US20100319918A1

US20100319918A1 - Cement additive for the enhanced treatment of oil and gas wells and related methods of use

Info

Publication number: US20100319918A1
Application number: US12/868,501
Authority: US
Inventors: Lloyd Byron Spangle
Original assignee: Individual
Current assignee: Individual
Priority date: 2008-01-25
Filing date: 2010-08-25
Publication date: 2010-12-23
Also published as: US7670994B1; CA2713212C; US20100314112A1; CA2713212A1; WO2009094056A1; WO2009094662A2; WO2009094662A3; CA2713238A1

Abstract

Cement mixtures and methods are disclosed for enhancing fluid loss prevention in oil and gas wells comprising an electrolyte, a polymer and a cross linking agent.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority as a continuation of U.S. Non-provisional patent application Ser. No. 12/704,333, filed Feb. 11, 2010 which further 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 INVENTION

The present invention relates to an improved cement additive for treating oil and gas wells. Various further embodiments relate to enhanced methods for treating oil and gas wells.

DESCRIPTION OF THE RELATED ART

Previous 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.
As such, the art field is in search of additives and methods to alleviate these issues.

SUMMARY OF THE INVENTION

Various embodiments of the present invention generally relate to additives and methods for treating an oil and/or gas well. In an embodiment, a method of the present invention generally comprises an improved cement additive for treating oil and gas wells that is added to a cement mixture comprising a polymer composition, such as, for example, a polyvinyl alcohol. In an embodiment, the additive is an electrolyte.
The cement polymer mixture undergoes cross linking when exposed to the cross linking agent. The electrolyte inhibits that cross-linking or polymerization. The additive has been shown to inhibit the cross linking such that cement mixture can achieve greater penetration into the formation before polymerization or cross-linking. 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 an embodiment, the cement mixture comprises an additive, a polymer, a suitable crosslinker for the polymer, and at least one cement. Further embodiments comprise at least one retarder. Various further embodiments comprise at least one defoamer. Various further embodiments comprise a perlite.
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.
In various embodiments, the cement mixture comprising the additive is added about the same time as the cross-linking agent.
In various embodiments, circulation can be started with addition of a first cement mixture comprising a polymer and a cross linking agent followed shortly thereafter by the addition of an additive comprising an electrolyte. In such an embodiment, the first cement mixture acts as a wiper to remove excess drilling mud.
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% (C₂S), 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.
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 an additive comprising an electrolyte is added such that the ratio of polymer to electrolyte is 1:1. In an alternate embodiment, the amount of an additive comprising an electrolyte added is in excess of the amount of polymer added. In an alternate embodiment, the amount of an additive comprising an electrolyte added is 50% in excess of the amount of polymer. In an alternate embodiment, the amount of an additive comprising an electrolyte added is about 100% in excess of the amount of the polymer. In an alternate embodiment, the amount of an additive comprising an electrolyte added is about 200% in excess of the amount of the polymer. In an alternate embodiment, the amount of an additive comprising an electrolyte added is about 500% in excess of the amount of the polymer. In an alternate embodiment, the amount of an additive comprising an electrolyte added is about 50% less than the amount of the polymer. In an alternate embodiment, the amount of an additive comprising an electrolyte added is about 75% less than the amount of the polymer. In an alternate embodiment, the amount of an additive comprising an electrolyte added is about 90% less than the amount of the polymer. In an alternate embodiment, the amount of an additive comprising an electrolyte added is about 25% less than the amount of the polymer. In general, any amount of an additive comprising an electrolyte can be used and can be governed by one of ordinary skill in the art based on the polymer, results, cost, and/or the like.
As such, in various embodiments methods for inhibiting fluid loss from an oil and gas well are disclosed comprising the steps of adding an electrolyte into a cement mixture comprising a cross linking agent and a polymer, and pumping said 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 polymerization of said polymer is inhibited, thereby inhibiting fluid loss from said well's borehole to said formation.
Various embodiments of the present invention comprise a fluid loss additive for use in a cement mixture to complete a well bore, said fluid loss additive comprising an electrolyte, a polymer and a cross linking agent. An embodiment comprises about 1% electrolyte to about 99% electrolyte, about 1% polymer to about 99% polymer, and about 0.1% cross linking agent to about 5% cross linking agent. An alternate embodiment comprises about 5% electrolyte to about 90% electrolyte, about 5% polymer to about 90% polymer, and about 0.1% cross linking agent to about 5% cross linking agent. An alternate embodiment comprises about 15% electrolyte to about 75% electrolyte, about 15% polymer to about 75% polymer, and about 0.01% cross linking agent to about 3% cross linking agent. An alternate embodiment comprises about 25% electrolyte to about 50% electrolyte, about 25% polymer to about 50% polymer, and about 0.01% cross linking agent to about 2% cross linking agent. In general, the relative proportions of the electrolyte, the polymer, and the cross linking agent can be varied. Various further embodiments comprise at least one of a retarder, a defoamer, and a polyanionic polymer.
Various embodiments of the present invention comprise a kit for inhibiting fluid loss from an oil and gas well comprising about 1% electrolyte to about 99% electrolyte, about 1% polymer to about 99% polymer, and about 0.1% cross linking agent to about 5% cross linking agent. An alternate embodiment of a kit comprises about 5% electrolyte to about 90% electrolyte, about 5% polymer to about 90% polymer, and about 0.1% cross linking agent to about 5% cross linking agent. An alternate embodiment of a kit comprises about 15% electrolyte to about 75% electrolyte, about 15% polymer to about 75% polymer, and about 0.01% cross linking agent to about 3% cross linking agent. An alternate embodiment of a kit comprises about 25% electrolyte to about 50% electrolyte, about 25% polymer to about 50% polymer, and about 0.01% cross linking agent to about 2% cross linking agent. In general, the relative proportions of the electrolyte, the polymer, and the cross linking agent in the kit can be varied. Various further embodiments of a kit comprise at least one of a retarder, a defoamer, and a polyanionic polymer.
Further embodiments comprise a wellbore treated to inhibit fluid loss with the composition as herein described.
In various embodiments, a pumpable cement mixture is disclosed comprising about 0.01% to about 5.0% electrolyte, about 0.01% to about 5.0% polymer, about 0.001 to about 0.1% cross linking agent, about 5% to about 50% water, and about 30% to about 95% cement. In an alternate embodiment, a pumpable cement mixture is disclosed comprising about 0.0001% to about 3.0% electrolyte, about 0.001% to about 3.0% polymer, about 0.0001 to about 0.3% cross linking agent, about 10% to about 40% water, and about 40% to about 90% cement. In an alternate embodiment, a pumpable cement mixture is disclosed comprising about 0.1% to about 3.0% electrolyte, about 0.1% to about 3.0% polymer, about 0.1 to about 0.3% cross linking agent, about 20% to about 30% water, and about 50% to about 70% cement. In general, various embodiments of the present invention are capable of comprising varying proportions of electrolyte, polymer, cross-linking agent, water and cement. Various embodiments further comprise at least one of a retarder, a defoamer, and a polyanionic polymer. Further disclosed is a completed wellbore comprising a pumpable cement mixture as herein disclosed.
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 EMBODIMENT

In 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 “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.
As used herein, the term “electrolyte” means and refers to a chemical compound that ionizes when dissolved or molten to produce an electrically conductive medium. Electrolytes commonly exist as solutions of acids, bases or salts. Furthermore, some gases may act as electrolytes under conditions of high temperature or low pressure. Electrolyte solutions can also result from the dissolution of some biological (e.g., DNA, polypeptides) and synthetic polymers (e.g., polystyrene sulfonate), termed polyelectrolytes, which contain charged functional group. Electrolyte solutions are normally formed when a salt is placed into a solvent such as water and the individual components dissociate due to the thermodynamic interactions between solvent and solute molecules, in a process called solvation. For example, when table salt, NaCl, is placed in water, the salt (a solid) dissolves into its component elements.
The additive is comprised of the following components:
one part PVA that is readily soluble such as DuPont's Elvanol is preferred, partially hydrated PVA such as Elvanol 50-42S8 is preferred.
a suitable crosslinker for the PVA such as boric acid, other soluble borates, titanates, or zirconates in the amount of approximately 0.05 parts by weight.
an electrolyte such as NaCl in the amount of approximately equal weight to the PVA (one part by weight.
a neutralizing compound such as calcium lignosulfonate in the amount of approximately 0.05 parts by weight).
a defoamer in the amount of approximately 0.1 parts by weight.
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-C₂₂straight or branched chain alkyl or aryl acrylamide, C₁-C₂₂straight 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-C₂₂straight or branched chain alkyl, aryl, allyl ethers, poly vinyl alcohol (PVA), and/or the like.
In general, any electrolyte can be used with various embodiments of additives of the present invention.
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, and an additive comprising an electrolyte, in various embodiments. Various further embodiments comprise an electrolyte, such as a salt.
In various embodiments, the additive comprising an electrolyte is added at the same time as the cement mixture. A cross linking agent or additive helps to inhibit fluid loss into the formation. Likewise, the additive comprising an electrolyte inhibits fluid loss into the formation.
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 and an additive comprising an electrolyte. In an alternate embodiment, a kit of the present invention comprises a polymer, an additive comprising an electrolyte, and a cross linking agent. Further kits may include, alternatively, retarders, defoamers, fluid loss additives, 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.

EXAMPLES

It has been discovered, in various embodiment and/or various conditions, that polyvinyl alcohol used in cementing formulations for fluid-loss prevention can be much more effective if a crosslinker such as borax or boric acid is used with an electrolyte, such as, but not limited to NaCl. Various further embodiments include a plasticizer, such as, but not limited to calcium lignosulfonate. Various further embodiments comprise a defoamer. In an effort to accomplish that objective, in an embodiment, we have found that a cement additive comprising about 1 part polyvinyl alcohol, about 1 part NaCl, about 0.05 parts borax, about 0.05 parts calcium lignosulfonate and about 0.12 parts defoamer prepared on weight basis in a dry blend and added at a concentration of about 1 percent by weight of the cement achieves the desired result. The proportions of constituents can be varied widely and are often chosen based upon a particular well and geological aspects of the well. As such, the proportions of components in various embodiments of the present invention can be varied widely.
In various embodiments, the percentage of cement additive is greater than 1 percent by weight of cement. In various alternate embodiments, the percentage of cement additive is less than 1 percent by weight of cement.
In an alternate embodiment, the ratio of polymer to electrolyte is such that an excess of polymer is used. Various suitable ratios include, but are not limited to about 1.1:1; 1.5:1; 2:1; 3:1; 4:1; 5:1; and greater than 5:1. In an alternate embodiment, the ratio of polymer to electrolyte is such that an excess of electrolyte is used. Various suitable ratios include, but are not limited to about 1:1.1; 1:1.5; 1:2; 1:3; 1:4; 1:5; and greater than 1:5. In general, any ratio of polymer to electrolyte can be used.
In various embodiments, a polymer is added with a crosslinker to a dry cement mixture which is then blended with water. Also, a liquid version of the polymer and/or crosslinker are capable of use. In various embodiments the polymer begins reacting with the caustic cement and hydrates the mixture of cement and water upon contact with the polymer. As such, the crosslinker is subjected to chemical reactions that are not desirable.
In various embodiments, various embodiments of the proposed new method involve changing the ionic environment to delay the polymer hydration. Such delay will allow the first hydration reaction of the cement mixture to take place before the polymer is in solution. In various conventional methods the crosslinker and polymer are sometimes neutralized by these initial cement reactions and are then not available for the intended purpose of fluid-loss control. The controlled solution of the invention overcomes this shortcoming of fresh water solubility of polymer in cement slurries. It was found that the solution alteration brought about by the salt (electrolyte) and/or lignosulfonate (plasticizer) resulted in less fluid loss from the cement slurry and less susceptibility to temperature effects on the polymer.
The amount of “Improved PVA-Mixture” needed for fluid-loss control is determined in laboratory testing procedures such as American Petroleum Institute Research Procedures 10B, as is known by one of ordinary skill in the art with reference to the teachings of the various embodiments of the present invention.
In one aspect, an improvement of embodiments of the present invention is that no different consideration or special mixing procedures are needed because of the “Improved PVA-Mixture.” The cementing operation is capable of being performed as it would normally be done.
It is conceivable that the benefit of controlled hydration of a crosslinker and PVA in glues or other conventional applications would be a logical use of the invention.

- Any crosslinker for a polymer such as borates, titanates, zirconates, and mixtures of these are possible candidates for various embodiments of methods of the present invention.
- A polymer should be readily soluble such as DuPont's Elvanol. Partially hydrated PVA such as Elvanol FL42B.
- An electrolyte such as NaCl is capable of use.

After the amount needed is known that amount will be added to the dry cement blend and taken to the job location. The results of using “Improved Polymer-Mixture” should be a much more effective control of slurry viscosity and fluidity of the pumped slurry. Also, loss of the fluid portion of the slurry should be significantly reduced.
Holcim class G Cement with the fluid-loss additive BOA-C: Samples of Holcim class G cement from Columbia have been tested with the fluid loss control additive designated BOA-C. BOA-C is the designation given to the additive disclosed herein. BOA-C has been found to perform with better compatibility to various cements than most other fluid-loss materials. The following tests give the concentrations in percent by weight of cement used. Fluid-loss tests were at a test pressure of 1000 psi using API-RP 10 standard research procedures. The R-61 is a retarder received from Columbia. Rheology tests were conducted using a Fann V-G Meter with a number 1 standard spring at 80° F. Preferred slurry density was 15.6 lb/gal.

Fluid-Loss Tests


Temp	ml/30	API
° F.	min.	(ml/30 min.

1.1% BOA-C + 46% water	80	13	26
1.1% BOA-C + 46% water	80	8	16
(2^ndtest)
0.75% BOA-C + 46% water	80	23	45
1.1% BOA-C + 0.3% R-61 +	110	11	21
46% water
1.1% BOA-C + 0.3% R-61 +	110	9	18
46% water (2^ndtest)
1.3% BOA-C + 0.125% R-61 +	110	16	32
46% water
1.0% BOA-C + 0.6% R-61 +	125	10	20
46% water

Rheology:


Atmospheric Consistometer			Yield Pt.
Viscosity (B_c)		Plastic Vis. (cps)	(lbs/100 ft²)

1.3% BOA-C + 0.125% R-61 +	down	53	62
46% water
initial-12
20 min.--16
1.3% BOA-C + 0.125% R-61 +	up	55	59
46% water
initial-12
20 min.--16
0.75% BOA-C + 46% water	down	51	62
initial-11
20 min.--15
0.75% BOA-C + 46% water	up	55	58
initial-11
20 min.--15

Compressive Strength:

1.1% BOA-C+46% water at 80° F. and 1000 psi curing pressure for 12 hours—844 psi
Fluid-Loss Tests Using BOA-C with EX490: The following laboratory tests show results using BOA-C fluid-loss additive. All tests are in accordance with API-RP 10 testing procedures. The tests listed are with a compatible retarder EX490. Viscosity is in Bearden Units from an atmospheric consistometer.

Cement System Components:

1. Lafarge G cement+1.3% BOA-C+1% EX490+44% water
2. Tijeras G cement+35% silica flour+2.3% BOA-C+1.35% EX490+60% water
3. Tijeras G cement+35% silica flour+2.3% BOA-C+1.0% EX490+60% water
4. Tijeras G cement+35% silica flour+2.3% BOA-C+0.75% EX490+60% water
5. Tijeras G cement+35% silica flour+2.3% BOA-C+0.625% EX490+60% water
6. Tijeras G cement+35% silica flour+2.3% BOA-C+0.5% EX490+60% water
7. Tijeras G cement+35% silica flour+2.0% BOA-C+0.75% EX490+60% water


Cement			Fluid Loss	Fluid Loss	Fluid Loss	Fluid Loss
System	Viscosity	Viscosity	(ml/30 min)	(ml/30 min)	(ml/30 min)	(ml/30 min)
Components	(initial)	(20 min.)	140° F.	167° F.	197° F.	220° F.

1. (test one)	11	12	34	—	—	—
1. (test two)	11	12	30	—	—	—
1. (test one)	12	9	—	37	—	—
1. (test two)	11	12	—	33	—	—
1. (test one)	12	7	—	—	31	—
1. (test two)	12	7	—	—	26	—
2.	18	10	—	—	—	29
2.	13	15	—	—	—	125
3.	13	15	—	—	—	45
4.	13	15	—	—	—	36
5.	13	30	—	—	—	32

6.

13

29

(test aborted due to viscosity increase)

7.	12	20	—	—	—	165

The conventional use of polymer, such as PVA, at the present time is a simple addition of the PVA and crosslinker to a dry cement then blended together before mixing with water. Also, a liquid version of the PVA and crosslinker is sometimes used which is then added to the mix water. In these methods the PVA begins reacting with the caustic cement hydrates the instant the mixture of cement and water contacts the PVA. Also, the crosslinker is subjected to chemical reactions that are not in a desirable progression. In various embodiments, the proposed new method involves changing the ionic environment to delay the PVA hydration in a caustic water solution of the cement mix water. This will allow the first hydration reactions of the cement to take place before the PVA, or other polymer, is in solution. In the conventional method the crosslinker and PVA are sometimes neutralized by these initial cement reactions and are not then available for the intended purpose of fluid-loss control. The controlled solution of the invention overcomes this shortcoming of fresh water solubility of PVA in cement slurries. It was found that the solution alteration brought about by the salt and lignosulfonate resulted in less fluid loss from the cement slurry and less susceptibility to temperature effects on the PVA.


Fluid Loss Study Using PVA in Portland Cement

Temperature

	80	100	110	125	110	110	110	110	110	110
	Mix 1	Mix 2	Mix 3	Mix 4	Mix 5	Mix 6	Mix 7	Mix 8	Mix 9	Mix 10

Cement	600	600	600	600	600	600	400	400	400	400
PVA	3	3	3	3	3	3	2	2	2	2
Boric acid	0.15	0.15	0.15	0.15	—	—	—	0.1	0.1	0.1
Borax	—	—	—	—	0.2	—	—	—	—	—
DWD	—	—	—	—	—	—	1	—	—	—
Defoamer	0.5	0.5	0.5	0.5	0.5	0.5	0.4	0.4	0.4	0.4
Retarder	—	1.2	1.8	2.4	1.8	1.8	1.2	1.2	1.2	1.2
Water	276	276	276	276	276	276	184	184	184	184
NaCl	—	—	—	—	—	—	—	8	4	2
Fluid loss (ml)	22	38	106	38	842	725	509	58	32	21

Temperature

	80	110	125	80	80	80	80	80	80
	Mix 11	Mix 12	Mix 13	Mix 14	Mix 15	Mix 16	Mix 17	Mix 18	Mix 19

Cement	400	600	400	400	400	400	400	400	400
PVA	2	2.6	2	2	2	2	2	2	2
Borax	0.2	0.26	0.2	0.2	0.2	0.2	0.2	0.2	0.2
Defoamer	0.4	0.33	0.22	0.4	0.4	0.4	0.4	0.4	0.4
Retarder	—	1.2	2.4	—	—	—	—	—	—
Water	184	264	176	184	184	184	184	184	184
NaCl	2	2.6	2	2	1	2	2	2	2
CaLignosulfonate	—	—	—	—	—	1	0.5	0.25	0.1
Fluid loss (ml)	>1000	17	20	>1000	>1000	26	20	17	15

Temperatures are in degrees Fahrenheit. Test pressure was 1000 psi. Components are in grams.
Testing was done following API RP 10 recommended procedures. Class G cement was used.

Claims

1. A method for inhibiting fluid loss from an oil and gas well, said method comprising the steps of:

adding an electrolyte into a cement mixture comprising a cross linking agent and a polymer, and

pumping said 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 polymerization of said polymer is inhibited, thereby inhibiting fluid loss from said well's borehole to said formation.

2. A fluid loss additive for use in a cement mixture to complete a well bore, said fluid loss additive comprising an electrolyte, a polymer and a cross linking agent.

3. The fluid loss additive of claim 2 comprising about 1% electrolyte to about 99% electrolyte, about 1% polymer to about 99% polymer, and about 0.1% cross linking agent to about 5% cross linking agent.

4. The fluid loss additive of claim 3, further comprising at least one of a retarder, a defoamer, and a polyanionic polymer.

5. A kit for inhibiting fluid loss from an oil and gas well comprising about 1% electrolyte to about 99% electrolyte, about 1% polymer to about 99% polymer, and about 0.1% cross linking agent to about 5% cross linking agent.

6. A wellbore treated to inhibit fluid loss with the composition of claim 2.

7. A pumpable cement mixture comprising about 0.01% to about 5.0% electrolyte, about 0.01% to about 5.0% polymer, about 0.001 to about 0.1% cross linking agent, about 5% to about 50% water, and about 30% to about 95% cement.

8. The pumpable cement mixture of claim 7, further comprising at least one of a retarder, a defoamer, and a polyanionic polymer.

9. A completed wellbore comprising the cement mixture of claim 7.

10. A fluid-loss cement additive comprising: about 1 part polyvinyl alcohol, about 1 part NaCl, about 0.05 parts borax, about 0.05 parts calcium lignosulfonate; and about 0.12 parts defoamer.

11. The fluid-loss additive of claim 10, wherein the fluid-loss additive is prepared on a weight basis in a dry blend and added at a concentration of about 1 percent by weight of the cement.