Compositions: coating or plastic – Coating or plastic compositions – Inorganic settable ingredient containing
Reexamination Certificate
1999-01-21
2001-01-09
Green, Anthony (Department: 1755)
Compositions: coating or plastic
Coating or plastic compositions
Inorganic settable ingredient containing
C106S725000, C106S727000, C106S728000, C106S802000, C106S808000, C106S809000, C106S810000, C106S823000, C166S293000
Reexamination Certificate
active
06171386
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to additives, cementing compositions and methods of use and, more particularly, but not by way of limitation, to additives, cementing compositions and methods for use in oil, gas, and geothermal wells.
2. Description of the Related Art
In downhole cementing operations, such as those that occur in oil, gas, and geothermal wells, it is known to use cementing compositions that contain, among other ingredients, a hydraulic cement and a latex (or lattice). A latex is a dispersion of organic polymer particles in water. Most latexes are milky white to off-white in color and vary in consistency or viscosity from low viscosity, water-thin fluids to very viscous liquids. The basic components of a latex are a polymer composition, surfactants and, in many cases, compounding ingredients.
The polymer composition, molecular weight, and particle sizes of the organic polymer in the dispersion have a significant effect on the properties of the liquid cement slurry as well as the hardened or cured cement. Because most latexes are made through a process of emulsion polymerization, with the exception of epoxy resin latexes, surfactants are present and a key ingredient in the latex. Most latexes contain a nonionic surfactant and an anionic surfactant. The nonionic surfactant is typically, but not limited to, a nonylphenol with 10 to 40 moles of ethoxylation and is the primary emulsifier. The concentration of nonionic surfactant typically ranges from 1 to 10 percent by total weight of the latex dispersion. Anionic surfactants are used at much lower concentrations, typically between 0.1 and 2 percent. Anionic surfactants function to control the rate of polymerization of the monomers being reacted to form the latex polymer.
Compounding ingredients are added after polymerization is complete to improve the latex product for the application. Compounding ingredients include bactericides, defoamers, antioxidizing agents, ultraviolet light (UV) stabilizers, and additional surfactants to improve workability of a cement formulation, improve freeze-thaw stability, reduce water-to-cement ratio, etc. Many surfactants added to improve workability (viscosity or consistency of the liquid cement slurry) or reduce the water-to-cement ratio function as dispersants for the cement particles.
The majority of latex types that have been or are being used with hydraulic cements, such as Portland cement, are: polyvinyl acetate, acrylic copolymers, styrene acrylic copolymers, vinyl acetate acrylic copolymers, vinyl acetate ethylene copolymers, vinylidene chloride and vinyl chloride copolymers, styrene butadiene copolymers (SB), and epoxy resin latexes. Each type of latex imparts different properties when used as an additive or polymeric modifier to hydraulic cement mixtures.
One of the most common latexes used in oil, gas and geothermal cement formulations is styrene butadiene (SB) latex. The most widely practiced application of styrene butadiene latexes is for prevention or control of gas migration or channeling after cementing based upon the art described in U.S. Pat. Nos. 4,537,918, 4,721,160 and 4,767,460 by Parcevaux et al. The art described by Parcevaux et al. in these patents is essentially a combination of the art described in U.S. Pat. Nos. 3,228,907, 4,151,150, and 4,039,345. Gas migration occurs when the well traverses a pocket of compressed gas and after a cement slurry has been injected into the well (either into the annular space between the casing and the borehole wall or interiorly of the casing). Gas migration or channeling occurs during the setting of the cement; from the time when setting of the cement has progressed such that the hydrostatic pressure of the cement column is no longer transmitted to the pocket of compressed gas but prior to the slurry sufficiently setting to oppose the migration of the gas into the setting cement under the pressure from the compressed gas pocket. The migrating gas permeates the cement during the course of its setting, creating a multiplicity of channels that may reach up to the surface of the well. Gas channeling can be a serious drawback, leading to weakening of the cement and to safety problems on the surface. In addition to preventing gas channeling or migration, SB latexes serve to increase adhesion of the cement to the casing and the formation, reduce fluid loss, and increase the elasticity and flexural strength of the set cement.
The key learning from the related art regarding the application of styrene butadiene latexes can be described as follows. First, the latexes are copolymers of styrene and butadiene having a styrene to butadiene weight ratio of about 30:70 to 70:30. This range is preferred because of the mechanism of action of latex for improved bonding and control of gas migration requires a latex that effectively forms films around the cement particles and coalesces when contacted by gas. Copolymer latexes with styrene content greater than about 70 percent do not form films that will provide the required mechanism of action. Copolymer latexes with a butadiene content greater than about 70 percent are so inherently unstable that, although they form effective films, they are for all practical purposes impossible to stabilize (control coagulation of the latex) in the presence of divalent ions present in cement slurries and at elevated temperatures. Essentially, SB latexes in cement compositions aimed at curtailing gas migration or channeling are generally limited to use at low temperatures (e.g., less than 200° F.) or require stabilizers. Furthermore, without stabilizers, particularly at high pH levels, SB latexes tend to flocculate.
Second, the mechanism of improved cement bonding is through the interaction of the latex coating of the cement particles with (a) the geologic formation of the borehole wall or drilling fluid filter cake deposited on the borehole wall and (b) with the surface of the steel, fiberglass or other material of construction for the well casing. Styrene butadiene copolymer latexes provide a natural adhesion to solids because of their film forming tendencies. Further, the coating of the particles and films formed between cement grains and casing or borehole wall surfaces effectively increase the contact surface area of the cement slurry. Since shear bond strength of cement is a direct function of surface area, effectively increasing the surface area directly increases the shear bond strength between the cement and surrounding surfaces.
Third, styrene butadiene copolymer latexes are inherently unstable in cement slurries and particularly at the elevated temperatures typically associated with well cementing. Temperature, the shear of mixing and pumping the cement slurry, the concentration of electrolytes, such as chloride salts of alkali earth metals (sodium chloride, potassium chloride and calcium chloride by example) and formation fluids such as brines, carbon dioxide, hydrogen sulfide, natural gas and oil all affect the stability of the latex during and after placement of the cement slurry. The fundamental cause of this instability is the stability of the latex emulsion itself. The type and quantity of surfactants used in the manufacture of the latex are selected for the stability of the emulsion of the two monomers (styrene and butadiene) in the polymerization process to form the latex copolymer. Additional surfactants of same or different types used in the preparation of the latex are added to stabilize the emulsion for its intended use. This is well known to those practiced in the art of coatings and application of latex modified cement coatings for construction industry applications. An example of this is in U.S. Pat. No. 4,039,345. Parcevaux et al (U.S. Pat. No. 4,767,460) simply selected suitable surfactants compatible with the electrolytes present in cement slurries and which were effective to stabilize the copolymer emulsion at elevated temperatures.
Fourth, the fundamental instability of styrene butadiene copolymer latexes is necessary to provide
Benchmark Research & Technology, Inc.
Green Anthony
Makay Christopher L.
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