川东北飞仙关组储层沥青与古油藏研究

在四川盆地东北地区(川东北地区)找到了迄今为止该盆地最大的天然气田――飞仙关组鲕滩气田。在该气田的鲕滩储层中不同程度地含有固体沥青,沥青含量在0.09%～2.50%之间;储集孔隙发育的残余鲕粒白云岩的沥青含量最高,沥青含量与天然气产量、气藏规模及储层物性之间呈正相关关系。应用全岩热模拟和环境扫描电镜实验新技术进行的沥青的产气模拟实验表明,沥青仍有产气潜力,并随成熟度增大,产气潜力降低;沥青模拟产物的碳同位素较轻,反映出了腐泥型母质的特点;沥青的甾萜类生物标志化合物分布正常:这些特征表明了储层沥青是古油藏原油裂解成气的中间产物。此外,天然气C1-C3组分进一步证实了鲕滩天然气主要为原油裂解气。在古构造背景下,根据优质储层展布、储层沥青含量的分布趋势,预测了古油藏分布范围。

THE STUDY ON BITUMEN AND FOREGONE POOL OF FEIXIANGUAN OOLITIC IN NORTHEAST SICHUAN BASIN

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.