垂直多井动态开采水合物边坡稳定性分析

天然气水合物是一种赋存在海底沉积物孔隙中的清洁能源，含量巨大，具有很好的开发前景和研究价值。垂直井作为开采水合物的一种主要方式，在开采过程中，会改变天然气水合物沉积层的环境条件，随着开采井释放出大量的气体和水，在地层中形成超压，过高的孔隙压力会降低沉积物的胶结强度，破坏沉积层的稳定性，诱发海底滑坡。借助Flac3D软件建立高精度的海底斜坡模型，基于有限差分法对垂直多井动态开采水合物过程中的边坡稳定性进行了数值模拟，模拟了不同开采方案条件下采用多井开采，水合物分解量、开采井压变化等不同影响因素产生的地层力学响应和位移变化，基于安全系数法进对于水合物开采引起的边坡稳定性进行了初步分析。结果表明：多井开采条件下，随着水合物分解程度的不断增大，海底斜坡稳定性逐渐降低，当水合物分解程度达到80%时，安全系数会降低到1.0以下，边坡会失稳；随着井压的不断降低，海底斜坡稳定性同样逐渐降低，当开采井压降低到4 Mpa以下时，安全系数会降低到1.05以下，边坡变为欠稳定状态，存在发生海底滑坡的风险。

Stability of hydrate slope in vertical multi-well dynamic mining

Natural gas hydrate is a clean energy occurring in the pores of seabed sediments. It has a large content and does not cause great harm to the environment, thus it has a good prospect and research value. Vertical wells as a main way of gas hydrates mining, the exploitation activities may alter the environmental conditions of the natural gas hydrate sediments, under which a large amount of gas and water would be released and result in overpressure in the strata, and the excessive pore pressure could reduce sediment consolidation strength, destroy the stability of the sediments, and induce submarine landslides. We established a high-precision underwater slope model with the aid of Flac3D software, and numerically simulated the slope stability in the process of vertical multi-well dynamic hydrate mining in finite difference method. The strata mechanical response and displacement changes caused by different influencing factors such as hydrate decomposition and well pressure change under different exploitation schemes were simulated. Using the safety factor method, the slope stability caused by hydrate mining was preliminarily analyzed. The results show that the stability of submarine slope decreases gradually with the increasing degree of hydrate decomposition under multi-well mining conditions. When the degree of hydrate decomposition reaches 80%, the safety factor will be lower than 1.0, and the slope will become unstable. With the decrease in well pressure, the stability of submarine slope also decreases gradually. When the well pressure drops below 4 Mpa, the safety factor will drop below 1.05, and the slope becomes less stable with a risk of submarine landslide.