A Model for Water Injection Into Frac-Packed Wells

Abstract

Summary Frac packs are increasingly being used for sand control in injection wells in poorly consolidated reservoirs. This completion allows for large injection rates and longer injector life. Many of the large offshore developments in the Gulf of Mexico and around the world rely on these completions for waterflooding and pressure maintenance. The performance of these injectors is crucial to the economics of the project because well intervention later in the life of the field is expensive and undesirable. For the first time, we present a model for water injection in frac-packed wells. The frac pack and the formation are plugged because of the deposition of particles from the injected water, and their effective permeability to water is continuously reduced. However, as the bottomhole pressure (BHP) reaches the frac-pack widening pressure, the frac-pack width increases and a channel that accommodates additional injected particles is created. Injectivity depends on the interstitial velocity of the injected water in the frac pack, volume concentration of the solids in the injected water, injection rate, injection-water temperature, size of proppants in the frac pack, width and length of the frac pack, and the initial minimum horizontal stress. In case of frac packs with large proppant size and high injection rates, the plugging of the frac pack is found to be negligible except in the building of a filter cake at the frac-pack walls. In the case of narrow frac packs with small proppant, significant plugging is expected, which leads to sharp permeability decline of the frac pack and a rapid rise in the BHP. The long-term injectivity of a frac-packed injector depends primarily on the filtration coefficient value of the frac pack, solids concentration in the injected water, and the injection rate. Frac packs are expected to maintain higher injectivities compared to any other completions such as openhole, cased-hole, perforated, or gravel packs.