银额盆地居延海坳陷石炭系—二叠系泥岩层电性特征

Electrical characteristics of Carboniferous-Permian mudstone beds in Juyanhai Depression,Yingen-Ejin Basin

银额盆地居延海坳陷钻井资料显示石炭系—二叠系岩性复杂,地层中火山岩体非常发育,地震成像难以识别石炭系—二叠系泥岩层和岩体顶底界面及内部结构。如何有效识别石炭系—二叠系泥岩层是该地区上古生界油气勘探取得突破的关键问题之一,为了解其电性特征,将大地电磁法数值理论模拟结果与实际观测资料相结合,重点对居延海坳陷石炭系—二叠系泥岩层和岩浆岩电性特征进行了分析研究,结果表明,坳陷的东、西部中浅层电性结构不同,石炭系—二叠系泥岩层和火山岩体发育规模差异明显。大地电磁测深能有效识别埋深4 km之内的低阻泥岩层分布;坳陷东部泥岩层相对发育,石炭系—二叠系泥岩层表现为低阻层电性特征,侵入岩体局部发育;坳陷西部发育厚层高阻火山岩体,石炭系—二叠系泥岩层表现为次高阻薄层状。这些认识为盆地地层识别和石炭系—二叠系油气勘探提供了电性信息。

Drilling data from the Juyanhai Depression in Yingen-Ejin Basin reveal that the lithology of Carboniferous Permian strata is complex,and the volcanic rock mass in the stratum is well developed.However,the top and bottom interfaces and the internal structure of the rock mass are difficult to identify through seismic imaging.Therefore,effectively identifying the Carboniferous-Permian mudstone layers is essential for oil and gas exploration in the Upper Paleozoic strata.To understand its electrical characteristics,through the combination of numerical simulations of magnetotelluric methods and practical observations,the electrical characteristics of Carboniferous Permian mudstone and magmatic rocks in Juyanhai Depression are analyzed and studied.The results show that the electrical structures of the middle and shallow layers in the east and west of the depression vary,and the development scales of the Carboniferous Permian mudstone and volcanic rocks are evidently different.Magnetotelluric sounding can effectively identify the distribution of low resistivity mudstone within a depth of 4 km;the mudstone layer in the east of the depression is relatively developed.The Carboniferous Permian mudstone layer is characterized by low resistivity,and the intrusive rock mass is locally developed;thick,high-resistivity volcanic rocks are developed in the west of the depression,and the Carboniferous Permian argillaceous rocks are present in sub-high-resistivity thin layers.These insights provide electrical information for the stratigraphic identification of the basin and the exploration of Carboniferous Permian oil and gas resources.