--> Tectonic Effects on Gas Accumulation, Production and Hydraulic Fracturing of the Lower Paleozoic Marine Shales on the Yangtze Platform in South China

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Tectonic Effects on Gas Accumulation, Production and Hydraulic Fracturing of the Lower Paleozoic Marine Shales on the Yangtze Platform in South China

Abstract

The Lower Paleozoic marine shales on the Yangtze Platform in South China are evaluated to hold the largest shale gas potential in China. The slowly moving shale gas exploration in China is due to complex tectonic setting for these marine shales on the Yangtze Platform. The Yangtze platform is divided into three tectonic regions: tectonically stable area with broad syncline and gentle fold in the Sichuan Basin in the Upper Yangtze Platform, tectonically transitional area with tight syncline and many faults in the Upper Yangtze Platform outside the Sichuan Basin and in the Middle Yangtze Platform, and tectonically active area with high structural deformation due to at least four intense tectonic events on the Lower Yangtze Platform. High shale gas content and high production rate from the overpressured marine shale reservoir in the recently discovered Fuling Shale Gas Field in SE Sichuan Basin reveals good shale gas accumulation and production potential in the tectonically stable area. Exploration and production tests in the tectonically transitional area show the dramatically reduced production rates in slightly under-pressured synclines and little or no production in areas close to faults. The tectonically active area has almost no shale gas shows. The variations of shale gas content, overpressure and production in different tectonic settings indicate the post-depositional tectonics has effects on shale gas generation, accumulation, overpressure preservation and production. Multi-stage intensive tectonic movements could have disrupted shale gas accumulation and caused the loss of early accumulated shale gas. Tectonics also affects the complexity of induced fractures created by hydraulic fracturing. Stress field analysis and hydraulic fracturing simulation imply that siliceous marine shale intervals in the areas less influenced by the collision between India and Eurasia plates are more favorable for hydraulic fracturing. The sweet spots are likely located in broad syncline and anticline in tectonically stable areas with small far-field horizontal stress.