RESUMO
Wettability alteration (from oil-wet to mixed- or water-wet condition) is the most prominent mechanism in low-salinity water flooding (LSWF) for enhanced oil recovery (EOR) in sandstone reservoirs. Although several factors influence the wettability alteration, many efforts have been made to find the main controlling factor. In this study, the influence of interface properties of sandstone/brine and thermodynamic equilibrium of sandstone minerals were evaluated to understand the wettability alteration during LSWF. A triple-layer surface complexation model built-in PHREEQC was applied to a quartz/brine interface, and the modeling results were verified with zeta potential experimental data. This model was combined with that of kaolinite/brine to predict sandstone/brine interface properties. The measured and predicted sandstone zeta potentials were between those obtained for quartz and kaolinite in the diluted seawater. The predicted surface potential of sandstone together with that of crude oil was used in extended Derjaguin-Landau-Verwey-Overbeek theory to estimate the attractive or repulsive force. Consideration of thermodynamic equilibrium between minerals and solution significantly increased the pH and hence resulted in an increase in negative surface potential in the surface complexation. This provided a strong repulsive force between crude oil and sandstone, thus resulting in a more water-wet condition.
RESUMO
BACKGROUND CONTEXT: Halo fixation is now universally performed in the initial reduction and fixation of unstable upper cervical spine injuries; however, persistent high instability and recurrent dislocations of the atlantooccipital and atlantoaxial joints after fixation are not well recognized. PURPOSE: The aim was to describe persistent instability of traumatic dislocations of the atlantooccipital and atlantoaxial joints after halo fixation and a useful method for preventing instability. STUDY DESIGN: This was a case report of a patient who survived traumatic dislocations of the atlantooccipital and atlantoaxial joints. PATIENT SAMPLE: A 73-year-old woman diagnosed with dislocations of the atlantooccipital and atlantoaxial joints along with multiple other injuries sustained in a traffic accident was included. METHODS: After initial closed reduction and halo fixation, congruity of the atlantooccipital and atlantoaxial joints was evaluated using, condylar gap, atlantodental interval, and flexion angulation of C1-C2 after the initial examination and before surgery. RESULTS: Changes in parameters 12 hours after halo fixation revealed re-dislocations and instability of the joints. Backrest elevation with halo fixation tended to reduce re-dislocations. Therefore, we carefully increased the backrest angle and measured the parameters at several angles of elevation within a range that did not affect vital signs to observe the effectiveness of elevation against re-dislocations. Elevation changed the parameters in an elevation angle-dependent manner, and these changes suggested that elevation was effective for reducing re-dislocation of both the atlantooccipital and atlantoaxial joints during halo fixation. With no major complications, this method enabled us to maintain good congruity of the joints for approximately 2 weeks until posterior spinal fusion with internal fixation. CONCLUSIONS: Backrest elevation with halo fixation appears safe to be performed without any other devices and is beneficial for blocking re-dislocation of both the atlantooccipital and atlantoaxial joints as well as possible secondary damage to the upper cervical spinal cord during the external fixation period.