修武盆地下寒武统荷塘组海相页岩孔隙特征

通过孔隙度实验、低温N₂吸附法和CO₂吸附法,对修武盆地RDZ01井下寒武统荷塘组页岩孔隙发育特征进行定量表征,结合总有机碳含量、矿物组成及有机质的热演化程度,讨论孔隙发育特征主控因素。结果表明：孔隙形态以楔形孔为主,并发育墨水瓶形孔及狭缝形孔。页岩孔隙度为1.24%~2.91%,具低孔隙度特征;微孔、中孔和大孔3类孔隙分别占总孔体积的35.45%、44.54%和20.01%。页岩总孔体积为5.33×10^-3 ~20.10×10^-3 cm³/g,其中低温N₂吸附法和CO₂吸附法平均孔体积分别为7.40×10^-3 cm³/g和2.24×10^-3 cm³/g;总比表面积为7.62~17.84 m²/g,其中低温N₂吸附法和CO₂吸附法平均比表面积分别为5.23 m²/g和7.41 m²/g。孔径分布的主峰值小于10.00 nm,微孔的结构复杂,0.30~0.70 nm的孔隙较为发育,大的比表面积为页岩气提供更多的吸附位。总有机碳含量是微孔发育的主控因素,同时促进中孔发育,对大孔的影响较弱;黏土矿物增多会降低页岩的孔隙度;高石英含量为总孔体积和总比表面积增大的有利因素。修武盆地下寒武统荷塘组海相页岩和鄂西地区下侏罗统自流井组页岩储集层特征相似,呈现良好的储集能力。

Pore Characteristics of Marine Shale in Lower Cambrian Hetang Formation in Xiuwu Basin

Based on porosity and low temperature N₂ and CO₂ adsorption experiments, the pore characteristics of the shale in the Lower Cambrian Hetang formation were quantitatively characterized. And combined with TOC, whole rock X-ray diffraction and previous research on the thermal evolution of organic matter, the controlling factors on the pore characteristics were discussed and analyzed. The results show that most pores are wedge-shaped, and less are like bottle-neck and slits. The porosity of the shale ranges from 1.24% to 2.91%, of which mesopores, micropore and macropore account for 44.53%, 35.45% and 20.01%, respectively. The total pore volume of the shale ranges from 5.33× 10^-3 cm³/g to 20.10×10^-3 cm³/g, of which the average pore volumes of BJH and DFT are 7.40×10^-3 cm³/g and 2.24×10^-3 cm³/g, respectively. The total specific surface area is 7.62 to 17.84 m²/g, of which the average specific surface areas of low-temperature N₂ adsorption and CO₂ adsorption are 5.23 m²/g and 7.41 m²/g, respectively. The peak pore size is less than 10.00 nm, and the micropore structures are complex. The pores of 0.30-0.70 nm are relatively developed, but the larger specific surface area provides more room adsorbing shale gas. TOC is the controlling factor on micropore development, and it is helpful to the development of mesopores, but influences less on macropores. Clay minerals reduce the shale porosity, while quartz is a favorable factor on the total pore volume and total specific surface area. With the similar characteristics to the Lower Jurassic Ziliujing formation shale in the western Hubei province, the marine shale of the Lower Cambrian Hetang formation in Xiuwu basin has a good reservoir capability.