基于裂缝性致密储层关键渗流参数的逆向渗吸速度计算

Characterization of Key Tight Oil Parameters and Mass Transfer of Counter-Current Imbibition in Fractured Tight Oil Reservoirs

在致密油藏水平井体积压裂开采过程中,压裂液通过缝网与基质接触并发生逆向渗吸作用,由于接触面积很大渗吸作用不可忽视;但目前关于表征致密储层的渗吸作用,从而研究渗吸对水平井体积压裂生产过程影响的研究尚未深入.为了解决以上问题,首先利用毛管束模型,通过考虑致密储层中边界层的特征,建立了解析的渗流参数计算表达式,用以计算致密储层的渗透率、毛管力、相渗曲线这3个关键渗流参数;同时,基于以上关键渗流参数和渗吸控制方程建立了适用于致密储层的渗吸速度计算模型;然后,将渗吸项作为源汇项加入到考虑缝网的双孔单渗模型中.最后,在真实水平井体积压裂开采过程中,耦合渗吸作用.研究表明,相比于不考虑边界层特征的致密油藏,边界层的存在将大幅度减弱储层的渗吸能力,同时也说明了在致密储层中,边界层的存在是不可忽视的,如果在渗吸计算中忽视致密储层的边界层特征会严重高估渗吸对致密储层产能的影响.

During the process of tight oil exploration,counter current imbibition effect is significantly different due to the presence of complex fracture network and flow characteristics in tight oil reservoirs.But at present,there is no proper model to simulate counter-current imbibition in fractured reservoir considering the characteristics of tight oil formation.In order to solve this problem,PEBI grids are used to match the complex fracture network,natural fractures and matrix are idealized as dualporosity medium,rate of mass transfer of imbibition between matrix and fractures is treated as source or sink term in dual porosity model.A new semi analytical model for the calculation of mass transfer function of counter-current imbibition in the presence of complex fracture network is established by using radial integration boundary element method（RIBEM）.In addition,to reflect the flow characteristics of tight oil,relative permeability and capillary pressure curve with the effect of boundary layer considered,and mixed wettability have also used in the mass transfer model.Besides,we show the capacity and practical application of the model with a field example from tight oil reservoir.From simulated results,it is concluded that counter-current imbibition plays an important role in improving the oil recovery and the existence of boundary layer reduces the contribution of imbibition to oil production dramatically.