Gas hydrates have become a new focus in resource exploration and development. However, the sand production problem in the exploitation process of gas hydrate reservoirs greatly restricts the commercial-scale operation of hydrates. In this paper, by introducing a plastic softening stage, a thermal-fluid-solid coupled mathematical model for sand production based on the skeleton failure and phase change of hydrates in reservoirs is established. By using the model, the sand production process of reservoirs at the wellhead under depressurization is truly simulated and the dynamic change of gas hydrates in hydrate reservoirs is analyzed. In addition, the mechanism and change law of sand production are analyzed mainly from the perspective of rock mechanics. Research result shows that the propagation rate of the pore pressure is always larger than the reduction rate of the hydrate saturation. When the pore pressure reduces to a point below the equilibrium pressure of hydrates, the hydrates are not immediately dissociated. The hydrates are dissociated only when the drawdown pressure exceeds a certain range; the hydrates are rapidly dissociated in the early phase. With the growth of the exploitation time, the reduction rate of the hydrate saturation obviously slows down; the sand production is first found at the position with the minimum horizontal principal stress and it hardly extends along the circumferential direction but constantly causes an erosion effect inwards the wellhead. The sand production undergoes three stages: initial, large-scale and stable sand productions. The large-scale sand production stage should be concerned in the exploitation process, during which it is the most possible to induce the large-area skeleton failure and further trigger the large-scale sand production.

天然气水合物已成为资源勘探开发的新热点。然而，天然气水合物储层开发过程中的出砂问题极大地制约了水合物的商业化运营。本文通过引入塑性软化阶段，建立了基于储层骨架破坏和水合物相变的出砂热-流-固耦合数学模型。利用该模型，真实模拟了井口减压下储层出砂过程，分析了水合物储层中天然气水合物的动态变化。此外，主要从岩石力学角度分析出砂机理和变化规律。研究结果表明，孔隙压力的传播速度总是大于水合物饱和度的降低速度。当孔隙压力降低到低于水合物平衡压力的点时，水合物不会立即解离。水合物只有在压降超过一定范围时才会解离；水合物在早期迅速分解。随着开采时间的增加，水合物饱和度的降低速度明显减慢；产砂首先出现在水平主应力最小的位置，几乎不沿周向延伸，但不断对井口造成冲蚀作用。出砂经历三个阶段：初期出砂、大规模出砂和稳定出砂。