海相与陆相页岩储层孔隙结构差异的影响因素

Influencing factors of pore structure differences between marine and terrestrial shale reservoirs

海相页岩和陆相页岩的孔隙结构差异明显。基于海相和陆相页岩在岩石组分、成熟度以及有机显微组分的差异开展的成因机理分析表明,页岩中不同岩石组分孔隙的孔径分布差异大,有机质孔隙在小孔径范围内占比多,黏土矿物孔隙与有机质孔隙的孔径分布特征相似,但亦发育中孔和宏孔。海相页岩的小孔径孔隙多由有机质提供,而陆相页岩的小孔径孔隙多来自黏土矿物。无论是海相页岩还是陆相页岩,其孔隙均以无机矿物孔隙为主,其次为有机质孔隙,所不同的是海相页岩中有机质孔隙的贡献率高于陆相页岩,而陆相页岩中黏土矿物孔隙的贡献率高于海相页岩。有机质孔隙在不同演化阶段的孔隙构成不同,未成熟阶段以发育镜质体和惰质体的原始胞腔孔隙为主,成熟阶段有机质孔隙的发育程度最差,高成熟—过成熟阶段以发育次生固体沥青孔隙为主。高成熟—过成熟海相页岩的有机质以腐泥组和固体沥青为主,其有机质孔隙发育程度高。在以松辽盆地沙河子组为代表的高成熟陆相页岩中,其有机质以镜质体和惰质体为主,原始胞腔孔隙损失大,含有少量固体沥青孔隙;在以鄂尔多斯盆地延长组为代表的低成熟陆相页岩中,由于腐泥组和固体沥青充填孔隙,使得页岩整体的孔隙发育程度变差。

Marine shale and terrestrial shale are obviously different in pore structure.The analysis of genetic mechanism based on differences in the rock composition,maturity and organic maceral of marine and terrestrial shale shows that different components in shale have great difference in pore size distribution,and the organic pores account for a high proportion in the range of small pore size.The pore size distribution characteristics of clay mineral are similar with organic pores,while mesopores and macropores are also developed in clay mineral.The small pores of marine and terrestrial shale are mostly provided by organic matter and clay minerals,respectively.Either marine or terrestrial shale mainly has inorganic mineral pores,followed by organic pores.The difference is that the contribution of organic pores in marine shale is higher than that in terrestrial shale,while the contribution of pores in clay minerals of the terrestrial shale is higher as compared with marine shale.The organic pore composition varies at different stages of evolution.In the immature stage,the original cellular pores of vitrinite and inertinite were dominantly developed.In the mature stage,the development of organic pores is the lowest.In the high-mature and over-mature stage,the pores of secondary solid bitumen were predominantly developed.The organic matter of high-mature and over-mature marine shale is dominated by sapropel and solid bitumen,showing the high development of organic pores.The high-mature terrestrial shale represented by Shahezi Formation in Songliao Basin mainly has the organic matter dominated by vitrinite and inertinite,suffering a large loss of original cellular pores,containing a few pores in solid bitumen.In the low-mature terrestrial shale represented by Yanchang Formation in Ordos Basin,the whole development of pores is low due to the filling of pores with sapropel and solid bitumen.