四川盆地侏罗系凉高山组页岩油地质特征

Geological characteristics of shale oil in the Jurassic Lianggaoshan Formation in Sichuan Basin

近年来,四川盆地侏罗系湖相页岩油勘探取得了重大突破,展现出巨大勘探潜力。为了进一步支撑深化勘探,基于野外露头、测井、钻井取心和系统取样分析资料,开展了四川盆地侏罗系凉高山组不同岩性组合条件下页岩地球化学特征、岩石脆性、孔隙结构及含油气性等研究,明确了优势页岩岩性组合类型。结果表明:凉高山组页岩发育层段可细分为纯页岩组合、介壳型页岩组合、粉砂型页岩组合3类5种岩性组合;5种岩性组合中页岩均处于热成熟阶段,但有机质含量、类型、脆性矿物含量存在差异,纯页岩组合中页岩TOC平均值大于1%,有机质类型为Ⅱ1型,脆性矿物含量大于52%;介壳型页岩组合中页岩有机质特征与纯页岩组合相似,但脆性矿物含量大于65%;粉砂型页岩组合中页岩TOC平均值小于1%,有机质类型为Ⅱ2型,脆性矿物含量大于65%。不同组合储集空间主要为微裂缝及无机孔(孔径10~500nm),但粉砂型页岩组合喉道较宽,孔隙连通性优于纯页岩组合及介壳型页岩组合。纯页岩组合游离烃含量大于1mg/g,含油性好,纯页岩组合和粉砂型页岩组合部分OSI大于100mg/g,可动性较强。综合分析认为,纯页岩组合与粉砂型页岩组合为页岩油勘探有利岩性组合。粉砂型页岩组合因具有良好的可压裂性,可成为凉高山组页岩油下步勘探的主要甜点层段。

In recent years,major breakthroughs have been made in the exploration of the Jurassic lacustrine shale oil in Sichuan Basin,showing great exploration potential.In order to support the further deepening exploration,the field outcrop,logging,well drilling,coring and systematic core sample experimental data are combined to analyze the geochemical characteristics,rock brittleness,pore structure and oil and gas bearing properties of shale with various lithologic combinations in the Jurassic Lianggaoshan Formation,and identify the lithologic combination types of the dominant shale.The results indicate that the lithologic combination of shale interval in Lianggaoshan Formation is classified into three categories and five types,i.e.,pure shale combination,shell type shale combination,and siltstone type shale combination;Among the five types of lithologic combinations,shale is in the mature stage,but there are differences in organic matter content,type,and brittle mineral content.The shale of pure shale combination has an average TOC of greater than 1%,TypeⅡ1 organic matter,and brittle mineral content of higher than 52%;The organic matter characteristics of the shale of the shell type shale combination are similar to those of the pure shale combination,but the content of brittle minerals is greater than 65%;The shale of the siltstone type shale combination has an average TOC of less than 1%,TypeⅡ2 organic matter type,and the brittle mineral content of greater than 65%.The main reservoir space of various combinations is composed of microfractures and inorganic pores(pore diameter of 10-500 nm).The siltstone type shale combination has a larger pore throat and better pore connectivity than the pure shale combination and shell type shale combination.The free hydrocarbon content of the pure shale combination is greater than 1 mg/g,showing good oil-bearing property.OSI of the pure shale combination and the siltstone type shale combination is greater than 100 mg/g of some samples,indicating good oil movability.The comprehensive analysis shows that pure shale combination and siltstone type shale combination are favorable lithologic combination for shale oil exploration.Benefiting from the good fracability,the siltstone type shale combination is the main sweet spot for shale oil exploration in Lianggaoshan Formation.