上扬子黔西北地区海相与海陆过渡相页岩气储层孔隙特征差异性研究

Study on the Difference of Pore Characteristics between Marine and Marine-continental Transitional Shale Gas Reservoirs in Upper Yangtze Region,Northwest Guizhou

为明确海相与海陆过渡相页岩孔隙特征之间的差异性,以上扬子黔西北地区为例,对区内广泛分布的海相龙马溪组、牛蹄塘组及海陆过渡相龙潭组页岩孔隙特征进行研究,分析页岩内部孔隙的类型、发育与分布模式,进一步探索其差异性成因。研究表明:海相页岩整体是以有机孔为主、石英与碳酸盐类矿物等刚性颗粒间孔为辅的孔隙分布模式,有机孔相对含量约占总孔隙的50%以上;海陆过渡相页岩孔隙的孔径较海相页岩大且变化范围大,为无机粒间/粒内孔与微裂缝占主体、有机孔次之的孔隙分布模式,其内部碳酸盐类矿物溶蚀孔/缝大量发育,有机孔相对含量仅占总孔隙的20%左右;形成时期沉积环境的差异是海相与海陆过渡相页岩孔隙发育存在差异的最主要原因,后期保存条件不同也会产生一定程度影响。针对储层孔隙特征进行差异性分析对页岩气资源勘探开发有重要的指导意义。

In order to clarify the differences between the pore characteristics of marine and paralic transitional shale,in the case study of Upper Yangtze Region,Northwest Guizhou,the pore characteristics of Longmaxi Formation marine shale,Niutitang Formation shale and Longtan Formation paralic transitional shale widely distributed in the area were studied,and the types and development and distribution patterns of pores inside the shale were analyzed to further explore the causes of difference.The study showed that,the overall pore distribution pattern of marine shale was dominated by organic pores and followed by rigid intergranular pores such as quartz and carbonate minerals,with the relative content of organic pores accounting for more than 50%of the total pores;the diameter of pores in marine-continental transitional shale was greater and more variable than that of marine shale,and the pore distribution pattern was dominated by inorganic intergranular/intragranular pores and microfractures,followed by organic pores,with a large number of dissolved pores/fractures developed in carbonate minerals,and the relative content of organic pores only accounting for about 20%of the total pores.The difference of sedimentary conditions in formation period was the root cause for the difference of pore development between marine and marine-continental transitional shale,and the different preservation conditions in the later stage also had a certain influence.Differential analysis of reservoir pore characteristics provides an important guidance to the exploration and development of shale gas resources.