鄂尔多斯盆地长7段泥页岩系孔隙特征及其演化规律

Pore Characteristics and Evolution of the Chang 7 Mud Shale in Ordos Basin

鄂尔多斯盆地延长组长7段泥页岩既是盆内优质烃源岩,又是有利的页岩气储层。页岩气储层孔隙特征和演化规律的研究,能够为分析页岩气储层储集性能、探讨页岩气赋存成藏过程和机理、预测页岩气"甜点区"提供指导。在总结国内外学者研究成果的基础上,采用氩离子抛光-场发射扫描电镜观察、高压压汞、气体吸附等分析测试方法,优化了前人对于页岩气储层孔隙的划分方案,将长7段泥页岩孔隙分为基质孔隙和裂缝孔隙两大类,进一步将基质孔隙分为粒间孔、粒内孔、晶间孔和有机质孔隙4个亚类;定性和定量地分析了研究区长7段泥页岩孔隙特征,孔隙形态复杂,以狭缝形和楔形为主,孔径分布范围宽泛(0.1~10 000nm),孔隙度为0.5%~6.6%,中孔(2~50nm)和宏孔(>50nm)是孔隙度的主要贡献者;提出泥页岩岩相类型、成岩作用、生烃作用和构造作用是影响泥页岩孔隙发育及演化的4个主控因素,建立了鄂尔多斯盆地长7段泥页岩孔隙演化模式。

The mud shale of the Chang 7group in Ordos Basin is not only the high quality hydrocarbon source rock,but also the favorable reservoir in the basin.The study on pore characteristics and evolution of this mud shale will provide guidance for analyzing the mud shale reservoir quality,exploring mechanism of the shale gas storage and gas-pool formation,predicting＇sweet spot＇area of shale gas.Based on observations of argon ion etching-field emission scanning electron microscopy,the pore classification scheme for shale gas reservoirs was optimized and the pore characteristics were analyzed qualitatively.Accordingly,the pores in the Chang 7mud shale are divided into fracture pores and matrix pores which can be further subdivided into interparticle pores,intrapaticle pores,intercrystalline pores and organic-matter pores.The size and morphology of the pores exhibit complicated structure and high heterogeneity.The interparticle pores and fracture pores are the main pore types while other types are less developed.Meanwhile,with measurement of mercury injection capillary pressure,the distribution of integrated pore size ranging from 0.1nm to 10 000 nm was obtained quantitatively by using the calculation model of DFT,BJH and Washburn.The analysis results show that mesopores（2-50nm）and macropores（〉50nm）are dominated in both pore size and volume.We suggest that the four main factors,lithofacies,diagenesis,hydrocarbon-generation and tectonism,affect the development and evolution of pores in the Chang 7mud shale during the burial process.Finally,the porosity evolution model for the mud shale of in the Ordos Basin is constructed after consideration of the major impact factors on pores.