Early enhanced strength cement composition

Abstract: An early enhanced strength cement composition useful in surface construction projects as well as in the construction of oil, gas and water wells comprises a hydraulic cement, water to form a slurry and hydrophobic silica powder. The cement may be foamed if desired.

Description: The present invention relates to the use of hydrophobic silica powder for providing early enhanced strength foamed and non-foamed cement compositions which can be utilized in a variety of applications. Hydraulic cement compositions, both foamed and non-foamed, are commonly utilized in surface construction applications as well as in the construction of oil, gas and water wells. For example, in the construction of wells, hydraulic cement compositions are used in primary cementing operations whereby strings of pipe such as casing and liners are cemented in well bores. In performing primary cementing, a hydraulic cement composition is pumped into the annular space between the walls of a well bore and the exterior surfaces of a pipe string disposed therein. The cement composition is permitted to set in the annular space thereby forming an annular sheath of hardened substantially impermeable cement therein. The cement sheath physically supports and positions the pipe in the well bore and bonds the exterior surfaces of the pipe to the walls of the well bore whereby the undesirable migration of fluids between zones or formations penetrated by the well bore is prevented. In carrying out primary cementing, the foamed or non-foamed cement compositions utilized must have adequate pumping time before placement and relatively short set times after placement within which the cement compositions attain high compressive strengths. If a well cement composition is slow to set, pressurized formation fluids can flow into and through the cement composition before and after it sets. Also, in well construction, it is important that the cement composition used sets and attains compressive strength as quickly as possible in order to prevent long drilling rig down time and the high costs associated therewith. Similar situations exist in surface construction projects. Heretofore, inorganic salts such as calcium chloride, sodium chloride and the like have been used as set accelerators and compressive strength enhancers in cement compositions. However, in very low temperature applications, such salts are relatively ineffective in providing accelerated set times and enhanced compressive strengths. Also, the heretofore used inorganic salts must often be used in high concentrations as a result of low temperature conditions to produce enhanced compressive strengths. The high concentrations drastically reduce the placement or pumping times of the cement compositions which are often too short for placing the compositions in the required locations. When set retarding agents are utilized to increase the placement or pumping times of the compositions, the enhanced compressive strength development of the cement compositions is also lost. Another disadvantage associated with the use of chloride salts is that such salts can cause steel pipe or steel structural members in contact with cement compositions containing the salts to rapidly corrode. DATABASE WPI Week 199426 Derwent Publications Ltd., London, GB; AN 1994-215625 XP002154567 & SU 1 808 995 A (VOLGO URALS HYDROCARBON RAW MAT MINING) discloses a plugging material containing Portland cement, gypsum, sulpho-aluminate hydraulic binder and a highly dispersed pyrogenic hydrophobised silica. The above is used as a plugging material for oil, gas and other wells, and exhibits increased storage life and improved stability. The hydrophobised silica is used as an emulsifier and foam extinguishing agent for drilling solutions. Tests showed that cement rock obtained from the above that had been stored for three to four months had properties comparable to rock obtained from freshly prepared material and as such the storage had not affected the properties of the subsequently produced cement rock. WO 90/11977A discloses cement slurries with a silicon oxide additive. The cement slurries are used in oil well cement where their primary purpose is to prevent reduction of cement slurry strength over time, particularly at high pressure and temperatures exceeding 100°C. WO 90/11977A teaches mixing amorphous silica with particles of less than one micrometer with water to provide liquid micro-silica, mixing the thus formed liquid micro-silica with silica flour with particles from 2 to 200 micro-metres and the thereby obtained silica mixture being added to a cement slurry. DATABASE WPI Week 198705 Derwent Publications Ltd., London, GB; AN 1987-033939 XP002154568 & JP 61 291441 A (MATSUSHITA ELECTRIC WORKS) discloses a cement composition which contains a fine particle filler, such as silica or calcium carbonate, treated with a water repelling or hydrophobic agent. CHEMICAL ABSTRACTS, vol. 116, no.18, 4 May 1992 (1992-05-04) Columbus, Ohio, US; abstract no. 179844s, Y. YABUNAKA, ET AL.: page 357; XP000285808 & JP 04 005002 A (ID.) 9 January 1992 (1992-01-09) discloses a slurry containing Portland cement, fly ash, cellulose pulp, mineral wool and water, being mixed with an anti-foaming agent containing silicone coated SiO 2 , followed by moulding to give cement plates. The silicone coated SiO 2 suppresses foaming and improves filterability and dewatering of the cement slurries. WO 99/28264A discloses a waterproofing additive for cement and / or concrete comprising at least one pozzolanic material (e.g.silica fume, microsilica and metakaolin) with at least one hydrophobic material. The aim of WO 99/28264A is to produce a cement composition wherein the waterproofing agent can effectively reduce the water absorption of the cement with little or no adverse affect on compressive strength. Thus, there are continuing needs for improved early enhanced strength cement compositions for use in surface construction projects and in the construction of wells. There is, however, now provided by the present invention use of a hydrophobic silica powder for providing early enhanced compressive strength to a cement composition, wherein said cement composition comprises hydraulic cement and water present in an amount sufficient to form a slurry. The hydrophobic silica is preferably present in the cement compositions in an amount in the range of from about 0.3% to about 5% by weight of cement in the compositions. If the time between when a cement composition of this invention is formed and when the composition sets is too short to place the composition in a desired location, a known set retarding additive can be added to the composition to increase the placement time without affecting the enhanced compressive strength development of the cement composition. The present invention also provides lightweight cement compositions, i.e. non-foamed cement compositions that have low densities, but provide high compressive strengths for cementing subterranean zones having low fracture gradients or for use in the construction industry generally. The methods of this invention for cementing a construction zone are basically comprised of the following steps. A cement composition of the invention is formed, the composition is placed in the construction zone, and then allowed to set into a hard mass therein. The expression "early enhanced strength cement composition" is used herein to mean a cement composition which has an accelerated set time and also has enhanced compressive strength after setting. Prior to this invention, inorganic salts such as calcium chloride, sodium chloride and the like have been used in cement compositions as set accelerators and compressive strength enhancers. However, in low temperature applications, i.e. applications wherein the cement temperature is in the range of from about 4°C to about 21°C (about 40°F to about 70°F), such salts are relatively ineffective in providing an early set or enhanced compressive strength to a cement composition. Also, such inorganic salts must often be used in high concentrations whereby they decrease the placement or pumping time, i.e., the time between cement composition preparation and when the cement composition sets, to a time period so short that the composition can not be placed or pumped into a desired location. Further, when chloride salts are utilized in cement compositions, they often cause corrosion to steel members in contact with the set cement compositions containing the salts. The improved early enhanced strength cement compositions of this invention attain early enhanced compressive strengths over a broad temperature range including at the low temperatures often encountered in offshore wells and in many surface construction projects, i.e., temperatures in the overall range of from about 4°C to about 54°C (about 40°F to about 130°F). Another novel beneficial characteristic of the cement compositions of this invention is that when longer placement or pumping times are required, a set retarding agent can be utilized without affecting the enhanced compressive strengths attained by the compositions. As mentioned, the early enhanced strength cement compositions of this invention can be foamed or non-foamed. The non-foamed cement compositions are basically comprised of a hydraulic cement, water present in an amount sufficient to form a slurry and hydrophobic silica powder to provide early and enhanced compressive strength to the cement compositions and/or to provide lightweight to the cement compositions. The foamed cement compositions are the same as the non-foamed compositions except that they further include a gas present in an amount sufficient to form a foam and a mixture of foaming and foam stabilizing surfactants present in an effective amount. A variety of hydraulic cements can be utilized in the foamed and non-foamed compositions including, but not limited to, those comprised of calcium, aluminum, silicon, oxygen and/or sulfur which set and harden by reaction with water. Such hydraulic cements include Portland cements, pozzolana cements, gypsum cements, high aluminum content cements and high alkalinity cements. Portland cements are generally preferred for use in the construction of oil, gas and water wells. Portland cements of the types defined and described in API Specification For Materials And Testing For Well Cements, API Specification 10, 5th Edition, dated July 1, 1990 of the American Petroleum Institute are particularly suitable. Preferred such API Portland cements include classes A, B, C, G and H, with API classes G and H being more preferred and class G being the most preferred. The water in the cement compositions can be fresh water, unsaturated salt solutions and saturated salt solutions including brines and seawater. The water is generally present in a cement composition of this invention in an amount sufficient to form a slurry which can be poured or pumped, i.e., in an amount in the range of from about 30% to about 150% by weight of cement in the composition. The hydrophobic silica powder in the compositions of this invention brings about the early and enhanced compressive strengths of the compositions. That is, the hydrophobic silica powder accelerates the time required for a cement composition of this invention to set and also brings about the attainment of enhanced high compressive strength by the set cement composition. As mentioned above, if the set time of a cement composition of this invention is too short to place or pump the cement composition into a desired location, a known set retarder of the type described hereinbelow can be included in the cement composition without affecting the attainment of enhanced compressive strength by the composition. The hydrophobic silica powder used in accordance with this invention is preferably silicone oil treated precipitated silica. The precipitated silica can be prepared by simultaneously adding sulfuric acid and sodium silicate solutions to water with agitation. The pH of the mixture during the reaction is maintained above about 9 whereby smaller particles are continuously dissolved during the precipitation of silica. As a result, uniform particle sizes are obtained. During the precipitation process, the properties of the silica can be varied by changing the ratio of reactants, the reaction time, the reaction temperature and the reaction mixture concentrations. The suspension that results from the precipitation process is filtered and dried followed by milling to reduce the size of the precipitated silica. The precipitated silica is hydrophobicized by spraying it with a uniform coating of silicone oil (polydialkylsiloxane) followed by heating. The quantity of silicone oil utilized is usually about 10% by weight of the precipitated silica. Particularly preferred such hydrophobic silica powder for use in accordance with this invention is commercially available under the trade designations SIPERNAT D-11™ and SIPERNAT D-13™ from the Degussa Company having a place of business in Chester, Pennsylvania. The SIPERNAT D-11™ has a BET surface area of about 90 square centimeters per gram while the SIPERNAT D-13™ has a BET surface area of about 85 square centimeters per gram. Other properties of the products are the same and are as follows: average particle size-less than 5 microns; tapped density-120 grams per liter; pH-9.5 to 11.5; moisture loss at 105°C after 2 hours-1.5%; ignition loss after 2 hours at 1,000°C-5%; methanol wettability-greater than about 60%; SiO 2 content-98%; and Na 2 SO 4 content-2%. The hydrophobic silica powder is generally included in a cement composition of this invention in an amount in the range of from about 0.3% to about 5% by weight of the cement in the composition. In preparing the compositions of this invention, a suitable dispersing agent can be included therein to facilitate mixing and lower the viscosities of the compositions. An example of a particularly suitable dispersing agent which can be utilized is the sodium salt of naphthalene sulfonate condensed with formaldehyde which is commercially available from Halliburton Energy Services of Duncan, Oklahoma under the trade designation CFR-2™. Such dispersing agents are also referred to as "plasticizers" and "superplasticizers" in the concrete industry. A non-foamed cement composition of this invention including the above described components can include hydrophobic silica as a density reducing additive. Density reducing additives such as hollow glass beads and the like have heretofore been utilized in well cement compositions to prevent excessive hydrostatic pressures from being exerted on formations penetrated by the well bore. Other cement compositions have utilized silicate salts, and silica fume which require excess water to reduce density; however, excess water contributes to numerous undesirable cement composition properties such as solids settling, free water and low compressive strength. Lightweight additives such as bentonite, sodium metasilicate and the like have been utilized to control free water, but they do not prevent low compressive strength. In accordance with the present invention, a non-foamed cement composition can be made lightweight by including hydrophobic silica powder in the cement composition. That is, in addition to the hydrophobic silica powder included in a cement composition of this invention to provide the early enhanced strength properties thereto, additional hydrophobic silica powder can be included to reduce the density of the composition. The hydrophobic silica powder has a very low bulk density, i.e., a bulk density in the range of about 0.12 grams per cubic centimeter. Due to its small particle size, high surface area and air trapped in its porous structure, when hydrophobic silica powder is mixed in a cement slurry it functions like small air pockets which reduce the density of the cement composition. When used as a density reducing agent, the additional hydrophobic silica powder is added to a cement composition so that the composition contains hydrophobic silica powder in a total amount up to about 5% by weight of cement in the composition. The high levels of hydrophobic silica required to reduce density require the use of dispersants or "plasticizers" to improve the workability of the cement or concrete slurry. Additionally, to ensure a homogeneous distribution of hydrophobic silica in cement slurries, water wetting agents such as surfactants or surface tension reducing polymers may be used. The water wetting surfactants which can be utilized in the cement compositions of this invention include, but are not limited to, non-ionic ethoxylated fatty alcohols or their anionic sulfate salts. Examples of the non-ionic ethoxylated fatty alcohols which can be used include ethoxylated nonylphenols with 3 to 12 moles of ethylene oxide. Examples of the anionic sulfate salts of ethoxylated fatty alcohols which can be used include fatty acid alcohol ether sulfates where the fatty acids are lauryl, coco or the like and are ethoxylated with from 3 to 12 moles of ethylene oxide and then sulfated. The water wetting polymers which can be utilized include, but are not limited to, polymeric surfactants in which the ratio of hydrophilic to lipophilic moieties is balanced whereby they are water soluble, but yet reduce the surface and interference tensions at the water-air interface. Examples of such polymeric surfactants which can be used include hydroxyalkylcelluloses, e.g., hydroxyethylcellulose, partially hydrolyzed polyvinyl acetates and lignosulfonates. The above described water wetting surfactants and water wetting polymers can be combined with the cement compositions of this invention in amounts in the range of from about 50 to about 1,000 parts per million parts by weight of hydraulic cement in the compositions. Small amounts of deaerating agents such as polydimethylsiloxane, or polypropylene glycol suspension, can be included in the cement compositions as needed to reduce or prevent the entrainment of air therein during preparation. The foamed compositions of this invention can include the same cement, water, hydrophobic silica, dispersing agent and water wetting agent components described above for the non-foamed cement compositions in the amounts given. In addition to those components, the foamed cement compositions include a gas present in an amount sufficient to form a foam and a mixture of foaming and foam stabilizing surfactants present in an effective amount. The gas is preferably selected from air and nitrogen, with nitrogen being the most preferred. While various mixtures of known foaming and foam stabilizing surfactants can be utilized to facilitate the formation of a foam and stabilize it, a preferred surfactant mixture is comprised of 2 parts by weight of an ethoxylated alkyl ether sulfate foaming surfactant having the general formula H(CH 2 ) n (OC 2 H 4 ) m OSO 3 Na wherein n is an integer in the range of from about 6 to about 10 and m is an integer in the range of from about 3 to about 10, and about 1 part by weight of a betaine foam stabilizing surfactant having the general formula R-CONHCH 2 CH 2 CH 2 N + (CH 3 ) 2 CH 2 CO 2 - wherein R is a radical selected from the group of decyl, cetyl, oleyl, lauryl and cocoyl. The mixture of foaming and foam stabilizing surfactants is generally present in a foamed cement composition of this invention in an amount in the range of from about 0.75% to about 5% by weight of water in the composition. As mentioned above, if either of the foamed or non-foamed early enhanced strength cement compositions of this invention do not have a placement or pumping time of long enough duration, a known set retarding agent can be included in the cement composition which lengthens the placement or pumping time without affecting the enhanced compressive strength of the composition after it sets. Examples of suitable such set retarding agents which can be utilized in accordance with this invention include, but are not limited to, sodium lignosulfonate, hydroxycarboxylic acids such as tartaric, citric and gluconic acids and synthetic polymers such as copolymers of AMPS™ and acrylic or maleic or itaconic acid or modified cellulose derivatives such as carboxymethylhydroxy- ethyl cellulose. Of these, sodium lignosulfonate is preferred. When used, the set retarding agent is included in a foamed or non-foamed cement composition of this invention in an amount in the range of from about 0.1% to about 3% by weight of cement in the composition. The methods of the present invention for cementing a construction zone on the surface or in a subterranean formation penetrated by a well bore comprises the following steps. A foamed or non-foamed early enhanced strength cement composition of this invention as described above is formed. Thereafter, the cement composition is placed or pumped into the construction zone, and the cement composition is allowed to set into a hard impermeable mass therein. In order to further illustrate the improved cement compositions and methods of this invention, the following examples are given. Example 1 Non-foamed cement compositions with and without hydrophobic silica powder were prepared utilizing Portland Class H cement and various amounts of synthetic seawater. The compositions including hydrophobic silica powder contained different amounts of the hydrophobic silica powder. Test portions of each of the cement compositions were tested in accordance with the procedures set forth in the API Specification 10 mentioned above to determine the times required for the compositions to set at a temperature of 49°C (120°F) and a pressure of 6.9 x 10 6 Nm -2 (1,000 psig). The 24 hour compressive strengths of the set cement compositions at the same temperature and atmospheric pressure were also determined by curing the samples in a thermostated water bath followed by determining their compressive strengths. Further, additional test portions of the cement compositions were tested using an Ultrasonic Cement Analyzer to determine their strength development profiles as a function of time at a temperature of 49°C (120°F) and pressure of 6.9 × 10 6 Nm -2 (1,000 psi). The results of these tests are given in Table I below. From Table I, it can readily be seen that the presence of hydrophobic silica powder in non-foamed cement compositions accelerated the set times and enhanced the compressive strengths of the set cement compositions. Example 2 Foamed cement compositions with and without hydrophobic silica powder and containing various other components were prepared utilizing Portland Class A cement and seawater in an amount of 38% by weight of the cement in the compositions. The compositions containing hydrophobic silica powder contained different amounts of the hydrophobic silica powder and hydrophobic silica powders having different surface areas. Several of the cement compositions included hydrophilic silica powder instead of hydrophobic silica powder. Finally, some of the cement compositions contained a dispersing agent comprised of the sodium salt of naphthalene sulfonate condensed with formaldehyde (Halliburton "CFR-2™"). All of the compositions were foamed with air and contained a mixture of foaming and foam stabilizing surfactants comprised of 2 parts by weight of an ethoxylated alkyl ether sulfate foaming surfactant and 1 part by weight of a betaine foam stabilizing surfactant. Unfoamed test portions of each of the compositions described above were tested in accordance with the procedures set forth in the API Specification 10 mentioned above to determine, their thickening times at 18°C (65°F) and a pressure of 6.9 x 10 6 Nm -2 (1,000 psig). Foamed test portions of each of the cement compositions were tested to determine the 24 hour compressive strengths of the compositions after setting at either temperatures of 7°C (45°F) or 13°C (55°F) and at atmospheric pressure in thermostated water baths. The compressive strength tests were also conducted in accordance with the procedures set forth in the above mentioned API Specification 10. Further, additional test portions of the unfoamed cement compositions were tested using an Ultrasonic Cement Analyzer to determine the compressive strength development profiles of the cement compositions as a function of time at 18°C (65°F) and 6.9 x 10 6 Nm -2 (1,000 psi). The strength values at 12 hours were also determined. Additionally, the thicknesses of the cement compositions before being foamed were observed. The results of these tests are given in Table II below. From Table II, it can be seen that the presence of hydrophobic silica powder in foamed cement compositions accelerates the set times and enhances the compressive strengths of the set cement compositions. Further, it can be seen that the hydrophobic silica powder can be used in combination with set retarders such as lignosulfonates to extend the placement or pumping time without significantly sacrificing compressive strength. For example, as shown in Table II, test cement composition No. 1 without hydrophobic silica powder has a pump time of 2 hours and 5 minutes and compressive strengths of 2.3 x 10 6 Nm -2 (338 psi) at 7°C (45°F) and 4.2 x 10 6 Nm -2 (610 psi) at 13°C (55°F). As shown for test cement composition No. 15, when 2% hydrophobic silica powder was used in combination with 0.3% sodium lignosulfonate set retarder, the pump time remains at 2 hours and 3 minutes, but the compressive strengths increased to 5.2 x 10 6 Nm -2 (752 psi) at 7°C (45°F) and 8.7 x 10 6 Nm -2 (1267 psi) at 13°C (55°F). Finally, the non-foamed cement compositions containing hydrophobic silica powder tend to be thick or viscous. However, when the compositions are foamed, the resulting foamed cement compositions have normal viscosities. The viscosities of the non-foamed cement compositions can be controlled by adding cement composition dispersing agents thereto. Example 3 Additional non-foamed cement compositions were prepared utilizing Portland Class H cement, various amounts of tap water and various amounts of hydrophobic silica powder. A control cement composition without hydrophobic silica powder was prepared and some of the compositions included a cement dispersing agent. The densities of the various cement compositions were measured to determine the density reductions brought about by the presence of hydrophobic silica powder in the cement compositions. The results of these tests are set forth in Table III below. Cement Composition Density Reduction With Hydrophobic Silica Powder Test Cement Composition No. Quantity of Water in Cement Composition, % by wt. of cement Quantity of Hydrophobic Silica Powder in Cement Composition, % by wt. of cement Quantity of Dispersing Agent in Cement Composition, % by wt. of cement Cement Composition Density kg/m 3 x 10 3 (lb/gal) 1 39 - - 1.97 (16.4) 2 39 1 - 1.77 (14.8) 3 39 2 0.23 1.75 (14.6) 4 39 3 0.35 1.73 (14.4) 5 43 1 - 1.71 (14.3) 6 54 2.8 - 1.43 (11.9) From Table III, it can be seen that the addition of hydrophobic silica to a non-foamed cement composition brings about a reduction in density of the cement composition. Example 4 A non-foamed cement composition of the present invention was prepared utilizing Portland Class H cement, water and hydrophobic silica powder. In addition, two other cement compositions of the same density were prepared utilizing Portland Class H cement, water and two different liquid density reducing agents sold by Halliburton Energy Services under the trade designations "SILICALITE™" and "ECONOLITE™." The above described cement compositions were cured at a temperature of 68°C (155°F) in an autoclave at 20.7 x 10 6 Nm -2 (3,000 psi) and the compressive strengths of the cured cement compositions were determined in accordance with the procedures set forth in the above mentioned API Specification 10. The results of these tests are set forth in Table IV below. From Table IV, it can be seen that the cement composition of reduced density in accordance with the present invention provides far superior compressive strength than do similar cement compositions containing prior art density reducing agents.

Claims: Use of a hydrophobic silica powder for providing early enhanced compressive strength to a cement composition, wherein said cement composition comprises hydraulic cement and water present in an amount sufficient to form a slurry. Use according to claim 1, wherein said hydrophobic silica is employed in an amount of from 0.3% to 5% by weight of the cement in said composition. Use according to claim 1 or 2, wherein said hydraulic cement is selected from Portland cements, pozzolana cements, gypsum cements, high aluminium content cements and high alkalinity cements. Use according to any of claims 1 to 3, wherein the water is fresh water, or an unsaturated or saturated salt solution. Use according to any of claims 1 to 4, wherein said water is employed in an amount of from 30% to 150% by weight of the cement in said composition. Use according to any of claims 1 to 5, wherein said composition further comprises a set retarding agent. Use according to claim 6, wherein said set retarding agent is selected from sodium lignosulfonate, hydroxycarboxylic acids, synthetic polymers and modified cellulose derivatives. Use according to claim 6 or 7, wherein said set retarding agent is present in an amount of from 0.1% to 3% by weight of the cement in said composition. Use according to any of claims 1 to 8, wherein said composition further comprises a water wetting agent. Use according to claim 9, wherein said water wetting agent is a water wetting surfactant. Use according to claim 10, wherein said surfactant is selected from non-ionic ethoxylated fatty alcohols and their anionic sulfate salts. Use according to claim 9, wherein said water wetting agent is a water wetting polymer. Use according to claim 12, wherein said polymer is selected from hydroxyalkylcellulose, partially hydrolyzed polyvinyl acetates and lignosulfonates. Use according to any of claims 9 to 13, wherein said water wetting agent is present in an amount of from 50 parts to 1,000 parts by weight per million parts of the cement in said composition. Use according to any of claims 1 to 14, wherein said composition further comprises a gas present in an amount sufficient to form a foam, and a mixture of foaming and foam-stabilizing surfactants. Use according to claim 15, wherein said gas is air or nitrogen. Use according to claim 15 or 16, wherein said mixture of foaming and foam stabilizing surfactants is present in said composition in an amount of from 0.75% to 5% by weight of water in said composition. Use according to any of claims 15 to 17, wherein said mixture comprises 2 parts by weight of an ethoxylated alkyi ether sulfate foaming surfactant having the general formula H(CH 2 ) n (OC 2 H 4 ) m OSO 3 Na wherein n is an integer of from 6 to 10 and m is an integer of from 3 to 10, and about one part by weight of a betaine foam stabilizing surfactant having the general formula R-CONHCH 2 CH 2 CH 2 N + (CH 3 ) 2 CH 2 CO 2 - wherein R is decyl, cetyl, oleyl, lauryl or cocoyl. Use according to any of claims 1 to 18, in primary cementing, whereby strings of pipe are cemented in well bores.

Inventors: CROOK RONALD J, FITZGERALD RUSSELL M, GRAY DENNIS W, REDDY BAIREDDY R, TRAXEL BRENT E, WAUGH BRYAN K, CROOK, RONALD J., FITZGERALD, RUSSELL M., GRAY, DENNIS W., REDDY, BAIREDDY R., TRAXEL, BRENT E., WAUGH, BRYAN K.
Applicants: HALLIBURTON ENERGY SERV INC, HALLIBURTON ENERGY SERVICES, INC.
Application year: 2000
Main classification: C04B22
IPC codes: C04B14, C04B28, C09K8