过渡相页岩气储层纳米级孔隙发育特征与影响因素——以太原西山古交地区山西组为例

Development characteristics and affecting factors of nanopores in transitional shale reservoirs:An example of the Shanxi formation

基于古交地区山西组页岩储层样品,利用场发射扫描电镜、高压压汞、低温氮吸附、X线衍射等实验,探究过渡相页岩纳米级孔隙的发育特征及影响因素。结果表明:研究区储层孔隙主要包括有机孔隙、黏土矿物孔隙、骨架矿物孔隙、微裂隙四类,以中孔为主,发育多种形貌;四类孔隙所占储集空间比例分别为22.4%、44.0%、27.2%、6.4%。过渡相页岩非均质性显著,孔隙分形分维值平均近2.7,显示非均质程度较强、空间结构复杂。孔隙孔径与总孔体积减小,比表面积增大,纳米孔及吸附点位增多;有机碳与石英质量分数增多,黏土矿物质量分数减少,孔隙发育程度增强。水进体系域下形成的凝缩层及高位体系域中的泥炭沼泽—分流间洼地、泥炭沼泽—分流间湾沉积组合是优质页岩储层发育的有利层位。

Based on the Shanxi formation shale reservoir samples of Gujiao area,the nanopore structure of transitional facies shale gas reservoirs and its influencing factors were studied using experimental techniques of field emission scanning electron microscopy(FE-SEM),high-pressure mercury injection,low temperature nitrogen gas adsorption and X-ray diffraction.The results show that the pores in transitional shale reservoirs have complex formation mechanisms and various types including organic pores,clay mineral related pores,matrix mineral intragranular pores,dissolution pores and microfractures,and so on.The mesoporosity is the predominant reservoir space and the shape of pores is complicated.Through image processing,the pore structure information is further extracted to realize the classified evaluation of organic pores,clay mineral pores,skeleton mineral pores and micro fractures.The results show that the proportion of the four types of pore space is 22.4%,44.0%,27.2%,6.4%respectivel.The transition facies shale has significant heterogeneity characteristics.The quantitative evaluation of heterogeneity by FHH fractal model shows that the fractal fractal dimension value of pore fractal is nearly 2.7,indicating a strong heterogeneity degree and complex spatial structure.The correlation analysis shows that as the pore size decreases,the volume of the total pore is reduced,the specific surface area is increased,and the increase of the pore size is favorable to the increase of the adsorption points.With the increase of TOC content and quartz content and the decrease of the clay mineral content,the pore development is enhanced.The condensate layer formed under the water system region as well as the peat swamps-distributary depressions and the peat swamp-distributary bay sedimentary assemblages in the high risk system domain are favorable beds for the development of high quality transitional facies shale.