Pump-in/ Flowback Tests Reduce the Estimate of Horizontal in-Situ Stress Significantly

A M Raaen, SPE and M Brudy1, SPE, Statoil ASA

This paper presents field data from pump-in/flowback tests at different locations offshore Norway, illustrating that standard extended leak-off tests (XLOTs) in tight formations may overestimate the minimum horizontal in-situ stress by at least 20 bar, corresponding to 0.1 s.g. at 2000m. The pump-in/flowback test is a simple variant of an XLOT. After the shut-in period, fluid is allowed to flow back over a fixed choke, and the pressure and the returned volume are recorded as a function of time.

We compare results from several pump-in/flowback tests to the results of the conventional pump-in/shut-in method used for XLOTs. For the tests presented here, performed in tight formations, the true fracture closure pressure is shown to be up to 20 bar lower than what would be inferred from a traditional interpretation of the standard XLOT.

It is argued that the pump-in/flowback test in a majority of cases will be straightforward to interpret, and that it should hence be the preferred method for measuring the minimum horizontal in-situ stress.

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