青海省木里地区天然气水合物构造成藏机制——来自物理模拟实验的启示  

The structural accumulation mechanism of the natural gas hydrates in Muli region of Qinghai Province:Revelation from physical simulation experiment

作　　者：吴闯[1] 尹宏伟[1] 于常青[2] 皮金云[2] 吴珍云[3] 汪伟[1] 张佳星[1] 

机构地区：[1]南京大学地球科学与工程学院,江苏南京210023 [2]中国地质科学院地质研究所,北京100037 [3]江苏省地震局,江苏南京210014

出　　处：《天然气地球科学》2017年第5期771-784,共14页Natural Gas Geoscience

基　　金：中国地质调查水合物专项项目(编号:GZHL20110313);国家自然科学基金项目(编号:41272227;41572187)联合资助

摘　　要：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。The Muli region of Qinghai Province, where natural gas hydrates were drilled and discovered in 2008, has attracted more and more attention.Taking the Juhugeng mining area as an example, drilling data and fracture distri- bution 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 three groups of physical sandbox experiments.We try to illustrate a possible structural mechanism and influencing 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 controlling 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 migra tion channel by cutting strata from the deep strata to the shallow strata.The distribution of the regional detachment layer causes the wide development of the thin-skinned faults under the later regional shortening.These fault roots mainly located at the regional detachment layer,and nearly no faults cut through the strata under the detachment layer.By analyzing physical experimental results and 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 the Muli region.In this area,the natural pyrolysis gas,migrating along the fractures caused by the major regional 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

关 键 词：天然气水合物 先存断层 滑脱层 木里地区 物理模拟 

分 类 号：TE122.1[石油与天然气工程—油气勘探]