O.R. Wagner, AMOCO Production Co.
In fluid-injection projects, the channeling or bypassing of injected fluids through fractures and high-permeability stringers results in poor reservoir sweep efficiency and low oil recovery. When the injected fluid is water, channeling problems have a less severe impact on the flood economics because water is relatively inexpensive, and it can be recovered and recycled through the reservoir to recover additional oil. However, many of the improved oil-recovery processes employ expensive fluids such as surfactants, micellar fluids, and solvents, which must produce oil during a single pass of a relatively small volume through the reservoir. Therefore, it is important to identify and correct any serious reservoir heterogeneities which would lead to channeling and to the inefficient use of the expensive improved recovery fluids. Some knowledge of the near wellbore reservoir heterogeneities can be derived from well logs and core permeability data. Pressure transient and pressure pulse tests are useful in detecting interwell fractures and in determining interwell communication. Other information is sometimes available from prior waterflood performance. A supportive method of determining reservoir interwell anatomy and reservoir performance in an improved recovery process is the tracing of interwell flow of injected water during an initial waterflood. During the past several years, the results of approximately 20 tracer programs that have been conducted in reservoirs undergoing waterfloods, gas drives, and alternate water-solvent injection have These tracer programs have provided the proving ground and the opportunity for screening the performance of numerous water and gas tracer materials and for arriving at a suite of "preferred" tracers for waterfloods and gas drives. This paper discusses the use of chemical and radioactive tracers to identify sweep problems in a tertiary miscible pilot area in West Texas, two potential micellar pilot areas in Wyoming, a Wyoming waterflood, and a hydrocarbon miscible project in Alberta, Canada.