Experimental Investigation of Gas/Water/Sand Production Behaviors in Hydrate-Bearing Sediments under Bottomhole Pressure Regulation: Roles of Depressurization Amplitude and Rate

Summary

Natural gas hydrates are considered a promising clean energy source due to their high energy density and huge resources; however, uncontrolled sand production and reservoir instability remain major challenges during marine hydrate exploitation through depressurization. Therefore, we conducted laboratory-scale experiments on synthetic water-saturated hydrate-bearing sediments under various depressurization amplitudes and rates to examine coupled gas/water/sand production responses to bottomhole pressure (BHP) regulation. The results indicate that BHP regulation modulates the multiphase production behaviors, and the observed responses can be interpreted within a thermal-hydraulic-mechanical-chemical (THMC) coupling framework. Depressurization amplitude and rate mainly affect the final stress state and transient hydrodynamic disturbance, respectively, and increasing amplitudes enhance overall productivity and gas production efficiency, whereas the increase in sand production becomes less pronounced beyond a transition point under the tested conditions. Increasing rate yields negligible gains in overall productivity while diminishing gas efficiency and causing an approximately linear increase in sand production. On the basis of these results, we propose a preliminary, staged BHP regulation strategy, adopting a conservative initial rate, followed by a controlled increase and deep depressurization near the quadruple point pressure, combined with robust physical sand control methods. While further numerical and experimental validation is required, these findings expand the understanding of gas/water/sand production behavior and provide a reference for future studies on production strategies, sand control, and risk assessment of field trials.