近临界水在油页岩层的渗流行为研究

The in-situ technology has been the trend of exploitation for oil shale. A concept is put forward to in-situ conversion of oil shale that using sub-critical water as a heat transfer medium and extractant since it could crack and extract the kerogen matter in oil shale at a lower temperature (350 °C). The extraction rate of organics from the shale largely depends on the permeation of sub-critical water in oil shale. In order to study the permeability variation of oil shale under sub-critical water environment with high temperature and pressure, in this project, a high temperature seepage equipment would be designed and assembled for oil shale sample with sub-critical water as the flow medium, through the transformation of permeameter and combination with a digestion analog device of oil shale. This equipment is used to simulate the seepage characteristics of sub-critical water in oil shale underground in order to study the effects of the original rock stress, the temperature and pressure of sub-critical water on the permeability of oil shale. and establish the seepage model. On the basis of investigation of the seepage flow law of sub-critical water, a seepage model would be established by finite element analysis software so as to provide some theoretical and experimental supports for the implementation of the in-situ extraction technology of oil shale by sub-critical water.

油页岩的原位开采技术是油页岩资源开发的热点，近临界水作为一种新兴的绿色溶剂可以在较低温度下（350℃）裂解与提取油页岩内部的干酪根有机质。近临界水在油页岩中的渗流效果很大程度的影响了其对油页岩内部有机质的提取速率。为研究油页岩在高温高压近临界水环境下渗透率的变化情况，本项目通过对渗透仪进行改造设计，与油页岩浸提模拟装置相结合，装配以近临界水为流动介质的油页岩高温渗透流动装置。利用该装置模拟近临界水在地下油页岩层进行渗透提取时的渗流状态，考察原岩应力、近临界水的温度与压强等参数对油页岩渗透率的影响，建立数学模型。研究近临界水在油页岩层中渗流提取的一般规律，通过有限元分析软件，建立油页岩的近临界水法原位提取实验渗透模型。为实施近临界水法油页岩原位开采技术提供一定的理论与实验的支撑。

为考察近临界水在油页岩原位渗流提取效果，本项目研制装配了一套油页岩高温高压三轴渗透率测量系统，其岩心夹持器部件使用特制的薄铜箔和石墨垫作为密封套件，使该设备能够对岩心样品开展最高350℃、50MPa条件下的近临界水渗透提取试验。但项目研究发现，由于油页岩的致密性和较高的粘土矿物含量，在模拟地层压力条件下，改温度压力条件下的近临界水在油页岩中仍无法渗透。.结合近临界水法油页岩原位开采技术中的压裂工艺，将项目方案修正为研究近临界水在油页岩层裂隙中渗流并对油页岩层内干酪根有机质进行逐渐渗流提取的过程。.项目采用对油页岩岩心样品进行人工造缝后在渗透率测试装置中开展近临界水在油页岩层的渗流模拟实验。实验结果表明，水能够很好的在裂隙内渗流，且渗透性不受地层压力的大小影响。油页岩岩心的束缚提取实验表明，近临界水温度越高提取速率越快，油页岩内部孔隙增大也越明显。油页岩在310℃的近临界水中内部干酪根有机质开始有效地分解与释放，在350℃近临界水中提取150h可获得最大提取率，油页岩孔隙度也从8.2%增大到66.0%。.最后项目以课题组在吉林省农安建设的油页岩原位开采先导试验工程为参考开展了近临界水法油页岩原位开采数值模拟，综合模型在温度场和渗透率场的模拟结果可以看出，通过工作井与生产井的间歇式交换，油页岩层能够更快的加热到理想温度，渗透率同时也得到提高。当注水时间达到80天，油页岩层内的干酪根有机质可以基本完全分解，但由于渗透率改善效果较温度变化小，需要将中间部位的有机质也都提取出来则需要在适当的延长渗流提取时间。