USE OF CATALYST COMPOSITION FOR CEMENTING A WELLBORE AND CEMENT SLURRY FOR THE SAME

Abstract

The present invention relates the use of acatalyst composition consisting of ammonium chloride, aluminum chloride, and magnesium oxide for addition to cement for oil well cementing. Moreover, the invention relates to a method of cementing a wellbore, comprising the steps of: i) drilling a wellbore; ii) introducing a casing string into the wellbore; iii) preparing a cement slurry based on a combination of cement and a catalyst composition consisting of ammonium chloride, aluminum chloride, and magnesium oxide; iv) pumping said cement slurry into the wellbore; and v) allowing said cement slurry to set. In addition, the invention relates to a cement slurry for cementing a wellbore, comprising i) cement, ii) water; and iii) a catalyst composition consisting of ammonium chloride, aluminum chloride, and magnesium oxide.

Description

BACKGROUND

The present invention relates to a catalyst composition for use in cementing a wellbore, a method for cementing a wellbore and to a cement slurry.

Patent EP 1 349 819 (corresponding to U.S. Pat. No. 7,316,744) of the present inventor discloses a composition for reinforcing cement, which contains: a) sodium chloride, potassium chloride, magnesium chloride, calcium chloride, strontium chloride, barium chloride and/or ammonium chloride; b) aluminum chloride; and c) silica and/or zeolite and/or apatite. EP 1 349 819 is incorporated by reference in its entirety.

This composition for reinforcing cement according to EP 1 349 819 is commercially available from PowerCem Technologies B.V. under the registered trade names of PowerCem and RoadCem.

In U.S. patent applications of the present inventor U.S. Ser. No. 13/654,920 and U.S. Ser. No. 13/540,181 the use of said composition for reinforcing cement according to EP 1 349 819 for cementing wellbores is disclosed.

It is an aim of the present invention to provide an alternative cement slurry using a more reactive, catalytic composition.

SUMMARY OF THE INVENTION

This aim is obtained by the use of a catalyst composition consisting of I) ammonium chloride, II) aluminum chloride, and III) magnesium oxide for addition to cement for oil well cementing.

In other words, the present invention relates to a method of cementing a wellbore, comprising the steps of: i) drilling a wellbore; ii) introducing a casing string into the wellbore; iii) preparing a cement slurry based on a combination of cement and a catalyst composition consisting of I) ammonium chloride, II) aluminum chloride, and III) magnesium oxide; iv) pumping said cement slurry into the wellbore; and v) allowing said cement slurry to set.

Moreover, the invention relates to a cement slurry for cementing a wellbore, comprising i) cement, ii) water; and iii) a catalyst composition consisting of I) ammonium chloride, II) aluminum chloride, and III) magnesium oxide.

In an embodiment, said cement slurry comprises between 50 and 85 wt %, preferably between 65 and 75 wt % of I) cement, and between 20 and 40 wt %, preferably between 25 and 30 wt % of II) water, and between 0.1 and 10 wt %, preferably between 1 and 3 wt %, more preferably between 1.5 and 2.5 wt % of catalyst composition III).

In an embodiment, the total quantity of components from group I) may be 1 to 25% by weight, preferably 5 to 15% by weight, more preferably 8 to 13% by weight; most preferably 10 wt. % based on the total weight of I)+II)+III).

In an embodiment, the total quantity of components from group II) may be 10 to 50% by weight, preferably 20 to 40% by weight, more preferably 25 to 35% by weight, most preferably 30 wt. % based on the total weight of I)+II)+III).

In an embodiment, the total quantity of components from group III) may be 5 to 40% by weight, preferably 10 to 30% by weight, more preferably 15 to 25% by weight, most preferably 20 wt. % based on the total weight of I)+II)+III).

DETAILED DESCRIPTION OF THE INVENTION

Extensive studies by the present inventor have revealed that with the use of the composition of EP 1 349 819 (viz. comprising sodium chloride, potassium chloride, ammonium chloride, magnesium chloride, calcium chloride, aluminum chloride, silica, magnesium oxide, magnesium hydrogen phosphate, magnesium sulfate, sodium carbonate, and cement) a certain combination of specific components are responsible for the activation of the remaining components. The present catalytic composition comprises these specific components and imposes reactivity on the other components to a full oxidation reaction when water is added to the dry mixture.

Based on this remarkable and surprising finding, the inventor has arrived at the present invention.

Without wishing to be bound by a theory, the following is observed. Several of the components of the RoadCem or PowerCem product of EP 1 349 819 comprise water of crystallization in their crystal structures. This water of crystallization reacts with some of the reactive components, such as aluminum chloride. This crystal water is e.g. believed to deactivate aluminum chloride in a preliminary oxidation reaction. The release of this water of crystallization is increased during the process of mixing the components together in which mixing process mixing equipment, such as crushers, might be used which generate heat.

When a high grade aluminum chloride is used in the preparation of the RoadCem or Powercem products, this grade is lowered upon storage. Higher grade aluminum chloride is more expensive than lower grade aluminum chloride and when the higher quality does not provide an additional reactivity since it has deactivated, it is not of any commercial use to start with a high grade aluminum chloride. With the catalyst and method of preparation of the additive of the present invention, this deactivation does not occur since the catalyst composition in only mixed with the remaining (water of crystallization containing) components of the composition for reinforcing cement shortly before it is used. In that case, there is not sufficient time for the deactivation to occur and the higher reactivity of aluminum chloride is maintained. The technical effect, is to supply a highly reactive catalyst composition for use in cementing of well bores.

The catalyst composition according to the present invention is prepared and stored separately from the remaining components. Shortly before using RoadCem or PowerCem product of EP 1 349 819 for cementing a well bore the catalyst composition is mixed with the remaining components. This is hence a novel method of preparing a cement slurry for cementing a wellbore using the composition as disclosed in U.S. Ser. No. 13/654,920 and U.S. Ser. No. 13/540,181.

An additional advantage of the present catalytic composition as revealed by research carried out by the present inventors is that it is possible to use a better grade (higher purity) aluminum chloride, such as 99% (2N), 99.9% (3N), 99.99% (4N) or even 99.999% (5N) Aluminum chloride, without deactivation.

The catalyst composition can be added to cement to increase the reactivity of cement and provide a high energetic value of the cement. Thus the present invention relates to the use of the catalyst composition to reinforce cement for high-demanding applications, for example cementing of wellbores.

The catalyst composition of the present invention, viz. the catalyst will in the future probably be marketed by PowerCem Technologies B.V. under the trademark of RC-C (RoadCem-catalyst).

Cement is a salt hydrate consisting of a fine-ground material which, after mixing with water, forms a more or less plastic mass. Cement hardens both under water and in the outside air. Cement is capable of bonding materials suitable for that purpose to form a mass that is stable also in water. The cement standards according to European standard NEN-EN-197-1 are as follows: CEM I is Portland cement; CEM II is composite Portland cement; CEM III is blast furnace slag cement; CEM IV is pozzolan cement and CEM V is composite cement.

Preferred Embodiments of All Aspects of the Present Invention

The present invention is preferably a mixture of noble metals (e.g. aluminum) and non-noble metals (e.g. magnesium) which combined give a synergistic reaction to the formation of stable crystalline structures.

For an optimum composition of the catalyst, the total quantity of components from group I) may be 1 to 25% by weight, preferably 5 to 15% by weight, more preferably 8 to 13% by weight; most preferably 10 wt. % based on the total weight of I)+II)+III).

For an optimum composition of the catalyst, the total quantity of components from group II) may be 10 to 50% by weight, preferably 20 to 40% by weight, more preferably 25 to 35% by weight, most preferably 30 wt. % based on the total weight of I)+II)+III).

For an optimum composition of the catalyst, the total quantity of components from group III) may be 5 to 40% by weight, preferably 10 to 30% by weight, more preferably 15 to 25% by weight, most preferably 20 wt. % based on the total weight of I)+II)+III).

Without wishing to be bound to any specific theory, experimental results indicate that the components which are present in the catalyst composition form crystalline structures when added to cement material which are well bonded together and are homogeneously distributed, in between the cement particles, and thereby bind the cement particles. Hardened cement which is prepared without this binder or with known binders has a relatively open structure when viewed on a microscopic scale, with crystalline agglomerations which are not homogeneously distributed. Consequently, the interaction between the crystalline agglomerations and also between the cement particles and the crystalline agglomerations is poor.

The crystalline compounds which are formed by this additive are surprisingly homogeneously distributed and may be in the form of acicular (viz. needle-like) structures. The homogeneous distribution results in an optimum strength and stability. The water in the cement is bound in and to the crystalline structures. Consequently, there are no local concentrations of water, and therefore the formation of potential weak spots is avoided.

The present catalyst composition has been found be induce the forming of nanoscale crystalline compounds. Hence, the function of the catalyst of the present invention is the formation of durable crystal structures.

The catalyst composition according to the present invention can be prepared by combining the required components and dry-mixing them. The catalyst composition according to the invention is preferably assembled from the abovementioned components in pure form (>97%, or even>98%, or even>99%).

The sole components of the catalyst composition are ammonium chloride, aluminum chloride, and magnesium oxide. Thus the catalyst composition is constituted by these three components. No other components are present. One of the uses of the catalyst composition of the present invention is as an (nano-engineered) additive for oil well cementing. The present catalyst composition improves flexibility and increases compressive strength.

One important use of concrete or cement in the oil and gas field is as so-called “well cementing” or the cementing of the drilling or oil well. For this use deep bores are drilled into the ground or soil. The inside of these bores are covered by a metallic layer or pipe that is used to guide the oil from the oil field up to the surface (=casing string). These metallic layers should adhere to surrounding environment (i.e. soil or rock). In order to obtain this adhesion between the metallic layer (casing or casing string) and the surroundings cement is often used.

Wellbores are protected and sealed by cementing, i.e. for shutting off water penetration into the well, to seal the annulus after a casing string (viz. a long section of connected oilfield pipe) has been introduced down the wellbore, or to plug a wellbore to abandon it.

Cementing is carried out using a cement slurry that is pumped into the well. In this method, usually the drilling fluids that are present inside the will are replaced by cement. The cement slurry fills the space between the casing and the actual wellbore, and hardens to create a seal. This presents external materials entering the well flow and positioning the casing string into place permanently.

A cement slurry is wet cement obtained by mixing dry cement and water and optionally one or more additives.

The cement slurry for cementing a wellbore according to the present invention, comprises i) cement, ii) water; and iii) a catalyst composition consisting of I) ammonium chloride, II) aluminum chloride, and III) magnesium oxide.

In an embodiment of the cement slurry, said slurry comprises between 50 and 85 wt %, preferably between 65 and 75 wt % of: I) cement, and between 20 and 40 wt %, preferably between 25 and 30 wt % of; II) water, and between 0.1 and 10 wt %, preferably between 1 and 3 wt %, more preferably between 1.5 and 2.5 wt % of composition III).

The wet cement (viz. cement slurry) is obtained by the use of mixers (e.g. hydraulic jet mixers, re-circulating mixers or batch mixers) from water and dry cement and one or more additives.

For wellbore cementing Portland cement is most frequently used (calibrated with additives to 8 different API classes). Examples of additives are accelerators, which shorten the setting time required for the cement, as well as retarders, which do the opposite and make the cement setting time longer. In order to decrease or increase the density of the cement, lightweight and heavyweight additives are added. Additives can be added to transform the compressive strength of the cement, as well as flow properties and dehydration rates. Extenders can be used to expand the cement in an effort to reduce the cost of cementing, and antifoam additives can be added to prevent foaming within the well. In order to plug lost circulation zones, bridging materials are added, as well.

A method for well cementing is known in the art. After casing string has been run into the bored well, an cementing head is attached to the top of the wellhead to receive the slurry from the pumps. A so-called bottom plug and top plug are present inside the casing and prevent mixing of the drilling fluids from the cement slurry. First, the bottom plug is introduced into the well, and cement slurry is pumped into the well behind it, viz. within the casing and not yet between the casing and its surroundings. Then the pressure on the cement being pumped into the well is increased until a diaphragm is broken within the bottom plug, permitting the cement slurry to flow through it and up the outside of the casing string, viz. outside of the casing and hence between the casing and its surroundings. After the proper volume of cement is pumped into the well, a top plug is pumped into the casing pushing the remaining slurry through the bottom plug. Once the top plug reaches the bottom plug, the pumps are turned off, and the cement is allowed to set.

Since wellbores are very deep, setting or hardening at deep depths and under conditions of high temperature and/or high pressure, and optionally corrosive environments, there are stringent requirements for the cement.

A few of the challenges today with respect to well cementing are discussed below.

Despite recent technological advances with elastomers, polymers, fibres and reactive components that self-heal micro fissures, the cement sheath between the casing string and the surrounding rock/soil is not always able to deliver an acceptable long-term solution for today's demanding drilling environment. Changes in down hole conditions with pressure and temperature fluctuations impose stresses on the cement sheath. Consequently, shrinking and de-bonding of the cement sheath creates very small micro cracks allowing fluid migration. Besides these external forces that cause cement sheath damage an evaluation of conventional oil well cement sheath on the nanoscopic scale from 1-100 nm reveals that the chemical bond between components within the cement itself is relatively brittle.

Examples of the challenges are: i) micro cracks occurring because of fluctuations in pressure and/or temperature inside the well; ii) undesired gas migration due to shrinkage or expansion of the cement; iii) corrosion of the protective casing, which costs hundreds of millions and which reduces longevity.

There are several demands required in the field of well cementing, viz. with respect to density, permeability, shrinkage, bonding, chemical resistance, setting time, viscosity, flexibility, and durability. Moreover, downhole temperature can exceed 200° C.

An example of preferred product criteria for cement for wells are the following:

• • Density: value<1300 kg/m³
  • Permeability: material has to be impermeable
  • Shrinkage: material may not shrink, expansion is preferred
  • Bonding: good bond required with steel
  • Chemical resistance: high chemical resistance required
  • Thickening time: materials needs to be workable up to 6 hours
  • Viscosity: preferably 300 CP
  • Flexibility: stretch of 2% without fracturing

Known Portland cement consists of five major compounds and a few minor compounds. The composition of a typical Portland cement is as follows: 50 wt. % of tricalcium silicate (Ca₃SiO₅ or 3CaO.SiO₂); 25 wt. % of dicalcium silicate (Ca₂SiO₄ or 2CaO.SiO₂); 10 wt. % of tricalcium aluminate (Ca₃Al₄O₆ or 3CaO.Al₂O₃); 10 wt. % of tetracalcium aluminoferrite (Ca₄Al₂Fe₂O₁₀ or 4CaO.Al₂O₃.Fe₂O₃); 5 wt. % of gypsum (CaSO₄.2H₂O)

Without wishing to be bound to any specific theory, experimental results discussed in prior patent applications of the present inventor U.S. Ser. No. 13/654,920 and U.S. Ser. No. 13/540,181 (both incorporated by reference in its entirety) indicate that the components which are present in the composition for reinforcing cement used in the present application form crystalline structures when added to cement material which crystalline structures are well bonded together and are homogeneously distributed, in between the cement particles, and thereby bind the cement particles.

Without wishing to be bound to a theory, the following is observed. When water is added to cement, each of the compounds undergoes hydration and contributes to the final product. Only the calcium silicates contribute to strength. Tricalcium silicate is responsible for most of the early strength during first 7 days. Dicalcium silicate, which reacts more slowly, contributes only to the strength at later times. Upon the addition of water, tricalcium silicate rapidly reacts to release calcium ions, hydroxide ions, and a large amount of heat. The pH quickly rises over 12 because of the release of alkaline hydroxide (OH—) ions. This initial hydrolysis slows down quickly with a corresponding decrease in heat.

The reaction slowly continues producing calcium and hydroxide ions until the system becomes saturated. Once this occurs, the calcium hydroxide starts to crystallize. Simultaneously, calcium silicate hydrate begins to form. Ions precipitate out of solution accelerating the reaction of tricalcium silicate to calcium and hydroxide ions, also called Le Chatelier's principle. The evolution of heat is then dramatically increased again.

The formation of the calcium hydroxide and calcium silicate hydrate crystals provide “seeds” upon which more calcium silicate hydrate can form. The calcium silicate hydrate crystals grow thicker which makes it more difficult for water molecules to reach the anhydrate tricalcium silicate. The speed of the reaction is controlled by the rate at which water molecules diffuse through the calcium silicate hydrate coating. This coating thickens over time causing the production of calcium silicate hydrate to become slower and slower. The majority of space is filled with calcium silicate hydrate, what is not filled with the hardened hydrate is primarily calcium hydroxide solution. The hydration will continue as long as water is present and there are still anhydrate compounds in the cement paste.

Dicalcium silicate also affects the strength of concrete through its hydration. Dicalcium silicate reacts with water in a similar manner as tricalcium silicate, but much more slowly. The heat released is less than that by the hydration of tricalcium silicate because the dicalcium silicate is much less reactive. The other major components of Portland cement, tricalcium aluminate and tetracalcium aluminoferrite also react with water. Heat is evolved with cement hydration. This is due to the breaking and making of chemical bonds during hydration.

The strength of cement bound products is very much dependent upon the hydration reaction just discussed. Water plays a critical role, particularly the amount used. The strength of the product increases, when a lower amount of water is used. The hydration reaction itself consumes a specific amount of water. The empty space (porosity) is determined by the water to cement ratio. The water to cement ratio is also called the water to cement factor (abbreviated by wcf) which is the ratio of the weight of water to the weight of cement used in the slurry. The wcf has an important influence on the quality of the cement produced.

Low water to cement ratio leads to high strength but low workability. High water to cement ratio leads to low strength, but good workability. A person skilled in the art of cement is able to determine the optimum water cement factor based on the component used in the slurry and the purpose of the cement slurry.

Time is also an important factor in determining product strength. The product hardens as time passes. The hydration reactions get slower and slower as the tricalcium silicate hydrate forms. It takes a great deal of time up to several years for all of the bonds to form, which eventually determines the product's strength for the life of the well.

When the catalyst composition according to the present invention is used as additive, moisture remains necessary for hydration and hardening. The five major compounds of the hydration process of cement still remain the most important hydration products but the minor products of hydration probably change. Furthermore, the rate at which important hydration reactions occur and the relative distribution of hydration products changes as a result of the addition of the present inventive composition. In addition, the crystallization of calcium hydroxide accordingly occurs at different rates and the reduction of heat generation from the hydration reactions occurs. There are more crystals formed during the reactions and the relevant crystalline matrix is much more extensive.

When adding the present composition, the water changes chemically in sphere, electrical load, surface tension and reaches a chemical/physical equilibrium in the matrix. This complex process depends of the type and mass of materials involved in the cement slurry. Similar to the chemical processes physical aspects are part of the equilibrium process in the matrix when the amount of water, trapped as free water is reduced and the crystals grow into the empty void space. This makes the product less permeable to water and more resistant to all types of attack that are either water dependant or water influenced. A bigger fraction of the water is converted to crystalline water than is the case with the reactions in the absence of the present inventive composition. The reduced porosity and increased crystalline structural matrix increases compressive, flexural and breaking strength of the product and change the relative ratio between these strengths.

As before the strength of the product increases when less water is used to make a product. The hydration reaction itself now tends to consume a different amount of water. When the present inventive composition is mixed with oil well cement it is also possible to use salt water and achieve a good end result. According to the best mode of the invention, 12.5 kilogram of Dyckerhoff cement API Class G is mixed with 4.75 kilogram water and 375 of the catalyst composition, comprising one part ammonium chloride to two parts magnesium oxide to three parts aluminum chloride.

Embodiments disclosed in the present invention for one aspect of the invention are, were applicable, also intended to be used for other aspects of the inventions, and vice versa. The present invention is further explained in the appended claims.

Claims

1. Use of a catalyst composition consisting of I) ammonium chloride, II) aluminum chloride, and III) magnesium oxide for addition to cement for oil well cementing.

2. Composition according to claim 1, wherein the total quantity of I) is 1 to 25% by weight, preferably 5 to 15% by weight, more preferably 8 to 13% by weight; based on the total weight of I)+II)+III).

3. Composition according to claim 1, wherein the total quantity of II) is 10 to 50% by weight, preferably 20 to 40% by weight, more preferably 25 to 35% by weight, based on the total weight of I)+II)+III).

4. Composition according to claim 1, wherein the total quantity of III) is 5 to 40% by weight, preferably 10 to 30% by weight, more preferably 15 to 25% by weight, based on the total weight of I)+II)+III).

5. Method of cementing a wellbore, comprising the steps of: i) drilling a wellbore; ii) introducing a casing string into the wellbore; iii) preparing a cement slurry based on a combination of cement and a catalyst composition consisting of a) ammonium chloride, b) aluminum chloride, and c) magnesium oxide; iv) pumping said cement slurry into the wellbore; and v) allowing said cement slurry to set.

6. Cement slurry for cementing a wellbore, comprising i) cement, ii) water; and iii) a catalyst composition consisting of I) ammonium chloride, II) aluminum chloride, and III) magnesium oxide.

7. Cement slurry according to claim 6, comprising between 50 and 85 wt %, preferably between 65 and 75 wt % of I) cement, and between 20 and 40 wt %, preferably between 25 and 30 wt % of II) water, and between 0.1 and 10 wt %, preferably between 1 and 3 wt %, more preferably between 1.5 and 2.5 wt % of catalyst composition III).