Our previous contact angle measurements showed that phase change plays an essential role in wettability, thus impacting heavy-oil recovery. While oil is the strongly wetting phase in the steam zone, it becomes the opposite in the condensation (hot-water) zone—regardless of temperature. We also showed that the reverse wettability can be changed using new generation chemicals including thermally resistant chemicals (special surfactants, alkalis, water soluble solvents, and ionic liquids). Even though they reveal useful information, contact angle measurements are limited in accounting for the importance of the wettability alteration effect on the phase distribution/entrapment and oil recovery. Micromodel studies are then preferred to assess these characteristics.
All observations and measurements in this research were conducted at temperatures up to 200°C on glass bead micromodels. The models were initially saturated with brine solution and then displaced by two types of mineral oils (450 cP and 111,600 cP at 25°C) to maintain initial water and oil saturation. Hot-water was then constantly injected into the micromodels to evaluate the impact of phase change and wettability status on residual saturation development. Similar parameters were also evaluated in pure steam injection by elevating the temperature to match the steam temperature and maintaining pressure below saturation pressure. Next, several chemical additives screened from the previous contact angle and thermal stability measurements were introduced during both hot-water and steam applications to observe their ability in modifying phase distribution, wettability state, and oil recovery at different pressures and temperatures.
The result of the experiments in the glass bead micromodel presented that phase distribution and wettability state were sensitive to steam phase (vapor yielded oil-wet or condensate yielded water-wet case). This phenomenon also aligned with the previous hypotheses indicating that phase change has an impact on the wettability state and residual oil saturation. At any circumstances, wettability alteration with chemicals was possible with the anionic surfactant and SiO2 nanofluid. The shape and characteristics of the trapped oil with and without chemicals were identified through micromodel images and suggestions were made as to the conditions (pressure, temperature, and time to apply during the injection application) at which these chemicals show optimal performance.
Study and analysis of phase distribution and wettability change in micromodels during hot-water and steam applications provide useful data and understanding of interfacial properties, oil trapping mechanism, and recovery performance of rock/bitumen/hot-water or steam system in the reservoirs. For practitioners, chemical additives were recommended, validated by visual images and thermal stability tests.