富有机质Woodford页岩孔隙演化的热模拟实验

Porosity evolution of the organic-rich shale with thermal maturity increasing

通过高温热模拟实验加热未成熟的露头样品,获得5个不同成熟阶段的页岩样品,然后用比表面积分析仪测试这5个页岩样品的纳米孔隙,从而研究富有机质页岩的孔隙演化。结果表明,随着成熟度的增加,富有机质页岩发育大量纳米孔隙,孔隙度随着热成熟度增高而增加,完全不同于基质孔隙度的演化规律。随着成熟度增加,有机质不断转化为油气,基于有机质转化为油气过程中的物质平衡理论计算的孔隙度增加量与测试的孔隙度增加量吻合。因此,富有机质页岩孔隙度随着成熟度增高而增加,与有机质转化为油气的热降解过程有关。

To study porosity evolution of organic-rich shale, five immature shale samples collected from outcrops were analyzed by py- rolyzing them in a thermal simulation experiment. Organic-rich shale samples with different thermal maturities were obtained in the lab and their maturities referred to immature, early bitumen-formation, late bitumen-formation, late oil formation and oil-cracking stages, respectively. Nano-pores in these five shale samples were then measured on a specific surface area analyzer. A series of nitro gen adsorption isotherms were measured, which showed that nano pores increase with thermal maturity increasing and so does the porosity in the organic rich shale, which is obviously different from the porosity evolution in matrix. The porosity changes little at the oil window, but drastically increases in the gas window, which is consistent with calculated value based on the mass balance theo- ry. Therefore, it can be concluded that increase in porosity of the organic rich shale results dominantly from the organic matter con version of oil to gas.