Abstract: A method for controlled release of acid in a subterranean carbonaceous formation is achieved by placing in the openhole section of a wellbore within the formation a crosslinked acid of a volume substantially equal to the volume of the openhole section, then using tubing placed within the openhole section to circulate into the crosslinked acid a composition containing a breaker for the crosslinked acid at a matrix rate while removing the tubing from the openhole section, breaking the crosslinked acid while the tubing is removed, closing the backside and squeezing the uncrosslinked acid into the subterranean carbonaceous formation. In one non-limiting embodiment the openhole section may be substantially horizontal.

Abstract: A method for removing or dissolving calcareous materials in a subterranean formation or in a wellbore consists of two basic steps. In the first step, an aqueous acid solution is injected into the formation or wellbore. The aqueous acid solution contains between from about 15 to about 99 weight percent of an organic acid selected from formic acid, acetic acid or a mixture of formic acid and acetic acid. Water or brine is then injected into the formation or wellbore. The amount of water or brine injected into the formation or wellbore is an amount sufficient to reduce the concentration of organic acid in the formation or wellbore to no greater than 10 weight percent.

Abstract: A particulate gel breaker for the controlled reduction in viscosity of aqueous acid compositions used in fracture acidizing of subterranean formations, such as in oil and gas wells, is formed for use with crosslinked polymer gels which are crosslinked with organometallic compounds, such as titanium or zirconium. The gel breaker is composed of particles containing complexing materials such as fluoride, phosphate, sulfate anions and multi-carboxylated compounds, which are capable of complexing with the organometallic crosslinking compounds of the gel. The particles are coated with a water insoluble wood resin coating which reduces the rate of release of the complexing materials of the particles so that the viscosity of the gel is reduced at a retarded rate. The gel can thus be introduced into the well at a sufficiently high viscosity for fracturing and to allow time for the acid to penetrate the formation before the acid is released.

Abstract: A retarded aqueous hydraulic cement slurry is provided containing, in addition to water and a hydraulic cement, a retarder selected from the group consisting of: (a) alkaline earth metal salts of mono- and di-carboxylic acid derivatives of simple sugars, (b) alkaline earth metal salts of borate esters of mono- and di-carboxylic acid derivatives of simple sugars, and (c) mixtures of any two or more of the foregoing. Unexpectedly, the retarder of the present invention is compatible with polyamine type fluid loss agents and with certain thixotropic cements. Also, the retarder is sufficiently water soluble so that it can be prepared as a liquid additive, thereby simplifying mixing procedures in remote locations such as offshore well platforms.