Several types of prefracture injection tests, such as step-rate tests and minifracs, are commonly performed for optimizing frac-pack treatments. Originally, the industry developed most of these tests to diagnose the fracturi ng behavior of low-permeability, hard-rock formations. The analysis of these tests1  with bottomhole gauge data is reported in this paper. In addition, the execution and analysis of some of these tests have been modified in recognition of the differences between higher-permeability formations as compared to conventional low-permeability, harder-strength formations.

A matrix injection-falloff test (MlFOT) is proposed that can be used to estimate the approximate permeability and skin value of the formation before the frac-pack. This test can also help users determine fluid-loss behavior and identify possible reservoir limitations under certain circumstances. Step-rate/step-down tests are commonly used as a means of determining fracture extension pressure (FEP) and closure stress as well as identifying any near-wellbore restrictions or multiple fractures. Properly analyzed minifracs measure fluid-loss behavior of the fracturing fluid and also can be used to identify special problems, such as perforation friction, tortuosity, and multiple fractures. These parameters are then used to determine fluid volumes, pump rates, and proppant addition schedules for the actual treatment. Bottomhole gauge data from several wells indicate that near-wellbore tortuosity or perforation restrictions are not a major concern for Gulf of Mexico formations. However, there is some evidence of multiple fracture propagation.

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