Study On Recovery Mechanism And Control Method Of Horizontal Well Steam Flooding In Offshore Heavy Oil Reservoir

The study on mechanism of steam flooding in offshore horizontal wells with large well spacing and irregular well pattern and effective control method after steam channeling are not sufficient.In this dissertation,the recovery mechanism and control method for offshore steam flooding horizontal wells are studied.Through numerical simulation and laboratory experiments,the recovery mechanism and production characteristics of steam flooding in offshore horizontal wells are studied,and the advantages and disadvantages of steam flooding in offshore horizontal wells with large well spacing and irregular well pattern are compared with those in vertical wells.The change law of physical properties of steam flooding reservoirs in horizontal wells is studied,and the identification method of dynamic connectivity between wells is proposed.The optimization method of horizontal well location and injection-production parameters suitable for steam flooding of horizontal wells with irregular offshore well pattern is proposed.The high-temperature resistant foam system and dispersed sludge plugging system were screened and developed through laboratory experiments,and the chemical control effect of steam flooding in horizontal wells was studied.According to the geological and reservoir characteristics of NB 35-2 Oilfield,the recommended injection-production parameters of horizontal steam flooding suitable for this oilfield are given by numerical simulation,and the development effect is analyzed.Through laboratory experiments and numerical simulation,the recovery mechanism and production dynamic characteristics of steam flooding in offshore horizontal wells with large well spacing are studied.Combined with production dynamic,steam flooding in horizontal wells can be divided into four stages: thermal communication,effective displacement,steam breakthrough and breakthrough denudation.The main exploitation mechanisms are pressure displacement,thermal viscosity reduction and distillation denudation.The advantages and disadvantages of horizontal well steam flooding and vertical well steam flooding with irregular well pattern at sea are compared.Irregular well pattern with large well spacing offshore steam flooding has the characteristics of low well pattern density,long well interval,wide reservoir contact range,fast steam injection speed and high dryness,long time in thermal connection stage and displacement stage,and long time for stable production after production increases.Disadvantages lie in the few horizontal well locations,the influence of reservoir heterogeneity and well trajectory,etc.,which easily lead to uneven reservoir production along horizontal well intervals,and it is difficult to control injection and production after steam channeling.Based on the principle of material balance,a calculation method of dynamic connectivity between injection-production wells of steam flooding in horizontal wells considering different change mechanisms such as steam expansion and condensation is proposed.The connectivity between different injection-production wells can be obtained.The effectiveness of the method is verified by the conceptual model,which is consistent with the dynamics of steam flooding wells in the field,and can be used for injection-production parameter regulation and plugging measures design.Based on intelligent optimization algorithm,the optimization method of horizontal well steam drive well location and injection-production control parameters is established.Compared with conventional single factor analysis or orthogonal test method,the efficiency and effect of scheme design can be effectively improved.The effectiveness of this method is verified by example analysis,and the overall economy of horizontal well steam drive project can be effectively improved through optimization.This method can be used to guide the optimization design of offshore thermal recovery well location and injection-production parameters.A high temperature resistant foam system suitable for steam flooding in offshore horizontal wells was screened through laboratory experiments,and a dispersed sludge system was developed.Through the analysis of three-dimensional physical simulation experiment,both the high-temperature resistant foam and dispersed sludge system can play the role of steam channeling inhibition and improving the recovery degree by plugging the crude oil steam seepage channel on the basis of the initial steam flooding in horizontal wells.Chemical plugging and adjustment can improve the recovery degree of steam flooding in horizontal wells by about 12%.Taking NB35-2 Oilfield as the target,the recommended injection-production parameters of steam flooding for horizontal wells with irregular well pattern in the target well group are optimized as follows: steam injection rate of 350 tons/day,bottom hole dryness greater than 40%,and production-injection ratio of 1.4.Chemical plugging and adjustment scheme and efficient steam injection string suitable for offshore thermal recovery wells are designed to meet the field implementation requirements of steam flooding for offshore horizontal wells.The field implementation effect is good,and the scheme design index and expected development effect are achieved.The research results of this paper provide some theoretical guidance for the effective development of steam flooding in offshore horizontal wells.