鄂尔多斯盆地中东部太原组灰岩成藏地质条件分析

Analysis of limestone reservoir forming geological conditions of Taiyuan formation in central and eastern Ordos basin

鄂尔多斯地台古生代以陆表海和海陆过渡相沉积为主,寒武系、奥陶系及下二叠统太原组普遍发育碳酸盐岩,海相碳酸盐岩往往具有发育时期老、埋藏深、后期成岩作用改造强等特点,使其成藏地质条件更加复杂。以上古生界二叠系太原组为例,综合运用岩心观察、物性分析、地震属性等资料,对盆地中东部二叠系太原组灰岩成藏地质条件进行研究。结果表明,太原组灰岩以特低孔渗为特征,主要岩性为泥晶灰岩、(含)生物碎屑泥晶灰岩、(泥晶)生物碎屑灰岩;构造活动对储层裂隙的发育起关键作用,明显改善了储层渗透性,灰岩内发育的溶蚀孔洞、裂缝,为天然气提供了良好的储集空间和运移通道,有利于天然气聚集成藏;依据灰岩顶底接触岩性的不同,将源内灰岩天然气生储盖组合细分为三种类型,其中,Ⅰ型底煤泥生-中灰储-顶泥封型组合含气性最好,Ⅱ型底煤泥生-中砂、灰储-顶泥封型组合含气性次之。

The Paleozoic Ordos platform is dominated by continental sea and sea-land excessive deposits,and carbonate rocks are widely developed in Cambrian,Ordovician and lower Permian Taiyuan formation.Marine carbonate rocks are often characterized by older development period,deeper burial and strong late diagenetic transformation,so there are still great challenges to the study of high-quality carbonate reservoir space types in China.By taking Taiyuan formation as an example,based on the data of core observation,physical property analysis and seismic attributes,the reservoir forming geological conditions of Permian Taiyuan Formation in central and eastern basin are studied.The results show that limestone of Taiyuan formation is characterized by ultra-low porosity and permeability,which is mainly composed of micritic limestone,bioclastic limestone and bioclastic limestone,and the tectonic activity plays a key role in the development of reservoir fissures and significantly improves reservoir permeability.The dissolution pores and fractures developed in limestone provide good reservoir space and migration channels for natural gas,which are beneficial to natural gas accumulation.According to the different lithology of limestone top bottom contact,the source reservoir cap rock combination of limestone natural gas in the source is divided into three types.Among them,the type Ⅰ bottom slime generation-medium ash storage-top mud sealing combination has the best gas content,and followed by the type Ⅱ bottom slime generation-medium sand,ash storage-top mud sealing combination.