Evidence for Kaijiang-Liangping Trough and Its Role for Giant Gas Accumulations in the Sichuan Basin

Yigang Wang, Chunchun Xu, Xianping Huang, Guang Yang, Haitao Hong, Maolong Xia, and Yingchu Wen
Exploration and Development Research Institute of, Chengdu, China

The Kaijiang-Liangping Trough, formed during the late Permian Dongwu orogeny, has exerted significant control on the type, scale and distribution of reefs in the Upper Permian and oolitic shoals in the Lower Triassic strata in the Sichuan Basin. The dominant lithologies in the trough facies are dark silicilith, siliceous limestone and argillite in the Upper Permian Dalong Formation and pelagic sediments and carbonate gravity flow sediments in the Lower Triassic strata. Porous reservoirs are generally lacking in the trough facies, whereas the few discovered pools usually consist of small fractured reservoirs. Gas fields with larger reef reservoirs are developed along the margin of carbonate ramp and platform around the trough, with the single field area over 10 km² and gas reserves > 3 bcm. In contrast, gas fields with small patch reef reservoirs occur on the wide carbonate ramp and platform, with the size of individual reservoir being smaller than 5 km² and gas reserves < 1 bcm. Progradation of the platform changed the trough into a carbonate platform during later stage of the Early Triassic. Oolitic dolomites developed on the platform subsequently formed important reservoirs in this area. In particular, high quality gas reservoirs are formed within the 200-300 m of the Lower Triassic massive dolomites along the platform margin of the Kaijiang-Liangping Trough. The marginal facies, extending over an area of 10,000 km², provides a rich habitat for giant gas accumulations, as indicated by the discovery of at least eight reef gas fields in the Upper Permian and 15 oolitic gas fields in the Lower Triassic strata.

AAPG Search and Discovery Article #90078©2008 AAPG Annual Convention, San Antonio, Texas