鄂尔多斯盆地古隆起东侧奥陶系马家沟组中组合成藏地质条件

鄂尔多斯盆地古隆起东侧奥陶系马家沟组中组合发育白云岩储层,其特征明显有别于靖边气田奥陶系顶部风化壳储层。通过储层岩性分析、流体包裹体测试分析,结合钻井、地球化学、试油等相关资料,从烃源、储层、沉积等方面对鄂尔多斯盆地古隆起东侧马家沟组中组合成藏地质条件进行了系统分析。结果表明,古隆起东侧马家沟组中组合马5⁵ 、马5⁷和马5⁹亚期处于次一级海侵沉积背景,水动力条件强,滩相沉积发育,在隆起周边形成自形程度高的粗粉晶-细晶结构的晶粒状白云岩储层,具有晶粒均一、连通性好且发育白云石晶间孔等特征;受加里东末期构造抬升运动影响,古隆起东侧奥陶系顶部剥露为中组合地层,与上覆上古生界煤系烃源岩直接接触,形成了良好的源、储配置关系;受上倾方向岩相变化控制,在空间上中组合滩相白云岩逐渐相变为泥晶灰岩,形成分布不连续、局部富集的岩性圈闭。

Geological conditions for hydrocarbon accumulation in middle reservoir-source rock combination of the Ordovician Majiagou Formation on the east side of the paleo-uplift in Ordos Basin

The dolomite reservoirs in middle reservoir-source rock combination of the Ordovician Majiagou Formation on the east side of paleo-uplift in Ordos Basin are obviously different from the weathering crust reservoirs at the top of the Ordovician in Jinbian gas field.A systematic study had been carried out on the geological conditions for hydrocarbon accumulation in these dolomite reservoirs in respect of source rocks,reservoirs,sedimentation based on results of reservoir lithology characterization and fluid inclusion testing as well as analysis of drilling data,geochemical and testing data.The results show that the middle reservoir-source rock combination of the Formation experienced strong hydrodynamics against a brief regression sedimentary settings.Beach facies were well developed and formed dolomite reservoirs.The dolomite features in highly automorphic coarse powder and fine-crystal texture,uniform grains,excellent connectivity and well-developed intercrystal pores.Affected by tectonic uplifting during the late Caledonian,the top Ordovician at eastern side of the paleo-uplift were denuded and came into contact with coal-measure source rocks,providing favorable source-reservoir combination.Controlled by lithofacies transformation at updip direction,the dolomites of beach facies in the middle reservoir-source rock combination of the Formation change gradually into micrite,forming discontinuous lithological traps.