Study On Mechanism Of Enhanced Oil Recovery And Start The Residual Oil By Micro-nano Of Elastic Microsphere

Micro-nano of elastic microsphere is a new deep profile agent, which mechanism of enhancing oil recovery in the layer porous media has not been very clear. Research on the flow steering ability and EOR mechanism of elastic microsphere in the reservoir plays a significant role in promoting the application of the technique. Based on the analysis of pore structure of reservoir rock, the size and distribution of rock pore throat were calculated by applying the capillary pressure curve and parallel capillary bundles model and two-dimensional variable cross-section micro-bundle model, which provided a theoretical basis for the size design of flow steering microsphere. Besides, the formation mechanism of residual oil in the micro-capillary was analyzed and the largest capillary radius of the remaining oil at any point in the actual reservoir was calculated. Using the tensor analysis method, the mathematical model of supplementary pressure produced by microsphere when it passed through pore throat was established and the factors which influenced the additional pressure were analyzed. Moreover, how the additional pressure produced by microspheres generated fluid shift, started driving the remaining oil from the smaller capillary and enhanced oil recovery were studied.The result showed that the pore throat of reservoir rock had a nano-micron grade scale. That required matching nano-mcron microspheres which could migrate in rocks, block up pore throat to make water flow around, and pass through the pore throat by the elastic deformation and then block up the next pore throat. The root cause of remaining oil formation was the different capillary force in different capillary. The farther from the well in reservoirs, the smaller the pressure gradient, the larger in the capillary radius which could drive the crude oil, the larger the maximun capillary radius of storaging remaining oil and the greater the the residual oil saturation. When the elastic microspheres through a pore throat and generate additional pressure, including three stages are the contraction phase of the entrance, through the pore throat stage and breakthrough pore throat stage. In which the contraction phase of the entrance elastic microspheres generate the largest additional pressure that accounted for 60% of the total additional pressure. With the increase of pore throat ratio, shear rate, apparent viscosity, porosity factor, the additional pressure are increased. Elastic microsphere's diameter has an important effect on additional pressure, the larger the microsphere's diameter, the smaller the pore throat, the larger the additional pressure. Elastic microsphere in reservoir entry into the larger flow channel firstly and block the throat, produce additional pressure, displacement pressure and the additional pressure can make the fluid to change flow direction, start the remaining oil in smaller pipe that unable to start before.