致密岩心带压渗吸实验及多尺度模拟研究

Simulation Study on Forced Imbibition of Tight Rock Samples and Multi-Scale Modeling

摘要: 致密储层孔喉半径小，毛细管压力高，渗吸动力强，压裂后若不立即放喷，可依靠压后焖井过程中的压差驱替和自发渗吸提高原油采出程度。为探索该过程机理，进行了带压渗吸实验和多尺度模拟研究：首先，将岩心单面开启，进行带压渗吸实验，模拟压裂完成后裂缝壁面在停泵压力下的渗吸行为。其次，建立基于CT扫描的孔喉尺度模型，分别获得驱替和渗吸的相对渗透率曲线和毛细管压力曲线。最后，以相渗曲线和毛管压力曲线为纽带建立矿场尺度模型，进行油藏尺度模拟。结果表明：①岩心带压渗吸条件下的采收率比自发渗吸提高约10%~15%；②通过调整孔喉尺度模型的微观孔隙参数进行渗吸采收率的拟合，可分别计算得到驱替和渗吸的相对渗透率及毛细管压力曲线；③油藏尺度下对基质赋予渗吸属性、对裂缝赋予驱替属性，可对开采初期的产量变化有较好描述。

Abstract: Because of small pore throat radius and high capillary pressure and strong imbibition force in tight reservoirs, if open flow was not implemented immediately after fracturing, in the soaking time after hydraulic fracturing, oil recovery was enhanced by displacement of differential pres-sure and imbibition displacement. To investigate the mechanism of this process, experiments with forced imbibition and multi-scale modeling were performed. Firstly, a one end open core sample was used to perform the experiment of imbibition under forced pressure for simulating the imbibition on the surface of fractures under pressure difference after fracturing. Secondly, a pore- throat scale model based on CT scanning was established to obtain respectively the relative permeability curves and capillary pressure curves of imbibition and displacement. Eventually a field scale numerical model was established to simulate the water and oil flow based on the relative permeability and capillary pressure with matrix and difference of fractures. The results show that ① oil recovery of forced imbibition is about 10% - 15% more than that of spontaneous imbibition, ② adjusting the micro pore parameters in pore-throat scale model for oil recovery matching, the curves of relative permeability and capillary pressure of displacement and imbibition are obtained, ③ by simulation under reservoir scale, the attributes of matrix with imbibition and fractures for displacement are determined , it can be used for well description of yield changes at the initial stage of production.