Study On Pore Structure And Wettability Of Shale Reservoir In Lianggaoshan Formation In Eastern Sichuan

In recent years,the focus of oil and gas exploration of Jurassic strata in the Sichuan Basin has shifted from central Sichuan to eastern Sichuan,where significant breakthroughs have been achieved in the lacustrine shale of Lianggaoshan Formation,indicating a great exploration potential of shale oil and gas in Jurassic in this region.Therefore,a comprehensive evaluation of shale pore structure,wettability and their impact on oil-bearing properties is of great significance in guiding the exploration and development of shale oil and gas in the Lianggaoshan Formation in eastern Sichuan.This paper focuses on the problems of imprecise characterization of pore structures and the unclear understanding of the wettability characteristics of shale reservoirs in the Lianggaoshan Formation in eastern Sichuan.Based on the investigation of a large number of relevant literature and internal project materials,key core samples and field profile samples were selected for organic carbon analysis,whole-rock XRD and clay mineral XRD testing,low-temperature N₂ and CO₂ gas adsorption experiments,nuclear magnetic resonance experiments,CT scanning,scanning electron microscopy,and contact angle measurement experiments.The research was carried out on geological characteristics,shale lithofacies,pore structure and wettability,and the influence of pore structure and wettability on oil-bearing properties was analyzed.The results show three lithofacies developed in the Lianggaoshan Formation in eastern Sichuan:organic-rich clayey shale,organic-matter-mixed laminated shale,and long-time-rich laminated shale.The main types of storage space in Lianggaoshan Formation shale are residual intragranular pores,clay mineral inter-crystalline pores,and a small amount of organic pores,as well as development of nano-scale microcracks,the organic-rich clayey shale lithofacies having the most developed pores.The pore size distribution of shale is mainly dominated by medium-sized pores,with a small number of micropores and relatively underdeveloped macropores.The wettability of Lianggaoshan Formation shale is mainly hydrophilic and intermediate-wetted,with the organic-rich clayey shale lithofacies having strong hydrophobicity and lateral hydrophilicity greater than longitudinal hydrophilicity.The higher the content of oil-wet minerals in shale,the stronger the oil wettability;the higher the temperature,the stronger the oil wettability.The oil-bearing property and mobility of Lianggaoshan Formation shale are positively correlated with pore structure and wettability.Within the micro-pore range,the larger the pore volume and average pore size,the stronger the oil-bearing property;the larger the contact angle,the stronger the oil wettability and the stronger the oil-bearing property and mobility.The organic-rich clayey shale lithofacies have developed pores,mainly intermediate-wetted,with certain mobility and good exploration potential.