A NEW METHOD OF ANALYZING WELL TESTS IN FRACTURED WELLS USING SANDFACE PRESSURE AND RATE DATA

Analysis of variable flow rate tests has been of special interest rece ntly because, in many cases, it is impractical to keep a flow rate con stant long enough to perform a drawdown test. Further, in many other d rawdown and buildup tests, the early data were influenced by wellbore storage effects, and the duration of these effects could be quite long for low-permeability reservoirs. For hydraulically fractured wells, t he early-time period represents linear flow. Current methods of analys is of multirate tests, in fractured wells, use both the superposition of constant-rate solution method and the rate-normalized type-curve ma tching for the pseudoradial flow period; and only the rate-normalized type-curve analysis for the linear flow period. This paper presents a mathematical model which describes drawdown and buildup tests in hydra ulically fractured wells. A new and simple method of analysis based on this model is presented for drawdown and buildup tests in oil and gas wells. This new method uses a specialized plot approach to analyze th e linear flow data and combines it with the superposition of constant- rate solution method for the analysis of pseudoradial flow data. It do es not require prior knowledge of the fracture type (uniform-flux or i nfinite-conductivity); in fact it predicts the fracture type. This met hod is useful for the analysis of simultaneously measured downhole pre ssure and sand-face rate data. Data of three well tests reported in th e literature were analyzed by the new method and the results including the comparison with those obtained by other methods are presented and discussed.