THE STUDY ON BITUMEN AND FOREGONE POOL OF FEIXIANGUAN OOLITIC IN NORTHEAST SICHUAN BASIN
川东北飞仙关组储层沥青与古油藏研究

The biggest Feixianguan oolitic gas field has been found in northeast area of Sichuan basin up to date. The reservoir in northeastern Sichuan basin generally contains solid bitumen and its content is 0.09% to 2.50%. Of all the types of reservoir rocks, the content of bitumen is the most abundant in the oolitic dolomite. The abundance of bitumen is related to the gas yield, gas pool scale and reservoir continuity. Novel methods such as whole rock pyrolysis and Environmental Scanning Electron Microscope (ESEM2020) are utilized to simulate and observe gas generation from the reservoir bitumen. The results show that the potential of gas generation from bitumen is related to bitumen maturity, and that newly generated gas has light carbon isotope composition. The distibution of sterance and terpane biological markers in reservoir bitumen is normal, and there is no 25-norhopane of degration and water washing. The bitumen is interpreted to be residue of liquid hydrocarbon cracking. The ratio of ln(C_1/C_2) and ln(C_2/C_3) in Feixianguan gases keeps the character of crude oil cracking gas. Based on the palaeohigh, the distribution of foregone pool have been predicted according to the reservoir distribution and bitumen content. The finding can be applied to guidance of further exploration of natural gases.