Selective Plugging of Injection Wells by In Situ Reactions

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Abstract
Introduction Petroleum engineers have long realized that producing horizons are not homogeneous. Severe permeability variations have been proven through core analysis and electrical surveys. After obtaining initial flush production through waterflooding, operators have shown concern about the distribution of water in the zone being flooded. At first, the efficiency of most floods was often an unknown factor. But efforts were soon directed toward the development of a method of accurately determining the distribution of flood water. Initial attempts to obtain necessary data were frequently very time-consuming and depended upon a uniform hole size for accurate information. Since many wells that were undergoing flooding operations had been shot, data of this type were inaccurate and misleading. Early Research In the early spring of 1951, a research project was instigated to develop a method of effectively treating water injection wells to greatly reduce the permeability of the above described thief zones. It was soon realized that it would be extremely difficult, if not impractical, to hope to be able to actually equalize the permeability of the entire horizon. Past research and field applications reported singular success when the surface of the formation was selectively plugged. There is adequate proof that additional oil was recovered as the result of these treatments and the process was a definite contribution to the industry. The procedure had two major drawbacks, however. One being that where there are no horizontal bedding planes to isolate the selectively plugged zone and where the vertical permeability is relatively high, the injection water quickly goes around the surface plug and again enters the zone of highest permeability. The other is that an injection well will develop a formation pressure which will cause a back flow of formation fluids when water injection is stopped. Such a back flow normally washes away the surface plugging chemicals and thus reopens the offending zone so that it may accept flood water again.

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