Comparative analysis of well patterns on depressurization performance in boundary-sealed class 1 hydrate reservoirs: from five-spot to cluster horizontal wells

As a vital future energy resource, achieving high-efficiency exploitation of natural gas hydrates (NGHs) still faces challenges, and depressurization combined with other enhancement technologies, such as reservoir stimulation, may be the optimal path. Unlike previous studies that mainly focused on the impact of boundary sealing on single-well or complex-structure well types, this work systematically compared the production performance of two well-net modes under boundary sealing conditions. Based on China’s first offshore NGH trial production, and a numerical simulation method combined with J index (mainly affected by well type) was used to systematically compare the short- and long-term yield-increasing effects of five-spot wells (FSW) and cluster horizontal wells (CHW) for depressurization of Class 1 hydrate reservoirs with boundary sealing. The results indicate that both types of wells have better productivity performance due to the low-permeability barrier formed by boundary sealing to suppress water invasion and concentrate pressure energy to decompose hydrates, but their performance differs over time. The five-spot wells showed a more substantial overall improvement. Compared with the base case, with the boundary sealing, the cumulative gas production ( V g ) of the five-spot wells and cluster horizontal wells increased by 169.8% and 155.1%, respectively, and the gas-to-water ratio ( R gw ) increased by 680.6% and 409.3%, respectively. Although the cluster horizontal wells performed well in the first 120 days, the five-spot wells with boundary sealing performed well after 120 days and achieved a higher J index of 9.5 after 720 days. The results indicate that cluster horizontal wells demonstrate higher short-term gas production efficiency, whereas five-spot wells offer long-term development potential. The optimal engineering decision should therefore be based on whether the project’s core strategic objective is short-term pilot verification or long-term development. These findings provide a theoretical reference for multi-well development strategies in Class 1 hydrate reservoirs under boundary sealing conditions.