塔里木盆地柯坪露头区震旦系微生物白云岩储层微观表征

Micro-characterization of microbial dolomite reservoir of Upper Sinian Qigeblak Formation in Keping area,Tarim Basin

塔里木盆地寒武系盐下超深层领域资源量巨大,震旦系是该领域风险勘探的重要层系之一,虽然早些年该层系内尚未取得较大突破,但当前深层震旦系的勘探已经初现成效,进一步突破值得期望,其中储层特征、品质和规模认识不深是制约下一步勘探的重要因素之一。研究以塔里木盆地西北缘阿克苏地区柯坪露头区为例,在对震旦系奇格布拉克组进行精细解剖的基础上,系统地开展了330个样品的铸体薄片分析和6个样品的氩离子抛光—扫描电镜分析,同时优选4个典型微生物白云岩储层样品,开展了基于工业CT的储层三维微观孔喉结构表征。结果表明:(1)奇格布拉克组微生物白云岩储层主要发育粒间(溶)孔、粒内(溶)孔、晶间(溶)孔、微生物格架孔、溶蚀孔洞和溶缝,其中泡沫绵层石白云岩和黏结颗粒白云岩的孔洞最发育,储层孔隙的发育与岩相具有明显的相关性;(2)奇格布拉克组微生物白云岩储层为具有中高孔、中低渗特征的孔隙—孔洞型储层,平均孔隙度为3.3%,最大孔隙度为19.6%,优质储层厚度约为53.7 m(孔隙度≥2.5%),储地比约为0.31,具有一定规模;(3)微孔隙(孔径≤10μm)在不同类型微生物白云岩中普遍发育,对提高储层的储集性能具有重要意义,初步推断其形成主要与微生物早期热解作用有关,热解形成的有机酸和CO;对碳酸盐矿物溶蚀和初始孔隙的保存起到了重要作用。研究成果为塔里木盆地寒武系盐下超深层领域勘探提供了可靠依据。

The Cambrian subsalt super-deep zone in the Tarim Basin has huge resources. The Sinian is one of the important strata for risk exploration in this field. Although no major breakthrough has been made in the strata in the early years,the current deep Sinian exploration has achieved initial results,and further breakthroughs are worth expecting. Among them,the lack of deep understanding of reservoir characteristics,quality and scale is one of the important factors restricting the next step of exploration. The study took the Keping outcrop area on the northwestern margin of the Tarim Basin as an example. Based on the fine dissection of the Sinian Qigeblak Formation,330 samples of cast thin sections and six samples of argon ion polishing were systematically carried out. Meanwhile,four typical microbial dolomite reservoir samples were selected and three-dimensional microscopic pore throat structure characterization was carried out based on industrial CT. It was clarified that:(1)The microbial dolomite reservoir of the Qigeblak Formation mainly developed intergranular(dissolved)pores,intragranular(dissolved) pores,intercrystalline(dissolved) pores,microbial framework pores,dissolution pores and dissolution cracks. Among them,the pores of foamy dolomitic dolomite and cohesive granular dolomite are the most developed. The development of pores has obvious correlation with lithofacies.(2)The microbial dolomite reservoir of the Qigeblak Formation is a pore-vug type reservoir with medium-high porosity and medium-low permeability,with an average porosity of 3.3% and maximum porosity. The thickness of the highquality reservoir is about 53.7 m(porosity≥2.5%),and the storage-to-land ratio is about 0.31,which is of scale.(3)Micro-pores(pore size≤10 μm)are generally developed in different types of microbial dolomites,which is useful for improving the reservoir. The storage performance of sulphate is of great significance. It is preliminarily inferred that its formation is mainly related to the early pyrolysis of microorganisms. The organic acids and CO;formed by pyrolysis play an important role in the dissolution of carbonate minerals and the preservation of initial pores. The research results provide a reliable basis for the exploration of the Cambrian subsalt ultradeep zone in the Tarim Basin.