Research On Optimization Models Of Operating Condition And Methods Of Performance Control For Steam Flooding

According to the preliminary statistics,there are about 4-5 trillion barrels of heavy oil resources with high development value in the world,which are still buried in the ground.Therefore,the prospect of further research on the theory and practical technology of enhancing heavy oil recovery such as steamflooding is very broad.The different steamflooding conditions in different stages should be based on different theoretical basis and appropriate parameter control methods to solve the problems in production,which has not been fully noticed by previous theories and methods.Therefore,in order to ensure the whole process of steamflooding to operate under the optimal operating conditions and further improve the oil recovery,it is urgent to carry out the research on the theory of phased optimization design and the adjustment method of technical parameters of steam flooding.This paper is closely related to the engineering practice andtechnology problems in different stages of Qi40 block industrial steamflooding test in Liaohe Oilfield,the theoretical model and technical parameter control method of steamflooding phased optimization were systematically and deeply studiedbytheoretical research,numerical simulation and field test.Based on the theoretical analysis of the relationship among the heat loss rate of the overlying strata,the heat loss rate in the reservoir,the stored energy rate of the steam belt and the produced heat energy rate along with the oil recovery process and the heat energy injection rate on the ground,the defects of Marx-Langenheim's classical theory that neglects the effect of steam over flow are corrected,and the energy balance equation of the steamflooding reservoir is established the theoretical analysis of steamflooding and calculation basis of engineering design.The energy balance analysis of steamflooding shows that there are about 2/3 of surface heat injection energy stored in the upper cap and lower zone of steamflooding,and the effective use of this energy can improve the development effect and economic benefit of steamflooding.Aiming at the highest utilization rate of underground thermal energy,a mathematical model for calculating the thickness,area and volume of the steam zone in a steamflooding reservoir and a mathematical model for predicting the production of steamflooding based on semi-analytical and semi-empirical method are established.The calculation method for predicting the economic development life of steamflooding and the oil steam ratio and other important indexes are proposed.The optimal heat injection(steam injection)rate on theground under two conditions before and after the steam breakthrough is established.These results enrich the theoretical knowledge of heavy oil thermal recovery and form a relatively complete theoretical analysis and operation technology system of surface heat injection in the whole process of steamflooding.In this paper,the influencing factors of heat injection and heavy oil recovery before and after steamflooding breakthrough and the law of change with time are clarified.The new theoretical model and method established provide theoretical basis for the optimization design and control of injection production parameters in the whole process of steamflooding.It is found that the coverage area and volume of steam zone are not only a function of surface heat injection time,reservoir rock and fluid thermal physical parameters,but also are in a positive proportion to the surface constant speed heat injection rate.The total amount of surface constant speed heat injection before steam breakthrough plays a decisive role in the formation and expansion of steam zone volume in the reservoir.The research shows that the mathematical model of the coverage area of steam belt established in this paper solves the problem that the calculated value of Marx-Langenheim's classical theoretical formula is less than the actual value.Through theoretical research and full statistical analysis of successful steamflooding cases such as the pilot test of steamflooding in block Qi 40,it is proposed that the steamflooding can be successfully operated under the optimal operating conditions by optimizing the operating conditions in stages and adjusting the injection production parameters in real time,so as to improve the recovery rate of steamfloodingThe first stage is constant steam quality or constant steam injection rate stage.In this stage,the steam injection rate and steam qualitywill be optimized based on the actual situation of the reservoir,and the optimized steam injection rate and steam qualitywill be applied in the whole stage to operate stably.The second stage is the stage of constant steam quality or variable steam injection rate.This stage is from the steam breakthrough time to a later time(t1).In this stage,the operation timet1should be optimized with the highest recovery rate as the objective.Between the steam breakthrough time and time t1,the steam quality used in the previous stage should be kept unchanged,and the steam injection rate operation should be changed according to the reduced heat injection equation established in this paper.The third stage is the stage of constant steam injection rate or variable steam quality.This stage is from time t1 to the economic development period tn of steamflooding.In this stage,the steam injection rate at time t1 is kept unchanged,and the steam quality operation is changed according to the decreasing heat injection equation established in this paper.Based on the particularity of different stages of steamflooding,this paper puts forward the optimization design,calculation and parameter control methods and sperific implementation steps of the whole process of steamflooding operation conditions.Based on the theoretical design and calculation method in this paper,the optimal development scheme design results of steamflooding,including well layout,well pattern density,production injection ratio and other factors,can be easily given,which provides guidance for the operation of steamflooding in stages under the optimal operating conditions and lays the foundation for successful steamflooding.The theory and method in this paper are verified by the pilot test of steamfloodingand variable quality in denudation stagein block Qi 40.The field test results are in good agreement with the theoretical analysis and design calculation results in this paper,which fully proves the correctness and practicability of the theoretical model of steamflooding,the optimization design of injection production parameters and the control method in this paper.The results of theoretical analysis and field test show that the whole process of successful steamflooding generally needs to go through the stages of heat connection,steam displacement,steam breakthrough and denudation adjustment in the later stage of development,and each stage follows its own scientific laws.In this paper,a theoretical model is established according to the actual working conditions of different production stages,and a new method is proposed to pursue the optimal operating conditions for steamflooding,which is of great significance and practical value for effectively improving the recovery rate of steamflooding.