A Laboratory Study of Ionic Effect of Smart Water for Enhancing Oil Recovery in Carbonate Reservoirs

Abstract

Enhanced oil recovery by smart waterflooding represents an implementable and attractive emerging oil recovery technology. For sandstone reservoirs, smart waterflooding has shown an outright incremental oil recovery in most laboratory and field tests while some promising experimental data have been presented from carbonates. It seems more difficult to assume a favorable performance for some reservoir formation a priori while dismissing the other, so more data and better understanding of the underlying mechanism in carbonates are needed. This paper describes a series of experiments on Middle East carbonate core plugs designed to determine the impact of formation water and different versions of seawater (which has its sulfate concentration increased in the ratio (0.5:1:2:4:8) on oil recovery, wettability and surface charge modification. The results obtained lead to the following conclusions: Coreflooding experiments at 2300F and 3000psi with formation brine and various versions of seawater coupled with spiking sulfate concentration executed on carbonate core aged showed an incremental recovery of about 10% OOIC; An increasing concentration of sulfate in the seawater makes a Crude Oil/Brine/Rock system less oil-wet; The higher the sulfate concentration, the greater the repulsive forces in the electrical double layer, thereby forming an aggregate and detaching the oil from the rock surface, while increasing the sulfate concentration beyond four times seems ineffective as it gave a swift increase in pH and rock surface charges; The results obtained are therefore discussed within the framework of mechanisms previously described for smart water's ability to enhance oil recovery. The study concluded that a relatively economical modification of injection brine composition could considerably increase oil recovery.

Significance of Fines and their Correlation to Reported Oil Recovery

“…It was observed that none of the effluent samples had any insoluble salt fractions present (as shown in Figure 7). Thus no precipitate was observed in the effluent vials (Awolayo et al 2014). All mobile fines must have got dissolved as solubility of anhydrite increase significantly with decrease in temperature.…”

“…In data set 4 lime stone reservoir core plugs was flooded with 3 different brines of varied SO 4 2concentration (Awolayo et al 2014). For first 10 PV, high salinity formation water was introduced.…”

“…For first 10 PV, high salinity formation water was introduced. Thereafter for the following 8 PV normal sea water was injected and for the final 7 PV Sea water with four times sulphate was injected (Awolayo et al 2014). The reported effluent concentration corresponding to each PVI was used to back calculate the brine speciation in reservoir condition.…”

“…During these water flooding experiments (Vo et al 2012;Chandrasekhar et al 2013;Awolayo et al 2014;Shariatpanahi et al 2010;RezaeiDoust et al 2009) the composition of the effluent has been calculated at ambient concentration and this composition has been there after co-related the observed oil recovery. But the effluent that came out of core plug at elevated pressure /temperature could have had significantly different properties.…”

Importance of Fines in Smart Water Enhanced Oil Recovery (SmW-EOR) for Chalk Outcrops

“…2011). For carbonate reservoirs it has also been shown that increase in SO 4 2-concentration is associated to oil recovery only up to an optimum concentration, beyond which no additional oil recovery is observed (Awolayo et al 2014).…”