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The Puguang Gas Field – New Giant Discovery in the Mature Sichuan Basin, Southwest China

Yongsheng Ma, Xusheng Guo, Tonglou Guo, Rui Huang, Xunyu Cai, and Guoxiong Li
Southern Exploration and Development Co., Sinopec, Kunming, China

The giant Puguang Gas Field (GIIP < 4 TCFG) was discovered in 2003 in the Eastern Sichuan Fold-Thrust Belt in the mature Sichuan Basin, SW China. The field is a structural-stratigraphic trap closed by lateral depositional change and dip closure. The trap evolved from a paleo-oil reservoir originating in the Triassic-Jurassic. Entrapment of thermal gas occurred during deep burial in the Jurassic-Cretaceous. Tertiary-Quaternary compression transformed the paleo-trap into the present gas reservoir. The gas is derived from Cambrian and Permian source rocks, which reached peak gas generation during Late Jurassic-Cretaceous.

Gas is contained in the Lower Triassic Feixianguan and the Upper Permian Changxing formations. The reservoirs consist predominantly of oolitic dolomites deposited in shelf/platform-margin shoal and reef environments. The reservoir rocks have average porosity of 8% and permeability up to 3300 mD. Porosity includes intraparticle, intra- and intercrystalline, moldic and vuggy porosity and fractures, resulting from late burial dissolution.

Discovery of the Puguang Field exemplifies successful application of new play concept and new technology in a mature basin. The discovery resulted from shifting structure-focused exploration strategy to targeting stratigraphic trap in reef/shoal dolomites, and benefited from advanced high-resolution seismic techniques. The discovery will not only broaden the exploration scope in the Sichuan Basin, but also provide an excellent analogue for exploration in other fold and thrust belts worldwide.