鄂南奥陶系平凉组微生物碳酸盐岩特征与储集意义

The Characteristics and Storage Significance of Microbial Carbonate Rocks in the Ordovician Pingliang Formation of Southern Ordos Basin

微生物碳酸盐岩储层是近年来石油地质领域研究的热点之一。微生物结构在储层储集空间的形成过程中扮演重要角色。鄂尔多斯盆地发育大量微生物碳酸盐岩,但关于鄂尔多斯盆地南部奥陶纪微生物碳酸盐岩鲜有报道。本文对鄂南陈炉任家湾剖面进行详细野外观测和薄片观察,描述了微生物岩的岩石学特征和储集空间特征,综合分析了微生物岩的沉积环境,探讨了微生物碳酸盐岩孔隙演化与成岩过程的关系。研究认为:鄂尔多斯盆地南部奥陶系平凉组发育含生屑泥晶灰岩、砾屑灰岩、砂屑灰岩和藻灰岩四种岩石类型,微生物碳酸盐岩主要发育在藻灰岩中,以凝块石最多,叠层石次之,树形石最少。陈炉任家湾剖面平凉组沉积时期属于台地边缘相–台地前缘斜坡相环境,而凝块石和叠层石主要发育在台地边缘相之中相对低能的环境,且鄂南平凉组中的礁、滩、微生物丘往往共生。微生物碳酸盐岩储层储集空间类型多样,以葡萄花边构造溶孔、凝块颗粒间溶孔、海绵体腔孔、层间溶孔、窗格孔为主。微生物碳酸盐岩储层的形成受微生物结构、成岩作用以及沉积微相等多种因素共同控制。储集空间受到微生物结构的影响,在准同生期受溶蚀改造形成,其后又经历了表生期溶蚀改造,但经过充填胶结作用后,孔隙减小或消失。沉积微相总体上控制着微生物岩储层类型及其展布特征。鄂尔多斯盆地南部奥陶系可能存在微生物岩储层,微生物碳酸盐岩储层将是今后的油气勘探中的一类重要类型。

Microbial carbonate reservoir is one of the research hotspots in petroleum geology in recent years. Microbial structure plays an important role in the formation of reservoir space. A large number of microbial carbonate rocks are developed in Ordos Basin. However, there is no report on Ordovician Microbial Carbonates in the southern Ordos Basin. In this paper, the field observation and thin slice observation are carried out in the field outcrops of Chenlu Renjiawan in the southern Erdos basin. The petrological characteristics and reservoir space characteristics of the Microbial Carbonates are described. The sedimentary environment of the Microbial Carbonates is synthetically analyzed, and the relationship between the pore evolution and the diagenesis process of the Microbial Carbonates is discussed. The study suggests that: Four types of rock containing bioclastic mudstone limestone, gravel limestone, sand-clastic limestone, and algal limestone are developed in Ordovician Pingliang Formation in the southern Ordos Basin. Microbial carbonate is mainly developed in algal limestones. Most of them are thrombolites, followed by stromatolites and dentrolite. The depositional period of the Pingliang Formation in the field outcrop of Chenlu Renjiawan belongs to platform margin facies to platform foreslope facies, while the thrombolites and the stromatolites are mainly developed in the relatively low energy environment in platform margin facies. The reefs, shoals and microbial carbonate rocks in the Pingliang formation of southern Erdos are often symbiotic. There are various types of reservoir space in microbial carbonate reservoirs, mainly including grape-lace structure pores, intergranular dissolved pores of thrombolites, cavernous pores, interlaminar pores and pane pores. The formation of microbial carbonate reservoir is controlled by many factors such as microbial structure, diagenesis and sedimentary microfacies. The reservoir space is affected by the microbiological structure. At the penecontemporaneous stage, the reservoir is transformed by precipitation corrosion, followed by a supergene corrosion modification. However, after the cementation, the pores decrease or disappear. The sedimentary microfacies control the type of reservoir and its distribution characteristics in general. The microbial carbonate reservoirs in the Ordovician system in the southern Ordos basin may exist, and the microbial carbonate reservoir will be an important type of oil and gas exploration in the future.