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天然气水合物以胶结及孔隙填充等形式存在于深海能源土中,开采时因其分解会劣化地层力学特性进而引发海底事故,使得人们对能源土开采过程进行中力学特性的变化愈发重视。在前期室内试验的基础上,将一个温度-水压-力学二维微观胶结模型引入离散元商业软件PFC2D中,通过对排气、排水性较好的土体进行升温及降压法开采进行数值模拟,并将模拟结果与相同条件下的室内试验结果对比,验证了该胶结模型的适用性。进一步分析了颗粒接触分布与颗粒平均纯转动率(averaged pure rotation rate,APR)在水合物分解时的变化情况。升温分解过程中随温度升高,颗粒总接触分布各向异性程度增大;胶结接触逐渐减少并始终保持主方向为水平方向,无胶结接触增多并始终保持主方向为竖直方向;APR值逐渐增大且正负值分布逐渐趋于集中。降压分解过程中随反(水)压降低,颗粒总接触由各向同性分布逐渐发展为主方向为竖直方向的各向异性,APR值较小且分布均匀;恢复反压后,试样进一步破坏,颗粒总接触各向异性更加明显,APR值增大且正负值呈集中分布。
Gas hydrate exists in deep-sea energy soil in the form of cementation and pore filling. Due to its decomposition, the hydrate will deteriorate the mechanical properties of the formation and lead to a seafloor accident. Therefore, people pay more attention to the change of mechanical properties in the process of energy earth mining. Based on the previous laboratory tests, a temperature-hydrodynamic-mechanical two-dimensional microcosmic cementing model was introduced into discrete element commercial software PFC2D. Numerical values were obtained by heating and depressurizing the soils with better exhaust and drainage properties The simulation results are compared with the indoor test results under the same conditions to verify the applicability of the cementing model. The changes of particle contact distribution and averaged pure rotation rate (APR) during hydrate decomposition were further analyzed. With the increase of temperature, the anisotropy of the total contact distribution increases with the increase of temperature. The cementation contact decreases gradually and the main direction is always horizontal, and the cementation contact increases and the main direction is vertical. The APR value gradually increases Increase and positive and negative distribution gradually tends to focus. During the step-down decomposition process, with the decrease of anti-water pressure, the total contact of particles gradually developed from the isotropic distribution to the anisotropy with the main direction vertical, with a small APR value and uniform distribution. After the back pressure was restored, the sample Further destruction, the total contact anisotropy particles more obvious, APR value increases and positive and negative values were concentrated distribution.