Geology of giant gas fields in China

Hydrocarbon generation from coal, extracted coal and bitumen rich coal in confined pyrolysis experiments

“…Coal measures are the most important source rocks for hydrocarbon gases in Chinese gas reservoirs, especially the giant gas fields (e.g., Dai et al, 1997Dai et al, , 2003Dai et al, , 2005Dai et al, , 2008. Several studies of the Kela 2 gas field, the largest in the Tarim Basin, China, demonstrated that hydrocarbon gases in this field were generated from Jurassic coal source rocks at the postmature stage (R o % > 1.3, Zhao et al, 2002;Liang et al, 2003;Zhao et al, 2005).…”

“…Dai et al (2008) indicate that the hydrocarbon gases in most giant gas fields discovered in China are dominantly derived from coal source rocks. However, the generation of hydrocarbon gases from humic coals is complex and poorly understood.…”

Origins of natural gases from marine strata in Northeastern Sichuan Basin (China) from carbon molecular moieties and isotopic data

“…We first carried out kinetic experiments for low-maturity kerogen by heating to the temperature range between liquid hydrocarbon generation and cracking (390-400°C for this sample). Next we Table 1 List of seven large (>30 billion m 3 ) gas fields (Dai et al, 2008;Ma et al, 2008 physically separated the residual kerogen and liquid hydrocarbon (bitumen) by chloroform extraction. Both the extracts and residual kerogen were used for kinetic experiments of gas generation under the same experimental conditions.…”

“…One reason is that they have different structures of gas traps and migration paths. The migration paths for gasses from Carboniferous pools are mainly through pores of weathered carbonate whereas those for Triassic pools are fault cracks (Dai et al, 2008;Ma et al, 2008), which may be another reason controlling the migration fraction. TSR will also promote the gas dryness increasing, which may be another important control for Triassic gases.…”

“…Gases have been discovered in marine strata from Silurian to Jurassic, but most gas reservoirs are found in the Carboniferous Huanglong formation, Permian Changxing formation, and Lower Triassic Feixianguan formation. Currently, seven large gas fields with gas reserves larger than 30 billion cubic meters have been discovered in marine strata of Northeastern Sichuan (Table 1), the Wolonghe, Wubaiti, Shapingchang, Luojiazhai, Dukouhe, Tieshanpo and Puguang gas fields (Dai et al, 2008). Wang et al (2004) recognized that the natural gases of marine strata in eastern Sichuan originated from secondary cracking of previously formed oil, though some studies argue different viewpoints Ma et al, 2008).…”