四川盆地东缘湘西北地区牛蹄塘组页岩储层特征及r影响因素

摘要

四川盆地东缘湘西北地区牛蹄塘组具有分布广、厚度大、埋藏适中、有机质丰度高以及热演化程度高等特点,资源前景广阔,是近年来南方页岩气勘探重点.文章以该区参数井——花页1井为研究对象,通过岩心、岩屑观察,采用薄片鉴定、X-衍射矿物分析、物性测试、扫描电镜、低温氮气吸/脱附实验等系统手段,研究储层特征,综合分析储层的影响因素.在深水陆棚相,牛蹄塘组发育黑色炭质页岩、硅质页岩,以富含炭质、硅质及黄铁矿,低黏土矿物(伊利石为主)含量为特征,页岩属特低孔、特低渗类型储层.SEM和低温氮气吸/脱附实验表明,储层主要发育圆筒孔(有机质孔)、狭窄平行板孔(粘土矿物层间孔)、四面开口的锥形管孔(粘土矿物粒间孔)以及锥形平板孔(微裂缝);中孔(2~50 nm)提供了平均60.3%的BJH体积.多种因素共同影响微观孔隙发育:深水泥质陆棚控制了孔隙发育物质基础;丰富TOC促进有机质孔(尤其是大孔)发育;矿物组成及含量控制了孔隙发育类型及程度;有机质热演化作用促进有机质孔、微裂缝发育.%The Niutitang Formation in northwestern Hunan Province,eastern margin of Sichuan Basin is regarded as hav-ing great potential and one of the major shale gas exploration targets with its wide distribution,large thickness,favorable burial depth,high content of organic matter,high maturity and etc,in south China.An parameter well,the Huaye-1,in the Formation of the area,was chosen to be studied with systematic means including observation of thin sections,XRD mineral analyses,physical property tests,SEM imaging and low-temperature N2 adsorption/desorption experiments with core and drilling cutting samples,to probe into the characteristics and influencing factors of the reservoirs.The deep shelf facies of the Niutitang Formation developed dark carbonaceous shale and siliceous shale rich in carbonaceous and sili-ceous material,as well as pyrite,but lean in clay minerals ( mainly illites) .The shale reservoirs are of ultra-low porosity and permeability.The SEM images and low-temperature N2 adsorption/desorption experiments show that the reservoirs contain mostly cylindrical pores ( organic pores) ,narrow parallel-plate pores ( clay mineral interlayer pores) ,tapered tube pores with openings around ( intergranular pores among clay minerals) and tapered plate pores ( micro-crack) .The meso-pores ( sized between 2 to 50 nm) contribute an average of 60.3%of BJH volume.The development of the micropores is found to be affected by multiple factors: the deep-water muddy continental shelf provided the material basis for the pores,the high content of TOC facilitated the growth of organic pores (especially organic macropores),the composition and content of minerals dominated the types and amounts of the pores,and the thermal evolution of organic matter promo-ted the development of organic pores and micro-cracks.