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中国南方地区主要发育下寒武统、上奥陶统—下志留统、下二叠统、上二叠统4套区域性黑色页岩,分布广泛,其中下志留统龙马溪组在渝东南地区最为发育。由于渝东南地区是我国页岩气勘探的先导试验区,因此分析渝东南地区龙马溪组黑色页岩的分布规律对研究该区页岩气分布特征尤为重要。通过对渝东南地区志留系进行岩石地层对比,对野外露头进行精细分析,建立研究区志留系层序地层格架,将志留系划分为8个三级层序,即ssq1、ssq2、ssq3、ssq4、ssq5、ssq6、ssq7、ssq8,再通过分析其横向展布特征,最终确立研究区北部和西部2个黑色页岩沉积中心。笔者主要从2个方面分析黑色页岩沉积富集的控制因素:①通过分析古地貌特征,分析有利于黑色页岩沉积的沉积环境;②通过分析龙马溪组黑色页岩短期相对海平面变化,得出短期相对海平面变化对有机碳含量和有机质类型的控制规律。该控制因素对于寻找页岩气赋存的有利层段具有重要的指示意义。
There are four sets of regional black shales in the Lower Cambrian, the Upper Ordovician-Lower Silurian, the Lower Permian and the Upper Permian in southern China, and are widely distributed. Among them, the Lower Silurian Longmaxi Formation in Chongqing Southeast most developed. Because southeastern Chongqing is the pilot area for shale gas exploration in China, it is very important to analyze the distribution characteristics of black shale in the Longmaxi Formation in southeastern Chongqing to study the shale gas distribution characteristics in this area. Based on the lithostratigraphic correlation of the Silurian in the southeastern Chongqing area, a detailed analysis of the outcrop in the field was conducted to establish the Silurian sequence stratigraphic framework in the study area. Silurian was divided into 8 third-order sequences, namely ssq1, ssq2 and ssq3 , Ssq4, ssq5, ssq6, ssq7 and ssq8, and then analyzed their lateral distribution characteristics to finally establish two black shale sedimentary centers in the north and west of the study area. The author mainly analyzes the controlling factors of sedimentation enrichment of black shale from two aspects: (1) analyzing the sedimentary environment conducive to the deposition of black shale by analyzing the features of paleogeomorphology; (2) analyzing the short-term relative sea level change of the black shale in Longmaxi Formation, The control law of short-term relative sea-level change on organic carbon content and organic matter type was obtained. This controlling factor is of great importance to the search for favorable intervals of shale gas occurrence.