Study On Sweep Efficiency And Front Of Offshore Heterogeneous Thick Oil Layer For Polymer Flooding

Offshore oil is of strategic significance to national economic development and energy security.At present,Bohai oilfield produces more than 80% oil of China.Bohai oil field has unique characteristics such as large thickness,strong reservoir heterogeneity,high crude oil viscosity,large spacing of injection wells,high development speed and the sweep efficiency is thus difficult to obtain.The development strategy of "fuzzing the boundary between second and tertiary flooding " also highlights the importance of the injecting timing in the development of offshore oil fields.Therefore,it is urgent to carry out research on the sweep efficiency of different types of thick layers and the influencing factors.In this paper,the viscosity characterization method for the properties of polymer flooding considering the untouchable pore volume is established,and the steady-state relative permeability curve is established.The physical models of planar homogeneous thick oil layer,longitudinal heterogeneous thick oil layer,3d homogeneous thick layer with or without interlayers are manufactured according to the similarity criterion modeling gravity.The characterization methods of sweep effects include the dynamic saturation distribution,the sweep area map,the sweep front map and quantifies the sweep efficiency,displacement efficiency,fluid absorbent profiles(quantitative),the velocity of the sweep front.Comparative experiment of homogeneous thick layer for water flooding and polymer flooding experiments are firstly carried out.The main direction of sweep improvement is determined by the dynamic saturation distribution and the sweep efficiency and the contribution of different stages for polymer flooding process are both obtained.In this paper,the migration velocity of the sweep front is determined by the dimensionless dimensionality of the sweep front perpendicular to the direction of the main line.A numerical fitting model is established to accurately simulate the results of physical simulation,and the effects of parameters such as oil viscosity and reservoir thickness are obtained utilizing this model.A polymer flooding mathematical model considering the change of polymer flooding solution viscosity,the untouchable pore volume,the coefficient of permeability decline and the rock adsorption is established.Also a stream tube method of 9 points well pattern model is established then the frontal velocity,the water breakthrough time and the recovery degree of different stream tubes are solved,and the effects of fluids viscosity on the recovery degree and the sweep efficiency of the 9 points well pattern for polymer flooding are thus obtainedBased on the results of the comparative experiment of homogeneous thick layer for water flooding and polymer flooding,the effects of polymer flooding for vertical heterogeneous thick layer is "hysteretic stratified,effective step by step",and the effects of polymer injection timing are summarized."Effect onset time" and "the degree of effect" are defined to evaluate the figure of the absorbent profiles,and the absorbent profiles of different injecting timing are compared quantitatively which explains the effects of injecting timing on the absorbent capacity and the sweep efficiency laterally.Based on the results of the comparative experiment of homogeneous thick layer with or without interlayers,a conclusion that the thick insulation layer effectively restrains the action of gravity and interlayer channeling,which brings lager threshold pressure and better sweep effects and displacement efficiency is summarized.A numerical simulation of polymer factors is carried out using a real complex reservoir model by stratigraphic extraction.The experimental results of the are verified by numerical simulation.At the same time the sweep effect curve under different injection PV number and the terminal value and value-added of sweep efficiency for polymer flooding under different factors are analyzed,and the permeability variation coefficient,viscosity of crude oil and polymer injection timing are determined as the main factors that affect the polymer flooding sweep effect.