Interfacial and Colloidal Forces Governing Oil Droplet Displacement: Implications for Enhanced Oil Recovery

Growing oil demand and the gradual depletion of conventional oil reserves by primary extraction has highlighted the need for enhanced oil recovery techniques to increase the potential of existing reservoirs and facilitate the recovery of more complex unconventional oils. This paper describes the interfacial and colloidal forces governing oil film displacement from solid surfaces. Direct contact of oil with the reservoir rock transforms the solid surface from a water-wet to neutrally-wet and oil-wet as a result of the deposition of polar components of the crude oil, with lower oil recovery from oil-wet reservoirs. To enhance oil recovery, chemicals can be added to the injection water to modify the oil-water interfacial tension and solid-oil-water three-phase contact angle. In the presence of certain surfactants and nanoparticles, a ruptured oil film will dewet to a new equilibrium contact angle, reducing the work of adhesion to detach an oil droplet from the solid surface. Dynamics of contact-line displacement are considered and the effect of surface active agents on enhancing oil displacement discussed. The paper is intended to provide an overview of the interfacial and colloidal forces controlling the process of oil film displacement and droplet detachment for enhanced oil recovery. A comprehensive summary of chemicals tested is provided

Low salinity waterflooding in carbonate reservoirs: review of interfacial mechanisms

Carbonate rock reservoirs comprise approximately 60% of the world’s oil and gas reserves. Complex flow mechanisms and strong adsorption of crude oil on carbonate formation surfaces can reduce hydrocarbon recovery of an oil-wet carbonate reservoir to as low as 10%. Low salinity waterflooding (LSW) has been confirmed as a promising technique to improve the oil recovery factor. However, the principal mechanism underpinning this recovery method is not fully understood, which poses a challenge toward designing the optimal salinity and ionic composition of any injection solution. In general, it is believed that there is more than one mechanism involved in LSW of carbonates; even though wettability alteration toward a more desirable state for oil to be recovered could be the main cause during LSW, how this alteration happens is still the subject of debate. This paper reviews different working conditions of LSW, previous studies, and field observations, alongside the proposed interfacial mechanisms which affect the colloidal interactions at oil–rock–brine interfaces. This paper provides a comprehensive review of studies on LSW in carbonate formation and further analyzes the latest achievements of LSW application in carbonates, which helps to better understand the challenges involved in these complicated multicomponent systems and potentially benefits the oil production industry

CO2 wettability of seal and reservoir rocks and the implications for carbon geo-sequestration

We review the literature data published on the topic of CO2 wettability of storage and seal rocks. We first introduce the concept of wettability and explain why it is important in the context of carbon geo-sequestration (CGS) projects, and review how it is measured. This is done to raise awareness of this parameter in the CGS community, which, as we show later on in this text, may have a dramatic impact on structural and residual trapping of CO2. These two trapping mechanisms would be severely and negatively affected in case of CO2-wet storage and/or seal rock. Overall, at the current state of the art, a substantial amount of work has been completed, and we find that: 1. Sandstone and limestone, plus pure minerals such as quartz, calcite, feldspar, and mica are strongly water wet in a CO2-water system. 2. Oil-wet limestone, oil-wet quartz, or coal is intermediate wet or CO2 wet in a CO2-water system. 3. The contact angle alone is insufficient for predicting capillary pressures in reservoir or seal rocks. 4. The current contact angle data have a large uncertainty. 5. Solid theoretical understanding on a molecular level of rock-CO2-brine interactions is currently limited. 6. In an ideal scenario, all seal and storage rocks in CGS formations are tested for their CO2 wettability. 7. Achieving representative subsurface conditions (especially in terms of the rock surface) in the laboratory is of key importance but also very challenging

Depression anxiety stress and substance use in medical students in a 5year curriculum

Background. The mental health of medical students is a global concern, and medical training has been described by some as being detrimental to the health of medical students, affecting both their student experience and professional life.Objectives. To determine the prevalence of depression, anxiety, stress and substance use among preclinical students in a 5-year outcomes-based medical curriculum. The study also investigated the association of selected demographic factors with these outcomes.Methods. All University of the Free State medical students in semesters 3 (n=164) and 5 (n=131) during 2015 were included in this cross-sectional study. Depression, anxiety and stress levels were measured by means of the Depression Anxiety Stress Scales (DASS-21). Demographic questions were included in an anonymous self-administered questionnaire. Lifetime and past month substance use were determined.Results. A prevalence of 26.5% for moderate to extremely severe depression, 26.5% for moderate to extremely severe anxiety, and 29.5% for moderate to extremely severe stress was recorded. Female students had significantly higher stress levels, but not increased anxiety. Relationship status and accommodation were not associated with these outcomes. Lifetime use of methylphenidate, lifetime use of alcohol, and past month use of alcohol were associated with depression.Conclusion. The study revealed high levels of depression, anxiety and stress in 2nd- and 3rd-year medical students compared with the general population, but the levels were comparable to those of medical students elsewhere in the world. Past month substance use of alcohol and cannabis was lower than in international studies, but nicotine use was higher

Depression, anxiety, stress and substance use in medical students in a 5-year curriculum

Background. The mental health of medical students is a global concern, and medical training has been described by some as being detrimental to the health of medical students, affecting both their student experience and professional life.Objectives. To determine the prevalence of depression, anxiety, stress and substance use among preclinical students in a 5-year outcomes-based medical curriculum. The study also investigated the association of selected demographic factors with these outcomes.Methods. All University of the Free State medical students in semesters 3 (n=164) and 5 (n=131) during 2015 were included in this cross-sectional study. Depression, anxiety and stress levels were measured by means of the Depression Anxiety Stress Scales (DASS-21). Demographic questions were included in an anonymous self-administered questionnaire. Lifetime and past month substance use were determined.Results. A prevalence of 26.5% for moderate to extremely severe depression, 26.5% for moderate to extremely severe anxiety, and 29.5% for moderate to extremely severe stress was recorded. Female students had significantly higher stress levels, but not increased anxiety. Relationship status and accommodation were not associated with these outcomes. Lifetime use of methylphenidate, lifetime use of alcohol, and past month use of alcohol were associated with depression.Conclusion. The study revealed high levels of depression, anxiety and stress in 2nd- and 3rd-year medical students compared with the general population, but the levels were comparable to those of medical students elsewhere in the world. Past month substance use of alcohol and cannabis was lower than in international studies, but nicotine use was higher