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The AAPG/Datapages Combined Publications Database
AAPG Bulletin
Abstract
DOI: 10.1306/11182018244
Prediction of the gas-generating characteristics of the Qiongzhusi and Longmaxi Formations, Yangtze Platform, southern China, using analogues
Brian Horsfield1, Caineng Zou2, Jian Li3, Shengyu Yang4, Nicolaj Mahlstedt5, David Misch6, Doris Gross7, Ma Wei8, Yifeng Wang9, Jingqiang Tan10
1GEOS4 GmbH, Michendorf, Germany; German Research Centre for Geosciences (GFZ), Potsdam, Germany; [email protected]
2Research Institute of Petroleum Exploration and Development (RIPED), PetroChina, Beijing, China; [email protected]
3RIPED, PetroChina, Beijing, China; [email protected]
4GFZ, Potsdam, Germany; present address: School of Geosciences, China University of Petroleum (East China), Qingdao, China; [email protected]
5GEOS4 GmbH, Michendorf, Germany; GFZ, Potsdam, Germany; [email protected]
6Department of Applied Geosciences and Geophysics, Montanuniversitaet Leoben, Leoben, Austria; [email protected]
7Department of Applied Geosciences and Geophysics, Montanuniversitaet Leoben, Leoben, Austria; [email protected]
8RIPED, PetroChina, Beijing, China; [email protected]
9RIPED, PetroChina, Beijing, China; [email protected]
10Central South University, Changsha, China; [email protected]
ABSTRACT
China has been said to have the largest putative shale gas resources in the world. The highest potential
occurs in the Sichuan Basin, with the overmature Qiongzhusi (Cambrian) and Longmaxi (Silurian) Formations as prime exploration targets. Here, the likelihood of late gas formation is examined using less mature equivalents from the Georgina Basin (Australia) and the Baltic Basin (Lithuania). We consider the respective
functions
of kerogen and polar bitumen in gas generation with reference to the Eagle Ford, Yanchang, Niobrara, and Vaca Muerta Formations. Both of the lower Paleozoic shales are bitumen poor in a geochemical sense, this being in stark contrast to the Mesozoic shales, which are bitumen rich. Kerogen is, therefore, the major gas precursor in the Cambrian and Silurian of the Sichuan Basin. Graptolites and solid bitumen are petrographically dominant. The solid bitumen exhibits flow structures and is deduced to be highly polar because it is insoluble in dichloromethane. Secondary cracking kinetics determined for the Arthur Creek are closely similar to source rocks containing predominantly paraffinic oil. Late gas generation from very stable refractory kerogen structures via alpha-cleavage reactions at maturities above 2% equivalent vitrinite reflectance (Ro) was verified, and importantly, the upper ceiling for late gas generation in Paleozoic shales of the Sichuan Basin is set at 3% Ro. As far as the Qiongzhusi shale is concerned, raising the prospective acreage to a 3% Ro limit brings an additional contribution of 40 mg HC/g total organic carbon of late gas charge. The same is true for the extensive fairway of the Longmaxi shale along the western flank of the basin, close to the subcropping erosional edge.
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