Study On Gas-Assisted Steam Stimulation In Shallow Extra Heavy Oil

Shallow super heavy oil reservoirs are widely distributed at home and abroad.Due to the high viscosity of crude oil,shallow burial,low formation temperature and lack of natural energy,the fluid in shallow ultra heavy oil reservoir does not have flow properties.During steam injection thermal recovery,with the increase of huff and puff cycles,the decline increases,the oil recovery rate decreases,the formation water storage rate increases,the production oil steam ratio decreases,and the recovery effect gradually becomes worse.Therefore,it is very important to study how to exploit shallow super heavy oil efficiently.In this paper,the heat transfer law in the pores under the condition of heat injection was studied,and the condensation heat transfer law of multi-component hot fluid was studied by using the condensation heat transfer device.One dimensional core experiment of multi-component thermal fluid was carried out by using a sandpack,and the influence of steam flow in porous media under different injection production parameters was analyzed.Then an experimental method of cyclic steam stimulation（CCS）with energy storage vessel was established.Based on this,one-dimensional core physical simulation experiments of CCS under different injection and production conditions were carried out,and the variation laws of temperature field,oil production rate,back pressure increase and recovery factor were tested.Finally,based on the laboratory experimental results,the reservoir numerical simulation study was carried out,and the influence of reservoir physical properties and heat injection process parameters on the production effect was analyzed,and the optimization countermeasures of shallow super heavy oil heat injection huff and puff process were put forward.The results show that the condensing period of steam becomes longer and the condensing efficiency decreases due to the formation of gas film between steam and condensate.The condensation heat transfer coefficient decreases with the addition of multi-component gas,which indicates that the multi-component gas can inhibit the condensation heat transfer of steam.In the one-dimensional core heat transfer experiment,with the increase of steam and multi-component gas injection flow rate,the deep temperature of the model increases.The higher the steam injection pressure,the easier the steam condenses into hot water,which is not conducive to the steam carrying heat.The steam heat transfer effect of mixed injection is better than that of slug injection.Through a one-dimensional core physical simulation experiment for gas-assisted CSS,the optimal steam-gas ratio is 1:10.The increase of formation permeability,steam injection temperature,steam injection volume and the decrease of crude oil viscosity can improve the recovery of CSS.According to the reservoir numerical simulation,the optimal injection ratio of thermal injection development is optimized.It is beneficial for the thermal injection development of shallow extra heavy oil reservoir to adopt the injection parameters such as higher CO₂ ratio,larger steam injection volume and injection temperature,and good reservoir physical parameters such as higher formation permeability,lower viscosity and larger reservoir thickness.The results of numerical simulation and physical simulation are basically consistent.The research results provide theoretical guidance for improving the effect of CCS in heavy oil reservoir.