| 摘要 |
An aqueous fluid for treating underground, carbon dioxide-containing formations penetrated by casing regions of a wellbore, prior to the cementing of casings into the wellbore, comprises: (i) water, (ii) an agent which substantially increases (preferably by at least about 50 percent) the solubility of lime in water, and (iii) lime in an amount at least about saturating the water in the fluid. The lime in the treatment fluid reacts with carbon dioxide in penetrated formations to produce insoluble calcium carbonate, which blocks pores in the formations. Insoluble calcium hydroxide, formed by reaction of the lime with the water in the treatment fluid, deposits as an insoluble filter cake on the walls of the borehole where the fluid penetrates formations. The calcium hydroxide filter cake may react with the carbon dioxide to form additional calcium carbonate which helps the filter cake form a tight, impermeable barrier at the borehole. The formation is thus sealed at the borehole and the escape of pressurized fluids from penetrated formations into the borehole is prevented, thereby preventing gas-caused wormholes in the casing cement. If pressurized formations penetrated by the borehole do not contain carbon dioxide, injection of the treatment fluid is preceded by the injection of an aqueous solution containing carbon dioxide or a carbon dioxide precursor, thereby providing the carbon dioxide needed for the formation of the calcium hydroxide and calcium carbonate for sealing off the formations.
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