EVALUATION OF THE EXCELLENT TRIASSIC TO SILURIAN MARINE HYDROCARBON SOURCE ROCKS IN XUANHAN-DAXIAN AREA OF NORTHEAST SICHUAN BASIN

Wells Puguang 5 and Maoba 3 were important in Xuanhan-Daxian exploration area in northeastern Sichuan basin,which supplied important evidence for the studies of the oil and gas accumulation conditions of this area.The organic geochemistry synthetic section was established by the data of TOC,chloroform bieuminous "A" and the hydrocarbon generation potential of the drilled marine sequences by wells Puguang 5 and Maoba 3.Synthetic analysis based on the organic geochemistry section,combining with regional geology information,indicated that there were two sets of excellent marine source rocks developed in the Triassic to Silurian strata of the area,i.e.the Upper Permian Longtan Formation black mudstones and carbargillite,and the Mid-Lower Silurian black mudstones.The solid bitumen occurred in Feixianguan oolite reservoir and Changxing biogenetic reef reservoir was characterized by thermal evolution origin,abundant contents and wide distribution,indicating that there were ancient oil pools in Feixianguan and Changxing reservoirs.The ancient oil pools were believed to be excellent secondary hydrocarbon generation source.Furthermore,the muddy limestone of Maokou Formation and the fuscous limestone of Qixia Formation were medium quality of source rocks.Existence of a lot of excellent hydrocarbon source rocks and secondary hydrocarbon generation source could supply abundant matters for the hydrocarbon accumulation in this area.