"Impulse fracture" is an injection test used to determine formation permeability and reservoir pressure. The test consists of a small-volume water injection to create a short fracture and a shut-in period afterwards to record pressure falloff. The pressure falloff after fracture closure is used to deduce permeability and reservoir pressure. The fracture can pass the near-wellbore damaged area and have the true formation exposed to flow transients. Also, fracturing may sometimes be difficult to avoid for injections in low-permeability formations.

The theory and analysis of impulse fracture are based on an instantaneous-source solution to the diffusivity equation. Numerical simulation examples and field case studies are used to support the validity of the analysis. The applicability of impulse fracture in gas reservoirs is demonstrated by numerical simulation results from a multi-fluid-bank simulator and by field cases. The impulse-fracture injection test is an economical and simple means to determine formation permeability. The test can be conducted in conjunction with mini-fracture or micro-fracture stress-test injections.

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