Numerical investigation of the natural gas hydrate production tests in the Nankai Trough by incorporating sand migration

A large number of data on gas production and reservoir characteristics were released after the 2013 and 2017 offshore natural gas hydrate production tests in the Eastern Nankai Trough of Japan. However, the systematic comparison of the two production tests is still limited. Therefore, in this study, we first reviewed the gas and water production processes of the three production boreholes in the two production tests. Some problems were found by comparing the gas and water production rates of each production well and with the existing numerical simulation results. For instance, the gas production rate of well AT1-P3 was extremely low and, distinguished with the previous simulation results, the gas production rates of wells AT1-P and AT1-P3 didn’t increase with time. Considering the severe sand production in these two wells, we speculated that the plugging of sand control device (SCD) caused by solid particles deposition was the cause of the above problems. Thus, for the first time, numerical simulation considering the sand production and SCD plugging was performed to evaluate the gas and water production performance of the three production wells. In addition, a preliminary analysis of the production efficiency of each well was carried out. The simulation results showed that a serious plugging occurred at well AT1-P3, which is responsible for its low gas production. In contrast, well AT1-P had a slight plugging, and well AT1-P2 avoided severe sand production owing to the reduced pressure drop, and obtained much higher gas production rate than well AT1-P3 with a lower pressure drop. Furthermore, the simulation results indicated that economically viable gas production is difficult to achieve with current production strategies even if the problems of sand production and SCD plugging are solved. This requires the use of some emerging production technologies in the future.