Unraveling the complex pressure propagation of two-time depressurization production in Shenhu hydrate reservoir: Insights for long-term exploitation

Abstract

Depressurization serves as the primary method for exploiting marine hydrate reservoirs, and understanding the long-term pressure propagation efficiency and identifying the potential limiting factors are crucial for enhancing and optimizing this approach. In this study, we employed numerical modeling to simulate two-time depressurization exploitation in the Shenhu hydrate reservoir, aiming to predict the long-term gas production and pressure propagation efficiency under various depressurization schemes. Our simulation results indicate: 1) The pressure propagates rapidly near the wellhead and gradually decelerates with distance due to the impeding influence of the reservoir's low intrinsic permeability and groundwater seepage in the covering strata. 2) Pressure propagation in single-well systems exhibits substantial variation among sublayers, resulting in limited areas of hydrate dissociation. Long-term gas production depends on the hydrate dissociation. Consequently, the total 5-year gas production for single-vertical-well and single-horizontal-well systems are only 3.59 × 106 m3 and 5.04 × 106 m3, respectively. 3) Multi-horizontal-well systems can significantly extend pressure propagation, but the maximum increase in gas production is only 47.0%. This is due to the reservoir's low permeability (2.3 mD), which severely hampers hydrate dissociation pressure, limiting it to 8 MPa. Therefore, optimizing depressurization requires reservoir modifications to enhance reservoir permeability.