Emerging Shale Gas and Shale Oil Plays in China

The investigation of regional source rocks , paleogeography and tectonic evolutions in China reveal China has vast potential shale plays spanning from Pre-Cambrian to Quaternary in three depositional settings of marine, lacustrine and transition. During Pre-Cambrian Sinian period, Doushantuo marine shale was mainly distributed in South China in shelf and slope setting. The Cambrian Qiongzhusi, Ordovician Wufeng and Silurian Longmaxi marine shales or their equivalent shales were deposited mainly in the ancient passive margin setting in South China Yangtze platform. These shales are thick (40-500m), widely distributed and have high TOC (1-8%), Ro (1.5-6%) and brittle mineral composition. Meanwhile, thick Cambrian and Ordovician shales with TOC of 0.5-5% and Ro of 0.4-3% were mainly deposited in restricted platform and basin setting in Tarim basin. The kerogens in these marine shales are mainly type I and II. During Carboniferous-Permian marine, the shales associated with coal were mainly deposited in transitional setting in north China, Tarim basin in NW China and Yangtze platform in South China, e.g., the typical transitional shales with type III kerogen in North China have high TOC of 2-20% and variable Ro of 0.6-2.5%. Since late Triassic, the organic rich shales are dominated by lacustrine shales, e.g., the Triassic Yangchang shale in Ordos basin, Triassic to Jurassic shales in Tarim basin, Jurrassic Badaowan and Xishanyao shales in Junggar, Jurrassic Ziliujing shales in Sichuan basin, Cretaceous Qingshankou shales in Songliao Basin, Cenozoic shales in East China (e.g. Shahejie shale in Bohai Bay basin), Quaternary shale in Qaidam basin, etc. They are mainly featured by type I and II kerogen , low Ro (<1.2%) and high TOC (up to 30%). The regionally extensive shales in the three depositional settings were generally formed during stable basin subsidence period or high sea or lake level period. The marine shales have decent brittle mineral content and almost no smectite. The lacustrine shales usually have sandstone interbeds and have more clay mineral content than marine shales. The Paleozoic marine shales are emerging thermogenic shale gas plays. The Meso-Cenozoic lacustrine shales with high TOC and medium or low Ro are emerging shale gas or shale oil plays respectively, while the shallow organic rich shales are usually biogenic shale gas plays. These emerging shale plays have been gradually demonstrated by historical and recent drilling.
 

AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California