大地电磁测深在湘东南坳陷页岩气勘探中的应用

为了解湘东南坳陷西南部地区深部构造特征,以及泥盆系—二叠系主要页岩气层系的分布、岩性等特征,以袁家向斜为研究对象,开展了4条大地电磁测深剖面资料的处理和定性、定量分析。通过对大地电磁测深资料的视电阻率拟断面、阻抗相位分析及二维连续介质反演,结合研究区的地质和物性特征,大致查明了剖面上主要断裂的位置、性质及发育特征,圈定了主要地质层系(电性层)的空间展布,并在此基础上探讨了该地区页岩气勘探的有利层系。研究成果表明:袁家向斜内部的断裂以SN向、NE向和NW向断裂为主,在剖面上多表现为铲式或坡坪式的构造样式;二叠系龙潭组发育优质含气性煤层,具有较好的煤层气勘探前景;泥盆系棋梓桥组下段低阻页岩连续且厚度大,可作为有利勘探页岩层系。

The application of magnetotelluric sounding to shale gas exploration in Southeast Hunan Depression

To understand the deep structure characteristics and the distribution and lithology of the main Devonian-Permian shale gas strata on the southwestern side of Southeast Hunan Depression,the authors carried out the processing and qualitative-quantitative analysis of data from four magnetotelluric sounding profiles in Yuanjia syncline. Based on the apparent resistivity section,impedance phase analysis and two-dimensional continuous media inversion of magnetotelluric sounding data and combined with the geological characteristics and physical properties of the study area,the authors found out the location,nature and development characteristics of main fractures as well as the spatial distribution of the main geological formation( electrical layer). On such a basis,the favorable shale gas strata exploration was discussed. The results show that the majority of the faults trend in SN,NE and NW directions in the Yuanjia syncline,showing structures such as " listric style" and " flat and ramp style" in the section. The Upper Permian Longtan Formation has high quality gas-bearing coalbed and good exploration prospect of coalbed methane. The low resistance shale of the lower member of Middle Devonian Qiziqiao Formation is continuous and thick,and hence it can be regarded as a favorable exploration shale formation.