Traditional methods of pressure-transient analysis rely on homogeneous reservoir models and require assumptions on reservoir shape and well-flow regimes. Unsteady flow rates offer further complexity because traditional methods are dependent on past production history. Crump and Hite (2008) proposed a new method for estimating average reservoir pressure that applies to heterogeneous reservoirs and only requires knowledge of the pressure-buildup data. The Crump and Hite (2008) method relies on obtaining the first few eigenvalues of a diffusion equation to predict average reservoir pressure. A large buildup time may be required for a successful application of the method, depending on the magnitude of the first eigenvalue.

This work applied the Crump and Hite (2008) method to a real field case. A reservoir was produced by a single horizontal well for a period of a few years, which was followed by a shut-in period of approximately 200 days. The first four eigenvalues could be extracted, providing an estimate of average reservoir pressure. The pressure derivative was computed with a total-variation-regularization method, which showed lower noise levels compared with finite-difference methods. The extended version of the Crump and Hite (2008) method for shorter buildup times did not show a substantial reduction of the buildup-time requirement.

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