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Differing from conventional emulsions, water‐in‐oil (W/O) emulsions are produced with no additional surfactants in this study. The testing results show that both interfacial tension (IFT) and dilational modulus at all salinities and pH are much higher than those of normal emulsions. A high IFT is not good for making emulsions, but a higher dilational modulus will contribute to more stable emulsions. Emulsion stability declines slightly as salinity increases and the most unstable W/O emulsion appears at pH = 7. To deeply understand the effects of salinity and pH on emulsion stability, petroleum acid is extracted and characterized using Fourier transform ion cyclotron resonance mass spectrometry.

N2 and CO2 assisted steam huff-n-puff method has been proposed as the primary strategy to develop a new heavy oil reservoir located in the northeast of China having average oil viscosity of 5000mPa·s, reservoir pressure of 14MPa and temperature of 56°C. Prior to field application, a laboratory study from phase behavior to numerical simulation was conducted in this work. The experimental data showed that the swelling of the heavy oil as a result of CO2 dissolution varied almost linearly with pressure, but appeared independent on N2 pressure. CO2 markedly outperformed N2 in swelling heavy oil reducing viscosity and extracting hydrocarbon. In huff-n-puff simulation, averagely 4% and 6% of additional heavy oil was produced by steam injection compared to CO2 and N2 injection after natural depletion. In the scenario of gas assisted steam process, a more noticeable incremental oil recovery (>10%) was produced, which thus demonstrated its potential in this reservoir. The mechanisms of oil recovery stimulation were further elucidated using numerical simulation from the point of parameter variations for pressure, viscosity, temperature, and oil saturation.

The foam performance in the presence of oil plays an important role in foam application in enhancing oil recovery. The present study systematically investigated the effect of oil type, oil content, surfactant type, surfactant concentration, alkane chain length, salinity, and polymer concentration on foam performance in both the absence and presence of oil. The results showed that oil viscosity and oil density as well as oil component all contributed to foam performance in the presence of oil. Within a certain oil content, both light oil and heavy oil had a positive effect on foam, but heavy oil had a higher tendency to stabilize the foam. The order of foam performance by different surfactants was changed by the oil. It is noteworthy that heavy oil is detrimental to sodium dibutyl naphthalene sulfonate (BM) foam. Light oil can improve foam performance while heavy oil can harm foam in some specific cases. Lower salinity, longer alkane chain length, higher surfactant concentration and the presence of a polymer all benefited foam in the presence of crude oil.

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