四川盆地南部下志留统龙马溪组页岩孔隙结构特征

页岩的孔隙结构特征对页岩气的储集和运移有着显著的影响。不同的孔隙结构表征技术往往适用于特定的孔隙尺寸范围,而由于页岩孔径大小变化范围较大且发育大量的纳米级孔隙,对其孔隙结构进行合理的表征十分困难。为此,综合利用低压N_2吸附法、高压压汞法以及岩心核磁共振法对四川盆地南部下志留统龙马溪组页岩的孔隙结构特征进行了深入研究,探讨了影响孔隙发育的主要因素。结果表明:①该区龙马溪组页岩孔隙形状复杂,孔径分布普遍具有双峰或三峰特征,主要发育孔隙直径介于0~10 nm的微孔和中孔,也有少量大孔和微裂缝发育;②页岩样品的矿物成分以石英和黏土矿物为主,而后者是页岩微孔和中孔发育的主要贡献者,其含量与岩样微孔体积和中孔体积均具有正相关性;③此外,有机碳含量也是控制该区泥页岩孔隙发育的主要因素之一,主要通过有机质热演化生烃作用影响孔隙的发育;④目前的测试手段难以对直径小于2 nm的孔喉进行准确测试,这也是未来攻关的技术难点。

Pore structure characteristics of Longmaxi shale in the southern Sichuan Basin

The pore structure of shale gas reservoirs has a strong impact on gas storage and migration. However, it's very difficult to characterize the pore structure of shales due to a wide range of pore sizes and a large number of nano-scale pores. In this paper, the low pressure N2 adsorption, high pressure mercury injection and nuclear magnetic resonance are used to characterize the shale reservoir pore structure of Longmaxi Formation in the Sichuan Basin. Experimental analysis shows that: ① the pore size distribution of Longmaxi shale in the Sichuan Basin is bimodal or trimodal, with the dominant pore diameter in the range of 0 - 10 nm, but a small number of large pores and developed microfractures; ②The main components of the shale samples are quartz and clay minerals, with the latter being the main contributor to micro and meso-pores in the shale, and its content being positively correlated with the micro and meso-pore volumes in shale; ③The content of total organic carbon is a key factor controlling the pore space development in shale through hydrocarbon generation of organic matters; ④The pore throat less than 2 nm in diameter can't be tested accurately by current experimental methods, which will be a key point in the future study.