CHARACTERISTICS OF THE SINIAN RESERVOIR BITUMEN IN WEIYUAN-ZIYANG AREAS OF THE SICHUAN BASIN AND ITS SIGNIFICANCE

There is large amount of bitumen in the Sinian Dengying Formation in Weiyuan-Ziyang areas,the Sichuan Basin.The occurrence of the bitumen is dominated by dissolution pore-filling and fracture pore-filling,with the intergranular-filling in the second and the micrograined disseminated-type in the least.Based on the biomarker characteristics,the bitumen can be divided into two types:one to Well Wei 117 as the representative,and the other to Wells Wei 118,Zi 1 and Zi 6 as the representative.There is a positive correlation between the reservoir property and the content and occurrence of bitumen.The reflectivity values of the bitumen are in two sections with similar evolution levels in different strata.With analysis of geological conditions,the bitumen in these areas was thought as epigenetic reservoir bitumen and sourced from oil-cracking.The content and distribution of the reservoir bitumen showed the gas source kitchen of oil-cracking gas.The occurrence,reflectivity value and biomarker characteristics showed that there were two stages of bitumen,and the second was majority while the first was minority.Based on these and the structural evolution history,the gas accumulation process was recovered.