Study On Parameter Optimization Of Multiple Thermal Fluid-water Alternate Flooding In Middle And Late Stage Of Water Flooding In Offshore Z Oilfield

The development and utilization of heavy oil resources occupy an important position in the oil industry.The development methods and means of heavy oil reservoirs are various.For ordinary heavy oil reservoirs with relatively low crude oil viscosity,after the development of natural energy,the secondary oil recovery method of conventional water flooding is usually used to supplement the formation energy to improve the recovery efficiency.With the continuous development,the contradiction of heavy oil reservoir development in the middle and late stages of water flooding has gradually become prominent.For example,due to the high viscosity and poor fluidity of crude oil,serious breakthrough of injected water,rapid increase of water cut in oil wells and rapid decline of production have been caused.And affected by reservoir physical properties,resulting in uneven plane pressure distribution,slow formation energy supplement and low formation pressure maintenance level.Based on this,this paper takes the ordinary heavy oil reservoir in offshore Z oilfield as the research object.In view of the problems existing in the middle and late stages of water flooding development of ordinary heavy oil reservoirs,the optimization of multiple thermal fluid and water alternate flooding parameters is studied.The main work and achievements are as follows:(1)Using Eclipse numerical simulation software,on the basis of fully collecting the geological reservoir data of the target block,the numerical simulation model of the target block is established,and the phase state of the formation fluid is fitted by PVTi module.After the phase state fitting is completed,the production history of the target block is fitted.The fitting accuracy of water content in the whole region is 93.49%,and the fitting accuracy of liquid production is 96.58%.The fitting effect is good,and the subsequent development effect of the target block can be predicted.(2)The development mode of the target block is studied.According to the change of water content and formation pressure,the development process of the target block is divided into three stages:natural energy development,water flooding development and subsequent supplementary energy development.Through economic evaluation,the formation pressure boundary of natural energy development and water flooding development stage is given,and the permeability boundary of energy supplement development mode selection in the middle and late stages of development is given.Combined with the actual situation of the target layer,the multiple thermal fluid and water alternate flooding is selected as the alternative development method according to the chart.(3)From the perspective of recovery degree and oil exchange rate of injection fluid,the influence of different injection parameters on the development effect of multiple thermal fluids and water alternate flooding in the middle and late water flooding of heavy oil reservoirs is analyzed,and the influence degree of each factor is analyzed by grey correlation method.The results show that the well spacing has the greatest impact on the development effect in the static parameters,and its correlation coefficient is 0.667.Among the dynamic parameters,the injection amount of multiple hot fluids has the greatest impact on the development effect,and its correlation coefficient is 0.713.(3)The injection parameters of multi-component thermal fluid and water alternate flooding in the middle and late stages of water flooding in the target block are optimized by designing the orthogonal scheme.The optimal injection parameters are as follows:the total injection volume is 711.2×10~4 m~3,the injection cycle is 1 cycle,the gas-water ratio is 1:1,and the injection rate is 1.30×10~4 m~3/d.The transfer timing is that the comprehensive water content of the whole region reaches 85%.At the same time,considering the actual needs of the oilfield,the injection parameters of multi-component hot fluid and water alternate flooding in different water cut stages are optimized.The optimization results are as follows:with the continuous development of the oilfield,the comprehensive water cut of the oilfield is continuously improved.In the process of multi-component hot fluid and water alternate flooding,the gas injection speed,water injection speed,gas-water ratio should be gradually increased and the alternate period should be maintained for one month.