Study On Collaborative Optimization Of Polymer Flooding And Well Pattern Infilling In Offshore Oilfield

Polymer flooding and well pattern infilling have been implemented in some blocks of offshore oil fields in China,but the mechanism of polymer flooding combined with well pattern infilling is not clear.Therefore,it is of great significance for the development of polymer flooding and well pattern infilling to study the reasonable well pattern density,optimize well pattern infilling mode,learn about mechanism of polymer flooding combined with well pattern infilling,and optimize the combination mode in offshore oil field.In this paper,a numerical simulation model of typical reservoir is established based on the specific block of offshore oil field.By the classical relationship between oil recovery factor and well pattern density,a new water flooding and a polymer flooding models of oil recovery factor and well pattern density are established,and a reasonable calculation method of well pattern density for water flooding and polymer flooding in offshore oil fields is established.The reasonable well pattern density under different crude oil viscosity is obtained.It is recognized that the higher the crude oil viscosity,the greater the reasonable well pattern density,and the reasonable well pattern density of polymer flooding is larger than that of water flooding,and the higher the oil price is,the more reasonable well pattern density difference between polymer flooding and water flooding is.Based on the established numerical simulation model,the different infilling development effects of the reverse nine-point well pattern,five point well pattern and line water flooding are comprehensively analyzed from the angles of residual oil,effective residual oil,sweep coefficient,oil washing efficiency,recovery factor and net present value,and selected the best infilling modes of these three well patterns.The development effect of the selected infilling mode combined with polymer flooding is furtherly analyzed.In terms of mechanism,the results show that the residual oil is mainly distributed in the area near the new water injection wells and infilled oil wells.And the sweep coefficient of infilled polymer flooding combination is smaller than that of the sum of infilled water flooding and polymer flooding.And infilled polymer flooding increases the proportion of grid number in high oil washing efficiency interval,which makes the low oil washing efficiency region be transformed into higher oil washing efficiency area,while 0.6-0.7 oil washing efficiency range increases the highest proportion.In terms of oil recovery and net present value,infilled polymer flooding is the highest relative to basic water flooding,infilled water flooding and polymer flooding.By analyzing the sequence and timing of polymer flooding and well pattern infilling combination,it is recognized that the recovery factor of infilling-polymer flooding is 1%~2% higher than that of polymer-infilling flooding.And in higher oil price,the net pay value of infilling-polymer flooding is larger than that of that of polymer-infilling flooding,while the result is opposite under the lower oil price.And earlier the combination time of infilling and polymer flooding is,the larger the net present value is,while the oil recovery does not change much.By optimizing infilled polymer flooding of the reverse nine-point well pattern,five point well pattern and line water flooding are,the optimum polymer injection rate are 0.06PV/a,0.06PV/a,0.08PV/a,the concentration of polymer injection are 1750mg/L,1750mg/L,1500mg/L,and the size of polymer slug is 0.4PV,0.4PV,and 0.3PV respectively.