This invention relates to cementing pipe in a well drilled into the earth and more particularly is related to cementing pipe against evaporite sections penetrated by the well.
In the completion of a well drilled into the earth, pipe or casing is normally lowered into the well and a cement slurry is pumped down the well and up the annular space formed between the pipe and the wall of the well. The cement slurry is then maintained in the annular space to allow it to set and bond with the pipe and the wall of the well to thereby hold the pipe in place and to prevent fluids from flowing behind the pipe. Many different cements and cement slurries have been used for this purpose though portland cement and calcium aluminate cement are probably the most commonly used cements. Various additives and formulations have been used with these cements in forming slurries having particularly desirable properties. For example, clays selected from the group of bentonite and attapulgite have been added to cement slurries as have sodium chloride, calcium chloride, dispersing agents, and gypsum.
In U.S. Pat. No. 3,937,282 to Stanley H. Shryock et al., there is described a composition for cementing casing in wells drilled through permafrost zones. The Shryock et al. slurry consists essentially of a hydraulic cement, gypsum, a monovalent chloride salt, and a setting time retarding agent and water. In U.S. Pat. No. 3,071,481 to Horace J. Beach et al. there is described a gel cement composition for use in cementing wells. This composition consists essentially of a hydraulic cement, a colloidal clay, sodium chloride or calcium chloride, and an organic dispersing agent. In U.S. Pat. No. 3,467,193 to Joseph U. Messenger, there is described still another cement composition for use in cementing wells. This cement composition describes the use in a slurry of hydraulic cement of a turbulence inducer and silica or diatomaceous earth particles having sizes of from 0.1 to about 44 microns in diameter. In copending U.S. application Ser. No. 714,713, CEMENTING AGAINST EVAPORITES, filed Aug. 6, 1976, now U.S. Pat. No. 4,089,376 by Joseph U. Messenger, there is described a method of cementing pipe against an evaporite section wherein there is used a cement slurry formulated from hydraulic cement silica flour, attapulgite, sodium chloride, weighting agent, dispersing and retarding agent, and water to have a density within the range of 13.0 to 21.0 pounds per gallon.
In the placing of cement slurries in a well, preflush solutions, washer or spacer solutions are often used intermediate the cement slurry and the drilling mud located in the well to prevent the contamination of the slurry by drilling mud and filter cake formed therefrom. For example, in U.S. Pat. No. 3,291,211 to Joseph G. Savins et al., there is described for this purpose a solvent containing a dissolved solute which imparts viscoelastic properties to the liquid. In U.S. Pat. No. 3,348,612 to Joseph U. Messenger, a slug of liquid having mutual solubility for oil and water is used ahead of a cement slurry. In U.S. Pat. No. 3,467,193 to Joseph U. Messenger, there is used a preflush comprised of formation water containing dispersants. In U.S. Pat. No. 3,688,845 to Joseph U. Messenger, there is described a preflush solution for use in a well having an oil base drilling mud therein which preflush solution is comprised of an oil and a dispersant and has a lower viscosity and a lower gel strength than the drilling mud. In U.S. Pat. No. 3,411,580 to Oscar B. McKinney et al., there is described a preflush solution that is comprised of water, a polysaccharide, and a cross-linking agent. In U.S. Pat. No. 3,884,302 to Joseph U. Messenger, there is flowed ahead of a cement slurry an aqueous alkaline wash having a pH of at least 10 followed by an aqueous preflush having a characteristic of forming a viscous film upon contact with a fluid having a pH of at least 10.