Pore-scale processes in tertiary low salinity waterflooding in a carbonate rock: Micro-dispersions, water film growth, and wettability change.

HYPOTHESIS: The wettability change from oil-wet towards more water-wet conditions by injecting diluted brine can improve oil recovery from reservoir rocks, known as low salinity waterflooding. We investigated the underlying pore-scale mechanisms of this process to determine if improved recovery was associated with a change in local contact angle, and if additional displacement was facilitated by the formation of micro-dispersions of water in oil and water film swelling. EXPERIMENTS: X-ray imaging and high-pressure and temperature flow apparatus were used to investigate and compare high and low salinity waterflooding in a carbonate rock sample. The sample was placed in contact with crude oil to obtain an initial wetting state found in hydrocarbon reservoirs. High salinity brine was then injected at increasing flow rates followed by low salinity brine injection using the same procedure. FINDINGS: Development of water micro-droplets within the oil phase and detachment of oil layers from the rock surface were observed after low salinity waterflooding. During high salinity waterflooding, contact angles showed insignificant changes from the initial value of 115°, while the mean curvature and local capillary pressure values remained negative, consistent with oil-wet conditions. However, with low salinity, the decrease in contact angle to 102° and the shift in the mean curvature and capillary pressure to positive values indicate a wettability change. Overall, our analysis captured the in situ mechanisms and processes associated with the low salinity effect and ultimate increase in oil recovery.

Pore-scale imaging and analysis of low salinity waterflooding in a heterogeneous carbonate rock at reservoir conditions.

X-ray micro-tomography combined with a high-pressure high-temperature flow apparatus and advanced image analysis techniques were used to image and study fluid distribution, wetting states and oil recovery during low salinity waterflooding (LSW) in a complex carbonate rock at subsurface conditions. The sample, aged with crude oil, was flooded with low salinity brine with a series of increasing flow rates, eventually recovering 85% of the oil initially in place in the resolved porosity. The pore and throat occupancy analysis revealed a change in fluid distribution in the pore space for different injection rates. Low salinity brine initially invaded large pores, consistent with displacement in an oil-wet rock. However, as more brine was injected, a redistribution of fluids was observed; smaller pores and throats were invaded by brine and the displaced oil moved into larger pore elements. Furthermore, in situ contact angles and curvatures of oil-brine interfaces were measured to characterize wettability changes within the pore space and calculate capillary pressure. Contact angles, mean curvatures and capillary pressures all showed a shift from weakly oil-wet towards a mixed-wet state as more pore volumes of low salinity brine were injected into the sample. Overall, this study establishes a methodology to characterize and quantify wettability changes at the pore scale which appears to be the dominant mechanism for oil recovery by LSW.

Antenatal administration of vitamin K1: relationship to vitamin K-dependent coagulation factors and incidence rate of periventricular-intraventricular hemorrhage in preterm infants; Egyptian randomized controlled trial.

OBJECTIVES: To determine the effect of maternal antenatal administration of vitamin K1 on activity level of vitamin K-dependent coagulation factors and on the occurrence of periventricular-intraventricular hemorrhage (PIVH). METHODS: This study was conducted on 90 infants who were classified into; Group A: 30 preterm whose mothers received antenatal vitamin K1, Group B: 30 preterm whose mothers did not receive antenatal vitamin K1, and Group C: 30 healthy full term newborns as a control group. All newborns were subjected to measurement of the activity level of vitamin K-dependent coagulation factors (FII, FVII, FIX and FX). Cranial ultrasound was done on the 1st, 3rd and 7th days of life. RESULTS: Group B showed significantly lower activity level of FII and FX with higher incidence of PIVH compared with group A. Neonates who developed PIVH by the 7th day in both group A and B had significantly lower activity level of vitamin K-dependent coagulation factors. CONCLUSION: when antenatal vitamin K1 was given to pregnant women at imminent risk of preterm labor, their preterm neonates were able to achieve a clotting status approaching that of full term neonates and are less liable to develop PIVH.