One of the most useful tools available for the purpose of formation evaluation is the transient pressure test. Basically, this test requires that the flow rate of a well be changed and that the associated change in bottom hole pressure be measured as a function of time. Proper interpretation of the resulting data can yield information necessary for a comprehensive program of reservoir analysis. The primary objective of this paper is to review the most successful method of transient pressure analysis for the purpose of evaluating reservoir flow capacity, formation damage, and reservoir fluid pressure. Examples of these determinations are presented. Transient pressure data are influenced by a number of factors. However, the most severe problems are caused by wellbore storage, formation damage, and reservoir boundary effects. The early transient data are most strongly affected by well storage and formation damage; later transient data are affected by boundaries. In most cases of practical interest, it is the intermediate time data which can be analyzed to evaluate the reservoir parameters of interest. This paper reviews the use of type curves and recently developed correlations for the purpose of identifying the interpretable data. An analysis of the formation damage factor as it is related to the well flow efficiency is presented. The significance of the flow efficiency is that, when combined with formation permeability data, it provides valuable insight into the selection, and into the anticipated effectiveness, of formation stimulation treatments.

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