过成熟页岩在半封闭热模拟实验中孔隙结构的演化特征

Evolutionary Characteristics of Pore Structure for Over-Matured Shales in Semi-Closed Thermal Simulation Experiment

为研究过熟页岩孔隙结构的演化规律及控制因素,选用上扬子寒武系牛蹄塘组和志留系龙马溪组2套过熟页岩开展热模拟实验,结合X-衍射、氮气和二氧化碳吸附以及扫描电镜研究其孔隙结构的演化特征.龙马溪组样品孔体积在500℃时得到最大提高,为原样的1.35倍;牛蹄塘组样品孔体积在450℃时上升为最高,较原样提高到1.13倍.利用吸附数据计算出牛蹄塘组样品微孔体积是龙马溪组样品的1.72倍,龙马溪组中孔体积是牛蹄塘组样品的1.44倍.结果表明:(1)牛蹄塘组页岩有机质生烃潜力弱且原始微孔体积高,生烃量少又不易排出,孔隙结构改善较差;(2)龙马溪组页岩石英含量较高抗压能力较强,利于中-大孔隙的发育与保存,也有利于烃类生成后排出,孔体积得到较大提高.

In order to study the evolution law of pore structure of over-matured shale,two groups of over-matured shales,which were collected from Cambrian Niutitang Formation and Silurian Longmaxi Formation in the Upper Yangtze region,were selected to carry out semi-closed thermal simulation experiments.Meanwhile,X-ray diffraction analysis,CO2 and N2 isotherm adsorption as well as FE-SEM observations were used to determine mineralogical compositions and study the nanopore evolution characteristics.The pore volume of Longmaxi samples increases to the maximum at 500℃,and the pore volume is 1.35 times higher than that of the original sample.The pore volume of shale samples in Niutitang Formation rises to the maximum at 450℃,which is 1.13 times higher than the original sample.Combined with N2 and CO2 adsorption data,the micro-meso-macro pore volume of the samples in the two groups was calculated.The micropore volume of the samples in the Niutitang Formation is 1.72 times higher than that in the Longmaxi Formation,and the mesopore volume of the samples in the Longmaxi Formation is 1.44 times higher than that in the Niutitang Formation.These results show that follows(1)The shale of Niutitang Formation has weak hydrocarbon generation potential and high original micropore volume,with little hydrocarbon generation and difficulty in discharging,resulting in relatively poor pore structure improvement.(2)Longmaxi Formation has high quartz content and strong compressive resistance,which is conducive to the development and preservation of meso-macropores,as well as hydrocarbon generation and subsequent extraction,so the pore volume is greatly improved.