海相页岩气储层孔隙表征、分类及贡献

Characterization,classification and contribution of marine shale gas reservoirs

以渝东南彭水地区五峰组-龙马溪组页岩气为例,开展低温二氧化碳吸附(LTCA)、氮气吸附(LTNA)、核磁共振(NMR)、压汞、扫描电镜以及氦测孔隙度等孔隙表征实验,全面刻画页岩孔隙结构,建立全孔径表征及分类方法,研究它们在页岩气赋存和渗流等方面的差异贡献。结果表明,氦测孔体积最大;其次为LTNA和NMR,两者分别在刻画较小孔(<10nm)和较大孔方面优势明显,联合二者可表征页岩全孔径分布。全孔径分布揭示页岩气孔隙分布范围宽,但70%孔体积集中在孔径小于25 nm。结合分形特征,以5,25和100 nm为界,将其划分为微孔、小孔、中孔和大孔。微孔、小孔和中孔主要受有机质含量和粘土矿物含量的影响;此外,中孔还受粒内溶蚀孔的影响,而大孔主要由粒间孔和粘土层间缝构成。微孔和小孔分别为页岩吸附气、游离气提供主要场所;小孔和中孔相互连接,为页岩气在基质中渗流提供通道。研究成果对页岩气储层分类、渗流机理认识等具有指导意义。

The Wufeng-Longmaxi Formations shale gas in Pengshui area,southeastern Chongqing,was studied through several pore characterization experiments including low-temperature carbon adsorption(LTCA),low-temperature nitrogen adsorption(LTNA),nuclear magnetic resonance(NMR),high pressure mercury intrusion porosimetry(MIP),scanning electron microscopy(SEM),and Helium porosity measurement.The shale pore structure was comprehensively described,and the characterization and classification methods of full range of pore size were established to study their individual contributions to shale gas occurrence and migration.The results show that the pore volume by Helium porosity measurement is the largest,followed by LTNA and NMR.The latter two have obvious advantages in characterizing smaller(<10 nm)and larger pores,and thus the combination of LTNA and NMR can be applied to the characterization of full range pore size distribution of shale.The distribution reveals a wide range of shale gas pore distribution,but 70%of the pore volume is concentrated in pores less than 25 nm in diameter.Combined with fractal features,the pores can be divided into micropores,small pores,mesopores and large pores in diameter with a lower boundary of 5 nm,25 nm and 100 nm.The pore throat size is mainly a result of organic matter and clay contents.The larger pores are composed of intergranular pores and inter-clay-layer fractures.The mesopores are also affected by intragranular dissolved pores.The micropores and small pores are the main sites where the shale adsorbed gas and free gas occur.The small pores and mesopores are inter-connected,providing channels for the shale gas to migrate in the matrix.The research results are significant as it may guide the classification of shale gas reservoirs and the understanding of infiltration mechanism.