Dynamic Analysis of Exploitation of Different Types of Multilateral Wells of a Hydrate Reservoir in the South China Sea

Abstract

The multilateral well exploitation technique is a technical approach to the efficient exploitation of natural gas hydrate that deserves to be explored. In this paper, a numerical model of an ideal hydrate reservoir is developed based on logging data from well SHSC-4 in the Shenhu area of the South China Sea in 2017. It focuses on the simulation study of the mechanism of hydrate exploitation by multilateral wells. Meanwhile, it analyzes the changes in the temperature field, pressure field, and hydrate solid-phase concentration during the gas production by multilateral wells. The simulation results indicate that the multilateral well technology can increase the hydrate production capacity by a factor of 18–25 compared to vertical well depressurization. The main mechanism of the multilateral well production increase is to accelerate the dissociation rate of hydrate by increasing the pressure reduction area between the wellbore and the reservoir, rather than reducing the seepage resistance of gas production. Based on the changes in hydrate solid concentration, it can be seen that the hydrate in the mixed layer is always decomposed before that in the pure hydrate layer under any exploitation method. Furthermore, from the changes in temperature field, pressure field, and hydrate solid concentration, it can be observed that the cluster multilateral well is the best way to exploit hydrate in the first 2 years, and in long-term production, the best way of exploitation is the fishbone multilateral well.