The Structural Accumulation Mechanism Of The Natural Gas Hydrates In Muli Region Of Qinghai Province

Natural gas hydrate is a potential energy source in 21st Century because of its small pollution and high heat.In 2008,the natural gas hydrate samples were first drilled and detected in permafrost regions of China,and also the first natural gas hydrate discovered in the low and middle latitude plateau permafrost regions,it has aroused the attention of geologists.Natural gas hydrate is a hot issue in the energy field at the present stage.China is a country with larger frozen soil area,natural gas hydrate was found in permafrost region in Muli area of Qinghai province,It has important practical significance for the energy situation and energy outlook of our country.This article taking the Juhugeng mining area as an example,drilling data and fracture distribution characteristics of the Muli region show that the distribution of natural gas hydrates accumulation has certain regularity.Natural gas hydrates are mostly distributed near a pre-existing major regional fault F1.While in the adjacent areas,no natural gas hydrates formed although these areas have similar physical and chemical condition.Based on the previous studies,combining with regional geologic and structural characteristics,we designed and ran five groups of physical sandbox experiments and four groups of Numerical simulation experiments.We try to illustrate a possible structural mechanism and influence factors of the accumulation pattern of natural gas hydrates in our research region.Modeling results show that the combination of pre-existing fault and detachment layer has a control role on structural deformation of the Muli region.Pre-existing fault is a major regional fault,which reactivates under the later regional shortening,and forms a migration channel by cutting strata from the deep strata to the shallow strata.The distribution of the regional detachment layer causes the widely development of the thin-skinned faults under the later regional shortening.These faults roots mainly located at the regional detachment layer,and almost not faults occurs cutting through the strata under the detachment layer.By analyzing physical experimental results and numerical experiments results,the structural patterns,and the distribution characteristics of the natural gas hydrates in the research area together,we propose a possible structural accumulation pattern of natural gas hydrates in Muli region.In this area,the natural pyrolysis gas,migrating along the fractures caused by the major regonial pre-existing fault,generated in the deep strata and accumulated in the shallow strata where the favorable physical and chemical conditions can be provided.While in the other places far away from the major regional fault in the research area,no natural gas hydrates can be accumulated in the shallow strata,because the deep migration channel developed unconditionally due to the lack of the major regional fault rooting to the gas source region in the deep strata.