内蒙古西部银根-额济纳旗地区石炭系-二叠系碳酸盐岩沉积模式及其石油地质意义

根据碳酸盐岩建造基底的成因,将研究区石炭纪-二叠纪的碳酸盐台地划分为火山垫高型(HEP)、三角洲垫高型(DEP)、海岸沉没型(CSP)和陆架变浅型(SSP)4类.不同类型的碳酸盐台地具有不同的沉积模式,造就了地层形态及夹层岩性各异的沉积建造,形成不同的生储盖组合.火山垫高型碳酸盐岩建造,基底和建造内的火山岩或火山碎屑岩、建造石灰岩和砂砾岩夹层构成储集层,建造上覆或侧翼的浅海相暗色泥岩和建造石灰岩、暗色泥岩夹层为烃源岩,建造上覆的浅海相泥岩为盖层,形成较复杂的自生自储式岩性圈闭;三角洲垫高型碳酸盐岩建造,储层主要是基底的辫状三角洲(扇三角洲)砂砾岩和建造内的砂砾岩夹层,烃源岩为建造上覆或侧翼的浅海相暗色泥岩和建造内的暗色泥岩夹层,侧翼或上覆的暗色泥岩为盖层,构成较复杂的自生自储式岩性圈闭;海岸沉没型和陆架变浅型的碳酸盐岩建造,储层可能仅有石灰岩,烃源岩和盖层为浅海相暗色泥岩,形成相对简单的自生自储式岩性圈闭.

Depositional models of the Permo-Carboniferous carbonate rocks and their significance in Yingen-Ejinaqi area,Inner Mongolia,China

On the basis of the origin of the pedestal on which the carbonate platforms were built, carbonate platforms in Yingen-Ejinaqi and their surrounding areas can be classified into four types, namely volcano-elevated carbonate platform (VEP), delta-elevatedcarbonate platform (DEP), coast-subsiding carbonate platform (CSP) and shelf-shoaling carbonate platform (SSP). All the carbonateplatforms have different depositional models, which cause big differences in the strata morphology and interlayer lithology. Furthermore, this results form different assemblages of source rock, reservoir and seal. For the volcano-elevated carbonate formation, reservoirsfor oil and gas consiste of volcanic rocks, pyroclastic rocks from the volcanic pedestal and within its formation, as well as interbededlimestone and sandy conglomerates; source rocks are composed of dark shelf mudstone above or at the lateral side of its formation, interbeded limestone and dark mudstone within the formation; while seal rocks are those shallow marine fades mudstone above the formation, all these make up a complicated lithologic trap for oil and gas with self-generation and accumulation. For the delta-elevated carbonate formation, reservoirs are mainly composed of pedestal sandy conglomerate of braided-delta/fan-delta origin and interbeded sandyconglomerates within its formation, source rocks come from those shallow marine fecies dark mudstone above or on the lateral side of theformation and the interbeded dark mudstones, while seal rocks are dark mudstone above or on the lateral side of the formation, thus turnsinto a complicated lithologic trap for oil and gas with self-generation and accumulation. The formations of the coast-subsiding carbonateand the shelf-shoaling carbonate belong to simpler oil-and-gas lithologic trap with self-generation and accumulation, reservoir madeprobably of only limestone, the source rocks and the seal rocks are both composed of dark shelf mudstone.