Comparison of modeling and actual gas production behaviors and reasons of discrepancy: Nankai Trough gas hydrate production test cases

Abstract:

Comprehensive data sets were obtained during the gas production attempts from a gas hydrate reservoir in the Eastern Nankai Trough (2013 and 2017) including gas and water production rates, downhole pressure and temperature monitoring data, log- and core-derived reservoir property information, and the seismic volume. Numerical simulation works using a compositional and thermal-coupling numerical model (MH21-Hydres) have been conducted before and after each production test for production behavior prediction purposes and history matching to re-evaluate reservoir property information. The actual production behaviors had some deviation from the prediction of the numerical model, such as non-incremental temporal profile of gas production rates, some inconsistency of temperature data and derived vertical and temporal production profiles, and difference of production behaviors among wells those were drilled within an area of 60 m radius area. To narrow-down the gap between the model and actual and to understand nature of the gas hydrate reservoir and physical processes during the gas hydrate dissociation, comparison of the modeling results and obtained data were reiterated along with re-examination of the geological and geophysical data. As results of the study, two features, vertical and horizontal heterogeneity of the formation and complexly disturbed situation of near-wellbore region due to unconsolidated nature of the sediments, were extracted as the main reasons of the discrepancy of the model and actual production behaviors.