Implosive Shock Treatment of Injection Wells

Abstract

Abstract The gradual, but continuous increase in pressure required to maintain specific injection rates, with resultant greater operational expense, is a problem common to many injection wells. This problem became critical in the development of the world's largest waterflood project. To combat this problem, new tools and techniques to "shock treat" the injection wells were developed in this field. Extensive use of the shock treatment has proven its effectiveness in improving injection profiles in this field. The treatment has also been effective in other fields in correcting formation interface plugging in both injection and production wells. However, only in injection well applications have there been sufficient jobs to warrant drawing any definite conclusions. Introduction The increase in pressure in an injection well can be due to filling of the reservoir and/or partial plugging of the formation. The causes of formation plugging can be filtrates from original drilling and completion fluids, scales precipitated out of the injection water, bacterial accumulation, injection of incompatible fluids, or the migration of silts from within the formation to form bridges. A new implosive shock treatment has been developed and has proven to be an effective aid in the removal of the plugging caused by filtrates, scales and silts. This paper is a report on a cross section of shock treatments as applied to two different waterflood projects. The following topics pertinent to shock treatments are discussed: remedial efforts leading to the development of shock treatments; mechanics of shock treatments; characteristics required in the tools employed; operational precautions; results of the treatments; and geologic, and general descriptions of the wells in these fields. This can serve as a guide in predicting the applicability of the shock treatment to correct plugging in specific wells in other fields. Conventional Remedial Efforts Formation interface plugging is a problem as old as the oil industry, and several common efforts to correct the condition have evolved over the years. In some areas the following conventional methods are considered to be satisfactory, but in others they have proven to be either ineffective, too costly, or prohibitively time consuming. Acid Washing Acid washing is commonly employed in the attempt to dissolve the plugging materials. Many materials which can cause plugging of the formation interface are not affected by acids and so remain in place. When employed to remove elements that are acid soluble, the treatment does not provide an effective means for flushing the residues. It would certainly be ill advised, in many cases, to force the plugging elements or their residues further back into the formation. Swabbing Swabbing is the most time-honored of the conventional methods, but it is also the most time consuming. Often this method does not create sufficient pressure reduction of fluid velocity to effectively remove an adequate quantity of the plugging materials. Drill-Stem Test Drill-stem test equipment is well known throughout the industry, but is only occasionally employed as a treatment to remove elements plugging the formation interface. By design, the equipment chokes the flow of fluid into the tubing, thereby reducing its effectiveness in removing plugging elements. In the world's largest waterflood project when injection rates began to decline conventional remedial methods were applied; but they proved to be deficient, for the same reasons as outlined previously. Limited but encouraging results with the drill-stem test equipment, under certain conditions, led to the development of the tools necessary to make shock treatments an outstanding success. Shock Treatment Shock treatment is the subjecting of the formation or a portion of a formation to an almost instantaneously applied pressure differential (i.e., implosion) for the purpose of loosening elements plugging that formation and sustaining this differential for a period of time sufficient to cause the plugging elements thus loosened to flow from the formation into the wellbore. JPT P. 128ˆ