Constant head-transient method using pressure and flow data for determining permeability and specific storage of tight rocks

Abstract

This paper describes a ‘constant head-transient method’ for estimating permeability and specific storage of tight rock samples, such as shale and crystalline rocks. Experimental tests are conducted using a cylindrical rock sample subjected to confining pressure, through which pressure diffusion occurs from a constant upstream pressure (or constant head) to a finite downstream storage. Unlike the pulse-transient method, the upstream fluid flow into the sample can be measured using a syringe pump because of no change in upstream pressure. By minimizing the downstream storage, the test time can be significantly reduced, but only the downstream pressure transient data do not yield accurate results on permeability and specific storage estimations. By combining the flow data with the pressure data, the proposed method aims at saving the test time and improving the accuracy of their estimations in extremely low permeability rock samples.

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  A constant head-transient method for measuring the hydraulic properties of tight rocks was developed with a boundary condition of constant upstream pressure and finite downstream storage.

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  The test time can be saved by minimizing the downstream storage, and the upstream flow can be measured to improve the accuracy in measuring the hydraulic properties.

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  Combining the flow and pressure objective functions yields the best curve fitting for both pressure and flow curves.