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青海省木里地区,2008年钻探岩心中首次钻取天然气水合物实物样品,从而引起了地质学家们越来越多的关注。以木里地区聚乎更矿区为例,结合分析该区域的钻井资料以及断裂分布特征,发现天然气水合物的成藏分布存在一定的规律,即该区天然气水合物主要集中于一条先存深大断层F1的两侧,而邻近区域在具有相似物化条件下却并未发现天然气水合物的存在。因此在前人研究基础上,结合区域地质构造特征,设计了3组物理模拟沙箱实验,试图从构造的角度来阐述研究区天然气水合物可能的构造成藏机制及其影响因素。实验模拟结果表明,先存断层和区域滑脱层对木里地区构造演化具有明显的控制作用。先存断层属于区域性深大断裂,其在后期应力作用下再活化,形成切割地层深部的运移通道;而区域性滑脱层的分布则造成挤压应力作用下区域性薄皮滑脱断层的广泛发育,这些断裂的根部主要集中到区域性滑脱层之上,滑脱层之下地层则基本未被断裂切穿。对比分析物理模拟实验结果及研究区构造特征,结合研究区天然气水合物的分布特征,提出了木里地区天然气水合物可能的区域性“断裂运移、下生上储”成藏模式,即深部热解气沿着深大先存断层运移至冻土层下有利位置富集成藏,并在有利的物化条件下形成天然气水合物,而在研究区其他区域,深部运移通道不发育,则在浅部地层未见天然气水合物的富集成藏。
In the Muli area of Qinghai Province, the first physical sample of gas hydrate was drilled in the drilling core in 2008, which attracted more and more attention of geologists. Taking polygamy orefield in Muli area as an example, combining the analysis of drilling data and fracture distribution in this area, it is found that there is a certain law of gas accumulation in gas hydrate, that is, the gas hydrate in this area mainly concentrates in a deep Fault F1 on both sides, while the adjacent area with similar materialized conditions but did not find the existence of gas hydrate. Therefore, based on the previous studies, combined with the regional geological structure features, three groups of physical simulation sandbox experiments were designed to attempt to explain the possible mechanism of formation and accumulation of natural gas hydrate and its influencing factors from the perspective of structure. The experimental results show that the pre-existing faults and the regional detachment strata play a significant role in controlling the tectonic evolution in the Muli area. The preexisting fault is a regional deep fault that reactivates under the late stress to form a migration channel in the deep of the cutting formation. The distribution of the regional slip layer results in the extensive development of the regional thin skin slip fault under compressive stress The roots of these faults are mainly concentrated on the regional slip layer, and the strata beneath the slip layer are basically not broken and cut through. By comparing the results of physical simulation experiments with the tectonic features of the study area and combining with the distribution characteristics of gas hydrate in the study area, it is proposed that the regional gas hydrates in the Muli area may have the regional pattern of “fault migration, subsurface accumulation and accumulation” That is, the deep pyrolysis gas migrates along the deep and large pre-existing faults to a favorable location under the permafrost layer to accumulate and accumulate, and form gas hydrate under favorable physical and chemical conditions. In other areas of the study area, deep migration channels do not develop , No enrichment of gas hydrate is found in the shallow strata.