Analysis of an Extended Well Test to Identify Connectivity Between Adjacent Compartments in a North Sea Reservoir

Abstract

The paper demonstrates the usefulness of extended well tests and advanced interpretation techniques to complement seismic information with an example from a North Sea reservoir. This reservoir is heavily faulted but seismic indicated that the faults were discontinuous, thus suggesting good communication between the various parts of the reservoir. To verify this, tests were run on the two wells already drilled: an extended four month test on a vertical well, followed by a four and a half month shut-in; and a conventional test on a horizontal well. The extended test was analyzed in both the conventional way (one flow period at a time) and by deconvolution of the entire pressure and rate histories. The combination of the interpretations of the tests on both wells allowed to delineate compartments in the reservoir, to assess their connectivity and to correct the seismic information.The paper illustrates the difficulty of interpreting data in the conventional way, as most interpretable flow periods are short (200 hours maximum) compared to the length of the test and individually may be misleading, as derivative shapes tend to be dominated by features reflecting the way log derivatives are calculated rather than by the geology. It is shown that deconvolution is free from these limitations and provides a much clearer picture of the well behavior.

From Straight Lines to Deconvolution: The Evolution of the State of the Art in Well Test Analysis

“…21 shows deconvolution applied to a 10 ½ month extended test, which included a series of drawdowns and build ups for 4 ½ months and a 6 month build up (the test is described in Ref. 97). Because the flow periods in the initial 41/2 period were too short, the test could only be interpreted with the final build up, i.e.…”

Diagnosis of Reservoir Behavior From Measured Pressure/Rate Data

“…Analytic methods (Marhaendrajana 2005;Marhaendrajana and Blasingame 2001) have also been proposed to handle well interference in multiwell reservoirs. Gringarten (2005) showed that the reservoir-compartmentalization question can be addressed by deconvolving simultaneously measured pressure/rate data for wells across a perceived fault barrier. Multidisciplinary approach has also been reported to address the compartmentalization question (Bigno et al 1998).…”