New Methods for the Analysis of Drillstem Test Data

Abstract

Abstract This paper presents new procedures for analyzing pressure buildup data obtained from drillstem tests. The new methods apply for cases where the produced fluid does not reach the surface during the flowing period so that, the flow period represents a slug test. The combined effects of variable flow rate, short producing time and changing wellbore storage generally make it difficult to apply conventional analysis methods to DST buildup data. Two new straight-line methods for analyzing buildup data presented in this work account for both the variable rate during the flow period and producing time effects. If the buildup well-bore storage-skin group Csd exp(2s) is small, then shortly after shut-in, a well-defined straight line is obtained for both methods. Using the slope of the straight line obtained by either method, it is shown that the flow capacity (kh), the skin factor (s) and the initial reservoir pressure (pi) can be determined. If the group Csd exp(2s) is large, longer shut-in times are needed before the proper straight line can be obtained. However, for the latter case, it is shown that a multi-rate equivalent time can be constructed so that standard type-curve matching can be performed to obtain estimates of the flow capacity and the skin factor. A field example is presented to illustrate the applications of the proposed methods.