Feasibility Study Of Secondary Polymer Flooding In Glutenite Oilfields At Ultra-high Water Cut Stage

In order to meet the adjustment of development mode after polymer flooding,there is a need to study the feasibility of secondary polymer flooding in certaincondition. Based on the reserch of development characters during polymer floodingand characters of remaining oil distribution after polymer flooding in VupStrata ofShuanghe Oilfield, a well pattern optimization was made for secondary polymerflooding. On this basis, the feasibility of secondary polymer flooding in VupStrataof Shuanghe Oilfield was proved.Some results was discovered and some conclusions was drawn during the studyof feasibility of secondary polymer flooding in VupStrata of Shuanghe Oilfield, suchas those show below.1. The main factors that affect polymer flooding are water flooding degree,reservoir properties, reservoir heterogeneity, the coverage degree of the well array,the use of profile control and separate injection. In order to improve thedevelopment effect, it’s better to inject high concentration polymer solution inregion which is better in petrophysics, and it’s better to do it early in polymerflooding state. Also, it’s better to inject low concentration polymer solution in regionwhich is not good in petrophysics. In region with strong heterogeneity, it’s better touse more profile control and separate injection.2. There was some strange phenomenon which was discovered in the process ofhistory matching of polymer flooding, that the percolation resistance force of thereservoir will change after polymer frontal’s arrival to production well. In order tofix this problem, a set of different parametre was given to the simulator.3. Actual conditions of premature polymer production proved that reservoirsimulation can not simulate reservoir heterogeneity, so the potential of remaining oilin north region of well network could not be showed by simulation result. In themean time, the interference which was made during the history matching has causeda more uniform sweeping, which made the saturation of remaining oil higher when it’s actually relatively lower, and made it lower when it’s actually relatively higher.Theoretical results showed that the average break-through time of polymer in wellsis2.9years, but the actually time is1years, so the watered out area on the plane isabout a third in total. Based on this, and combined with the result of reservoirsimulation, it can infer that the remaining oil of VupStrata of Shuanghe Oilfield islocated in by-passed oil area between oil well and another oil well which next to it.4. Field test proved that subsequent water flooding could not handle the rapiddecline of oil production rate in VupStrata of Shuanghe Oilfield after polymerflooding. Meanwhile, ASP flooding and SP flooding were proved to be notcompatible with formation water in Shuanghe Oilfield, so subsequent water flooding,ASP flooding, SP flooding are all not suitable for VupStrata of Shuanghe Oilfieldafter polymer flooding. As a result, secondary polymer flooding which can continueto expand swept volume and don’t have any compatibility problem, become the onlychoice for the development of VupStrata of Shuanghe Oilfield after polymerflooding.5. Combine with the result of remaining oil distribution, three scheme of wellpattern modification are made by the way of completing injection-production pattern,changing direction of fluid flow and reuseing of old wells. The prediction forultimate oil recovery of all these three new well patterns was given by reservoirsimulation, and the result showed that the third well pattern modification scheme isthe best.6. Based on modification of old well pattern, optimal injection parameters ofsecondary polymer flooding were determined by orthogonal test single factoranalysis method. The optimal injection parameters are:1.05for injection-productionratio,0.12PV/a for injection rate,0.5PV for slug size and1700mg/L for polymerconcentration. The recovery ratio of secondary polymer flooding which using newwell pattern and adopt the optimal injection parameters is5.46%higher than that ofsubsequent water flooding which using original well pattern., and the accumulatedoil production is19.9×104t larger. Assume the price of crude oil is50Dollars perBarrel(2640yuan per ton), the secondary polymer flooding in VupStrata of Shuanghe Oilfield can earn245.91million yuan in total, after deducting the costs ofwell drilling, oil recovery, surface engineering and the cost of polymer powder.Thus, secondary polymer flooding is feasible in high permeability gluteniteoilfields which are at high water cut stage.