Seepage Mechanisms And Development Optimization Of Preformed Particle Gel Flooding

Preformed particle gel(PPG)flooding is one of the newly developed in-depth profile control methods used to enhance oil recovery for high water cut oilfields.However,the flow of PPG suspension in porous media is very complex,involving not only the general flow characteristics of rigid particle suspension but also the special properties of deformation and recovery.Now,the microscopic seepage mechanisms including these characteristics have not been established,which is the key problem restricting the field application and development of PPG flooding.Besides,optimal design of injection and production strategy on the basis of microscopic seepage mechanisms is another important issue when carrying out PPG flooding.Therefore,it is of practical significance to carry out studies on seepage mechanisms and development optimization of PPG flooding.As well known,solid particle suspension exists widely in many research fields such as the natural world,industrial production and biomedical engineering.So this study is the frontier topic in the research field of seepage mechanics and has important theoretical value.Firstly,the microscopic flow of particle suspension in porous media is studied based on the numerical simulation method developed for microscopic seepage of rigid particle suspension.The law of particle retention and permeability impairment are obtained.Secondly,the paper develops a practical technique for deformation processing and then proposed a new simulation method for microscopic seepage of deformable particles.This solves the long-standing hard problem of microscopic simulation of suspension flow in porous media when the properties like density are very different within and out of the particle boundary.On this basis,the microscopic seepage mechanisms of PPG in porous media are studied.For the first time,the mathematical model of critical pressure gradient for deformation and passing through the pore-throat is established by using microscopic simulation method.Next,the macroscopic simulation method for PPG flooding is proposed on the basis of microscopic seepage mechanisms.In fact,this method realizes the dynamics simulation of particle plugging or deformation process according to the matching relations between particle size and throat diameter.This macroscopic simulation method is used to carry out researches on influencing factors of PPG flooding.Finally,considering the large amounts and wide range of development parameters and the expensive computational cost,the paper develops an improved particle swarm optimization method guided by uniform design(PSO-UD)and also a new version of simultaneous perturbation stochastic approximation method amended by finite difference gradient(SPSA-FD).The two methods are both used to carry out production optimization studies in a PPG flooding reservoir model.From the studies on flow of particle suspension in porous media,the following findings are obtained.With the increase of particle diameter,the retention becomes closer to the inlet and the permeability impairment is severer.The injection rate has an important effect on particle retention amount and their distribution locations,which determines together the severity of permeability impairment.As the particle volume fraction and total injection amount increases,the particle retention and permeability impairment increase correspondingly.The particles with different diameters can enter different parts of the heterogeneous porous media and cause permeability impairment.From the studies on microscopic seepage mechanisms of PPG in porous media,the following results are obtained.The critical pressure gradient for a PPG to deform and pass through a given throat has a good exponential relationship with particle-throat diameter ratio,and it also has a linear relationship with the elastic modulus.When the PPG transports in a two-channel model,the fractional flow of one channel will increase while that of the other channel will decrease at the same time.The increase and decrease of fractional flow alternate continuously between the two channels.The changing range increases as the elastic modulus and particle-throat diameter ratio increases.This result illustrates the phenomenon of the changing flow direction in a microscopic point.Besides,the flow resistance of injected water can be increased and fluctuates continuously resulting from the plugging and deformation of PPG in porous media.The flow resistance and fluctuation increases with particle-throat diameter ratio,elastic modulus and particle number concentration.This result illustrates how PPG reduces the flow capability of injected water in PPG flooding project.The studies on influencing factors of PPG flooding generate the following conclusions.The enhanced oil recovery increases with the injection amount and concentration,but its growth rate decreases gradually.The injection rate,particle diameter and elastic modulus have an important effect on the deformation and deep migration of PPG.The oversize and undersize value may decrease the enhanced oil recovery.According to the optimization study of PPG flooding,both of the PSO-UD and SPSA-FD methods can converge to the optimal development strategy by using a limited number of simulations.Compared with the reference scheme,the two methods increase the incremental cumulative net present value of 122.2% and 111.1%,and increase the enhanced oil recovery of 2.1% and 1.9%,respectively.