Slug Test: Double-Porosity, Linear Boundary, and Variable Storage Effectsby Abraham S. Grader, Pennsylvania State Univ, University Park, United States,
Document Type: Proceeding Paper
Part of: Symposium on Ground Water
The intention of this paper is to focus on three aspects of the slug test that are not as familiar as the main analysis techniques: the effects of double-porosity formations, the effects of an impermeable linear boundary, and the effects of a variable storage well on the response of the slug test. The intention is to familiarize the reader with the deviations of the response from the standard response of a slug test well in a homogeneous formation. The signature of a double-porosity formation on the slug test is most significant under conditions that provide the transitional matrix flow effects at dimensionless heads greater than 0.0001. From a practical point of view, the interporosity transfer coefficient is the most likely variable to be determined from the slug test, and not the storage ratio coefficient. The effects of an impermeable linear boundary on the slug test can be significant for cases with a large wellbore storage and a small distance to the linear boundary. It is shown that in some cases boundary effects are evident even in the traditional semi-log presentation of slug test responses. The solution technique for the linear boundary slug test is significantly different from the conventional slug test, and employs a two-dimensional formulation. The effects of variable wellbore storage during a slug test have initially been studied as the closed chamber test. In such slug tests, the wellbore storage coefficient is a combination of fluid interface motion and multiphase compression in the wellbore. The nonlinearity of the storage does not provide for simple analytical solutions. Hence, numerical methods are used to study drillstem slug tests such as the air chamber test, or the closed chamber test.
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