基于传导、对流不同加热模式的油页岩孔隙结构变化的对比研究

Comparisons of pore structures of oil shale upon conduction and convection heating

原位热解开采是未来油页岩开发的主流趋势,其原位加热方式主要分为传导和对流2种加热模式。在油页岩原位热解开采过程中,孔隙是油气渗流的主要通道,孔隙结构的连通特征直接影响和控制着热解油气的产出过程。为此,利用马弗炉和蒸汽锅炉对φ8 mm×25 mm的圆柱体油页岩试件分别实施传导和对流加热,最高加热温度均为550℃,并基于显微CT和3D数字岩芯重建技术对加热前后油页岩孔隙的大小、分布以及变化规律进行综合研究,分析不同加热模式对于油页岩的孔隙结构影响的差异及机制。研究表明:油页岩经传导加热后孔隙率为原始孔隙率的2.90倍,而经蒸汽对流加热后孔隙率为原始孔隙率的3.51倍。可见,与传导加热相比,对流加热使油页岩受热均匀,换热面积更大,使油页岩中固体有机质热解更充分,促使油页岩中的孔隙快速向四周拓展连通成大规模的孔隙连通团。另一方面,蒸汽对流加热能迅速携带走附着在孔隙壁上和滞留在"死端"孔隙中的残留页岩油,提高了孔隙间连通性,有效增大了孔隙直径,形成比传导加热连通性更好的孔隙结构,同时蒸汽携带油气一起产出,提高了油气的回收率。因此,对流加热为油页岩原位热解开采的首选加热模式,研究结果为实现大规模油页岩原位注蒸汽开发提供了有利技术支撑。

In-situ pyrolysis is the mainstream trend of oil shale exploitation in the future. The in-situ heating methods are mainly divided into conduction and convection heating modes. In the process of in-situ pyrolysis of oil shale,the pores are the main channel for oil and gas seepage. The connection characteristics of the pore structure affect and control directly the production process of pyrolytic oil and gas. Therefore,in this paper,the cylindrical oil shale samples of φ 8 mm×25 mm are heated through conduction and convection with muffle furnace and steam boiler respectively. The maximum heating temperature is 550 ℃. With the micro-CT and 3 D digital core reconstruction technology,the size,distribution and evolution of pores of oil shale before and after heating were studied comprehensively,and the differences of different heating modes on pore structure of oil shale were analyzed. The results show that the porosity is 2.90 times of the original porosity after the conduction heating. However,after the steam convection heating,the porosity is 3.51 times of the original porosity. The convection heating heats the oil shale evenly and the area of heat exchange is larger,so that the pyrolysis of the solid organic matter in the oil shale is more thoroughly,prompting the pores in the oil shale to expand rapidly and to connect into the large-scale connected pore groups. In addition,the convection heating steam quickly carries away the shale oil that adheres to the pore wall and remains in the dead-end of pores,which improves the connectivity between the pores and increases the pore diameter effectively and forms a better connected pore structure than in the conduction heating. The steam carries away oil and gas together simultaneously,which increases the recovery ratio of oil and gas. Therefore,convection heating is the preferred heating mode for in-situ pyrolysis of oil shale.