Numerical Study On Optimization Control Of Injection-production In Heterogeneous Reservoir

Most of the oilfield reservoirs in China are continental clastic deposits.The physical properties of continental sedimentary reservoirs are poor,the heterogeneity is serious,and the exploitation is difficult.The conventional water injection methods have been unable to meet the engineering needs.It is of great social and economic value to improve the recovery factor for the crude oil of low-permeability layers and the exploitation effect of heterogeneous reservoirs.In order to alleviate the inter-layer and intra-layer contradictions of reservoir exploitation caused by heterogeneity,this thesis carries out numerical simulation and theoretical analysis of injection-production coupling and separated layer water injection regulation of heterogeneous reservoirs,the specific contents are as follows:The pressure-controlled injection-production coupling method can improve the recovery factor for the crude oil of low-permeability zone and achieve the exploitation effect of increasing and stabilizing production.In different exploitation stages,this method can meet the fluctuation range of reservoir pressure and maintain the reservoir pressure level by adjusting injection-production cycle.The greater the reservoir development degree,the difference of pressure control threshold,the greater the injection-production cycle.Compared with the fixed-cycle injection-production coupling method,the pressure-controlled injection-production coupling is more effective for the exploitation effect of heterogeneous high water cut reservoirs.The yield increase effect of this method depends on the pressure control threshold and the oil-water seepage ability of the high and low permeability zones in the reservoir,and with the increase of the pressure control threshold and the seepage ability,the increase effect will be better.The oil-water seepage ability of high and low permeability zones in reservoirs is closely related to the geological parameters.The results show that the intra-layer heterogeneity is the precondition for the injection-production coupling effect better than the conventional water injection.The injection-production coupling efficiency of compound rhythm reservoir is better than that of positive and reverse rhythm reservoir.For reservoirs with strong differences in intra-layer permeability and large proportion of low-permeability zones,the effect of injection-production coupling is more significant,and the bigger the ratio of vertical to horizontal permeability,the stronger the intra-layer oil-water seepage ability,the better the effect.In addition,for reservoirs with small rock compressibility and low oil viscosity,injection-production coupling is easy to obtain better yield-increasing effect.Injection-production coupling alleviates the difference of reservoir vertical water phase saturation and weakens capillary channeling.With the increase of capillary pressure,the yield increase effect of injection-production coupling decreases.Separated layer water injection is an effective technology to alleviate interlayer interference and achieve interlayer equilibrium displacement.This thesis studies the separated layer water injection effect of multi-oil layers and thick oil layer.For multi-oil layers,there is no interaction between interlayer,and the separated layer water injection based on residual oil saturation method can effectively achieve equilibrium displacement.For thick oil layer,the optimization technology of separated layer water injection can effectively alleviate the imbalance of displacement,the optimization direction is that the water injection amount is more distributed to the seepage layer with higher longitudinal position and lower permeability.With the increase of the difference of Intra-layer permeability and the ratio of horizontal to vertical permeability,the effect of separated layer water injection is more remarkable.The separated layer water injection method has the technical limit for thick oil layer.Due to the water-phase seepage among the different layers,the separated layer water injection regulation can only improve the recovery factor for the crude oil in the area near the injection well,while the area far away from the injection well will not be affected.Aiming at this problem,this thesis describes the waterflood swept area by introducing the concept of waterline distance,and uses the limit waterline distance to characterize the technical limit of the separated layer water injection.After the waterflood front reaches the limit waterline distance,the separated layer water injection control will fail.Due to that the limit waterline distance is determined by the water-phase seepage among the different layers,the technical limit of the separated layer water injection depends on the heterogeneity in reservoir,such as the layer thickness and permeability ratio.The results show that the separated layer water injection may gain the satisfied exploitation efficiency for the reservoir with the strong heterogeneity and large layer thickness.Simultaneously,the simulation results of the actual oilfield separated layer water injection optimization show that separated layer water injection improves the water injection development effect,but as the improvement of reservoir development degree,the yield increase effect of separated layer water injection decreases.This result verifies the existence of technical limit of separated layer water injection regulation.In view of the shortcomings of separated layer water injection that can’t affect the area far away from the water injection well,the potential-tapping strategy combined with separated layer water injection and separated layer production is adopted to further improve reservoir recovery factor and exploitation efficiency.In summary,this thesis has studied the efficiency and influencing factors of the pressure-controlled injection-production coupling method as well as the effect and technical limits of the separated layer water injection optimization.The pressure-controlled injection-production coupling method can satisfy the reservoir pressure fluctuation range and improve the waterflood swept area of low-permeability zone.The separated layer water injection method can alleviate the inter-layer contradiction and realize the reservoir equilibrium displacement.Both of these mining methods can improve the development effect of heterogeneous reservoirs,and have important reference value for the development and application of actual reservoirs.