Study On Petroleum Accumulation Characteristics In Piedmont Paleo-Slope Of Kongquehe Area In Tarim Basin

In combination with special geological features of Kongquehe slope, the idea of reservoir-forming system evaluation which is based on reformed-basin is introduced. Starting from an analysis of denudation thickness and remaining formation thickness, the palaeostructural features of Kongquehe slope and its neighboring areas are reconstructed. Taking the known reservoir dissection as cut-in point and considering the study of hydrocarbon generation and reservior formation as main line, this paper makes a further study on source rock characteristics, thermal evolution, O&G geochemical behavior and episodes of petroleum accumulation;then restores the petroleum accumulation process in the study area;establishes petroleum accumulation patterns;sums up the major control factors and makes clear the future exploration tendency.There are three sets of source rocks in Kongquehe Slope: Cambrian-Lower Ordovician, Middle-Upper Ordovician and Jurassic. Among them Cambrian-Lower Ordovician is the most important source rock and it has high standard of organic matter abundance and belongs to good kerogen type. According to researches of burial history and thermal evolution history of hydrocarbon source rock, the source rock in Cambrian-Lower Ordovician experienced complicated thermal evolution and is generally characterized by high maturity and early-stage hydrocarbon-generation, which can be specified: a large area of Kongquehe entered into hydrocarbon-generation in early-Caledonian;whole area of Kongquehe slope into hydrocarbon-generation in Later-Caledonian, and into high-over maturity period in Hercynian.Through comparative analysis of natural gas, crude oil carbon isotope, crude oil biomarker and maturity, the newly found hydrocarbon reservior mainly comes from Cambrian-Lower Ordovician. The occurrence shapes of hydrocarbon in Kongquehe slope and its adjacent area are wet gas and condensed oil, which is not in accordance with source rock in high-over maturity period nowadays. According to formation temperature, isotopic constitution and lighter hydrocarbon analysis of natural gas, it is believed that the crude oil and natural gas there derives from oil-cracked gases. Hydrocarbon generated in early stage may be preserved in stratum in the form of oil-cracked gases and dispersed organic matter, and turns into effective hydrocarbon kitchen in late petroleum accumulation.In combination with the analysis of typical hydrocarbon reservoir and structure evolution, the petroleum accumulation system of Kongquehe slope can be divided into three periods: from Caledonian to early-Hercynian, it is a period of formation and destruction;from late-Hercynian to Indosinian, it is a period of reconstruction and destruction;from Yanshanian to Xishaninan, it is an adjustment reservoir-forming period.Based on hydrocarbon generation and hydrocarbon charging period, hydrocarbon accumulation can be divided into three patterns: prototype palaeo-hydrocarbon in early period, mixed type in late period, and mixed source type. In accordance with hydrocarbon charging period and charging patterns, there are two types: prototype palaeo-hydrocarbon in early period, which is found to be the basic pattern, and palaeo-hydrocarbon type with secondary hydrocarbon reservior, which is believed to be the key object of further exploration and plays an important guiding role in reformed-basin exploration, hi the end, this paper points out anticline structural zones of Longkou and Weima-Kaiping are advantageous exploration zones.