Effect of well configuration, well placement and reservoir characteristics on the performance of marine gas hydrate reservoir

Reservoir simulations are used to forecast the long-term gas production from gas hydrate reservoirs. In the present work, we explore different well placements and well configurations to analyze the gas production strategy for an oceanic, unconfined, class-2, gas hydrate reservoir using an in-house three-dimensional finite volume simulator. In the past, for depressurization in an unconfined class-2 reservoirs, isolation of the aquifer zone by well placement is suggested. We show that for high pressure conditions in marine gas hydrate reservoirs, depressurization is ineffective even with horizontal producer placed far away from the aquifer. Therefore, Warm water injection is necessary along with depressurization. We demonstrate that, the injector placement and configuration determines the gas production behavior and producer conditions do not significantly impact the production potential. We also find that the unconfined aquifer below the hydrate zone helps in the warm water convection and proximity of the injector to the aquifer improves gas production behavior. However, for unconfined class-2 gas hydrate reservoirs with low initial pressure, depressurization is effective and leads to a very high recovery (80%) of the gas. The reservoir porosity governs the warm water injection which affects the available dissociation energy to the gas hydrates and hence the gas recovery. In a layered reservoir, the porosity of the hydrate layer adjacent to the overburden has significant impact on the gas production due to the available dissociation energy from the overburden.

Automated summary

Reservoir simulations are crucial for predicting long-term gas production from gas hydrate reservoirs. Various well placements and configurations were explored in this study to analyze gas production strategies for an oceanic, unconfined, class-2, gas hydrate reservoir. The effectiveness of depressurization and the necessity of warm water injection were demonstrated, with injector placement playing a critical role in gas production behavior. Additionally, the reservoir porosity and layering significantly affect gas recovery and production behavior.