Method of treating oil and gas wells
A two step process for treating an oil or gas well. The first step uses a cross linking agent, such as borax, as a preliminary wash for the well following drilling. The cross linking agent cleans the well of excess mud and pre-coats the tubing and the formation surfaces with the cross linking agent. The second step introduces a cement-polymer mixture into the well. A polymer, such as for example polyvinyl alcohol, that undergoes cross linking when exposed to the cross linking agent is employed. When the polymer comes into contact with the cross linking agent in the well, cross linking of the polymer occurs. This cross linking helps to prevent fluid loss into the formation. Also, because the cross linking agent wash previously cleaned the surfaces of the tubing and the formation, better bonding between the cement and the surfaces of the tubing and the formation occurs.
The present application claims priority as a continuation in part to U.S. Non-provisional patent application Ser. No. 12/019,933, filed on Jan. 25, 2008, now U.S. Pat. No. 7,670,994, issued Mar. 2, 2010 and International Application No. PCT/US08/80838, filed Oct. 22, 2008 which further claims priority to U.S. Non-provisional patent application Ser. No. 12/019,933, filed on Jan. 25, 2008, now U.S. Pat. No. 7,670,994, issued Mar. 2, 2010.
FIELD OF THE INVENTIONThe present invention relates to a method for treating oil and gas wells. Various further embodiments relate to enhanced methods for treating oil and gas wells.
DESCRIPTION OF THE RELATED ARTPrevious methods of fluid loss control have been attempted by a one step addition of fluid loss control additive to the cement, which hopefully reduces the ability of the liquid portion of the slurry from rapidly penetrating a permeable zone at the formation face. This creates a critical dependence of the fluid control on the use of a fluid loss control additive that functions at the temperature of the permeable zone. Also, the cement slurry must be designed to complement the requirements of the fluid loss additive for rheology of the fluid portion of the cement slurry. Most fluid loss control additives thicken the cement slurry into which they are mixed. Also, they may retard the hardening of the cement when it reaches its required destination. To deal with such properties, it is common for service companies to have many different fluid loss control additives and to select the “best fit” for the well conditions that are to be encountered.
SUMMARY OF THE INVENTIONVarious embodiments of the present invention generally relate to methods for treating an oil and/or gas well. In an embodiment of a method of the present invention generally comprises washing a well borehole with a wash composition comprising a cross linking agent, such as, for example, borax, and pumping a cement mixture into the borehole, to cement at least a portion of the borehole, the cement mixture comprising a polymer composition, such as, for example, a polyvinyl alcohol. In various embodiments, the washing step at least partially cleans the well of excess mud and at least partially pre-coats the tubing and at least partially pre-coats the formation face with the cross linking agent.
The cement polymer mixture undergoes cross linking when exposed to the cross linking agent. In various embodiments, when the polymer in the cement mixture comes into contact with the wash composition's cross linking agent, the polymer undergoes polymerization or cross linking. This cross linking helps to prevent fluid loss into the formation. In various embodiments, increased bonding between the cement mixture and the surfaces of the tubing and the formation face is exhibited with compositions and/or methods of the present invention.
Examples of components useful in the present invention can be found in U.S. Pat. Nos. 5,009,269; 5,850,880; 5,728,210, the contents of which are hereby incorporated by reference as if they were reproduced herein in their entirety.
As such, in various embodiments, compositions and methods are disclosed that use a two stage process that allows washing, with a wash composition, of the permeable zone of the well borehole's formation face and cementing the well borehole with a cement mixture comprising a polymer composition.
This method is not as temperature dependant in down hole borehole operations, as with the fluid loss additives disclosed in U.S. Pat. Nos. 5,009,269; 5,850,880; 5,728,210. In traditional processes using a wash composition comprising a cross-linking agent and a cement mixture comprising a polymer, operating conditions above about 200 degrees F. (93.3 degrees C.) results in partial degradation of the components of the wash composition and/or the cement mixture. However, surprisingly, embodiments of the present invention are capable of functioning from near freezing, i.e. about 32 degrees F. (0.0 degrees C.), to above 400 degrees F. (204.4 degrees C.), or the degradation temperature of the polymer.
In various embodiments, operating temperatures in excess of 400 degrees F. (204.4 degrees C.) are possible. Generally, an upper temperature limit is at or about the temperature where the components of the wash composition and/or cement mixture degrade. In an embodiment, the wash composition's components degrade at above 400 degrees F. (204.4 degrees C.). In an alternate embodiment, the wash composition's components degrade at about 250 degrees F. (121.1 degrees C.). In an alternate embodiment, the wash composition's components degrade above 400 degrees F. (204.4 degrees C.).
In various embodiments, temperatures below zero degrees Celsius are difficult to operate in because the components of the drilling mud begin to change phase or freeze. Typically, such environments are found in areas with permafrost. Additives can be included in the drilling mud to lower the freezing point but attention should be had to interference between the additives and the various components of the wash composition and/or the cement mixture, as such, operating conditions below zero are possible with various embodiments of the present invention.
In various embodiments, the cross linking agent to be used for washing, or as a “spacer” additive or drilling mud additive, is non toxic and environmentally clean. In an embodiment, the cost of this “spacer” additive for the wash is lower than a traditional complex chemical wash, as used in contemporary drilling operations. In various further embodiments, the cross linking agent is capable of being formulated as a non thickened water base fluid that will allow turbulent flow in the annulus at very low pump rates into the well borehole.
Turbulent flow is capable of producing a churning action within the well borehole ahead of injected wash, as confirmed by laboratory studies. Additionally, the detergent action of the cross linking agent together with the turbulent flow at least partially granulates excess mud adhering to the pipe and at least partially granulates the loose mud at the formation face and carries the material out of the well.
In various embodiments, during this washing step using a cross linking agent in the wash, a “seeding” will take place at the formation face which at least partially impregnates the mud cake with cross linking agent. The concentration will vary depending on the permeability at the formation face. Typically, the concentration of the cross linking agent will increase as the permeability of the formation face increases.
In various embodiments, a cross linking agent is capable being added to drilling mud, or “spacers”, to be available for polymerization with the polymer. In such embodiments, fluid loss control is capable of being obtained without a washing step, which step, in certain circumstances, might not be desired, such as when disposal of a wash composition is an issue. The drilling mud would impregnate the formation face with the cross linking agent and a subsequently pumped cement mixtures comprising a polymer would cross link at or about the formation face.
In various embodiments, a polymer can be added to the cement mixture either as a dry component, a liquid component, or as a combination dry and liquid component. Typically, a polymer is comparatively low cost to conventional prior art complex fluid loss compositions. Further, with embodiments of the present invention, less material than conventional fluid loss compositions is required. In one embodiment, less composition is required because of the permeability block occurring at or about the formation-cement interface, where the reaction of the polymer and cross linking agent takes place. Accordingly, the application of the cross linking agent and the polymer is more targeted, producing less waste.
Otherwise, in various embodiments, if the reaction of the cross linking agent and the polymer had taken place in the cement slurry prior to reaching the permeable formation face, such as when the cement slurry is injected, the slurry would typically be much thicker because of the polymerized polymer, thereby requiring more water to reduce the viscosity of the at least partially polymerized cement slurry.
Focusing the reaction at the pressure differential interface, or formation face, means that a cement mixture of an embodiment of the present invention requires less loading with viscosity lowering agents and/or water/fluid.
In various embodiments, the cement mixtures are suitable for subterranean applications such as well completion and remedial operations. It is to be understood that “subterranean applications” encompass both areas below exposed earth and areas below earth covered by water such as ocean or fresh water. In various embodiments, the cement mixtures include a sufficient amount of water to form a pumpable slurry.
The density of the cement mixtures may vary. In various embodiments, the cement mixtures may comprise a density of from about 4 lb/gallon to about 23 lb/gallon. In alternative embodiments, the cement mixtures may comprise a density of from about 12 lb/gallon to about 17 lb/gallon. In other alternative embodiments, the cement mixtures may be low-density cement mixtures with a density of from about 5 lb/gallon to about 12 lb/gallon. In general, the density can be selected for the drilling operation.
In various embodiments, the cement mixture comprises at least one cement such as hydraulic cement, which includes calcium, aluminum, silicon, oxygen, and/or sulfur and which sets and hardens by reaction with water. Examples of hydraulic cements include but are not limited to Portland cements (e.g., classes A, C, G, and H Portland cements), pozzolana cements, gypsum cements, phosphate cements, high alumina content cements, silica cements, high alkalinity cements, and combinations thereof.
Type I Portland cement is known as common or general purpose cement. It is commonly used for general construction especially when making precast and precast-prestressed concrete that is not to be in contact with soils or ground water. The typical compound compositions of this type are 55% (C3S), 19% (C2S), 10% (C3A), 7% (C4AF), 2.8% MgO, 2.9% (SO3), 1.0% Ignition loss, and 1.0% free CaO.
Type III has a relatively high early strength. Its typical composition is 57% (C3S), 19% (C25), 10% (C3A), 7% (C4AF), 3.0% MgO, 3.1% (SO3), 0.9% Ignition loss, and 1.3% free CaO. The gypsum level may also be increased a small amount. This gives the concrete using this type of cement a three day compressive strength equal to the seven day compressive strength of types I and II. Finally, other cement types useful in the cement blend of the present invention include (high-early set) HE and class C cements.
In various embodiments, a permeable, Micro-Cluster Silica Material may be used in the cement mixtures. A Perlite-derived material capable of use in the present invention comprises microcellular fillers that are inert, inorganic, hollow glass particles with irregular spherical geometries. These particles are commercially available and sold under the name Sil-cell® by Silbrico Corporation (Hodgkins, Ill.). Sil-cell® particles have a greater tensile strength than the usual spherical bubbles. Sil-cell® has a low effective specific gravity (E.S.G.=0.18) and makes cost effective the manufacture of adhesives, auto body putty, cultured marble, coatings, wall patching compounds and stucco in which Sil-cell® is incorporated. The approximate composition of Sil-cell® is 73% silicon dioxide, 17% aluminum oxide, 5% potassium oxide 3% sodium oxide, 1% calcium oxide and trace elements.
The use of a low shear, folding type mixer is desirable to minimize particle breakage when using Sil-cell®. Thus, low shear testing procedures were used to mix compositions with Sil-cell®. Tests where high shear was used resulted in break-up of the structures and release of the entrapped gas. If the micro-clusters are completely broken-up, they no longer occupy the space in the liquid slurry needed to eventually intake the excess water used to initially mix and pump the slurry. The resulting slurry would be weakened when it hardens into set cement. Silbrico Corporation product Sil-43BC used in these preferred composition tests has an average particle size of about 35 microns with a range of 1 to 150 microns, and at least 95 percent less than 75 microns. Generally, a grade of micro-cluster silica material has an average particle size ranging from about 30 to about 80 microns and a range of distribution from about 1 micron to about 200 microns. More desirably, the permeable, micro-cluster silica material has an average particle size ranging from about 30 to about 50 microns and a range of distribution from about 1 micron to about 200 microns and even better an average particle size ranging from about 30 to about 40 microns and a range of distribution from about 1 micron to about 150 microns.
The micro-clusters of glass bubbles in Sil-cell® have high permeability. The high permeability allows the micro-clusters to exchange void air space (when hydraulic pressure is applied) with water from the cement matrix that surrounds the micro-cluster. On the other hand, when structures that are not permeable (which is the case with micro-spheres and micro-beads), the micro-clusters would be subject to collapse under pressure. The use of crushable structures under high hydraulic pressure results in dramatic rheology change when collapse takes place. This can render such a slurry unpumpable or at a severe density change due to the collapse of the air space.
The use of the permeable non-crushing, micro-clusters of glass bubbles avoids this possibility. The Ideal Gas Law can be used to calculate the density change with pressure. The increase in pressure is directly related to the decrease in volume of gas. Also, simulated pressure conditions can be used in unique testing methods to predict the rheology profile and hydration characteristics of the cement mixture. Testing has verified the integrity of the micro-clusters of glass bubbles after water has invaded the permeable structures under high hydraulic pressure. Thus, the micro-cluster retains its dimensions while filling with water from the surrounding fluid.
A sufficient amount of water is added to the cement mixture to make the cement mixture pumpable. 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, or a non-aqueous fluid. The water may be present in the amount of from about 16 to about 180 percent by weight of cement, alternatively from about 28 to about 60 percent by weight of cement. In general, any amount of water can be used as would be understood by one of ordinary skill in the art.
In various embodiments an amount of cross linking agent is added to adequately cover the formation face. In an embodiment, the amount of cross linking agent added is in excess of the amount of cross linking agent needed to impregnate the formation face. In an alternate embodiment, the amount of cross linking agent added is 50% in excess of the amount of cross linking agent needed to impregnate the formation face. In an alternate embodiment, the amount of cross linking agent added is 100% in excess of the amount of cross linking agent needed to impregnate the formation face. In an alternate embodiment, the amount of cross linking agent added is 200% in excess of the amount of cross linking agent needed to impregnate the formation face. In an alternate embodiment, the amount of cross linking agent added is 500% in excess of the amount of cross linking agent needed to impregnate the formation face. In general, any amount of cross linking agent can be used and can be governed by one of ordinary skill in the art based on coverage, results, cost, and/or the like.
In various embodiment an amount of polymer is added to is added to adequately cover the formation face and/or react with the cross linking agent, thereby polymerizing. In an embodiment, the amount of polymer added is in excess of the amount of polymer needed to polymerize on, in, or about the formation face. In an alternate embodiment, the amount of polymer added is 50% in excess of the amount of polymer needed to polymerize on, in, or about the formation face. In an alternate embodiment, the amount of polymer added is 100% in excess of the amount of polymer needed to polymerize on, in, or about the formation face. In an alternate embodiment, the amount of polymer added is 200% in excess of the amount of polymer needed to polymerize on, in, or about the formation face. In an alternate embodiment, the amount of polymer added is 500% in excess of the amount of polymer needed to polymerize on, in, or about the formation face. In general, any amount of polymer can be used and can be governed by one of ordinary skill in the art based on coverage, results, cost, and/or the like.
In various embodiments of the present invention, the total amount by volume of fluid loss additive need, wherein the fluid loss additive comprises the polymer in the cement mixture and the cross linking agent in the wash composition (or drilling mud), is between about 1.0% and 90% of contemporary fluid loss additive. In an alternate embodiment, the total amount by volume of fluid loss additive needed is between about 5.0% and 75% of contemporary fluid loss additive. In an alternate embodiment, the total amount by volume of fluid loss additive needed is between about 10% and 50% of contemporary fluid loss additive. In an alternate embodiment, the total amount by volume of fluid loss additive needed is between about 15% and 25% of contemporary fluid loss additive. In an alternate embodiment, the total amount by volume of fluid loss additive needed is 0% due to enhancements of various embodiments of the present invention.
In various embodiments of the present invention, the total amount by weight of fluid loss additive need, wherein the fluid loss additive comprises the polymer in the cement mixture and the cross linking agent in the wash composition (or drilling mud), is between about 1.0% and 90% of contemporary fluid loss additive. In an alternate embodiment, the total amount by weight of fluid loss additive needed is between about 5.0% and 75% of contemporary fluid loss additive. In an alternate embodiment, the total amount by weight of fluid loss additive needed is between about 10% and 50% of contemporary fluid loss additive. In an alternate embodiment, the total amount by weight of fluid loss additive needed is between about 15% and 25% of contemporary fluid loss additive. In an alternate embodiment, the total amount by weight of fluid loss additive needed is 0% due to enhancements of various embodiments of the present invention.
In various embodiments, a two stage method and also the type of additives used in the method should be a significant improvement for fluid loss prevention and permeable interface sealing. Such a technique or method could be utilized in any type of permeable situation to minimize leak off of fluid from a well bore, pond, lake, dam, etc.
The foregoing has outlined rather broadly the features of the present disclosure in order that the detailed description that follows may be better understood. Additional features and advantages of the disclosure will be described hereinafter, which form the subject of the claims.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTIn the following description, certain details are set forth such as specific quantities, sizes, etc. so as to provide a thorough understanding of the present embodiments disclosed herein. However, it will be obvious to those skilled in the art that the present disclosure may be practiced without such specific details. In many cases, details concerning such considerations and the like have been omitted inasmuch as such details are not necessary to obtain a complete understanding of the present disclosure and are within the skills of persons of ordinary skill in the relevant art.
The following definitions and explanations are meant and intended to be controlling in any future construction unless clearly and unambiguously modified in the following Description or when application of the meaning renders any construction meaningless or essentially meaningless. In cases where the construction of the term would render it meaningless or essentially meaningless, the definition should be taken from Webster's Dictionary, 3rd Edition. Definitions and/or interpretations should not be incorporated from other patent applications, patents, or publications, related or not, unless specifically stated in this specification or if the incorporation is necessary for maintaining validity.
As used herein, the term “mud cake” means and refers to a caked layer of clay adhering to the walls of a well or borehole, formed where the water in the drilling mud filters into a porous formation during rotary drilling.
As used herein, the term “lignosulfonate” means and refers to lignosulfonates, or sulfonated lignins, and are water-soluble anionic polyelectrolyte polymers.
As used herein, the term “PVA” or “polyvinyl alcohol” means and refers to a partially hydrolyzed polyvinyl acetate polymer having at least about 80 percent of the acetate groups hydrolyzed. PVA has been a desired fluid loss control agent because of its low cost, its lack of a set retarding function, and the fact that it is not totally water soluble, so that its effect on slurry viscosity is minimal. However, the PVA-based materials previously used have been less effective at temperatures above about 50 degrees C. because the PVA becomes essentially water-soluble. Also, PVA has not been particularly effective in cement slurries formulated with fresh water.
As used herein, the terms “cross link” and “polymerize” are used interchangeably, unless such use would be irrational.
Various embodiments of the present invention can use any cross linking agent. The cross-linking agent can comprise a borate releasing compound or any of the well known transition metal ions which are capable of creating a cross-linked structure. Examples of cross-linking agents include, but are not limited to, borate releasing compounds, a source of titanium ions, a source of zirconium ions, a source of antimony ions and a source of aluminum ions. Generally any cross linking agent can be used.
A cross linking agent can come from any source, such as sodium tetraborate, potassium tetraborate, boric acid, boron oxide, or calcium hexaboride, and the like. Titanate and zirconate cross-linking agents can be used as full or partial substitutes for the water-soluble borates, but are not as preferred.
In general, any polymer can be used with various embodiments of the present invention, such as a polymerization product formed by polymerizing a 2-acrylamido-2-methylpropane sulfonic acid, 2-methacrylamido-2-methylpropane sulfonic acid, sulfonated styrene, vinyl sulfonic acid, allyl ether sulfonic acids such as propane sulfonic acid allyl ether, methallyl ether phenyl sulfonates, acrylic acid, methacrylic acid, maleic acid, itaconic acid, n-acrylamidopropyl-n,n-dimethyl amino acetic acid, n-methacrylamidopropyl-n,n-dimethyl amino acidic acid, n-acryloyloxyethyl-n,n-dimethyl amino acidic acid, n-methacryloyloxyethyl-n,n-dimethyl amino acidic acid, n-acryloyloxyethyl-n,n-dimethyl amino acidic acid, n-methacryloyloxyethyl-n,n-dimethyl amino acidic acid, crotonic acid, acrylamidoglycolic acid, methacrylamidoglycolic acid, 2-acrylamido-2-methylbutanoic acid and 2-methacrylamido-2-methylbutanoic acid. Nonionic monomers which can be used in the formed (synthesized, intercalated) polymer include, but are not limited to, C1-C22 straight or branched chain alkyl or aryl acrylamide, C1-C22 straight or branched chain n-alkyl or aryl methacrylamide, acrylamide, methacrylamide, n-vinylpyrrolidone, vinyl acetate, ethoxylated and propoxylated acrylate, ethoxylated and propoxylated methacrylate, hydroxy functional acrylates such as hydroxyethylacrylate and hydroxypropylacrylate, hydroxy functional methacrylates such as hydroxyethylmethacrylate and hydroxypropylmethacrylate, n,n-dimethylacrylamide, n,n-dimethylmethacrylamide, styrene, styrene derivatives and C1-C22 straight or branched chain alkyl, aryl, allyl ethers, poly vinyl alcohol (PVA), and/or the like.
In embodiments utilizing PVA, at least in part, while not intending to be bound, the mechanism by which PVA controls fluid loss is believed to be different from that of other fluid loss materials. Most fluid loss additives are high molecular weight polymers that are totally water-soluble and form some type of a structure between the cement particles, which reduces the permeability of the filter cake. PVA is not totally water-soluble below about 50 degrees C., but is, instead, “water-swellable.” The individual PVA particles swell and soften to form small gel-balls in the slurry. These gel-balls deform by flattening, and become a part of the filter cake, greatly reducing the filter cake permeability, thus giving extremely good fluid loss control. Because PVA is not totally water-soluble, it does not significantly increase the slurry viscosity. PVA does not retard the set of cement.
Variations in the degree of hydrolysis of the polyvinyl alcohol, the molecular weight of the polyvinyl alcohol, and the inclusion of up to 25 percent by weight of substituents on the polyvinyl alcohol, such as methacrylate, methmethacrylate and the like are within the scope of the present invention. In addition, the preferred embodiment can contain calcium sulfate in a form such as dihydrate or anhydrite, but present in an amount equivalent to from 0 to 60 percent by weight of calcium sulfate hemihydrate.
The surfactant can be any of a wide range of materials such as ethoxylated alkyl phenols, ethoxylated primary or secondary alcohols, ethoxylated fatty alcohols, ethoxylated amines, ethoxylated amides, ethoxylated fatty acids, ethoxylated diamines, and ethoxylated quaternary ammonium chlorides. Suitable surfactants are described in detail in U.S. Pat. No. 5,105,885, the contents of which are hereby incorporated by reference as if it was reproduced herein in its entirety.
Antifoam materials useful in the present invention are usually polypropylene glycols but any suitable substitute can be utilized.
Cement retarding additives can also be added to the fluid loss additives. At temperatures above 80 degrees F., cement sets in a short period of time. Retarders, such as lignosulfonate materials, lengthen the time the cement slurry will stay liquid, allowing the slurry to be pumped down the casing and back up the annulus before setting.
For embodiments comprising sulfonated polymer dispersing agents, such materials are capable of being sulfonated polymelamine, sulfonated polystyrene or vinyl sulfonate polymers or mixtures of these. Other sulfonated polymer materials can be substituted provided that materials can be prepared at low pH and neutralized to form salts of the polymers. The salts can be sodium, potassium, lithium, ammonium, calcium, magnesium, and the like. The sulfonated polymer is added in a quantity of 0.05 to 2.0 percent by weight of the cement. These sulfonated polymers are available in liquid or powdered form. The weight percent specified is based on sulfonated polymer only and does not include the weight of any water that may be present in the liquid form.
In preparing the low viscosity dry mixed fluid loss control additive of the present invention, the components to the cement can be added as a single blend, or as individual components, or in any combination or order of addition.
The present invention is both compositions and methods for treating an oil or gas well and uses a cross linking agent, such as borax, as a preliminary wash for the well.
In various embodiments, a preliminary wash is capable of use to clean the well and pre-coat the tubing and the formation surfaces with the cross linking agent. In various embodiments, next, the cement mixture with polymer is pumped into the well. When the polymer comes into contact with the cross linking agent, the polymer undergoes polymerization or cross linking A cross linking agent helps to inhibit fluid loss into the formation. Also, because the cross linking agent wash cleaned the surfaces of the tubing and the formation, this results in better bonding between the cement and the surfaces of the tubing and the formation.
In various embodiments, the interface of the cross-linker and polymer forms a wiper that at least partially cleans the wellbore and/or pipe of excess drilling mud during fluid circulation through an annulus. In an embodiment, a wiper of crosslinker and polymer is capable of use before the flow of cement into the annulus, thereby cleaning the annulus of at least a portion of the excess mud. In an alternate embodiment, a wiper of crosslinker and polymer is capable of use immediately preceding the flow of cement into the annulus, thereby cleaning the annulus of at least a portion of the excess mud. In various embodiments, the use of a wiper of the present invention reduces drilling time because a separate circulation cleaning step is not needed.
EXAMPLESThis invention has been proven using borax as a common cross linker for polyvinyl alcohol (PVA) as the cross linking agent active ingredient by Applicants in the laboratory. These materials have been used before as fluid loss control agents, but only as a combined one step package. When used as a pre-blended or combined fluid loss control agent, the reaction of cross linking occurs in the cement slurry at the initial mixing time when water is added to the dry cement materials. As a result of this reaction in the early slurry life, the cross linking reaction creates a fragile structure that is temperature limited to about 200 degrees F. and requires a great excess of fluid loss material to control the fluid loss. Also the early reaction creates an increase in viscosity and possible gelatin of the slurry. Such rheology problems increase the demands on pumping equipment and change the desired state of turbulent flow to plug flow or laminar flow. Turbulent flow is an accepted method to increase mud removal and subsequent bond improvement.
The addition of fine particulate material, such as for example calcium carbonate, which has been ground or precipitated to less than 50 micron in average diameter, to the polyvinyl alcohol prior to mixing it with the cement will be beneficial. These particles are carried by the polyvinyl alcohol as it begins to soften in the aqueous slurry and can contribute to the plugging action of the permeable formation. The addition of fine particulate material which is initially non-reactive in the early reaction of cement hydration by has a surface binding to the polyvinyl alcohol to carry by a gluing action the solid particles which help to crate the “plug” for fluid loss prevention. The Portland cement particles cannot usually function in this manner since upon hydration, the surface of the cement goes into solution in a “sloughing” action. Also, this is considerably more important if the particular cement slurry formulation has high gel strength properties. Such a gelled slurry will usually not allow the cement grains to move the desired fluid loss plug area.
Applicants have documented using borax as a pre-wash and primer for cross linking a following polyvinyl alcohol in testing done in accordance with American Petroleum Institute procedures as outlined in API RP 10 publication. Variation from the strict test procedures were done in regard to simulation of a mud cake formation face as the permeable interface for fluid loss tests. The standard filter medium was 3.5 sq. in. in area. A 45 mm screen (No. 325) was supported by a 250 mm screen (No. 60). In order to simulate a mud covered formation face, the tests were conducted by sandwiching a 1/16 smear of thick bentonite mud between Whatman No. 1 qualitative filter paper. The mud was soaked with 2 ml of a solution containing 0.2 grams of borax. This “mud sandwich” was placed on the standard screen and fluid loss tests were conducted as outline in the API procedures. To verify the improved control of the invention, tests were run using the “mud sandwich” without borax and without the following polyvinyl alcohol.
Tests show that the polyvinyl alcohol, or other polymer, can be reduced to less than 0.1 percent by weight of dry cement and still maintain excellent fluid loss control at the low temperatures. The conventional pre-cross linked method uses as much as 10 times as much fluid loss additive. Temperature limits easily were above the 200° F. (93.3° C.) limit of the conventional technique and were in fact found to extend to the break down temperature of the polyvinyl alcohol which is above 300° F. (148.9° C.) for the particular polyvinyl alcohol tested. It is believed that the temperature could exceed this for a material with higher temperature stability.
As such, various embodiments of the present invention comprise a method for inhibiting fluid loss from an oil and gas well, said method comprising the steps of, separately:
washing a well borehole with a wash composition, said wash composition comprising a cross linking agent, wherein said cross linking agent at least partially impregnates a formation's face and
pumping a cement mixture into said well's borehole to cement at least a portion of a formation face, said cement mixture comprising a polymer composition, wherein said polymer polymerizes in, on, or about said formation's face upon exposure to said cross linking agent, thereby inhibiting fluid loss from said well's borehole to said formation. In various embodiments, the step of washing at least partially cleans the well of excess mud. In various further embodiments, the step of washing at least partially impregnates at least one of said borehole's tubing and said borehole's formation face with said cross linking agent. In various embodiments, the cross linking agent is added to the well along with oil-based drilling mud or “spacer”. As such, in various embodiments, the cross linking agent is at least one of borax, boric acid, water soluble borates, sodium borates, calcium borates, potassium borates, titanates, zirconates, and mixtures thereof. In various further embodiments, a fine particulate material is added to the polymer prior to mixing it with the cement mixture, such as calcium carbonate. In various embodiments, the polymer is at least one of polyvinyl alcohol, a low viscosity partially hydrolyzed polyvinyl alcohol such as DuPont Elvanol® 51-05S8.
Various further embodiments disclose a method for inhibiting fluid loss from an oil and gas well, the method comprising the steps of, separately:
washing a well with a reactant agent that creates a thickened reaction product when a secondary mixture is encountered, and
adding secondary mixture to the well's borehole which forms a thickened reaction product upon exposure to the reactant, thereby inhibiting fluid loss from the well's borehole to the well borehole's formation.
In all embodiments, the step of washing is capable of being removed and the cross linking agent is included with a drilling fluid circulated in the well's borehole prior to adding the cement mixture.
Various further embodiments disclose a kit for inhibiting fluid loss from an oil and gas well comprising:
a wash composition, the wash composition comprising a cross linking agent and
a polymer composition, wherein the polymer polymerizes in, on, or about the formation's face upon exposure to the cross linking agent, thereby inhibiting fluid loss from the well's borehole to the formation.
Various further embodiments disclose a polymerized well borehole, the polymerized well borehole formed by a method as herein disclosed.
A method for reducing an amount of fluid loss additive necessary to inhibit fluid loss from an oil and gas well, the method comprising the steps of, separately:
washing a well borehole with a wash composition, the wash composition comprising a cross linking agent, wherein the cross linking agent at least partially impregnates a formation's face and
pumping a cement mixture into the well's borehole to cement at least a portion of a formation face, the cement mixture comprising a polymer composition, wherein the polymer polymerizes in, on, or about the formation's face upon exposure to the cross linking agent, thereby inhibiting fluid loss from the well's borehole to the formation, wherein between about 0.1% and about 90% by volume of a contemporary fluid loss additive is used to inhibit fluid loss. In various embodiments, the fluid loss additive's components are the same as the components of the contemporary fluid loss additive.
In all methods and kits herein disclosed, the cement mixture is capable of comprising a permeable, micro-cluster silica material present in an amount from about 10 percent to about 30 percent by weight of the cement mixture, wherein the permeable, micro-cluster silica material has an average particle size ranging from about 30 to about 80 microns and a range of distribution from about 1 micron to about 200 microns.
Further embodiments of the present invention comprise kits. Kits of the present invention are capable of containing different constituents or components of the cement mixture. In an embodiment, a kit of the present invention comprises a polymer. In an alternate embodiment, a kit of the present invention comprises a polymer and a cross linking agent. Further kits may include, alternatively, retarders, defoamers, fluid loss additives, glass beads, perlite and/or the like.
The invention may be embodied in other specific forms without departing from its spirit or essential characteristics. The described embodiments are to be considered in all respects only as illustrative and not restrictive. The scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description. All changes to the claims that come within the meaning and range of equivalency of the claims are to be embraced within their scope. Further, all published documents, patents, and applications mentioned herein are hereby incorporated by reference, as if presented in their entirety.
Additional ExamplesPrevious methods of fluid-loss control has been attempted by a one-step addition of fluid-loss control additive to the cement, which hopefully reduces the ability of the liquid portion of the slurry from rapidly penetrating a permeable zone at the formation face. This creates a critical dependence of the fluid control on the use of a fluid-loss control additive that functions at the temperature of the permeable zone. Also, the cement slurry must be designed to compliment the requirements of the fluid-loss additive for rheology of the fluid portion of the cement slurry. Most fluid-loss control additives thicken the cement slurry they are mixed into. Also, they may retard the hardening of the cement when it reaches the destination. To deal with such properties it is common for service companies to have many different fluid-loss control additives and to select the “best fit” for the well conditions that are to be encountered.
What we have discovered and developed is a composition and method that uses a two-stage process to allow the use of one “BorePrime” (such term is not meant as a limitation but as a short hand identification of the process) composition which can function as a pre-wash and “seeding” of the permeable zone of the formation face, and a second or follow-up composition which can be the actual cement slurry which contains the reactive “PrimeBloc” (such term is not meant as a limitation but as a short hand identification of the process) composition. The “Prime” method is not as affected by temperature as most fluid-loss additives and can function from near freezing 32° F. (0.0° C.) to above 400° F. (204.4° C.). Further enhancements of the base bore prime technology have resulted in the discovery of mixtures, processes and compositions whereby the fluid loss additive is capable of being added at about the same time as the cement mixture.
“BorePrime” is to be used as a pre-wash or as a “spacer” additive or drilling mud additive that is non-toxic and environmentally clean. As a chemical wash the cost is very low compared to complex chemical washes. The “BorePrime” can be formulated as a non-thickened water base fluid that will allow turbulent flow in the annulus at very low pump rates. The turbulent flow has been observed in laboratory simulations that show the churning action that occurs at the front of the injected wash. The detergent action of the “BorePrime” together with the turbulent flow will granulate the excess mud adhering to the pipe and the loose mud at the formation face and carry the material out of the well. During this cleaning action a “seeding” will take place at the formation face which impregnates the mud cake with “BorePrime” chemical. The concentration will vary depending on the permeability at the formation face; the higher concentration typically going into the more permeable zones.
“BorePrime” can also be used in drilling mud or “spacers” to be available when later injection of “PrimeBloc” takes place. Thus fluid-loss control could be obtained without the necessity of the “BorePrime” wash, which in certain circumstances might not be desired. There is the possibility that a wash is not always an option if such things as disposal of fluids is an issue.
In various embodiments, “PrimeBloc” can be added to the cement mixture as a dry or liquid fluid-loss control additive that requires a “BorePrime” wash to be used ahead or to be used when the drilling mud or “spacer” has previously carried the “BorePrime”. The “PrimeBloc” is also very low in cost compared to complex fluid-loss control additives and requires an order of magnitude less material than conventional additives, in various embodiments because of the permeability block occurring at the formation-cement interface where the reaction of the “PrimeBloc” and “BorePrime” takes place. If the reaction had taken place in the cement slurry prior to reaching the permeable formation, the slurry would be much thicker and usually have to contain more water to reduce the viscosity of the reacted chemicals. Concentrating the reaction at the pressure-differential interface means the cement slurry doesn't have to carry materials which can cause excessive viscosity or otherwise excessive amounts of fluid-loss control material. Likewise this frees the slurry designer from the excess viscosity of most fluid-loss control methods. Testing at the low temperatures has shown fluid-loss control with less than 0.1 percent fluid-loss control additive in the “PrimeBloc” whereas a one stage fluid-loss test using conventional methods and materials requires 1 percent or more.
In various embodiments, the discovery of a two-stage method and also the type of chemicals in the method should be a significant improvement for fluid-loss prevention and permeable interface sealing. Such a technique could be utilized in any type of permeable situation to minimize leak-off of fluid from a well-bore, pond, lake, or dam. In alternate embodiments, the use of an additive should result in significant improvement for fluid loss prevention and permeable interface sealing.
Description of an Embodiment of Prime TechnologyIn various embodiments, this discovery has been proven in an embodiment using a common crosslinker for polyvinyl alcohol (Borax) as the “BorePrime” active ingredient. The “PrimeBloc” active ingredient used in our laboratory work was PVA (polyvinyl alcohol). These materials have been used before as fluid-loss control agents but only as a combined one-step package. When used as a pre-blended or combined fluid-loss control agent the reaction of cross-linking occurs in the cement slurry at the initial mixing time when water is added to the dry cement materials. As a result of this reaction in the early slurry life, the cross-linked reaction creates a fragile structure that is temperature limited to about 200° F. (93.3° C.) and requires a great excess of fluid-loss material to control fluid loss. Also, the early reaction creates viscosity increase and possible gellation of the slurry. Such rheology problems increase the demands on pumping equipment and changes the desired state of turbulent flow to plug flow or laminar flow. Turbulent flow is an accepted method to increase mud removal and subsequent bond improvement.
Using borax as a pre-wash and primer for cross-linking a following polyvinyl alcohol has been documented in our laboratory testing under American Petroleum Institute procedures as outlined in API RP 10 publications. Variations from the strict test procedures were done in regard to simulation of a mud caked formation face as the permeable interface for fluid-loss tests. The standard filter medium is 3.5 sq. in. in area. A 45 mm screen (No. 325) is supported by a 250 mm screen (No. 60). In order to simulate a mud covered formation face our tests were conducted by sandwiching a 1/16 smear of thick bentonite mud between Whatman No. 1 qualitative filter paper. The mud was soaked with 2 ml of a solution containing 0.2 grams of borax. This “mud sandwich” was placed on the standard screen and fluid-loss tests were conducted as outlined in API procedures. To verify the improved control of the invention tests were run using the “mud sandwich” without borax and without the following polyvinyl alcohol.
Polyvinyl alcohol contents of less than 0.1 percent by weight of dry cement used produced excellent fluid-loss control. The conventional pre-crosslinked method uses as much as 10 times as much fluid-loss additive. Temperature limits easily were above the 200° F. (93.3° C.) limit of conventional technique and were in fact found to extend to the break down temperature of the polyvinyl alcohol which is above 300° F. (148.9° C.) for the particular polyvinyl alcohol our testing was utilizing. It is only logical that the temperature could exceed this for a material with higher temperature stability.
Mud Impregnated ScreenFor testing, a modified filter has to retain Bore Prime chemical in such a way as to simulate a cementing job that used the Bore Prime in a pre-wash or spacer type application pumped ahead of a cement slurry. Simulating a permeable formation face that has a mud cake imbedded was the objective. To accomplish this a stainless screen without the 325 mesh but with only the 60 mesh back-up was used as the base for the simulation filter. Mud cake was a mixture of bentonite and water at a paste consistency that was layered across the back of the back-up screen. A dose of approximately 1 ml of the Bore Prime wash was then applied to the mud face that was against the 60 mesh. Next, a Whatman filter (cat. # 1003-055) that had been pre-soaked and air dried was lain on the 60 mesh and wetted with 1 ml of the Bore Prime wash. The cap of the fluid-loss cell that the back-up screen attaches to was then pushed against the mud side of the back-up screen, allowing the mud to move into the 60 mesh screen and against the Whatman filter paper.
This prepared filter was then inserted in the fluid-loss cell and tested as required by API RP10b. If a test at moderate to high temperature was to be run, then the prepared filter was held out of the fluid-loss cell until the cell was ready to receive the cement slurry. This alternate procedure is necessary to avoid dehydration of the mud cake on the prepared filter before testing.
Generally, any mock or simulated mud procedure can be used as long as a control is run.
Mud SandwichA “mud sandwich” filter can be used instead of the mud impregnated screen. To prepare this type filter use 60 mm diameter Whatman #3, which can be cut from (Whatman Cat No 1003 070) using a circle cutter such as AC-1 circle cutter from (www.buttonsonline.com). Use two papers with a layer of mud paste (100 g bentonite in 500 ml water) between them approximately 2 mm thick. The mud and papers should be dosed with Bore Prime wash made from 1 gram of Bore Prime in 100 ml of fresh water. This “mud sandwich” should be attached to the stainless screen using mud as an adhesive to hold the sandwich during assembly of the fluid-loss cell prior to running the fluid-loss test. As before mentioned, do not preheat this sandwich since it will dehydrate. Add it to the cell just before adding the cement slurry.
ResultsSlurry and mud compositions:
Claims
1.-14. (canceled)
15. A method for inhibiting fluid loss from an oil and gas well, said method comprising the steps of, separately: washing a well borehole with a wash composition, said wash composition comprising a cross linking agent, wherein said cross linking agent at least partially impregnates a formation's face and pumping a cement mixture into said well's borehole to cement at least a portion of a formation face, said cement mixture comprising a polymer composition, wherein said polymer polymerizes in, on, or about said formation's face upon exposure to said cross linking agent, thereby inhibiting fluid loss from said well's borehole to said formation.
16. The method of claim 15, wherein the step of washing at least partially cleans the well of excess mud.
17. The method claim 15, wherein the step of washing at least partially impregnates at least one of said borehole's tubing and said borehole's formation face with said cross linking agent.
18. The method of claim 15, wherein said cross linking agent is added to said well borehole along with an oil-based drilling mud or “spacer”.
19. The method of claim 15, wherein said cross linking agent is at least one of borax, boric acid, water soluble borates, sodium borates, calcium borates, potassium borates, titanates, zirconates, and mixtures thereof.
20. The method of claim 15, further comprising the step of: adding fine particulate material to the polymer composition prior to mixing it with the cement mixture.
21. The method of claim 20, wherein the fine particulate material is calcium carbonate.
22. The method of claim 15, wherein the polymer is at least one of polyvinyl alcohol or a low viscosity partially hydrolyzed polyvinyl alcohol such as DuPont Elvanol(R) 51-05S8.
23. A method for inhibiting fluid loss from an oil or gas well, said method comprising the steps of, separately: washing a well with a reactant agent that creates a thickened reaction product when a secondary mixture is encountered, and adding secondary mixture to the well's borehole which forms a thickened reaction product upon exposure to said reactant, thereby inhibiting fluid loss from said well's borehole to a formation adjacent to said well borehole.
24. The method of claim 15, wherein the step of washing is removed and said cross linking agent is included with a drilling fluid circulated in said well's borehole prior to adding said cement mixture.
25. A kit for inhibiting fluid loss from an oil and gas well comprising: a wash composition, said wash composition comprising a cross linking agent and a polymer composition, wherein said polymer polymerizes in, on, or about a formation's face upon exposure to said cross linking agent, thereby inhibiting fluid loss from said well's borehole to said formation through said formation's face.
26. A polymerized well borehole, said polymerized well borehole formed by a method of claim 15.
27. A method for reducing an amount of fluid loss additive necessary to inhibit fluid loss from an oil and gas well, said method comprising the steps of, separately: washing a well borehole with a wash composition, said wash composition comprising a cross linking agent, wherein said cross linking agent at least partially impregnates a formation's face and pumping a cement mixture into said well's borehole to cement at least a portion of a formation face, said cement mixture comprising a polymer composition, wherein said polymer polymerizes in, on, or about said formation's face upon exposure to said cross linking agent, thereby inhibiting fluid loss from said well's borehole to said formation through said formation's face, wherein between about 0.1% and about 90% by volume of a contemporary fluid loss additive is used to inhibit fluid loss.
28. The method of claim 27, wherein said fluid loss additive's components are the same as the components of the contemporary fluid loss additive.
29. The method of claim 27, wherein the step of washing is removed and said cross linking agent is included with a drilling fluid circulated in said well's borehole prior to adding said cement mixture.
30. The method of claim 15, wherein said cement mixture comprises a permeable, micro-cluster silica material present in an amount from about 10 percent to about 30 percent by weight of the cement mixture, wherein said permeable, micro-cluster silica material has an average particle size ranging from about 30 to about 80 microns and a range of distribution from about 1 micron to about 200 microns.
31. The kit of claim 25, further comprising: a permeable, micro-cluster silica material, wherein said permeable, micro-cluster silica material has an average particle size ranging from about 30 to about 80 microns and a range of distribution from about 1 micron to about 200 microns.
32. The method of claim 23, wherein the step of washing is removed and said cross linking agent is included with a drilling fluid circulated in said well's borehole prior to adding said cement mixture.
33. A polymerized well borehole, said polymerized well borehole formed by a method of claim 23.
34. The method of claim 23, wherein said cement mixture comprises a permeable, micro-cluster silica material present in an amount from about 10 percent to about 30 percent by weight of the cement mixture, wherein said permeable, micro-cluster silica material has an average particle size ranging from about 30 to about 80 microns and a range of distribution from about 1 micron to about 200 microns.
35. The method of claim 27, wherein said cement mixture comprises a permeable, micro-cluster silica material present in an amount from about 10 percent to about 30 percent by weight of the cement mixture, wherein said permeable, micro-cluster silica material has an average particle size ranging from about 30 to about 80 microns and a range of distribution from about 1 micron to about 200 microns.
Type: Application
Filed: Feb 11, 2010
Publication Date: Dec 16, 2010
Inventor: Lloyd Byron Spangle (Claremore, OK)
Application Number: 12/704,333
International Classification: E21B 33/13 (20060101); C09K 8/44 (20060101); C08F 8/00 (20060101);
