四川盆地海相富有机质页岩孔隙特征及赋存状态特征

Pore Characteristics and Occurrence Characteristics of Marine Organic-rich Shale in Sichuan Basin

为深入研究四川盆地龙马溪组页岩气赋存特征,通过物理实验与数学模型相结合的研究方法,开展低温液氮吸附实验和扫描电子显微镜实验,基于分子动力学研究了龙马溪组页岩的孔隙特征和甲烷生成特征。结果表明:根据低温液氮吸附的Brunner-Emmet-Teller(BET)模型,龙马溪组页岩的比表面积为4.32~29.50 m^2/g,平均比表面积为13.78 m^2/g。Barret-Joyner-Halenda(BJH)模型计算得出的页岩总孔隙体积为6.12~30.47 cm 3/g,平均孔径分布为3.83~4.52 nm,平均孔径为4.06 nm。龙马溪组孔类型主要包括有机质孔、微裂纹、粒内孔和粒间孔。龙马溪组埋藏深度界线为1370 m,表明随着埋藏深度的增大,龙马溪组游离气含量迅速高于吸附气,埋深越大,游离气含量越高。龙马溪组页岩储层中甲烷的吸附特性表明,随着孔径的变化,甲烷的吸附势能由正向负变化,并逐渐趋近于零。零点表示没有甲烷分子吸附在孔壁上,赋存状态从吸附态变为游离态为主。

In order to further study the occurrence characteristics of shale gas in Longmaxi Formation in Sichuan Basin,a low-temperature liquid nitrogen adsorption experiment and a scanning electron microscope experiment were carried out through a combination of physical experiments and mathematical models.The Longmaxi Formation shale was studied based on molecular dynamics Characteristics of porosity and methane generation.The following results are got from the research.According to the Brunner-Emmet-Teller(BET)model of low-temperature liquid nitrogen adsorption,the specific surface area of Longmaxi Formation shale is 4.32~29.50 m^2/g,with an average of 13.78 m^2/g.Barret-Joyner-Halenda(BJH)model calculated total shale pore volume is 6.12~34.47 cm 3/g,the average pore size distribution range is 3.83~4.52 nm,and the average pore size is 4.06 nm.The pore types of Longmaxi Formation mainly include organic pores,microcracks,intragranular pores and intergranular pores.The burial depth boundary of Longmaxi Formation is 1370 m,which indicates that with the increase of the burial depth,the free gas content of Longmaxi Formation is rapidly higher than that of the adsorbed gas.The adsorption characteristics of methane in Longmaxi Formation shale reservoir show that with the change of the pore size,the trend of methane adsorption potential energy changes from positive to negative,and gradually approaches zero.The zero point indicates that no methane molecule is adsorbed on the pore wall,and the occurrence state mainly changes from the adsorbed state to the free state.