延长组和龙马溪组典型页岩孔隙结构特征研究

STUDY ON PORE STRUCTURE CHARACTERISTICS OF THE TYPICAL SHALE OF YANCHANG FORMATION AND LONGMAXI FORMATION

页岩孔隙结构特征是反映其油气存储能力、流动能力和赋存状态的重要指标。为明确四川盆地和鄂尔多斯盆地典型页岩的孔隙结构特征,本文以重庆石柱、彭水地区的龙马溪组页岩和陕西宜君地区延长组长7段油页岩为研究对象,结合高压压汞和N_2吸附实验对3组页岩的孔隙结构进行了详细表征。基于分形理论中的Brooks-Corey模型和FHH模型,对大孔(介孔+宏孔)和微孔的不规则性和复杂性进行了深入探讨。结果表明:(1)龙马溪组和延长组页岩的孔隙形态均为墨水瓶形和平行板狭缝形;(2)孔径分布均呈多峰分布。龙马溪组页岩含微孔、介孔和宏孔,而延长组页岩以介孔和宏孔为主;(3)延长组页岩孔隙度、孔体积和分形维数均小于其他两个地区。因此,延长组页岩孔隙结构较为单一且致密性较好。研究成果可为两地页岩气的开发提供指导。

Shale pore structure is an important indicator that reflects its oil and gas storage capacity,flow capacity,and occurrence state.To investigate the pore structure characteristics of typical shales in the Sichuan Basin and the Ordos Basin,shale samples from the Longmaxi Formation in the Shizhu and Pengshui areas of Chongqing and the Chang 7 oil shale of the Yanchang Formation in the Yijun area of Shaanxi Province were collected,respectively.The pore structure characteristics of these three groups of shales were examined by mercury intrusion porosimetry and nitrogen adsorption tests.The irregularity and complexity of large pores(mesopores+macropores)and micropores were deeply investigated using the FHH model and the Brooks-Corey model.The results show that:(1)the pore morphology of the shales belongs to ink bottle shape and parallel plate slit shape;(2)the pore size distribution is multimodal.For the shale of the Longmaxi Formation,it contains micropores,mesopores,and macropores,while for the shale of the Yanchang Formation,most of the pores belong to mesopores and macropores;(3)compared with the shale of the Longmaxi Formation,the shale of the Yanchang Formation has lower porosity,pore volume,and fractal dimension.Therefore,the shale in this area possesses a simpler pore structure and a more compacted skeleton.