Analysis of pressure and pressure derivative without type curve matching, 4. Naturally fractured reservoirs

Abstract

An alternative method, referred to as direct synthesis, is proposed for interpreting pressure transient tests in naturally fractured reservoirs. This new method offers consistent and accurate results from pressure tests with or without all reservoir flow regimes observed during the test period. Direct synthesis utilizes the characteristic intersection points and slopes of various straight lines from a log-log plot of pressure and pressure derivative data. Values of these points are linked directly to the exact, analytical solutions to obtain reservoir or well parameters. The direct synthesis method offers the following advantages: (1) accurate results from using the exact, analytical equations to calculate reservoir parameters; (2) independent verification is frequently possible from a third unique point; and (3) useful information is obtained when not all flow regimes are observed, as a direct result of the additional characteristic values developed by the method. Application of this technique is presented for single-well pressure tests in an infinite-acting naturally fractured reservoir with pseudosteady-state interporosity flow. Both the effect of wellbore storage and skin are included in the analysis. New analytical and empirical expressions were developed as a result of this work. These expressions are an integral part of the technique and provide the desired accuracy and versatility. Several field examples are given to clarify the technique and also illustrate the accuracy acquired by the method. When possible, a comparative analysis with other methods is included.