四川盆地元坝地区千佛崖组二段细粒沉积岩岩相特征及储集性分析

Lithofacies characteristics and reservoir capacity of fine⁃grained sedimentary rocks of second member of Qianfoya Formation in Yuanba area,Sichuan Basin

四川盆地侏罗系千佛崖组页岩油气勘探前景良好,但目前对其细粒沉积岩基本沉积特征及发育规律的认识还不足。为此,利用细粒沉积学原理,依据岩心和测井资料,通过岩心精细描述、薄片鉴定、X衍射全岩分析及扫描电子显微镜观察等技术手段,精细描述了元坝地区千佛崖组二段(简称千二段)细粒沉积岩储层的物质组成、沉积构造、储集空间类型等地质特征,划分了岩相类型,并对主要岩相储层的物性特征和储集空间类型进行分析与比较,明确了有利层段发育位置。研究结果显示:(1)千二段陆相细粒沉积岩可划分成“黏土岩”和“粉砂岩”2种岩石类型,15种岩相类型。其中,富有机质块状黏土岩、富有机质块状含粉砂黏土岩、富有机质纹层状含粉砂黏土岩、富有机质条带状含粉砂黏土岩、富有机质块状粉砂质黏土岩和富有机质纹层状粉砂质黏土岩为6种主要岩相类型。(2)储层储集空间类型多样,包括黏土矿物层间缝、层理缝、黏土矿物晶间孔、黄铁矿晶间孔、溶蚀孔及有机孔等,其中黏土矿物晶间孔分布最为广泛。(3)6种主要岩相的平均孔隙度和渗透率分别为2%和0.023×10^(-3)μm^(2),富有机质纹层状含粉砂黏土岩、富有机质纹层状粉砂质黏土岩和富有机质块状粉砂质黏土岩的储集空间类型丰富,分布广、数量多,孔隙度与渗透率均高于其他岩相且TOC值较高,是最有利的储集岩相类型。(4)千二段有利层段位于其(1)小层全段、(2)小层的底部和(3)小层的中下部。

The shale oil and gas exploration potential of the Jurassic Qianfoya Formation in the Sichuan Basin is promising.However,there is still a lack of understanding regarding the basic sedimentary characteristics and development patterns of fine-grained sedimentary rocks.Therefore,utilizing the principles of fine-grained sedimentology,this study thoroughly examines the geological features of the fine-grained sedimentary rock reservoir in the second member of the Qianfoya Formation in the Yuanba area.This investigation includes the analysis of material composition,sedimentary structures,reservoir space types,and classification of lithofacies types.Subsequently,the physical characteristics and reservoir space types of the main lithofacies reservoirs are compared and analyzed.Finally,the study predicts the favorable intervals for development.The results reveal that the fine-grained sedimentary rocks in the second member of the Qianfoya Formation in the Yuanba area consist of two rock types:clay rock and siltstone,with a total of 15 rock facies types.Organic-rich massive clay rock,organic-rich massive silty clay rock,organic-rich laminated silty clay rock,organic-rich banded silty clay rock,organic-rich massive silty clay rock,and organic-rich laminated silty clay rock are the six major lithofacies types of fine-grained sedimentary rock.Additionally,various types of reservoir spaces exist,such as interlayer fractures among clay minerals,shale bedding fractures,intercrystalline pores among clay minerals,intercrys-talline pores among iron pyrite,dissolved pores,and organic matter pores.Among these,intercrystalline pores of clay minerals are the most widely distributed.The average porosity and permeability of the six major lithofacies types were found to be 2%and 0.023×10^(-3)μm^(2),respectively.The lithofacies of organic-rich laminated silty clay rock,organic-rich laminated silty clay rock,and organic-rich massive silty clay rock exhibit rich reservoir space types,wide distribution,large quantity,higher porosity and permeability compared to other lithofacies,as well as higher TOC values,making them the most favorable reservoir lithofacies types.The dominant stratum of the second member of the Qianfoya Formation in the study area is situated in substratum 1,the bottom of substratum 2,and the middle and lower parts of substratum 3.