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An Automatic History-Matching Workflow for Unconventional Reservoirs Coupling MCMC and Non-Intrusive EDFM Methods


 Technological advancements enable natural gas to be economically produced from ultratight shale rocks. However, due to the limited availability of long-term production data as well as the complexity of gridding, for reservoir simulation studies, in dealing with hydraulic fractures, an efficient automatic history-matching workflow in a probabilistic manner for performing history matching, production forecasting, and uncertainty quantification is highly needed. This can provide critical insights for the decision-making processes. In this study, we present an integrated history-matching workflow through coupling an innovative non-intrusive EDFM (Embedded Discrete Fracture Model) method, proxy modeling of KNN (K-Nearest Neighboring), and MCMC (Markov-chain Monte Carlo) sampling. The non-intrusive EDFM method can be applied in conjunction with any third-party reservoir simulators without the need of changing the source codes. Through non-neighboring connections, EDFM can accurately and efficiently handle hydraulic fractures, which does not require local grid refinement nearby fractures. The design of experiment is applied to perform sensitivity analysis with the purpose of identifying significant uncertain parameters. The KNN is utilized to build proxy model and its quality can be improved through multiple iterations of the workflow. The classic Metropolis-Hasting (MH) algorithm of MCMC is employed to perform sampling and predict posterior distribution of uncertain parameters. An application of the workflow to a horizontal shale-gas well from Marcellus shale is demonstrated and discussed in this study. Gas desorption effect is considered in the reservoir model. Six uncertain parameters are considered for this well including matrix porosity and permeability, fracture half-length, fracture conductivity, fracture height, and fracture water saturation. Based on 10 iterations and 250 simulation cases, 52 history-matching solutions with reasonable match results against actual gas and water production rates were identified. After history matching, we performed production forecasting for 30 years using all history-matching solutions under the constraint of constant flowing bottomhole pressure of 500 psi. Reliable P10, P50, and P90 of EUR (estimated ultimate recovery) predictions of gas recovery were determined as 11.9, 13.1, and 16.4 Bcf (billion cubic feet), respectively. In addition, the narrower posterior distributions of six uncertain parameters were quantified. The values with the highest frequency for each parameter are determined: porosity is 10.4%, permeability is 0.00034 md, fracture half-length is 450 ft, fracture conductivity is 2.85 md-ft, fracture height is 87.5 ft, and fracture water saturation is 38.8%.