深入分析不同沉积背景页岩储层物质基础、探究不同层系页岩储层发育主控因素是预测页岩气藏地质甜点的核心工作.中国南方海相页岩气已实现大规模商业开发,而海-陆过渡相和陆相页岩气勘探鲜有突破.选取川西南海相页岩、湘中海-陆过渡相页岩和川东北陆相页岩为研究对象,在沉积背景、地化特征、岩石学特征以及孔隙结构特征研究的基础上,通过对比多层系页岩储层特征,明确了不同层系页岩储集能力主控因素.研究表明:海相页岩发育Ⅰ型有机质具迁移和产孔能力,以有机质孔隙为主,优势岩相为富有机质硅质页岩,具有高孔体积(平均值0.026 cm3/g)和高比表面积(平均值28.99 m2/g)特征,有机质丰度是储集能力好坏的决定性因素;海-陆过渡相发育Ⅲ型有机质呈惰性,以粘土矿物孔隙为主,优势岩相为富含有机质泥质页岩,具有高孔体积(平均值0.023 cm3/g)和低比表面积(平均值6.33 m2/g)特征,合理的矿物组构匹配(硅泥比2/3)是储集能力好坏的决定性因素;陆相有机质显微组分混杂,以粘土矿物孔隙和有机质孔隙为主,优势岩相为富有机质泥质页岩和富有机质混合质页岩,孔体积(平均值0.017 cm3/g)和比表面积(平均值11.90 m2/g)适中,高腐泥质含量(大于60％)和合理的矿物组构匹配是储集能力优越的有利条件.不同沉积背景页岩物质基础在差异成岩改造作用下呈现出迥异的储集性能,勘探目标应依据特定页岩层系差别对待.

中国南方下古生界海相页岩经历了复杂的构造演化和热演化,页岩气含气量差异较大,成熟度对页岩气储层孔隙发育的控制作用是亟待解决的重要问题.选取不同成熟度的下古生界海相页岩作为研究对象,采用X射线矿物组分分析、扫描电镜、气体吸附、高压压汞和透射电镜实验,研究有机质演化程度对页岩储层孔隙结构的控制作用.结果表明,Ro小于3.0％的高演化页岩储层储集能力优于Ro大于3.0％的页岩储层,中孔孔体积、微孔比表面积的发育均明显更优;过演化有机质(Ro>3.0％)的孔隙受有机质石墨化影响,孔隙出现缩合、减小的趋势,对页岩储集空间起到破坏作用;Ro>3.5％的高过热演化页岩在经历压实作用、有机质石墨化和黏土矿物转化后储集能力下降严重,不利于页岩气藏的形成.

Matrix-related pore characteristics of between Lower Carboniferous shale and Middle Devonian shale in Guizhong Basin were investigated to explore the reservoir capacity. Via the combination of organic geochemistry analysis, X-ray diffraction, gas adsorption, mercury intrusion porosimetry, helium porosimetry and focused ion beam-scanning electron microscopy, material basics and physical properties were studied. Five lithofacies were divided as comparable units in two formations according to thermal maturity, OM abundance and mineral components, namely organic-moderate argillaceous shale with high thermal maturity (OMAS-H) and organiclean argillaceous shale with high thermal maturity (OLAS-H) in Lower Carboniferous Formation, and organiclean mixed shale with over thermal maturity (OLMS-O), organic-rich mixed shale with over thermal maturity (ORMS-O) as well as organic-rich calcareous shale with over thermal maturity (ORCS-O) in Middle Devonian Formation. Results showed that (1) OMAS-H and OLAS-H performed better porous features than OLMS-O, ORMS-O and ORCS-O, in terms of PV, PSA and porosity, (2) pores developed better in OMAS-H and OLAS-H than those in OLMS-O, ORMS-O and ORCS-O, in terms of pores of rigid grains, pores associated with clay flakes and OM-hosted pores, (3) specific PVs of OM were dramatically larger than those of mineral components, while specific PVs of OM in both OMAS-H (0.348 ml/g x 10(-6)) and OLAS-H (0.248 ml/g x 10(-6)) were about an order of magnitude higher than those in OLMS-O (0.055 ml/g x 10(-6)), ORMS-O (0.025 ml/g x 10(-6)) and ORCS-O (0.011 ml/g x 10(-6)). The ability of pore contribution largely depends on whether corresponding components are suited in the appropriate evolution stage with suitable thermal and pressure circumstance. Then sufficient degree of pore carriers (matrixes) need to be thought about, especially OM and clay as the secondary pore providers. Also, the demand for pore preservation highlights the importance of brittle minerals which can establish rigid frameworks. Therefore, in the case of controlling factors on pore characteristics, the importance ranking should be taken into consideration.

In this study, matrix-related pores from differing depositional shales were explored comparatively. Among of them, Lower Cambrian shale (3.83%Ro) and Lower Silurian shale (2.61%Ro) were marine sediments with abundant oil-prone kerogen and rich siliceous minerals, while Upper Permian shale (2.44%Ro) were transitional sediments with redundant gas-prone kerogen and rich clay. The morphology and geometry of pores were investigated via fractal analyses based on N-2 adsorption and direct imaging. The effects of organic matter (OM) within different shales were also highlighted through N-2 adsorption before and after OM isolation. Lower Cambrian shale possessed the lowest pore volumes (PV) (averaging 0.0109 ml/g) and the lowest pore surface areas (PSA) (averaging 9.09 m(2)/g) as well as the smallest average pore diameters (APD) (averaging 5.47 nm). Dissolved pore with dead-end openings was the main type. The PV and PSA of isolated OM were only approximately 1 and 2 times higher than that of corresponding samples, respectively. In contrast, Lower Silurian shale possessed the highest PV (averaging 0.0109 ml/g) and the highest PSA (averaging 9.09 m(2)/g) as well as relatively large APD (averaging 13.43 nm). Organic-hosted pores (OMP) with cellular structure is the main type. The PV and PSA of isolated OM were approximately 8.5 and 3 times higher than that of corresponding samples, respectively. Upper Permian shale with the largest averaging pore diameters (averaging 18.82 nm) presented high PV (averaging 0.0209 ml/g) similar to that of Lower Silurian shale, and a low PSA (averaging 10.85 m(2)/g) like that of Lower Cambrian shale. Pore associated with clay flakes was the main type. The PV and PSA of isolated OM were only approximately 0.6 times and 1 times higher than that of corresponding samples, respectively. For marine shale, matrix-related pore features are synergy effects of the matrix basis where pre-existing space controls the occurrence of porous OM and functions as the shelter for OMP with an appropriate thermal maturity. However, extensive diagenesis can overprint the effects of matrixes on pore properties, because oil-prone kerogen is sensitive to thermal maturity. The specific material composition of transitional shale limit pore properties, because dominant structured OM is thermally stable with limited migration ability and pore contribution. Hence, diagenetic differences and material diversities may be attributed to the discrepancies of pore properties between marine shale and transitional shale.