Mechanisms of mixed slurry flow of deep-sea hydrate exploitation

Marine gas hydrate test production faces several challenges, including low hydrate yield, severe sand sedimentation under jet-breaking conditions, and minimal or even absent fluid returns. To address these challenges and enhance gas hydrate production while maximizing the value of extraction equipment, a layered control engineering strategy is proposed. This strategy is based on the integrated vertical development approach encompassing natural gas hydrates, shallow gas, and natural gas reservoirs. Using a gas-liquid two-phase flow theory and considering both the self-dissociation behavior of hydrates and the effective transport conditions of solid-phase particles, a mathematical model for slurry lifting across different extraction stages was established. The model was solved and validated, ultimately producing a process flow diagram for natural-assisted lifting of hydrate slurry. During the horizontal drilling phase, effective transport of solid-phase particles can be achieved without additional gas injection when the drilling fluid flow rate exceeds 13 L/s. However, gas injection can be used to further accelerate solid particle transport, with an injection range of 0 to 67 L/s, depending on the drilling fluid input. During the hydrate fracturing and recovery stage, solid particle transport can be effectively maintained without additional gas injection when the fracturing flow rate is between 49 and 55 L/s. Within this range, gas injection can be adjusted from 0 to 129 L/s to meet the requirements of hydrate slurry flow. This research provides a reference for improving gas hydrate extraction yield, accelerating early commercialization of hydrate exploitation, and supporting China's “dual carbon” strategic goals.