Optimization Of Polymer Flooding Injection System In Conglomerate Reservoir

As an important part of domestic oil and gas resources,the characteristics of conglomerate reservoirs are quite different from sandstone reservoirs.The structure of conglomerate reservoir is complex,which has the characteristics of variable pore type combination,uneven distribution of pore and throat structure,poor separation coefficient,serious heterogeneity in inter layer and interior layer.In order to reduce the water content of the produced liquid and improve the oil displacement efficiency,the field experiment of polymer flooding in QD-1 conglomerate reservoir has been carried out in Xinjiang oilfield,but the results are unsatisfactory.The concrete performance in the reservoir is low,the water cut falling is slow and the effective time is short.In this paper,the polymer flooding injection system of QD-1 conglomerate reservoir is optimized based on the analysis of the geological conditions,and on the basis of analyzing the current situation of the flooding test,combining with the visualization techniques such as indoor static evaluation,dynamic physical model,nuclear magnetic physics imaging and environmental electron microscope scanning.The main research contents are divided into the following parts:(1)The basic performance evaluation of polymers to be used in QD-1 polymer flooding test,the influence of polymer concentration and molecular weight and shear velocity on polymer viscosity are analyzed,the basis for optimizing injection system composition and injection speed is provided.(2)Through indoor physical simulation experiments,the influence of polymer system combination and injection rate on the flow control and permeability of polymer was studied by means of resistance coefficient,residual resistance coefficient and viscosity loss rate.The inaccessible pore volume of polymer solution was determined by the double slug concentration profile method,for studying influences of polymer system composition and injection velocity on the polymer's sweep ability in conglomerate.The results show that with the increase of molecular weight of polymers,the resistance coefficient and the residual resistance coefficient rise,while the inaccessible pore volume volume increases,and with the increase of injection velocity,the coefficient of drag decreases with the increase of the resistance coefficient,while the void volume decreases.(3)Establishing the physical experimental model of polymer flooding flow degree under heterogeneous conditions,combining with the NMR imaging technology,the microscopic seepage experiment and the double parallel core oil displacement experiments are carried out,the influence of the polymer system composition and injection velocity on the oil displacement effect is studied.It is understood that in with compositions of "single section plug" and double slug polymers,such as "reducing molecular and fixed viscosity","fixed molecular and reducing viscosity","fixed molecular and increasing viscosity"," reducing molecular and reducing viscosity",the displacement effect of "reducing molecular and fixed viscosity","fixed molecular and reducing viscosity" polymer injection systems is better and the oil recovery efficiency of those two-stage plug systems can be improved by 1.29%-3.75%.The relative advantages of the two polymer systems are related to the permeability difference:the latter has a higher displacement efficiency when the differential is smaller(2),while the former is more efficient when the differential is higher(4 and 8).When adopting the double slug system of "reducing molecular and fixed viscosity",if the permeability of high permeability layer is high(1 OOOmD),the higher injection speed(5m/d)is suitable,and the lower injection speed(2.5m/d)is suitable if the permeability is low(400-700mD).The research results of this paper can provide the relevant basis and technical guidance for the optimization of the injection system and injection speed of polymer flooding test in QD-1 conglomerate reservoir,and it has a great significance to improve polymer flooding effect in conglomerate reservoir of Xinjiang oilfield.