Abstract: Single-phase microemulsions, comprising a solvent, a surfactant blend and a carrier fluid, are effective spacer fluids for use during cementing operations. The solvent may be selected from the group consisting of monoterpenes, diterpenes, and alkyl or aryl esters of short-chain alcohols. The surfactant blend comprises a water-wetting surfactant or nonionic surfactant, a co-surfactant and an oil-solubilizing surfactant. The carrier fluid is aqueous. The solvent and surfactant blend are combined with the carrier fluid to produce the well-treatment microemulsion.

Abstract: Single-phase microemulsions, comprising a solvent, a surfactant blend and a carrier fluid, are effective spacer fluids for use during cementing operations. The solvent may be selected from the group consisting of monoterpenes, diterpenes, and alkyl or aryl esters of short-chain alcohols. The surfactant blend comprises a water-wetting surfactant or nonionic surfactant, a co-surfactant and an oil-solubilizing surfactant. The carrier fluid is aqueous. The solvent and surfactant blend are combined with the carrier fluid to produce the well-treatment microemulsion.

Abstract: A technique enables performance of remedial treatments to block unwanted fluid migration in a well. The remedial treatment involves formation of a slurry with a swellable material. The slurry, including the swellable material, is pumped downhole and is directed to a remediation site. When deposited at the remediation site, the slurry establishes a desired remediation treatment able to block unwanted migration of a downhole fluid.

Abstract: A flexible cement stable at high temperatures contains an extender that is a finely ground bituminous coal and/or a finely ground coke prepared from coal and/or liquid hydrocarbons. Preferred cokes are made from bituminous coals and from petroleum, heavy oil, and oil from tar sands, oil shales or oil sands. The coke is present in an amount up to 100 percent by weight of cement and the particle size is preferably from 1 to 1000 microns. The coke is also effective as an extender, and the slurries and set cements have low specific gravity.

Abstract: A flexible cement stable at high temperatures contains an extender that is a finely ground bituminous coal and/or a finely ground coke prepared from coal and/or liquid hydrocarbons. Preferred cokes are made from bituminous coals and from petroleum, heavy oil, and oil from tar sands, oil shales or oil sands. The coke is present in an amount up to 100 percent by weight of cement and the particle size is preferably from 1 to 1000 microns. The coke is also effective as an extender, and the slurries and set cements have low specific gravity.