Evaluation of the Lower Producing Limit of the Pore Radius for Imbibition and Displacement Based on Shale Oil Reservoir Characteristics

Imbibition after fracturing is an important way of enhancingoilrecovery in shale oil reservoirs. It includes three steps: fracturing,huff and puff imbibition, and water flooding. The shale oil reservoirof the Lucaogou Formation in Jimsar Sag was taken as the researchobject to understand further the mobility of shale oil by imbibitionand displacement. First, the porosity, permeability, and wettabilityof the reservoir were analyzed via experimental methods such as nitrogenpermeability porosimetry, automatic mercury porosimetry, microscopicscanning electron microscopy (SEM), and nuclear magnetic resonancetechnology. The effects of imbibition and displacement processes onvarious pore sizes were comparatively studied based on the self-absorptionmethod combined with core nuclear magnetic resonance (NMR) to testthe wettability. The experimental results show that the reservoirhas well-developed micro nano pores and poor pore connectivity. Moreover,the wettability is neutral to oil wetting, and the average pore throatradius distribution is between 0.01 and 0.39 & mu;m. Small (r ( t ) < 0.09 & mu;m), medium(0.09 & mu;m < r ( t ) < 0.85 & mu;m), and large (r ( t ) >0.85 & mu;m) pores account for 42.56%, 28.64%, and 28.8%,respectively. Through pore size conversion, we can know that the lowerlimits of the fluid utilization radius for the infiltration and displacementprocesses are 10 and 40 nm, respectively. Therefore, reservoirs withpore distribution between 10 and 40 nm can be exploited through imbibition,while reservoirs above 40 nm are suitable for both imbibition andconventional displacement oil recovery.