大地电磁法在吉首地区页岩气勘探中的应用研究

Application of MT to Study Shale Gas Exploration in Jishou Area

吉首地区地形起伏大,灰岩出露,将大地电磁法应用于吉首地区页岩气勘探是正确的选择,丰富该区深部地质认识,主要目的是查明构造特征,以及各个层系的展布、埋深、厚度信息。根据该区岩石的电性特征,通过资料的精细处理与解释,获得视电阻率解释推断剖面图,结果表明,芷耳向斜地层整体较平缓,受区域构造控制北西翼较陡;目标层位下寒武统牛蹄塘组碳质页岩为低阻层,顶底埋深1000~2000 m,厚度100~350 m,遍布整个工区并向外延伸,2015H-D5揭露牛蹄塘组顶面埋深1390 m,底面埋深1650 m,与视电阻率解释推断剖面图顶底埋深误差小于7.8%,勘探精度较高。综上所述,大地电磁勘探能快速圈定页岩层沉积范围,埋藏深度,为页岩气资源潜力评价提供地质依据。

It is correct choice to apply the magnetotelluric method to the exploration of shale gas in Jishou area because of its large topographic fluctuation and limestone outcropping,and to enrich the deep geological knowledge of the area.The main purpose is to find out the structural characteristics and the distribution,burial depth and thickness information of each stratum.Through the fine processing and interpretation of the data,the apparent resistivity interpretation and inference profiles are obtained.According to the electrical characteristics of the rocks in the area,the results show that the whole Zhier syncline stratum is gentle,and the northwest wing is steep controlled by regional structure.The target layer∈n is characterized by low resistance relative to the surrounding rock layer with a depth of 1000~2000 m at the top and bottom and a thickness of 100~350 m,which extends all over the work area and extends outwards.2015H-D5 borehole ed that the∈ntop and bottom buried depth is 1390~1650 m.The error between the buried depth of∈n and apparent resistivity interpretation is less than 7.8%,and the exploration accuracy is high.In summary,magnetotelluric exploration can quickly delineate the depositional range and burial depth of shale beds,and provide geological basis for potential evaluation of shale gas resources.