Study On Mechanism And Mathematical Model Of Fracturing And Percolation Enhanced Oil Recovery In Medium And Low Permeability Reservoirs

In the old area of Daqing Oilfield,the water flooding development of the class III oil reservoirs with low and medium permeability is poor in injection ability,low recovery and unsatisfactory development effect.Therefore,field test research on fracturing and percolation enhanced oil recovery technology has been carried out for the class III oil reservoirs with low and medium permeability in Xingbei Development Zone of Daqing Oilfield,and good development results have been achieved.In order to further improve the effect of enhanced oil recovery by fracturing and percolation in medium and low permeability reservoirs,this study conducts a multidisciplinary and cross-disciplinary systematic study on the key scientific and technical problems in enhanced oil recovery by fracturing and percolation in medium and low permeability reservoirs in Xingbei Development Zone,Daqing Oilfield.This research has accomplished the following four aspects of work around this new technology:(1)According to the reservoir fluid characteristics of Xingbei Development Zone in Daqing Oilfield,the performance evaluation experiment of oil displacement agent was carried out,and the oil displacement agent with low interfacial tension,wettability reversal,good emulsifying performance and strong anti-adsorption performance was selected.The mechanism of enhanced oil recovery by fracturing and percolation was studied and the contribution of elastic energy,imbibition displacement and displacement pressure difference to enhanced oil recovery was quantified in the process of enhanced oil recovery by fracturing and percolation in class III oil reservoirs with medium and low permeability.At the same time,class III oil reservoir core parameters are measured by triaxial stress tester in Xingbei development area of Daqing oilfield,which provides a scientific basis for calculating fracture propagation law of enhanced oil recovery by fracturing and percolation.(2)Considering the physical and chemical mechanisms such as phase change,interfacial tension,adsorption and retention,diffusion/dispersion and percolation displacement,the mathematical models of enhanced oil recovery and displacement by fracturing and percolation in class III oil reservoirs with medium and low permeability are established and a numerical simulator for enhanced oil recovery by fracturing and percolation is developed,which realizes the dynamic numerical simulation of the whole process of enhanced oil recovery by fracturing and percolation,and strengthens oil recovery by fracturing and percolation.The design of displacement scheme and the optimization of displacement parameters provide a scientific means.(3)Considering the interaction of normal seepage pressure,tangential shear stress and fracture permeability coefficient in fracture and the interaction of seepage pressure,seepageaccumulation force and rock permeability coefficient in rock mass,a three-dimensional mathematical model of fluid-solid coupling fracture propagation under the condition of enhanced oil recovery by fracturing and percolation is established and a new finite element Picca iterative calculation method is proposed to realize the fracturing and percolation strength.Prediction of fracture propagation law and optimization of process parameters in chemical oil recovery process.(4)Taking the typical development well groups of class III oil reservoirs in Xingbei Development Zone of Daqing Oilfield as the research object,the numerical simulation of oil displacement performance and fracture propagation in the whole process of enhanced oil recovery by fracturing and percolation was carried out by using the self-developed simulator.The effects of phase change,interfacial tension,fluid phase viscosity,rock wettability,adsorption and retention,diffusion/dispersion on oil displacement effect during the whole process of enhanced oil recovery by fracturing and infiltration are quantified.The numerical simulation results of fracture propagation show that with the increase of elastic modulus,the fracture radius increases significantly and the maximum fracture height decreases linearly;the increase of construction displacement has no significant effect on the fracture radius,and will increase the fracture height greatly,and can effectively increase the maximum longitudinal percolation distance of fracturing fluid;the change of fracturing fluid viscosity has little effect on the fracture radius and height,but has little effect on the vertical fracture height.In order to further expand the sweep volume of fracturing fluid,smaller viscosity should be chosen.In this paper,the theoretical basis and relevant technical means of fracturing and percolation development for enhancing oil recovery of class III oil reservoirs are determined,which provides important technical support for the efficient development of class III oil reservoirs in Daqing Changyuan Oilfield and promotes the development and progress of effective development system of medium and low permeability reservoirs.It has important scientific significance and engineering value.