CO2 and viscosity breaker assisted steam huff and puff technology for horizontal wells in a super-heavy oil reservoir

In order to improve the recovery effect of steam huff and puff in a super-heavy oil reservoir, the displacement efficiency of CO2 and viscosity breaker assisted steam flooding was studied through in-lab displacement experiments. The viscosity reduction mechanism of CO2 and viscosity breaker assisted steam huff and puff for horizontal wells was realized by numerical simulation. The results show that the displacement efficiency of CO2 and viscosity breaker assisted steam flooding (80.8%) is higher than that of steam flooding (65.4%). The CO2 and viscosity breaker assisted steam huff and puff technology for horizontal wells realizes the rolling replacement of viscosity reduction of viscosity breaker, CO2 and steam, thus effectively reducing the steam injection pressure, expanding the steam sweep area, i.e., expanding the viscosity reduction region and improving oil production rate. The viscosity region can be divided into four compound viscosity reduction areas according to temperature distribution and viscosity reduction mechanism. They are steam compound viscosity reduction region, hot water compound viscosity reduction region, low temperature water compound viscosity reduction region, and CO2-viscosity breaker compound viscosity reduction region. Field tests show that the CO2 and viscosity breaker assisted steam huff and puff technology for horizontal wells is effective in reducing viscosity and improving production of super-heavy oil reservoirs with deep and thin layers, deep and heavy layers, shallow and thin layers. Key words: super-heavy oil, steam huff and puff, reservoir simulation, physical simulation, CO2, viscosity breaker