黄桥地区深源CO_2对二叠系—三叠系油气成藏的影响

Deep-sourced CO_2 Influence on Permian and Triassic Oil and Gas Accumulation in Huangqiao Region

黄桥地区CO2气田是我国陆上规模最大的CO2气田之一,主要是由古近纪以后岩浆火山活动地幔物质上涌形成的。该气田平面上临近深大断裂的交会部位,纵向上从下古生界到新近系盐城组都有分布。CO2是在相对较高温度下快速成藏的,且成藏时间晚于油气,二叠系—三叠系油气藏则以自生自储为主要特征。富含CO2的层位与主要的油气显示层位并不一致,CO2在向上运移的过程中很难将先进入储层的油气驱替出来,特别是在二叠系龙潭组致密的砂岩储层中。油气藏保存条件良好,但高温CO2带来的热量使原油大多热分解转化为轻质油,其品质好黏度低,有利于在物性相对较好的构造高点富集成藏。

Huangqiao gas field is one of the largest CO2-enriched gas fields in the China land.It was mainly formed by mantle material upwelling after the magma and volcanic activity in Neocene.The CO2-enriched gas field is located horizontally in the adjacent intersection of the great deep fault and distributed from early Paleozoic to Neocene Yancheng Formation.CO2 was rapidly accumulated at relatively high temperature conditions,and the time of CO2 accumulation is later than that of oil and gas accumulation.The Permian and Triassic oil and gas accumulation is characterized as self generation and self storage.The CO2 enriched layers are inconsistent with the oil/gas showing ones.During the upward migration process of CO2,it is difficult for CO2 to expulse out of the oil and gas from the early reservoir,specially from the tight sandstone reservoir in Permian Longtan Formation.The preservation conditions of oil and gas is good,but the high abundance heat energy which is associated with deep CO2 migration at high temperature makes the crude oil be cracked thermally into the condensates with high quality and low viscosity,thus,it is beneficial for oil and gas accumulation at top of structural high part with good quality reservoirs.