Comparison of the Methods for Analyzing Rate and Pressure Transient Data from Multistage Hydraulically Fractured Unconventional Gas Reservoirs

Abstract

AbstractIn this study, we provide a detailed review and comparison of the various graphical methods, available in the literature, to interpret/analyze rate and pressure transient data acquired from multistage hydraulically fractured horizontal wells (MHFHWs) completed in unconventional gas reservoirs. The methods reviewed are based on transient matrix linear flow (Ibrahim and Wattenbarger 2006; Nobakht and Clarkson 2012a, 2012b; Chen and Raghavan 2013) and boundary-dominated flow due to the stimulated reservoir volume (SRV). The methods for boundary-dominated flow are the contacted volume methods based on the ending times of linear flow (Wattenbarger et al. 1998; Behmanesh et al. 2015) and the material balance methods (FBMs); Agarwal-Gardner method (Agarwal et al. 1999) and conventional method involving plotting rate-normalized pseudo pressure versus pseudo time material-balance time. We delineate the advantages and limitations associated with each method and identify the best methods of interpretation and analysis. Three different production modes; constant rate (CR), constant bottomhole-pressure (CBHP), and variable-rate/bottomhole pressure, are considered. For comparison, various synthetic test data sets generated from a high-resolution spectral gas simulator, which treats nonlinear gas flow rigorously and accurately to simulate rate transient data, is used. Both synthetic noise-free and noisy rate/pressure data sets considering wide ranges of initial reservoir pressure and bottomhole pressure as well as real field data sets are used to compare the methods. For linear flow, the Nobakht-Clarkson method yields the best results, although its use is tedious as it requires an iterative procedure. The Chen-Raghavan method for linear flow seems to provide comparable results to the Nobakht-Clarkson method, but does not require iterative procedure. The Ibrahim-Wattenbarger method for linear flow analysis always overestimates flow capacity as compared to the other methods. For boundary dominated flow, the results show that the Agarwal-Gardner FBM method is quite vulnerable to the error in rate/pressure data, while the conventional FBM method is more robust to noise and provides more accurate estimates of gas in place. Among the methods based on the ending time of linear flow, it was found that unit-impulse method based on Behmanesh et al. (2015) provides best results for predicting gas in place.