川东地区侏罗系凉高山组致密砂岩储层特征及控制因素

CHARACTERISTICS AND CONTROLLING FACTORS OF JURASSIC LIANGGAOSHAN FORMATION TIGHT SANDSTONE RESERVOIRS IN THE EASTERN SICHUAN BASIN

侏罗系凉高山组作为四川盆地致密油气重点勘探目标,有利储层优选是实现其高效勘探的核心与关键,但目前仍受困于储层特征认识不清、致密成因解析不足等问题。运用铸体薄片、扫描电镜、高压压汞、包裹体测温等技术手段,以川东地区凉高山组致密砂岩为研究对象,在全面总结储层特征的基础上,建立成岩演化序列并解析砂岩致密化成因。研究结果表明:凉高山组主要为长石岩屑砂岩和岩屑长石砂岩;孔隙度分布在0.35%~7.71%之间,渗透率分布在0.00001×10^(-3)μm^(2)~0.07860×10^(-3)μm^(2)之间,为典型致密储层。砂岩整体压实胶结致密,仅发育少量原生孔隙和次生孔缝,储集空间以次生孔缝为主,发育两种类型孔喉结构。压实作用对原始孔隙度的平均减孔量为21.73%,是储层致密化的主导基础;胶结作用对原始孔隙度的平均减孔量为9.14%,其中,晚期方解石胶结通过占据孔隙空间大幅度降低储集性能,是储层致密化的重要因素;自生黏土矿物通过堵塞孔隙喉道、增强喉道迂回度等方式降低渗流性能,进一步加强了储层的致密程度;早期绿泥石胶结是研究区重要的保孔因素;溶蚀作用的平均增孔量为0.71%,长石、岩屑溶蚀增孔效应较低。

The unclear understanding of characteristics of Jurassic Lianggaoshan Formation tight oil and gas reservoir and its formation causes of tight oil and gas in Sichuan Basin have hindered the selection of favorable reservoir and the efficient exploration of reservoir.Based on the comprehensive summary of reservoir characteristics,combined with the analyses of cast thin section,scanning electron microscopy,high pressure mercury injection,inclusion temperature measurement and other technical means,the diagenetic evolution sequence of the tight sandstone of Lianggaoshan Formation in eastern Sichuan area is established and the causes of sandstone densification are analyzed.The results show that Lianggaoshan Formation is mainly composed of feldspar lithic sandstone and lithic feldspar sandstone.The porosity of sandstone ranges from 0.35%to 7.71%and permeability ranges from 0.00001×10^(-3)μm^(2)to 0.0786×10^(-3)μm^(2),showing characteristics of typical tight reservoir.The Lianggaoshan Formation sandstone has strong compaction and compact cementation as a whole,and only a few primary pores and secondary pores and fractures are developed.The reservoir space of the sandstone is dominated by secondary pores and fractures,and two types of pore throat structures exist in the rock.Analysis reveals that the average reduction of original porosity by compaction is 21.73%,which is the dominant basis of reservoir densification,and the average reduction of original porosity by cementation is 9.14%.Late calcite cementation significantly reduces res-ervoir performance by occupying pore space,which is an important factor for reservoir densification.It is recognized that autogenous clay minerals reduce seepage performance by Blocking pore throats and enhan-cing the roundabout degree of throats,which further intensifies the tightness of reservoir.Early chlorite cementation is an important pore protection factor in the study area.The average porosity increase of the dissolution is 0.71%,but the porosity increase effect of feldspar and debris is relatively low.