Wells – Processes – Cementing – plugging or consolidating
Reexamination Certificate
1999-07-15
2001-01-23
Bagnell, David (Department: 3672)
Wells
Processes
Cementing, plugging or consolidating
C507S216000
Reexamination Certificate
active
06176314
ABSTRACT:
This invention relates to improved low density cement slurry compositions and the use of same in the cementing of subterranean wells.
BACKGROUND OF THE INVENTION
Hydraulic cements are cements that can set under water. This setting property serves a variety of purposes. Hydraulic cements are often used in placement of pipes or casings within a well bore of a subterranean formation for the construction of oil and gas wells. In the oil and gas industry, successful cementing of well pipe and casing during oil and gas well completion sometimes requires cement slurries which need to be of a density that is much lower than that which the cement was originally designed for by the cement manufacturer. To achieve such low densities, there is often employed the addition of large amounts of water to the existing slurry. The amount of mixing water utilized is dependent upon the desired ultimate density for the slurry as well as the API classification of the cement. However, when the addition of mixing water is employed for lowering the density of the water-cement slurry, there is experienced a detrimental effect on several properties of the resulting slurry including that of an increase of free fluid.
Thus, there exists a need in the hydraulic cementing industry for an improved well cementing composition which will provide a desired low density system while avoiding the problem of free fluid formation.
It is thus an object of the present invention to provide a novel low density well-cement slurry system which is essentially free of the problem of free fluid formation.
Another object of this invention is to provide an improved system for the cementing of subterranean wells.
Other aspects, objects and the several advantages of this invention will be apparent from the following specification and appended claims.
SUMMARY OF THE INVENTION
In accordance with one embodiment of the present invention, it has been discovered that in the production of low density slurries through the addition of additional mixing water to a cement-water slurry mix that the addition to such a slurry system of a free-liquid inhibitor results in an improved low density slurry which avoids the problem of free fluid increase which is otherwise experienced.
The term “free fluid” as used herein is intended to mean that free liquid or water which is the supernatant fluid formed on top of the slurry column which provides an indication of the amount of settling of the cement particles during slurry placement. Excessive free water on top of the cement column will result in an incompetent zone close to the top of the liner, the pipe or the casing which will have to be remedied with an expensive squeeze job.
The term “free-fluid inhibitor” employed herein is intended to define a hydroxy ethyl cellulose composition which has a solution viscosity value as measured by a Brookfield LVT viscometer in the range of from about 5000 to about 50,000 cps.
Thus, by the present invention there is provided a novel low density cement slurry composition which comprises (a) a hydraulic cement, (b) water, and (c) a free-fluid inhibitor wherein said composition has a density in the range of about 11.0 pounds per gallon of slurry to about 15.0 pounds per gallon of slurry and said free-fluid inhibitor is present in an amount sufficient to essentially preclude the development of free fluid in the slurry.
The term “low density cement slurry” as employed herein is intended to mean a cement-water slurry having a density in the range of from about 11.0 to 15.0 pounds per gallon of slurry.
In another aspect of this invention, there is provided an improved process for the cementing of subterranean wells with a low density cement slurry through the use of these novel low density slurry compositions which avoid the development of undesirable free fluid in the system.
DETAILED DESCRIPTION OF THE INVENTION
The present invention relates to improved low density cementing composition and the method of using such low density cementing compositions.
The cementing compositions of this invention are comprised of a hydraulic cement, water and a free-fluid inhibitor additive which is present in an amount sufficient to preclude the development of free liquid in the cementing composition.
In this disclosure, the term “hydraulic cement” refers to any inorganic cement that hardens or sets with water. Hydraulic cements, for instance, include Portland cement, aluminous cements, pozzolan cements and the like. Thus, for example, any of the class A-H and J cements as listed in the API spec 10 First Edition, January 1982 are suitable for the invention.
Mixing water with the dry hydraulic cement compositions produces a slurry. A sufficient amount of water should be added to the hydraulic cement to form a pumpable slurry of the desired density. The water can be of any type water commonly used in the cement industry, such as fresh water, brines, sea water and the like.
If desired, the slurry composition can also have additional additives therein either formed by dry blending with the cement or added to the water used in forming the slurry. Such additives can be one selected from the group consisting of dispersants, accelerators, viscosifiers, retarders, extenders and foaming agents.
Examples of suitable dispersants are those selected from the group consisting of formaldehyde condensation products of naphthalene sulfonic acid, melamine sulfonic acid, ketone sulfonic acid, naphthol sulfonic acid and the alkali earth metal salts thereof Such dispersants can be used in an amount in the range of from about 0.1 to about 2.0 percent by weight of cement (BWOC).
Examples of suitable accelerators are those selected from the group consisting of calcium chloride, potassium chloride, sodium chloride, calcium nitrate, potassium nitrate and sodium nitrate. Such accelerators can be used in an amount in the range of from about 1 percent by weight of mixing water (BWOW) to saturation.
Examples of suitable viscosifiers are those selected from the group consisting of xanthan gum, guar gum and derivatives thereof, homo and copolymers of acrylamide, N-vinyl pyrrolidone, 2 acrylamide-3-methyl propane sulfonic acid, alkali metal salts thereof, N-vinyl acetamide, N-vinyl-N-methyl acetamide, N-N-dimethyl acrylamide, acrylic acid, itaconic acid and alkali earth metal salts thereof. Such viscosifiers can be used at concentrations in the range of about 0.1 to about 5.0 percent by weight of cement.
Examples of suitable retarders are those selected from the group consisting of lignosulfonic acid, hydroxy-basic acids, tannic acids, boric acid, polysaccharides, condensation and chain polymerization polymers, alkali earth metal salts thereof, zinc oxide, iron oxide and ferochrome lignosulfonate. Such retarders can be used at concentrations in the range of about 0.1 to about 10 percent by weight of cement.
Examples of suitable extenders are those selected from the group consisting of calcium sulfate, sodium and aluminum silicates, fly ash, bentonite, diatomite, filmed silica, ceramic beads, attapulgite, gilsonite, polystyrene foam beads, aluminum chlorohydrate, silica spheres and nitrogen gas. Such extenders can be used at concentrations in the range of from about 0.1 to about 75.0 percent by weight of cement.
Examples of suitable loss circulation agents are those selected from the group consisting of cellophane flakes, sized silica, ground rubber, seed hulls, saw dust, paper flakes, calcium carbonate, ground coal and fused coal. Such loss circulation agents can be used at concentrations in the range of from about 0.1 to about 20 percent by weight of cement.
Examples of suitable foaming agents are those selected from the group consisting of ethoxylated alcohols, alkylsulfonates, polyolefin sulfonates, alkyl alkene sulfonates, alkyl amine, fatty acid esters and petroleum sulfonates, Such foaming agents can be used at concentrations in the range of about 0.1 to about 5.0 percent.
When deemed appropriate, the slurries of this invention can have incorporated therein a gas such as nitrogen or carbon dioxide.
API Spec 10
Bagnell David
Dougherty Jennifer
Haag Gary L.
Phillips Petroleum Company
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