Development and Field Testing of Large Volume Remedial Treatments for Gross Water Channeling

Abstract

Smith, L.R., SPE-AIME, Pan American Petroleum Corp. Pan American Petroleum Corp. Fast, C.R., SPE-AIME, Pan American Petroleum Corp. Pan American Petroleum Corp. Wagner, O.R., SPE-AIME, Pan American Petroleum Corp. Pan American Petroleum Corp. August 1969 For fracture-caused channeling, an injected slurry of finely ground, light weight solids has proved successful. For water bypassing due to high permeability, alkaline silica gel mixtures having long set times form an effective deeply placed flow barrier. Introduction Injected water often channels through high flow capacity zones, resulting in poor sweep efficiency and reduced economic attractiveness of the waterflood. The offending channel may be either a fracture network or a high permeability zone extending between injection and production wells. In the study described here we were concerned with finding means of selectively plugging these offending zones, using low cost materials, and developing methods that would be practicable in the field. Since the requirements for practicable in the field. Since the requirements for fracture plugging and for matrix plugging are usually different, these are treated as separate problems. Channeling through fractures is often a problem in carbonate or tight sandstone reservoirs. Sometimes it is possible to improve sweep efficiency by altering the injection pattern or by lowering the injection pressure to permit the open fractures to close. Otherwise, the most direct remedial approach is to physically block flow within the fracture. Since the matrix permeability of many carbonate reservoirs is low, it is desirable to plug the fractures only in the interwell area so that plug the fractures only in the interwell area so that injectivity is not seriously reduced. A fracture plugging method that utilizes a large quantity of finely ground, low cost solids injected as a water slurry has been developed and has been applied successfully in field operations. To alleviate water channeling through high permeability matrix -rock requires a different approach permeability matrix -rock requires a different approach since solids in suspension will not penetrate the matrix. Acidic silica gels having relatively short set times have been used for this purpose. These treatments are commercially available. However, because of the relatively short gelation time for the acidic gels, large volume treatments usually are not possible, particularly in wells with low injectivity. In many instances small volume treatments do not lead to significant sweep improvements. When communication between the offending zone and other intervals is extensive, a large deeply-placed barrier will offer the greatest chance for improved oil recovery. Alkaline silica gels are especially well suited for large volume matrix plugging applications since it is possible to formulate mixtures having very long gel times. Treatment for Channeling in Fractures Fractures that cause bypassing in waterflooding are usually vertical and, in many fields, have a definite directional trend. Since most of this bypassing occurs in low permeability reservoirs, the natural flow capacity of the formations, exclusive of the fractures, is low. In some waterflood projects fractures have been found that extend from well to well for as much as 1,000 ft. Where it is not possible to reduce injection pressure to close them or to alter the injection pattern, it is necessary to plug these offending pattern, it is necessary to plug these offending fractures in the interwell area, yet maintain sufficient injectivity to permit successful flooding. JPT P. 1015