Study on application of wetting modifier in micro-nano pore micromodel of shale reservoir

According to the low porosity, ultra-low permeability and neutral partial oil wetting of shale reservoir, the corresponding microscopic model of capillary bundle is designed. The wettability of microscopic model changed by the compound system of molecular film agent (DM) and surfactant octadecyl trimethyl ammonium chloride (STAC) was studied. It is found that DM(1000mg/L)/STAC (concentration≤critical micelle concentration), the wetting modified contact angle is positively correlated with the STAC concentration, the maximum contact angle can reach 100.51°, and it is a monolayer adsorption with an average adsorption thickness of 2.064nm; Dm(1000mg/L)/STAC (concentration＞critical micelle concentration), the wetting modified contact angle is negatively correlated with the STAC concentration, and the adsorption layer is multilayer adsorption. Taking shale oil reservoir of Permian Lucaogou Formation in Jimusar sag as a feature, a capillary bundle model equivalent to pore throat diameter was etched, with radius of 5μm and depth of flow channel of 5μm. Then, through DM/STAC wetting modification, based on hydrophilic wetting and wetting modified capillary tube bundle model, the differential pressure-flow method was used to test the fluid percolation law. As a result, when the fluid flows at low speed, it is characterized by non-Darcy percolation and has a threshold pressure gradient. Moreover, the change of wettability causes the capillary force to turn, affecting the law of fluid percolation.