene rubber; epichlorohydrin rubber; fluorocarbon rubber; fluorosilicone rubber; polyurethane rubber; polyacrylic rubber; polysulfide rubber; or combinations thereof.
8. The method of claim 4 wherein the density and Young's modulus are repeatedly adjusted as needed until the density is within an optimized density range, and Young's modulus is within an optimized Young's modulus range to form a second optimized cement composition.
9. The method of claim 8 further comprising:
- determining a Poisson's ratio of the non-Portland base cement composition; and
- adjusting the Poisson's ratio as needed to within an optimized Poisson's ratio range.
10. The method of claim 9 wherein the optimized Poisson's ratio range is from about 0.05 to about 0.40.
11. The method of claim 9 wherein adjusting the Poisson's ratio comprises adding flexible compressible beads, a resilient material, gas, resilient graphite, natural rubber, styrofoam beads, styrene-butadiene copolymer, neoprene, synthetic rubbers, vinyl plastisol thermoplastics, nitrile rubber, butyl rubber, polysulfide rubber, EPDM rubber, silicone rubber, polyurethane rubber, or combinations thereof.
12. The method of claim 9 wherein the density, Young's modulus, and Poisson's ratio are repeatedly adjusted as needed until the density is within an optimized density range, Young's modulus is within an optimized Young's modulus range and Poisson's ratio is within an optimized Poisson's ratio range to form a third optimized cement composition.
13. The method of claim 1 wherein the optimized percentage of tensile strength relative to compressive strength range is from about 2% to about 20%.
14. The method of claim 1 wherein the adjusting the percentage of tensile strength relative to compressive strength comprises adding fibers, plastic fibers, carbon fibers, glass fibers, or combinations thereof.
15. The method of claim 12 wherein the density, Young's modulus, Poisson's ratio, and percentage of tensile strength relative to compressive strength are repeatedly adjusted as needed until the density is within an optimized density range, Young's modulus is within an optimized Young's modulus range, Poisson's ratio is within an optimized Poisson's ratio range and the optimized percentage of tensile strength relative to compressive strength is within an optimized percentage of tensile strength relative to compressive strength range to form a fourth optimized cement composition.
16. The method of claim 1 wherein the optimized cement composition develops a compressive strength of 50 psi within a time period of equal to or less than about 4 hours.
17. The method of claim 1 wherein the optimized cement composition develops a compressive strength of 500 psi within a time period of equal to or less than about 12 hours.
18. The method of claim 1 wherein the optimized cement composition has a density variation allowance of from about 0.01 ppg to about 1 ppg.
19. The method of claim 1 wherein the optimized cement composition has a thickening time of from about 30 minutes to about 10 hours.
20. The method of claim 1 wherein the optimized cement composition has a zero gel time of from about 5 minutes to about 110 minutes.
21. The method of claim 1 wherein the optimized cement composition has a transition time of from about 2 minutes to about 30 minutes.
22. The method of claim 1 wherein the optimized cement composition has a linear expansion of from about 1% to about 10%.
23. The method of claim 1 wherein the non-Portland cement composition comprises a metal oxide, a soluble chloride or phosphate salt, and water.
Type: Application
Filed: Feb 26, 2009
Publication Date: Aug 26, 2010
Applicant: Halliburton Energy Services, Inc. (Houston, TX)
Inventors: Ashok K. Santra (Duncan, OK), Bill Hunter (The Woodlands, TX), Hector Ramirez (Duncan, OK)
Application Number: 12/393,141
International Classification: E21B 33/13 (20060101); E21B 47/00 (20060101); E21B 33/14 (20060101);
