Numerical analysis on gas production performance by using a multilateral well system at the first offshore hydrate production test site in the Shenhu area

Abstract

Multilateral well technique is a promising approach to enhance gas recovery, especially in heterogeneous hydrate reservoirs with underlying free gas. However, little is known about the optimal deployment for multilateral wells on hydrate production. Herein, a 3D numerical model for predicting the combined production performance of hydrate reservoirs by using multilateral wells is proposed. The results indicate that the horizontal branch deployed at the interface between three-phase layer and free gas layer shows the best production potential when one branch is available. Then, effects of geometric parameters including branch deployment location, spacing, length, phase angle, and branch number on production behaviors are analyzed through orthogonal designs. The analysis shows dual-branch and quad-branch scenarios are most influenced by deployment location and branch length, and the corresponding optimal combinations are suggested respectively. By contrast, dual-lateral wells have the most favorable yield-increasing effects due to the synergistic depressurization, of which total gas production and productivity index are 123% and 81% higher than those of vertical wells. Additionally, well interference may exist between branches, which is unfavorable for gas recovery between the lateral branches and exacerbates with an increase in branch number. This research gives an in-depth insight into the industrialized co-production of hydrate and free gas.