Spacer fluids

Abstract: Spacer fluids providing an effective buffer between drilling fluids and cement slurries during well completion. The spacer fluids comprise a sulfonated styrene copolymer dispersant and one or more additional components such as surfactants, viscosifiers and weighting materials to form a rheologically compatible fluid between the drilling fluid and the cement slurry.

Description: BACKGROUND OF THE INVENTION Field of the Invention The present invention pertains to fluids for use in the drilling and completion of oil and gas wells. More specifically, the present invention relates to fluids which form a buffer between and prevent the mixing of various fluids used in the drilling and completion of oil and gas wells. The fluids will be hereinafter referred to as "spacer fluids". Description of the Prior Art In rotary drilling of wells, a drilling fluid is usually circulated down the drill string and back up the annulus between the drill string and the wellbore face. The drilling fluid can contain many different chemicals, but will most often contain a viscosifier, such as bentonite. When a casing string or liner is to be cemented into the wellbore, any drilling fluid and remnants of the viscosifier present in the wellbore are preferably removed to aid the bonding of the cement between the casing string or liner and the wellbore. In removing this drilling fluid from the wellbore and to clean the annulus, a wash or spacer fluid can be introduced ahead of a cement slurry. Spacer fluids are conventionally used in cementing operations related to well completion in the following manner. Drilling fluids and cement slurries are typically chemically incompatible fluids which undergo severe gelation or flocculation if allowed to come into contact. Thus, drilling fluid must be removed from the wellbore annulus immediately prior to cement slurry placement. Spacer fluids are pumped between the drilling fluid and the cement slurry to form a buffer and prevent the drilling fluid and the cement slurry from coming into contact. Spacer fluids should also possess certain rheological tendencies, such as turbulent flow at lower shear rates, which assist in granular solids removal and which encourage the removal of the drilling fluid filter cake from the walls of the well. Indeed, a common cause of failure in primary cementing is the incomplete displacement of drilling fluids which results in the development of mud filled channels in the cement. These mud filled channels may be opened during well production permitting the vertical migration of oil and gas behind the casing. Conventional spacer fluids are typically composed of an aqueous base fluid and a weighting agent. The weighting agent is included in the composition to increase the density of the spacer fluid to a desired value and to increase the erosion effect of the spacer fluid on the filter cake clinging to the walls of the formation. The fundamental properties of the aqueous base fluid are typically particle stability in suspension (anti-settling properties), fluid-loss control, favorable rheology, and compatibility with drilling fluids and cement slurries. These properties are directly related to the composition of the spacer fluid. Consequently, conventional spacer base fluids include at least: i) an anti-settling agent; ii) a fluid loss controlling agent; iii) a dispersing agent; and iv) a surfactant for obtaining a waterwetted surface to aid in cement bonding. As noted above, the final composition of conventional spacer fluids is obtained by adding a weighting agent to the aqueous base fluid. The anti-settling agent, fluid loss controlling agent and dispersing agent may be constituted by a single component of the composition or by plural components of the composition. In addition, a single component may function as more than one of the above-mentioned agents. The agents typically are soluble or dispersible in water. Depending on the water available on site and on the geological strata encountered, the aqueous base fluid typically includes fresh water, sea water, brine, or an aqueous composition containing one or more dissolved salts, such as NaCl, KCl, MgCl₂ and CaCl₂. The spacer base fluid, however, must retain its above-mentioned fundamental properties at all possible salt concentrations. Spacer fluids are conventionally used over a wide temperature range spanning from the relatively cool surface temperature to the bottom hole circulating temperature (BHCT) which may reach 200°C or greater in the case of geothermal wells. The term "anti-settling properties" refers to the capacity of the spacer fluid to keep the weighting agent particles in stable suspension throughout the cementing operation which may typically last for 1 to 4 hours or longer. A spacer fluid is considered to have good fluid loss control properties if the fluid loss measured according to API Specification 10, Appendix F is less than 100 ml/30min, and excellent if the fluid loss is less than 50 ml/30min. Favorable rheology of a spacer fluid implies that the fluid has minimum friction pressure while maintaining adequate suspension of solids. Since the spacer fluid is to be pumped between the drilling fluid and the cement slurry for removing and replacing the drilling fluid in the well annulus, it is very important that the spacer fluid be as compatible as possible with both the drilling fluid and the cement slurry. Such twofold compatibility in the past has been quite difficult to obtain, primarily because the drilling fluid and the cement slurry are incompatible fluids. The compatibility of a spacer fluid with a drilling fluid and a cement slurry is determined in the laboratory by studying the viscosity of binary or ternary mixtures of spacer fluid with drilling fluid and/or cement slurry varying over the range of 0 to 100% by volume for each component of the mixture. The compatibility of the spacer fluid with the drilling fluid and the cement slurry is considered to be excellent if the viscosity of a mixture of the spacer fluid and the drilling fluid or the cement slurry at a given shear rate and temperature is equal to or less than the viscosity of the more viscous component of the mixture at the same shear rate and temperature. Likewise, the viscosity of a mixture of all three components is considered to be excellent if it is less than or equal to the viscosity of the most viscous component at the same shear rate and temperature. Conventional spacer compositions, however, do not usually demonstrate good compatibility with mixtures of drilling fluids and cements while simultaneously presenting good rheological, fluid loss controlling and anti-settling properties over the entire range of shear rates and temperatures normally encountered in oil field services. The present invention has been developed with a view to providing improved spacer fluids that have enhanced compatibility with drilling fluids and cement slurries, that create and effectively maintain a buffer zone between a drilling fluid and a cement slurry even when all three components become commingled, and that enhance the bond between the cement and the surfaces of the borehole and casing. EP-A-0207536 teaches that the presence of bentonite in a spacer fluid is disadvantageous because it can only be used in non-saline water and is incompatible with cement. It describes a spacer fluid comprising a biopolymer, a high molecular weight sulfonated styrene or toluene-styrene polymer and a low molecular weight polyelectrolyte as a dispersing agent. EP-A-0320288 describes the formation of a cement composition by the conversion of drilling fluid. The final composition also includes a dispersant such as a sulfonated styrene copolymer. SUMMARY OF THE INVENTION The present invention provides improved spacer fluids which may be interposed between the drilling fluid in the wellbore and either a cement slurry or a drilling fluid which has been converted to a cementitious slurry. The spacer fluid serves as a buffer between the drilling fluid and the cement slurry, and as flushing agent to evacuate the drilling fluid from the wellbore resulting in improved displacement efficiency regarding drilling fluid removal and improved bonding of the cementitious slurry to surfaces in the wellbore such as the casing or drill pipe wall surfaces. The spacer fluid of the present invention comprises sulfonated styrene-maleic anhydride copolymer as a dispersant, bentonite, welan gum, a weighting agent and from 0.24 to 240ml/l of fluid of ethoxylated nonlyphenol surfactant having a mole ratio of ethylene oxide to nonylphenol in the range 1.5 to 15. The present invention also provides a method of using the spacer fluid. In the method of this invention, the spacer fluid is introduced into the wellbore, and a completion fluid, such as a cement slurry, is introduced to displace the spacer fluid. Those skilled in the art will further appreciate the above described features of the present invention together with other superior aspects thereof upon reading the detailed description which follows. DESCRIPTION OF PREFERRED EMBODIMENTS The overall process of cementing an annular space in a wellbore typically includes the displacement of drilling fluid with a spacer fluid or preflushing medium which will further assure the displacement or removal of the drilling fluid and enhance the bonding of the cement to adjacent structures. For example, it is contemplated that drilling fluid may be displaced from a wellbore, by first pumping into the wellbore a spacer fluid according to the present invention for displacing the drilling fluid which is then in turn displaced by a cement slurry or by the drilling fluid which has been converted to cement, for instance, in accordance with the methods disclosed in US-A-4 883 125. According to the present invention it has been determined that sulfonated styrene-maleic anhydride copolymer (SSMA), may be advantangeously included in spacer fluids because it is a high charge density material that is capable of dispersing mixtures of drilling fluid and cement slurry. Preferably, the sodium salt of SSMA is included in the spacer fluids of the present invention. Most preferably, the SSMA has a molecular weight of 5000 or less which products are commercially available as NARLEX D-72 from National Starch and Chemical Corporation or SSMA 1000 from Chemlink, Inc. Welan gum is a polymer made by an Alcaligenes bacteria identified as S-130. The chemical structure of welan gum is disclosed in US-A-4,342,866. The gum is a pseudoplastic, high efficiency viscosifier that is tolerant to salt and calcium and is more compatible with cementitious slurries than conventional viscosifiers. The gum also imparts substantial fluid loss control. In addition, welan gum maintains a stable yield point across a broad temperature range for improved solids suspension. The gum is commercially available under the trade name BIOZAN from Kelco, Inc. According to the present invention, the spacer fluid comprises SSMA, bentonite, welan gum, ethoxylated nonylphenol surfactant and a weighting agent. Preferably, the spacer fluid comprises a spacer dry mix which includes: 1) 10 to 50% by weight of SSMA as a dispersant; 2) 40 to 90% by weight of bentonite as a suspending agent; and 3) 1 to 20% by weight of welan gum as a pseudoplastic, high efficiency viscosifier tolerant to salt and calcium, available from Kelco, Inc. under the trade name BIOZAN. The spacer fluid also comprises: 4) 0.24 to 240 ml/l (0.01 to 10.0 gal per bbl) of aqueous base spacer of an ethoxylated nonylphenol surfactant having a mole ratio of ethylene oxide to nonylphenol ranging from 1.5 to 15, such as available from GAF under the trade name IGEPAL; and 5) Conventional weighting agents such as barite, hematite and calcium carbonate to provide the desired density. It is preferred that the weighting agent be added to the spacer fluid in an amount to give the spacer fluid a density at least equal to or greater than the density of the drilling fluid and less than or equal to the density of the cement slurry. The spacer fluid according to the present invention is quite compatible with conventional drilling fluids and cement slurries. The inclusion of SSMA provides good temperature stability to this spacer fluid so that it has a broad temperature range of applicability. The spacer fluid of the present invention also has the following advantageous properties: 1) The SSMA serves as a dispersant to provide enhanced compatibility with drilling fluids and cement slurries, and also as a stabilizer for bentonite at high temperatures. 2) The welan gum works in concert with the bentonite to provide the spacer fluid with the capability of maintaining acceptable suspension characteristics and fluid loss properties at a broad range of temperatures. 3) At high temperatures the bentonite undergoes controlled flocculation to provide long term suspension capability as the welan gum degrades in performance due to the high temperatures. 4) The primary function of the surfactant is a) as a water wetting agent to provide a more acceptable surface for cement bonding after exposure to water or oil base fluids and b) to provide spacer compatibility with water or oil base fluids. 5) The surfactant can also be selected to enhance the gel structure formed by the bentonite and/or the welan gum. The spacer fluid of the present invention results in improved primary cementing which in turn benefits external casing corrosion protection, selective stimulation and zonal isolation of producing formations thereby improving the water:oil ratio of produced fluids. The spacer fluid of the present invention acts as an effective buffer between the drilling fluid and the cement slurry, promotes good hole cleaning via turbulent flow, disperses mixtures of well bore fluids to ensure compatibility, and leaves the pipe and formation water wet to improve cement bonding. The spacer fluid may also include potassium chloride (KCl), sodium chloride (NaCl), calcium chloride (CaCl₂), magnesium chloride (MgCl₂), quarternary ammonium salts, zirconium oxy chlorides and other materials well known to those of ordinary skill in the art to inhibit the swelling of formation clays thereby preventing damage. In such cases, the spacer fluid preferably comprises about 3-5% by weight of water (BWOW) of KCl. The inclusion of KCl in the spacer fluid of the fourth embodiment makes the spacer fluid especially suitable for use in wells that are known to experience formation damage from fresh water in the well bore annulus. Table 1 provides mixing information for a spacer fluid according to the present invention. The spacer dry mix is prepared according to the above formula and for the particular spacer fluids illustrated in Table 1 comprises 33-34% by weight of SSMA, 62-63% by weight of bentonite and 4-5% by weight of welan gum. The sequence of addition of any of the spacer mix components is not critical. In practice the dry ingredients are preblended and bagged for easy handling. The spacer dry mix should be hydrated before adding weighting material. In Table 1 the abbreviation "ppg" means pounds per gallon of the drilling fluid. SPACER MIXING PROCEDURE 159 l (1 BBL) BASE SPACER SPACER DENSITY g/cc (ppg) kg (LBS) SPACER DRY MIX GAL WATER kg (LBS) BARITE 1.07 (9 ) 10.3 (22.8) 150 (39.6) 10.4 (23) 1.20 (10) 9.5 (21) 144 (38.1) 35.8 (79) 1.32 (11) 8.7 (19.2) 139 (36.6) 61.2 (135) 1.44 (12) 7.8 (17.3) 133 (35.2) 86.6 (191) 1.56 (13) 7.0 (15.4) 128 (33.7) 112 (247) 1.68 (14) 6.2 (13.6) 122 (32.3) 137 (303) 1.80 (15) 5.4 (11.8) 117 (30.8) 163 (359) 1.92 (16) 4.5 (10) 111 (29.3) 189 (416) 2.04 (17) 3.9 (8.7) 105 (27.8) 214 (471) 2.16 (18) 3.3 (7.3) 100 (26.3) 239 (527) 2.28 (19) 2.7 (6 ) 94.2 (24.9) 264 (582) To complete the spacer fluids represented in Table 1, an ethoxylated nonylphenol surfactant material is added to the fluid. Ethoxylated nonylphenol surfactants are made up of a hydrophobic component - nonylphenol and a hydrophilic component - ethylene oxide. A series of products with different hydrophobic - hydrophilic balances may be generated by altering the ratio of ethylene oxide to nonylphenol. The chemical structure of these surfactants is that of a polyoxyethylated nonylphenol, which may be represented by the following formula: where n represents the number of moles of ethylene oxide per mole of nonylphenol. The water solubility of these surfactants is directly proportional to the value of n. For example, to produce a completed water base spacer fluid from the compositions represented in Table 1, 0.78 l (0.2 gallons) of an ethoxylated nonylphenol surfactant containing 23% ethylene oxide and having a mole ratio of ethylene oxide per mole of nonylphenol of 1.5 is added per 159 l (1 bbl) of hydrated base spacer mix. A suitable ethoxylated nonylphenol surfactant for this purpose is available from GAF under the trade name IGEPAL CO-210. Also for example, to produce a completed oil base spacer fluid from the compositions represented in Table 1, 7.8 l (2.0 gallons) of an ethoxylated nonylphenol surfactant containing 65% ethylene oxide and having a mole ratio of ethylene oxide per mole of nonylphenol of 9 is added per 159 l (1 bbl) of hydrated base spacer mix. A suitable ethoxylated nonylphenol surfactant for this purpose is available from GAF under the trade name IGEPAL CO-630. This amount of surfactant prevents most emulsions from forming; however, if compatibility testing shows a higher yield point (YP) than desired, such as a YP over 50, or if oil wetting occurs, additional surfactant may be added in increments of 5 ml/l (0.2 gal/bbl) until the desired result is achieved. As noted above, 3-5% KCl by weight of water (BWOW), typically, may be added to the hydrated spacer fluids represented in Table 1 on an as needed basis to inhibit formation clay swelling and thereby minimize formation damage in fresh water sensitive zones. As shown in Table 2, the addition of KCl will increase the low temperature viscosity of the spacer fluid. Adding KCl prior to hydration of the mix would result in lower viscosity throughout the temperature range as compared to a mixture that did not include KCl. SPACER RHEOLOGY DATA YIELD POINTS @ 80 & 180° F SPACER DENSITY g/cc (ppg) YP @ 80° Pa (lbs/100ft²) YP @ 180° Pa (lbs/100ft²) YP @ 80° w/KCl Pa (lbs/100ft²) YP @ 180° w/KCl Pa (lbs/100ft²) 1.07 (9 ) 4.3 (9) 5.7 (12) 11.5 (24) 1.07 (9) 1.20 (10) 3.4 (7) 5.7 (12) 1.32 (11) 4.8 (10) 5.7 (12) 1.44 (12) 4.3 (9) 5.3 (11) 1.56 (13) 3.8 (8) 4.8 (10) 1.68 (14) 5.7 (12) 5.7 (12) 18.7 (39) 1.07 (9) 1.80 (15) 5.3 (11) 4.3 (9) 1.92 (16) 7.7 (16) 4.8 (10) 2.04 (17) 8.1 (17) 4.8 (10) 2.16 (18) 10.1 (21) 4.8 (10) 2.28 (19) 12.5 (26) 4.8 (10) 19.2 (40) 1.07 (9) The rheological properties indicated in Table 2 and the tables herein, including yield point (YP) and plastic viscosity (PV) indicated in pounds per hundred feet squared, were measured with a Model 35 Fann viscometer utilizing a #1 bob and sleeve and a #1 spring. A Fann viscometer uses a rotor and a bob which is attached to a spring, to measure the shear stress factor in a fluid. The bob and rotor are immersed in the fluid which is contained in a stationary test cup. The rotor, arranged in concentric alignment with the bob, causes the fluid to move at various shear rates, while the bob, by means of the attached spring, measures the torque exerted on itself. The performance of various of the spacer fluids represented in Table 1 with a neat cement slurry and a highly reactive water base drilling fluid from a South Texas well was measured and the results are reported in Table 3. By way of comparison, corresponding measurements were obtained from four commercially available prior art spacer fluids and these results are also reported in Table 3. DISPERSING POWER OF SPACER FLUIDS (Yield Points @ 80°F for a 25% cement, 25% drilling fluid and 50% spacer fluid by volume mixture) spacer density 1.08 kg/l (9 ppg) 1.68 kg/l (14 ppg) 2.28 kg/l (19 ppg) YP YP YP present invention 3.8 (8) 7.7 (16) 9.6 (20) prior art compositions 9.1-41.2 (19-86) 19.1-57.5 (40-120) 32.6-112.1 (68-234) As shown in Table 3, the spacer composition of the present invention demonstrates clear superiority over the prior art compositions as demonstrated by its consistently lower yield point upon contamination with downhole fluids. Spacer compositions in accordance with the present invention will be described in more detail with reference to the following examples. These examples are merely illustrative of the present invention and are not intended to be limiting. EXAMPLE 1: BAYOU SALE #1: 178 mm (7") LINER WATER BASE DRILLING FLUID SPACER PERFORMANCE A water base drilling fluid spacer composition in accordance with the present invention having a density of 2.06 kg/l (17.2 ppg) was prepared according to the following formula: 32 g/l (11.2 lb/bbl) spacer dry mix comprising 33.3% SSMA, 62.5% bentonite and 4.2% welan gum; 0.66 l per litre (27.7 gal/bbl) of fresh water; 217 kg (478 lbs) barite; and 2.4 ml/l (0.1 gal/bbl) of surfactant having a mole ratio of ethylene oxide to nonylphenol of 1.5. The fresh water base drilling fluid had a density of approximately 2 kg/l (17.0 ppg) and the fresh water base cement slurry had a density of 2.1 kg/l (17.5 ppg). The rheological properties of this spacer composition as well as the water base drilling fluid, cement slurry and various mixtures thereof are presented in Table 4. Fann Rheology Temp (°F) °C 600 300 PV YP Water base spacer (80) 27 145 85 60 25 (190) 88 105 64 41 23 Water base mud (WBM) (80) 188 143 45 98 (190) 81 49 32 17 Cement slurry ( 80) 447 231 216 15 (190) 247 137 110 27 95% spacer/5% WBM ( 80) 154 91 63 28 (190) 84 53 31 22 5% spacer/95% WBM ( 80) 185 145 40 105 (190) 101 67 34 33 50% spacer/50% WBM ( 80) 164 121 43 78 (190) 90 61 29 32 95% spacer/5% CMT ( 80) 161 97 64 33 (190) 113 74 39 35 5% spacer/95% CMT ( 80) 439 220 129 1 (190) 213 120 93 27 50% spacer/50% CMT 80) 225 157 64 33 (190) 164 101 63 38 EXAMPLE 2: Ship Shoal 332: 178 mm (7") Liner OIL BASE DRILLING FLUID SPACER PERFORMANCE An oil base drilling fluid spacer composition in accordance with the present invention having a density of 1.9 kg/l (16 ppg) was prepared according to the following formula: 2.84 kg (6.25 lbs). bentonite; 1.51 kg (3.33 lbs) SSMA; 0.19 kg (0.42 lbs) Biozan; 111 l (29.3 gal) water; 188.7 kg (416 lbs) barite; and 7.57 l (2.0 gal) of surfactant having a mole ratio of ethylene oxide to nonylphenol 9 to prepare 159 l (1.0 bbl) plus the 7.57 l (2 gallons) of surfactant for a total of 166.57 l (44 gallons) of the spacer composition. The oil base drilling fluid was an invert oil mud having a density of 1.89 kg/l (15.8 ppg). The cement had a density of 1.98 kg/l (16.5 ppg). The rheological properties of this spacer composition are presented in Table 5. The results shown in Table 5 demonstrate that while the spacer of the present invention and the prior art spacer performed without major rheological imcompatibilities, the spacer of the present invention demonstrated markedly superior results in the following areas: 1) Water-wetting and clean-up characteristics which leads to enhanced bonding and displacement; and 2) compatibility; negligible gelation increases the displacement efficiency of the spacer. EXAMPLE 3: MISSIPPI CANYON 160: 13-33/203 mm (8") CASING WATER BASE DRILLING FLUID SPACER PERFORMANCE A water base drilling fluid spacer composition including KCl was prepared in accordance with the present invention. The spacer fluid had a density of 1.44 kg/l (12 ppg) and was prepared according to the following formula: 5.67 kg (12.5 lbs) bentonite; 3.86 kg (8.5 lbs) KCl; 1.27 kg (2.8 lbs) SSMA; 0.77 kg (1.7 lbs) Biozan; 135 l (35.6 gal) sea water; 816 kg (180 lbs) barite; and 0.76 l (0.2 gal) of surfactant having a mole ratio of ethylene oxide to nonylphenol of 1.5 to prepare 159 l (1.0 bbl) of the spacer composition. The sea water base drilling fluid had a density of 1.41 kg/l (11.8 ppg) and the sea water base cement slurry had a density of 1.50 kg/l (12.5 ppg). The rheological properties of this spacer composition as well as a water base mud and cement slurry and various mixtures thereof are presented in Table 6. Fann Rheology @ 41°C (105° F) 600 (2) 300 PV YP Water base spacer 44 29 15 14 Water base mud 94 62 32 30 Cement slurry 29 22 7 15 95% Spacer/5% WBM 79 60 19 41 5% Spacer/95% WBM 70 45 25 20 50% Spacer/50% WBM 63 41 22 19 95% Spacer/5% CMT 52 36 16 20 5% Spacer/95% CMT 52 37 15 22 50% Spacer/50% CMT 62 42 20 22 25% WBM/50% Spacer/25% CMT 88 61 27 34

Claims: A spacer fluid for use in the drilling and completion of an oil well said fluid comprising sulfonated styrene-maleic anhydride copolymer as a dispersant, bentonite, welan gum, a weighting agent and from 0.24 to 240ml/l of fluid of ethoxylated nonylphenol surfactant having a mole ratio of ethylene oxide to nonylphenol in the range 1.5 to 15 A composition as claimed in claim 1, wherein the sulfonated styrene-maleic anhydride copolymer is employed in the form of the sodium salt. A composition as claimed in claim 2 wherein the molecular weight of the sulfonated styrene-maleic anhydride copolymer is less than 5000. A composition as claimed in any one of claims 1 to 3 wherein the weighting agent is selected from barite, hematite and calcium carbonate. A composition as claimed in any one of claims 1 to 4 further comprising a salt selected from potassium chloride, sodium chloride, calcium chloride, magnesium chloride, quaternary ammonium salts and zirconium oxy chlorides. A composition as claimed in claim 5 wherein said composition comprises from 3 to 5 percent by weight of water of potassium chloride. A spacer fluid as claimed in any one of claims 1 to 6 prepared from a dry mix comprising 10 to 50% by weight of sulfonated styrene-maleic anhydride copolymer 40 to 90% by weight of bentonite 1 to 20% by weight of welan gum. A spacer fluid as claimed in claim 7, wherein the dry mix comprises 33 to 34% by weight of sulfonated styrene-maleic anhydride copolymer 62 to 63% by weight of bentonite 4 to 5% by weight of welan gum. A spacer fluid as claimed in claim 7 or claim 8 wherein the surfactant contains 23% ethylene oxide, has a mole ratio of ethylene oxide to nonylphenol of 1.5:1 and is employed in an amount of 0.48l per 100l of fluid, or contains 65% ethylene oxide, has a mole ratio of ethylene oxide to nonylphenol of 9 and is employed in an amount of 4.8l per 100l of fluid. For use in a spacer fluid as claimed in claim 1, a dry mix as specified in claim 7 or claim 8. A method for cementing a wellbore penetrating an earth formation into which a conduit extends, said wellbore having a space occupied by a drilling fluid, said method comprising the steps of: (a) displacing said drilling fluid from said space with a spaces fluid as claimed in any one of claims 1 to 9; (b) displacing said spaces composition and filling said wellbore space with a settable cement composition.

Inventors: BRADSHAW ROGER D, CARPENTER ROBERT B, WILSON WILLIAM N, WILTON BONSALL S, BRADSHAW, ROGER D., CARPENTER, ROBERT B., WILSON, WILLIAM N., WILTON, BONSALL S.
Applicants: ATLANTIC RICHFIELD CO, ATLANTIC RICHFIELD COMPANY
Application year: 1990
Main classification: E21B33
IPC codes: C09K8, C04B24, C04B28