冻土区天然气水合物各向异性储层的AMT响应特征  

Characteristics of AMT response of anisotropic natural gas hydrate reservoirs in permafrost regions

作　　者：黄一凡 岳祖润[1] 胡祥云 HUANG YiFan;YUE ZuRun;HU XiangYun(School of Civil Engineering, Shijiazhuang Tiedao University, Shijiazhuang 050043, China;Hubei Subsurface Multi scale Imaging Key Laboratory, Institute of Geophysics and Geomatics, China University of Geosciences , Wuhan 430074, China)

机构地区：[1]石家庄铁道大学土木工程学院,石家庄050043 [2]中国地质大学地球物理与空间信息学院,地球内部多尺度成像湖北省重点实验室,武汉430074

出　　处：《地球物理学报》2018年第6期2629-2640,共12页Chinese Journal of Geophysics

基　　金：河北省自然科学基金(D2018210168); 国家自然科学基金(41630317,41474055); 湖北省自然科学基金创新群体项目(2015CFA019)联合资助

摘　　要：陆域天然气水合物通常发育于冻土层下方破碎带和岩层裂隙处,其储层会表现明显电性各向异性特征.音频大地电磁法(AMT)能有效探测陆域水合物储藏范围,且不易受高阻冻土层的压制和干扰,可用于陆域天然气水合物探测研究.本文采用AMT对角各向异性二维正演方法,对多种陆域天然气水合物各向异性储层模型及相关参数进行了模拟试算,分析其视电阻率和相位响应特征.结果表明AMT能清晰显示各向异性储层空间位置和分布情况,并对储层的水合物饱和度变化以及储层数量等特征都有所反映.天然气水合物电性各向异性模拟研究为这一新型潜力能源的勘查工作提供了新的思路.Natural gas hydrates（NGH）are ice-like crystalline solids formed with water and gas（CH4 mostly）at low temperature and high pressure,which are usually present in ocean and seabed sediments or permafrost regions.NGH are a potential and clean energy resource with great amounts especially in ocean regions.Although the reserves of NGH in permafrost regions are smaller than ocean regions,their cover and trap of upper frozen soil layers,and shallow and certain storage depth,make NGH exploration in these regions easy with less threat of gas leakage.In permafrost regions,NGH usually developed in rock fractures,cracks and lamination interlayers.As the hydrate is an electricity insulator,the considerable resistivity differences between the hydrate and strata make the NGH reservoirs show obvious electrical anisotropy.This paper presents a typical simplified reservoir model,in which the resistive NGH layers are interbeded with conductive strata.Hence the electrical anisotropy exists and can be expressed by horizontal resistivity and vertical resistivity jointly.The audio-frequency magnetotelluric method（AMT）can be used to infer subsurface conductivity structure by measuring 2 horizontal components of the natural electric field and 2 horizontal and 1 vertical components of the natural magnetic field at earth′s surface.With shallow penetration depth including hydrates layers′range,short measuring time and small cost,AMT is a useful tool for investigation of NGH reservoirs.In this paper,a 2 DAMT forward modeling method considering triaxial anisotropy is applied to examine the response characteristics of anisotropic NGH reservoirs in permafrost regions.Two synthetic models are presented,one is an 1 Dlayer model and the other is a 2 Dblock model,and both overly a relatively high resistivity layer representing a resistive frozen layer.In the 1 D model,responses in xy mode differ from yx mode,which prove the existence of anisotropy.In the 2 D model,while the width and depth become larger or smaller,the apparent resist

关 键 词：电性各向异性 天然气水合物 音频大地电磁 冻土区 

分 类 号：P319[天文地球—固体地球物理学] P631[天文地球—地球物理学]