Field Applications of High Temperature Organic Gels for Water Control

Abstract

Abstract As the need to reduce operating expenses has intensified, water control technology has also expanded. One active and continually developing area is the use of polymer gels to control water in both oil and gas fields. Polymer gels typically show a disproportionate permeability reduction which reduces water permeability more than the hydrocarbon phase permeability. A need exists for gels which can be employed in higher temperature reservoirs and which are easily applied in seawater for offshore installations. The organic gel system described in this paper provides a solution to these needs. Because the organic gel system does not employ metal crosslinkers, longer gel delays can be obtained at elevated temperatures and cooling of the reservoir prior to gel injection is not required. The gel system employs low cost, conventional polyacrylamides and is compatible with hydrogen sulfide containing fluids. The gel system can be prepared in seawater and is resistant to oxygen degradation The high temperature organic gel has been developed in the laboratory and tested in numerous field applications. A discussion of four field treatments performed with the organic gel shows the versatility of gels in treating many common problems in the water shutoff area. In two applications, gels have been used in place of cement for perforation abandonment. Polymer treatments were performed successfully in both fractured carbonate and matrix sandstone gas wells to reduce water production and enhance gas recovery. Gel stability has been demonstrated in the field at temperatures as high as 250 F. The gels have reduced water and increased hydrocarbon production. Introduction The use of polymer gels has broadened from the initial conception of shutting off unwanted water in producing wells; however, that practice continues today as the primary usage for polymer gels. Early applications involved the use of viscous polyacrylamide slugs which gradually evolved to the more sophisticated gel systems available today. As applied in the North Burbank Unit, Moffitt has stated that uncrosslinked polymer treatments had good results, but polymer flowback was a problem. Many additional uses have been proposed for crosslinked polymer gels; however, the five major application areas are casing hole repair. cement bond failure repair, zonal abandonment, profile modification and water control in thief zones and coning situations. In nearly every case. organic polymer gels compete with cement squeezes, plastic plugs and inorganic gel systems in the above mentioned applications. The advantages polymer gels have over competitive techniques include lower cost, ease of application, control over gelation time, compatibility with formation fluids and the ability to penetrate substantial distances into the formation. Each candidate well must be evaluated to select the optimum treatment program, considering the lifetime cost rather than the near term application cost. Failures of the technology in the past should be considered in evaluating gel treatments; however, polymer gels are now being applied more judiciously with tighter screening criteria, better design and execution and improved gel chemistry. Several years ago, we started a program to develop gel systems suitable for use in higher temperature reservoirs which primarily required seawater for mixing. The first part of this study was the evaluation of currently available gel systems and their limitations. From this work, a list of needs was assembled to guide the development of a suitable gel system. This effort resulted in the organic gel system discussed in this paper. Review of Currently Applied Technology There are many systems which have been developed for blocking water in porous media including polymer gels, precipitates, resins and cements. P. 419