桂中坳陷环江地区高-过成熟富有机质页岩储集性能研究及其对含气性的影响

Study on reservoir performance of high-over-mature organic-rich shale in Huanjiang area of Central Guangxi Depression and its influence on gas bearing property

桂中坳陷上古生界普遍发育富有机质泥页岩,相对于美国成功勘探的盆地而言,桂中环江地区富有机质页岩成熟度较高,缺乏储集性能及其含气性研究。利用沥青反射率代替镜质体反射率研究页岩的成熟度分布范围,通过压汞法分析孔径大小,进一步讨论孔隙度大小特征、比表面积、总孔容大小与页岩热演化的关系。数据表明:富有机质页岩以微孔—介孔为主,高—过成熟页岩仍具有一定的孔隙,当Ro,eq<3.0%,随着页岩成熟度增加,其比表面积和孔容略减小;当Ro,eq>3.5%时,随着页岩成熟度增加,其比表面积和孔容增大,从而增大了页岩的吸附能力,且同时微裂缝增多,增加了页岩气储集空间。因此,环江地区高—过成熟富有机质页岩仍有较好的储集性能,在生烃条件及保存条件等较好的情况下,其含气性仍具有较大潜力。

Organic-rich shale is generally developed in the Upper Paleozoic in Central Guangxi Depression.Compared with the successfully explored basins in the United States,the organic-rich shale in the Huanjiang area of Central Guangxi has a higher maturity and there is no research on its reservoir performance and gas bearing property.Asphalt reflectance instead of vitrinite reflectivity is used to study the maturity distribution range of shale.The pore size is analyzed by mercury intrusion porosimetry.The relationship between the characteristics of porosity,specific surface area,total pore volume and thermal evolution of shale is further discussed.The data shows that organic-rich shale is dominated by micropores and mesopores,and high-over-mature shale still has certain pores.When Ro,eq is less than 3.0%,as the shale maturity increases,its specific surface area and pore volume decreases slightly.When Ro,eq is greater than 3.5%,as the shale maturity increases,its specific surface area and pore volume increases,so the adsorption capacity of the shale increases.At the same time the micro-cracks increases,which increases the shale gas storage space.Therefore,the high-over-mature organic-rich shale in Huanjiang area still has a good storage performance,and there is a great potential for its gas-bearing property under the good hydrocarbon generation and preservation condition.