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 recently because, in many cases, it is impractical to keep a flow rate constant long enough to perform a drawdown test. Further, in many other drawdown 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, the early-time period represents linear flow. Current methods of analysis of multirate tests, in fractured wells, use both the superposition of constant-rate solution method and the rate-normalized type-curve matching 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 hydraulically 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 the linear flow data and combines it with the superposition of constant-rate solution method for the analysis of pseudoradial flow data. It does not require prior knowledge of the fracture type (uniform-flux or infinite-conductivity); in fact it predicts the fracture type. This method is useful for the analysis of simultaneously measured downhole pressure and sandface rate data. Data of three well tests reported in the literature were analyzed by the new method and the results including the comparison with those obtained by other methods are presented and discussed.