Shale Pore Evolution Characteristics Based on Semi-Closed Pyrolysis Experiment
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摘要: 富有机质页岩微观孔隙结构是影响页岩油气富集的重要因素,但热演化过程中的孔隙结构变化特征不甚清楚,是当前领域研究的难点.用新疆三塘湖盆地中二叠统芦草沟组低成熟油页岩样品开展高温高压半封闭体系热模拟实验,对各温度阶段的样品进行抽提,利用低温吸附技术定量表征未抽提和抽提样品的孔隙结构,揭示低熟到过成熟页岩样品的孔隙演化特征.结果表明:低熟-成熟阶段,中、大孔量随热模拟温度上升而降低,微孔量先降低再升高,高压及滞留油/沥青对所有孔隙均有一定的抑制作用;高-过成熟阶段,孔含量明显上升,残留沥青中会产生微孔及中、大孔.在热模拟实验中温度、压力条件对孔隙结构具有重要影响,有机质演化产物与孔隙演化趋势紧密相关.Abstract: The microscopic pore structure of organic-rich shale is an important factor affecting the enrichment of shale gas, but the characteristics of pore structure change during thermal evolution are not clear, which is difficult for the current research.Taking the low-mature oil shale samples of the Middle Permian Lucaogou Formation in the Santanghu Basin, Xinjiang as an example, a high-temperature and high-pressure semi-closed pyrolysis experiment was carried out, and the thermal simulation samples at various temperature stages were extracted, using low-temperature adsorption technique to characterize the pore structure of the un-extracted and extracted sample and to reveal the pore evolution characteristics of the low mature to over mature shale samples.The results show that in the low-mature to mature stage, the content of mesopores decreases with the increase of thermal simulation temperature, and the micropore content decreases first and then rises.High pressure and residual oil/bitumen have certain inhibitory effect for all pores.While at the high maturity stage, the pore content increases significantly, and the micropore and mesopore are generated in the residual bitumen.It indicates that temperature and pressure conditions have important influence on pore structure in thermal simulation experiments.The thermal evolution of organic matter and its evolution products are closely related to the evolution trend of shale pores.
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Key words:
- Santanghu Basin /
- Lucaogou Formation shale /
- pyrolysis experiment /
- pore evolution /
- bitumen /
- petroleum geology
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表 1 三塘湖芦草沟组页岩样品基础有机地球化学参数
Table 1. The basic geochemical data of the sample from the Santanghu Basin
样品 TOC(%) Ro(%) Tmax(℃) S1(mg/g) S2(mg/g) S3(mg/g) HI(mg/g TOC) OI(mg/g TOC) 页岩 10.67 0.52 436 0.57 53.08 4.84 497 45 表 2 热模拟实验页岩孔体积和比表面积
Table 2. Shale pore volume and specific surface area of thermal simulation experiment
温度(℃) 原始样品(P) 320 350 380 420 450 中、大孔孔体积(未抽提)(m3/g) 0.015 1 0.007 6 0.006 1 0.004 7 0.004 4 0.009 2 中、大孔比表面积(未抽提)(m2/g) 1.542 8 0.519 7 0.548 5 0.644 8 0.601 1 1.454 4 微孔孔体积(未抽提)(cm3/g) 2.475 5 1.323 3 1.026 0 2.373 9 2.469 5 3.876 7 微孔比表面积(未抽提)(m2/g) 11.31 6.04 4.69 10.84 11.28 17.71 中、大孔孔体积(抽提)(m3/g) 0.011 4 0.010 6 0.008 5 0.005 9 0.002 7 0.007 8 中、大孔比表面积(抽提)(m2/g) 1.191 6 0.907 1 0.711 6 1.076 7 0.498 1 1.154 0 微孔孔体积(抽提)(cm3/g) 2.389 2 2.909 2 1.571 5 2.944 9 1.853 8 3.442 5 微孔比表面积(抽提)(m2/g) 10.91 13.29 7.18 13.45 8.47 15.72 -
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