Heavy oil emulsions such as water in oil (W/O), oil in water (O/W), and water in oil in water (W/O/W) would be formed during the development of heavy oil reservoirs. The key to the efficient development of heavy oil reservoirs is to clarify the fluidity of heavy oil emulsions in formation pores medium. In this study, the main factors that determine the fluidity of heavy oil emulsion were analyzed under the condition of simulating the formation pores medium. The reasons for the difference between the viscosity of heavy oil emulsions in formation pores medium and the viscosity measured by laboratory rheometer were analyzed. Then, experiments have confirmed the shortcomings of the current screening and evaluation method of emulsified viscosity reducer. Finally, through experimental research and mechanism analysis, the mechanism of the emulsified viscosity reducer was studied and suggestions were made to improve the effect of emulsified viscosity reducer in the oil field. When heavy emulsions flow in a formation pores medium, since the size of the droplets would be larger than the size of the pores medium, when the heavy emulsion passes through the pores medium, it would receive additional resistance brought by the Jiamin effect. But when a rheometer is used for viscosity testing, this additional resistance is almost nonexistent. Therefore, the current method of viscosity test using rheometer cannot fully reflect the actual flow state of heavy oil emulsion in formation pores medium. The research in this paper proves that the larger the droplets of the emulsion, the less accurate the rheometer test results. Temperature, permeability, oil–water ratio, and the type of emulsified viscosity reducer all have a certain effect on the flow of heavy oil emulsion in formation pores medium. This article evaluated four types of emulsified viscosity reducers. When the viscosity test was performed by a rheometer, the results showed excellent viscosity-reducing effects. However, when simulating formation pores medium conditions, the effects of some types of emulsified viscosity reducers are not so good. It is no longer accurate to judge the effect of emulsified viscosity reducer by the way of measuring viscosity with a rheometer. It should be screened by the flow capacity of the heavy oil emulsions in formation pores medium. In oil field development, the contact area of heavy oil and emulsified viscosity reducer solution should be increased as much as possible and provide more time for the substitution effect of emulsified viscosity reducer molecules.

This study carried out interfacial tension (IFT) test, sand surface element analysis and scanning electron microscope (SEM) image, rock-oil-emulsification system interaction test, microstructure, droplet size distribution and stability of oil in water (O/W) emulsion to clarify the porous media flooding mechanism of hydrophilic Nano-SiO₂ enhanced emulsification system. Results shows that by adding small amount of Nano-SiO₂ (0.01 wt.%) into anionic surfactant fatty alcohol polyoxyethylene ether sodium hydroxypropyl sulfonate (AEOSHS) solution (0.5 wt.%), the IFT of oil-water effectively reduced, the adsorption loss of AEOSHS on the formation sand surface was reduced by more than 70%, the droplet size of formed O/W emulsion reduced by 50%. This greatly improves the effective concentration of AEOSHS and emulsify heavy oil ability in formation away from injection well. Moreover, the spreading ability of oil on core surface is greatly reduced, and the width of diffusion zone is narrowed. Meanwhile, a very clear dividing line of oil can be seen which shows that the wettability of core has changed to water wet. The stability of formed O/W emulsion was further enhanced, and the coalescence and migration process of droplet is extremely slow. The oil recovery of AEOSHS+ Nano-SiO₂ system can effectively increase 21.95% of original oil in place (OOIP). Both the sand-packed tube experiment and the microscopic visual oil flooding experiment show that the system can not only expand the sweep volume, but also improve the oil displacement efficiency, which means that the combination system can significantly improve the oil displacement effect.

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. Introduction: 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.