The Optimization Research Of Vertical Equilibrium Displacement For Multilayer Reservoir In Ultra-High Water Cut Stage

Multilayer reservoirs located in eastern china which mainly comprise clastic sedimentsfrom continental depositional environment are characterized by severe inter-layerheterogeneities which may induce sharper interlayer interference in ultra-high water cut stageand consequently hinder further enhancement of recovery. This adverse phenomenon, longyear’s field development experience indicates, could be minimized effectively through properstrata classification or reallocation either of water as to injection or oil as to production atsingle layer’s level. Based on thorough examination of interlayer interference, a set ofcomprehensive optimization workflow to realize vertical equilibrium displacement isproposed for multilayer reservoir in ultra-high water cut stage, combining with a series oftechniques which respectively are layer recombination, water or oil profile reallocation atseparate layer’s level and technology of variation of perforation density.By statistical analysis of101relative permeability curves from uncompartmentalizedreservoirs in Shengli oilfield, the correlation between characteristic parameters of relativepermeability curve and permeability is established which can be used to calculate relativepermeability curve so long as permeability is given. Through investigation how formation andfluid parameters change over time during the water flooding development, a new simulationsystem, based on black oil model, is presented which takes the time-dependent characteristicinto consideration such as permeability and viscosity. Besides, characteristic parameterswhich are used to quantify the extent of interlayer interference are also put forward. Usingthis simulation system, interlayer interference and mechanism are studied.The influence factors and relevant policy limit of layer recombination are analyzed. Thensensitivity analysis of those factors is carried out using the method of orthogonal design fromwhich the dominant factors are selected by screening. Further, a new evaluation index calledthe pseudo flow resistance is presented, which takes the difference of interlayer permeability,viscosity and remaining oil saturation comprehensively into account and therefore could serveas the characteristic index of layer recombination in ultra-high water cut stage. At last, thepolicy limit for multilayer recombination in ultra-high water cut stage is studied. Multi-leveloptimization technique for layer recombination is also proposed, and the corresponding software is programmed. This technique is applied into layer74-81of Shengtuo oilfield, andthe optimum recombination pattern is obtained.To realize equilibrium development effect among layers after conducting layerrecombination, two techniques are brought forward which are separate-layer water allocationand variable density perforation respectively. The former is based on B-L displacement theory,which can be used to calculate the water allocation of each layer. The latter is achievedthrough the optimization of perforation density of water wells whose mathematic model issolved by using genetic algorithm.The optimization research of vertical equilibrium displacement can weaken layerinterference effectively, which provides certain guiding significance for the development ofmultilayer reservoir in ultra-high water cut stage.