A Pressure Control Scheme On Steam-assisted Gravity Drainage

Steam assisted gravity drainage(SAGD)is a thermal recovery technology for heavy oil and oil sands.Due to the high energy consumption and heat loss of SAGD,it is necessary to improve it.An improved SAGD process,VP-SAGD,is proposed and studied in this thesis.Stimulation is achieved by rapidly reducing and restoring cavity pressure during SAGD.Firstly,the stimulation effect and mechanism of VP-SAGD were analyzed through reservoir numerical simulation,and parameter optimization was carried out.The solvent-assisted gravity drainage(ES-SAGD)was also applied,and the stimulation mechanism was compared.Finally,the multi-cycle VP-SAGD operation was optimized and an actual reservoir model was used to predict the stimulation effect of VP-SAGD.The results show that compared with SAGD,VP-SAGD can increase oil recovery by 20% and reduce cumulative SOR by 7%.For ES-SAGD,VP-ES-SAGD can increase cumulative oil production by 35% and decrease Cumulative SOR by 10%.The stimulation mechanism of VP-SAGD includes: indirectly changing the cavitation shape through pressure control,increasing the flow inclination Angle by about 40% and improving the drainage rate;The thickness of heating belt is reduced by about 50% and the heat transfer efficiency is improved.The stimulation mechanism of VP-ES-SAGD not only increases the oil drainage rate and heat transfer efficiency,but also changes the solvent distribution and increases the solvent content in the upper part of the cavity by about 75%,thus improving the solution viscosity reduction efficiency.Parameter analysis shows that the optimal time range of VP-SAGD is 4-6 years,and the lower the bottom hole pressure drop is in the stage of depressurization,the better the later stimulation effect is.The optimal hypotension timing range of VP-ES-SAGD is6-10 years.VP-SAGD technology is widely applicable to reservoirs.The effectiveness of VP-SAGD has also been demonstrated by real reservoir scale simulations.