The Geological Settings Of The Lower Paleozoic Gas-shale Sequences In The Southern Yangtze Block And The Structural Analyses Of The Testing Regions

Abstract: With the use of horizontal drilling and hydraulic fracturing, the shale gas has been the important component of the natural gas in the USA. While, in China, the shale gas exploration is still in the initial stage. The criteria and the methods used for establishing the prospective area for the shale gas exploration in the USA are analyzed and summarized in this paper. The geological setting of the gas shale sequences and the structure features of the exploring region in the southern Yangtze block are analyzed on the existing materials. And then, initial shale gas exploration prospective areas are proposed in the southern Yangtze Block. The following points are acquired in the thesis:1) Though systematically studying the criteria and the methods used for establishing the prospective area for the shale gas exploration in the USA,the paper summarized them as the the following two points, one is the gas shale own properties, the other is the criteria relating to the shale gas recovery process, and nine criteria are included in it. There are obviously different geological settings of the gas shale sequences between two countries, such as the target formations, the structure features and the surface.2) According to the regional geological data and the results of previous studies, Hetang formation, Wufeng-Longmaxi formation and Longtan formation are resured as the target formations of the Yangtze Block shale gas exploration. The early Paleozoic geological settings of the Yangtze Block are analyzed in the paper based on the available data, well data and seismic profile data are analyzed and interpreted, and then, distribution maps of the two Lower Paleozoic black shale formations in the Yangtze block, the contour maps of the TOC, Ro, thickness and depth of the gas shale formations are made. After the preliminary analyses about the geological settings and structural features, the more favorable areas of the southern Yangtze block for shale gas exploration are tentatively proposed as follows:the northeastern Sichuan, the southern Sichuan, the northern Guizhou, the southern Anhui, the southern Jiangsu, and the north Zhejiang.3) Through making the contour map of TOC, the thickness, the Ro, and interpretating on seismic profiles of the Hetang formation, Wufeng-Gaojiabian formation and Longtan formation in Xuancheng-Wuxi region, a preliminary analyses shows that the prospective areas are local areas of the Xuancheng-Ningguo-Lin’an and Jiangyin-Wuxi area.4) In the Weiyuan area, well data and seismic lines were analyzed and several lines were interpreted in detail. Based on these studies, a3D structural model was established for the area as well as the Jiulaodong Formation, which demonstrates the distribution of the formation. Besides, the structure and evolution of the Weiyuan anticline were studied, and the results indicate that the anticline is gentle in the NW limb and steep in the SE limb with few faults. Similarly, the Jiulaodong Formation is gentle except for in the southeast part of the study area. Moreover, detailed structural interpretations reveal that the formation experienced three stages of deformation: Caledonian, Indosinian and Himalayan, and the last deformation was the most intense. Combined these analyses, it is proposed that the Jilaodong Formation in the NW limb of the Weiyuan anticline is favorable for shale gas exploration.