Fluid-Fluid Interfacial Effects in Multiphase Flow during Carbonated Waterflooding in Sandstone: Application of X-ray Microcomputed Tomography and Molecular Dynamics.

Fluid-fluid interfacial reactions in porous materials are pertinent to many engineering applications such as fuel cells, catalyst design, subsurface energy recovery (enhanced oil recovery), and CO2 storage. They have been identified to control physicochemical properties such as interfacial rheology, multiphase flow, and reaction kinetics. In recent years, engineered waterflooding has been identified as an effective way to increase hydrocarbon recovery and solid-fluid interaction has been assessed as the key mechanism. However, in this study, we demonstrated that in the absence of solid-fluid interactions (in strong hydrophilic porous media), fluid-fluid interfacial reactions can significantly affect multiphase flow and thus lead to an increased hydrocarbon recovery during engineered carbonated waterflooding. We designed a microwaterflooding system to evaluate the interfacial reactions during two phase flow with engineered carbonated waters. Given that salinity controls the amount of dissolved CO2, we injected carbonated high salinity water and carbonated low salinity water to achieve different fluid-fluid reactions. We injected the carbonated water in a sandstone with 99.5% quartz under X-ray microcomputed tomography (µCT) scanning at a resolution of 3.43 µm per pixel. Image processing shows that carbonated low salinity waterflooding can recover 8% more oil than carbonated high salinity waterflooding, while the quartz-rich sandstone remains strongly hydrophilic in both samples. A gradual CT intensity distribution indicates an interfacial phase generation between carbonated brine and crude oil during carbonated waterflooding. Therefore, we attributed the additional hydrocarbon recoveries to the fluid-fluid interfacial reactions. To understand the effects of fluid-fluid reactions on interfacial properties, we performed molecular dynamics simulations to investigate the chemical species distribution at the interface, interfacial tension (IFT) changes, and CO2 diffusion. The MD simulation results revealed a layered structure of the interface, a lower CO2 diffusion coefficient in carbonated high salinity water, a lower IFT in carbonated low salinity water, a swelling hydrocarbon phase in carbonated low salinity water, and more CO2 accumulated at the interface between the hydrocarbon phase and carbonated low salinity water. This work provides a general and fundamental understanding of the influence of fluid-fluid interactions on the interfacial properties between carbonated water and the hydrocarbon interface.

Electrostatic Origins of CO2-Increased Hydrophilicity in Carbonate Reservoirs.

Injecting CO2 into oil reservoirs appears to be cost-effective and environmentally friendly due to decreasing the use of chemicals and cutting back on the greenhouse gas emission released. However, there is a pressing need for new algorithms to characterize oil/brine/rock system wettability, thus better predict and manage CO2 geological storage and enhanced oil recovery in oil reservoirs. We coupled surface complexation/CO2 and calcite dissolution model, and accurately predicted measured oil-on-calcite contact angles in NaCl and CaCl2 solutions with and without CO2. Contact angles decreased in carbonated water indicating increased hydrophilicity under carbonation. Lowered salinity increased hydrophilicity as did Ca2+. Hydrophilicity correlates with independently calculated oil-calcite electrostatic bridging. The link between the two may be used to better implement CO2 EOR in fields.

INTRAVENOUS DEXAMETHASONE IN COMBINATION WITH CAUDAL BLOCK PROLONGS POSTOPERATIVE ANALGESIA IN PEDIATRIC DAYCARE SURGERY.

BACKGROUND: This study was conducted to determine if intravenous dexamethasone combined with caudal block was able to prolong post-operative analgesia in pediatric daycare surgeries. METHODS: Sixty four ASA I or II children aged 3 to 10 year old scheduled for daycare open unilateral herniotomy received general anesthesia and caudal block using 0.25% levobupivacaine 0.75 mg.kg(-1) with suppository paracetamol 30 mg.kg(-1). After anesthesia induction, they were randomized to receive either intravenous dexamethasone 0.5 mg.kg(-1) (Group I) or same volume intravenous normal saline (Group II). Postoperatively, pain scores were assessed using Wong- Baker faces scale. At home, their parents assessed and recorded the pain scores, time to first oral paracetamol served and frequency of paracetamol given in two consecutive days post surgery. On the third postoperative day, these information were gathered from the parents via a phone call. RESULTS: There were statistically significant differences between Group I and Group II in the median time to first paracetamol (800 vs 520 min, p = 0.01), mean pain scores postoperative day 1 (1.9 ± 2.0 vs 3.5 ± 2.2, p = 0.05), mean pain score-postoperative day 2 (0.8 ± 1.6 vs 2.3 ± 2.0, p = 0.03) and mean frequencies of paracetamol given on postoperative day 2 (0.3 ± 0.8 vs 1.1 ± 1.0, p = 0.02). CONCLUSION: A single intravenous dexamethasone dose when combined with caudal block reduces postoperative pain, decreases paracetamol requirement and prolongs analgesic duration in children after open herniotomy.