基于岩心流动试验的德州市馆陶组松散砂岩渗透性分析

Analysis on Permeability of Loose Sandstone in Guantao Formation in Dezhou City Based on Core Flow Tests

摘要:

为揭示地热回灌过程中馆陶组松散砂岩渗透性演化机制，以山东德州馆陶组未固结砂岩（φ25 mm×50 mm）为研究对象，采用岩心流动仪开展多因素控制试验，系统分析温度（20~100 ℃）、围压（5~20 MPa）及注入速率（1.0~2.5 mL/min）对渗透率的影响规律。结果表明：温度升高会导致岩石渗透率整体下降，这与岩石颗粒热膨胀效应密切相关，且温度越高砾石排出量越大。德州馆陶组未固结砂岩埋深1 311~1 312 m，内部孔隙闭合的临界压力约为15 MPa，此时孔隙结构发生临界闭合，渗透率骤降48.9%。低注入速率下松散砂岩渗透率变化微弱可忽略，但注入速率提升会显著增加流体携砾量，影响岩体整体渗透率。推测高注入速率为诱发回灌井近井地带堵塞的主导因素，推荐采用“先低后稳、阶梯提升”的注入方法。

Abstract:

In order to reveal the permeability evolution mechanism of loose sandstone during geothermal reinjection, taking the unconsolidated sandstone of Guantao dormation in Dezhou city in Shandong province as the research object (φ25mm×50mm) , by using core flow meter, multifactor control test has been carried out. The influence of temperature (20~100℃), confining pressure (5~20MPa) and injection rate (1.0~2.5mL/min) on permeability has been analyzed systematically. It is showed that the increase of temperature will lead to the overall decrease of rock permeability, which is closely related to the thermal expansion effect of rock particles. The higher the temperature, the greater the gravel discharge. The critical pressure of pore closure in unconsolidated sandstone (buried depth is 1311~1312m ) of Guantao formation in Dezhou city is about 15MPa. At this point, the pore structure undergoes critical closure, and the permeability will drop by 48.9%. The change in permeability of loose sandstone under low injection rate is weak and negligible, but the increase of injection rate will significantly increase the amount of fluid carrying gravel and affect the overall permeability of rock mass. It is speculated that high injection rate is the dominant factor inducing blockage in the near wellbore area of the reinjection well. It is suggested that the injection strategy of "first low and then stable, step lifting" should be carried out in the recharge design.