川东北宣汉—达县地区三叠—志留系海相优质烃源层评价

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

普光5井、毛坝3井是川东北宣汉—达县地区重要的探井,为研究该区的油气成藏条件提供了宝贵的基础资料。对普光5井、毛坝3井等钻遇的海相地层的有机碳含量、氯仿沥青"A"、生烃潜量等进行分析,建立了该区的有机地化综合剖面。结合区域地质资料综合分析认为:宣汉—达县地区在三叠—志留系海相地层中发育了上二叠统龙潭组黑色泥岩及碳质泥岩、中下志留统黑色泥岩2套海相优质烃源岩。飞仙关组鲕粒滩和长兴组生物礁储层中固体沥青含量高、分布范围广、且为热演化成因,表明该储层中曾经存在着古油藏,是优质的再生烃(气)源。此外茅口组泥灰岩、栖霞组深灰色灰岩等有机碳含量也较高,综合评价为中等烃源岩。宣汉—达县地区多套优质烃源岩及再生烃源的存在,为该区的油气勘探提供了雄厚的物质基础。

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.