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

Abstract

Summary In 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 in this study do not address complex transport mechanisms and complex fracture networks, but do address transient matrix linear flow (Ibrahim and Wattenbarger 2006; Nobakht and Clarkson 2012a, 2012b; Chen and Raghavan 2013) and boundary-dominated flow (BDF). The methods for BDF are the contacted-volume methods based on the ending times of linear flow (Wattenbarger et al. 1998; Behmanesh et al. 2015) and the flowing material-balance (FMB) methods. The Agarwal-Gardner FMB method (Agarwal et al. 1999) and the conventional FMB method involve plotting rate-normalized pseudopressure vs. material-balance pseudotime. 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 (BHP) (CBHP), and variable-rate BHP—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 BHP, as well as real-field data sets, are used to compare the methods. For linear flow, the Nobakht-Clarkson method (Nobakht and Clarkson 2012a, 2012b) yields the best results, although its use is tedious because it requires an iterative procedure. The Chen and Raghavan (2013) method for linear flow seems to provide results that are comparable with the Nobakht-Clarkson method (Nobakht and Clarkson 2012b) but does not require an iterative procedure. The Ibrahim-Wattenbarger method (Ibrahim and Wattenbarger 2006) for linear-flow analysis always overestimates flow capacity compared with the other methods. Among the methods that discuss the ending time of linear flow, it was found that the unit-impulse method from Behmanesh et al. (2015) provides the best results for predicting gas in place. For BDF, the results show that the Agarwal-Gardner FMB method (Agarwal et al. 1999) is quite vulnerable to the error in rate/pressure data, whereas the conventional FMB method is more robust to noise and provides more accurate estimates of gas in place.