The Puguang gas field: New giant discovery in the mature Sichuan Basin, southwest China

The giant Puguang gas field, with a proven original in-place gas volume of 350 x 10(9) m(3) (12.3 6 TCFG), was discovered in 2003 in the eastern Sichuan fold-thrust belt of the mature Sichuan Basin, southwest China. The field is a combination structural-stratigraphic trap closed by lateral depositional change and fault closure. The trap evolved from a paleo-oil reservoir originating in the Triassic-Jurassic. The entrapment of thermal gas, which was derived from Lower-middle Silurian and Permian source rocks, occurred during deep burial in the Jurassic-Cretaceous. Tertiary-Quaternary compression transformed the paleotrap into the present gas reservoir. Gas is contained in the Lower Triassic Feixianguan and the Upper Permian Changxing reservoirs, which consist predominantly of dolomitized oolites deposited in shelf and platform-margin shoal and backreef environments. Reservoir quality is characterized by porosity of 1-29% and permeability of 0.01-9664 md, with buried depth greater than 5000 m (16,400 ft). The discovery of the Puguang field exemplifies the successful application of a new play concept and new technology in a mature basin. The discovery resulted from a shift in exploration strategy from structures to stratigraphic traps in reef and 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 analog for exploration in other fold-thrust belts worldwide.