低成熟度富有机质页岩微观孔隙结构特征表征——以广东茂名盆地油柑窝组为例

Characterization of micro-pore structure of low-maturity organic-rich shale:a case study of Youganwo Formation in Maoming Basin,Guangdong

以广东茂名盆地油柑窝组富有机质页岩为例,采用氩离子抛光—场发射扫描电镜(AIP FESEM)图像处理技术(Image Processing)、MATLAB软件,对微观孔隙进行定量统计,预测页岩微观孔隙发育特征。结果表明:研究区样品大量发育微纳米孔,包括有机质孔、粒间孔、粒内孔及微裂隙。页岩孔隙度低,约为1.56%。孔隙中,粒间孔最发育,孔隙率占比为94.82%,孔径为0.01~2.40μm;其次为有机质孔,孔隙率占比为4.22%,孔径为0.01~10.00μm,其中60%的孔隙孔径在50 nm以下;粒内孔最不发育,孔隙率占比小于1.00%。受沉积环境及储层成岩作用的影响,油柑窝组有机质及有机孔隙演化程度低,有机质成熟度介于0.40%~0.55%,与龙马溪组页岩储层相比,发育最广泛的纳米孔类型为矿物孔隙而非有机质孔,有机质质量分数与热演化程度是塑造优质页岩储层孔隙系统的关键因素。该结果可为低成熟度富有机质页岩储层孔隙结构演化提供依据。

The investigation of pore structure in immature-low matured organic-rich shale may provide some insights into the forming of pore network.By using FE-SEM in combination with argon ion beam cross sectioning and image processing,pore structure characteristics of immature-low matured organic-rich shale in Youganwo Formation,Maoming Basin were investigated.The results indicate that numerous nano-micro pores were identified,including organic matter pores,interparticle pores,intraparticle pores and micro-fractures.Based on the quantitative statistics of micro structure,the shale samples present a low porosity of 1.56%.Interparticle pores,as the most developed pore type,occupy the highest proportion of 94.82%of total visible porosity and pore sizes range between 0.01~2.40μm.Organic matter pores present a proportion of 4.22%with pore sizes ranging between 0.01~10.00μm.About 60%organic matter pores developed with diameters of less than 50 nm.Intraparticle pores are undeveloped with a proportion of less than 1.00%.Controlled by the sedimentary environment and diagenesis,organic matter in the Youganwo Formation shale shows a low degree of evolution with R o values of 0.40%~0.55%,and the most developed pore types are mineral related pores other than organic matter pores,compared with the Longmaxi Formation shales.The content of organic matter and the degree of thermal evolution are the key factors to shape the pore system of high quality shale reservoir,which can be used as important basis for the study of pore structure evolution of low-maturity organic-rich shale reservoirs.