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Cambrian Hydrocarbon Migration System and Reservoir-Controlling Pattern of Anyue Gas Field, Sichuan Basin


Great progress has been made through years of exploration in the dolomite reservoir of Lower Cambrian Longwangmiao Formation in Sichuan Basin in 2013, with 779.9 km2 proven gas-bearing area and 4403.8×108m3 proven geological reserves in Moxi Block. But there are only 527.57×108m3 predicted geological reserves in Gaoshiti Block which is much smaller than nearby Moxi Block while the reason is not clear. So it is significant to study the main controlling factors for the difference to guide further exploration of Longwangmiao Formation. With a method of combining geologic analysis and experiment data analysis, this study is focused on the types of deep Cambrian migration system, and their controlling on the reservoir. The Result indicates that the Cambrian migration pathway is one of main controlling factors of geological reserve difference between Moxi Block and Gaoshiti Block. The Cambrian migration system includes normal fault, permeable sandstone and dolomite. There are 37 faults in Moxi Block but only 14 faults in Gaoshiti Block. With the increase of fault number, scale and yield of hydrocarbon reservoir are gradually increased. The samples from sandstone of Canglangpu Formation are characterized by QGF spectral peak around 375nm and QGF Index value generally greater than 2. The QGF-E spectra for samples distribute in range of 30~500pc and spectral peaks around 370nm So the sandstone of Canglangpu Formation was the pathway for lateral migration of oil and gas. There are large amount of bitumen in the dolomite reservoir space of Longwangmiao Formation. There is a positive correlation between the reservoir property and the content bitumen. And the reservoir properties in Moxi Block are greater than that in Gaoshiti Block. The permeable dolomite is not only the pathway for lateral migration of oil and gas,but also the important hydrocarbon reservoir space. There is a positive correlation between the reservoir properties with the gas saturation. Under controlling of migration system, oil and gas generated from Cambrian source rock migrated upward along normal faults,which controls vertical distribution scope and scale of hydrocarbons, migrated laterally along the sandstone of Canglangpu Formation and then initially accumulated in the dolomite reservoir with high porosity and permeability. The difference of migration system is one of important reasons for great difference of geological reserves between Moxi Block and Gaoshi Block.