Gas and Electrical Heating Assisted Gravity Drainage(GEAGD in short) is a new heavy oil production technology, in which, dual parallel horizontal wells or combination of vertical well and horizontal well are involved as electric dipole moments to heat the reservoir in distributed resistive method. At the same time, the upper well is used as gas (N2, CO2, flue gas, hydrocarbon gas, etc.) injection well, and the lower as production well. GEAGD is applicable and potential to enhance oil production rate or oil recovery for heavy oil reservoirs produced by cold production or steam injection because it has many advantages such as high heating efficiency, eliminating oil-water flow effect on oil production, enlarging heating reservoir volume by injected gas, gravity assisted oil drainage by electrical heating and gas, pressure maintenance and heat insulation by gas cap gathered at the top of reservoir. Particularly, GEAGD is potential to recover heavy oil reservoir unfit for steam injection such as offshore heavy oil reservoir for it is difficult to install steam generator on the production platform with limited space.
In this work, primary theoretical analysis, simulation experiment, and numerical simulation are carried out to investigate feasibility and potential of producing heavy oil by GEAGD. Firstly, related theoretical foundation of GEAGD is introduced. Secondly, production performance and temperature and gas distribution in GEAGD process are analyzed based on experiment and numerical simulation in detail. At last, EOR principles of GEAGD are discussed.
Results of primary experiment show that larger oil production increase could be obtained by GEAGD process, and more than 6 times as much as cold production of oil production rate achieved by distributed heating GEAGD. At the same time, numerical simulation shows that more than 2 times of cumulative oil production could be obtained by dual-well concentrated heating GEAGD compared to cold production. Distributed heating or dual-well concentrated heating is recommended for GEAGD process, and heaters located in both injection well and production well or heater location in single injection well are preferred for concentrated heating GEAGD. Significant synergetic effects of gas and electrical heating are observed in GEAGD process, the gas sweep volume in GEAGD is enlarged by electrical heating compared to gas push process, at the same time, and heating volume is extended by gas flow and diffusion. Based on the achievement of this work, it is indicated that GEAGD is more feasible and potential to enhance heavy oil production than gash push and electrical heating.
Steam injection such as cyclic steam stimulation (CSS) and steam assisted gravity drainage (SAGD) is the main EOR processes for heavy oil production in the world, and more than 60% heavy oil is produced by steam injection. However, there are some disadvantages or challenges for conventional steam injection:
heat loss during steam flow in surface pipes and tubing (up to 20%~30% of steam enthalpy at the boiler outlet);
effect of condensed water-oil flow on oil production, heating efficiency reduction for the residued water;
sweep and heating efficiency decrease for steam phase splitting and steam overflow;
unfit for deeper reservoir, offshore reservoir, reservoir in desert district and other water sensitive reservoirs.
It is challenging to develop some innovative technology to recover steam stimulated reservoirs and unconventional heavy oil reservoirs such as offshore heavy oil reservoir not well recovered by cold production methods such as ESP.