不同开采方法下深海能源土离散元模拟

发布时间：2019-04-28 10:08

【摘要】：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。
[Abstract]:Natural gas hydrate exists in deep-sea energy soil in the form of cementation and pore filling. During exploitation, the decomposition of natural gas hydrate will degrade the mechanical properties of the formation and lead to seabed accidents. It makes people pay more and more attention to the change of mechanical characteristics in the process of energy exploitation. Based on the previous laboratory tests, a two-dimensional micro-cementation model of temperature-hydraulic-mechanics was introduced into the discrete element commercial software PFC2D. The numerical simulation was carried out by heating up and depressurizing the soil with better exhaust gas and better drainage. The simulation results are compared with the experimental results under the same conditions, and the applicability of the cementitious model is verified. The changes of the particle contact distribution and the average pure rotation rate (averaged pure rotation rate,APR) of the particles during hydrate decomposition were further analyzed. During the process of decomposition, the anisotropy of total contact distribution of particles increases with the increase of temperature, and the cementation contact decreases gradually and keeps the principal direction in horizontal direction, while the non-cementation contact increases and keeps the principal direction in vertical direction all the time. The value of APR increased gradually and the distribution of positive and negative values tended to concentrate. In the process of decomposing, with the decrease of reverse (water) pressure, the total contact of particles gradually develops from isotropic distribution to vertical anisotropy, and the APR value is smaller and the distribution is uniform. After the reverse pressure was restored, the specimen was destroyed further, the total contact anisotropy of particles was more obvious, and the APR value increased and the positive and negative values were distributed in a centralized manner.
【作者单位】：同济大学地下建筑与工程系;同济大学土木工程防灾国家重点实验室;同济大学岩土及地下工程教育部重点实验室;
【基金】：国家杰出青年基金(No.51025932) 长江学者创新团队(No.1029) 教育部博士点基金(No.20100072110048)
【分类号】：TU411;P751

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