Raudhatain Mauddud Carbonate Sensitivity to Low Salinity Injection

Low Salinity water- flooding is a relatively inexpensive EOR technology that can recover incremental oil. A laboratory coreflood evaluation was performed to investigate if a low salinity water will produce incremental oil from the Raudhatain Mauddud formation in Kuwait. The laboratory study primary objective was to investigate incremental oil recovery potential with the secondary objective of determining if a low salinity water will have any fluid flow ramifications.

Contact angle measurements were performed with waters varying in salinity from reservoir water with a TDS of 190,000 mg/L to 500 mg/L to determine wettability alteration. Core mineral composition was determined using X-ray diffraction analysis. X-ray fluorescence analysis determined ion composition. Linear corefloods using preserved core were used to determine if additional oil can be recovered by lowering injection water salinity and to determine if the injection water salinity will affect injectivity. Atomic adsorption spectroscopy was used to analyze coreflood effluent for cation concentrations.

Core contact angle measurements indicate no change in wettability when water salinity was reduced from 190,000 mg/L to 500 mg/L. Relative permeability determinations indicate the core is intermediate to water-wet. Average residual oil saturation to high salinity water was 0.348 PV. Seawater of ∼50,000 mg/L TDS dropped average oil saturation to 0.338 PV. Low-salinity water reduced residual oil saturation to an average of 0.295 PV for an average incremental oil recovery of 6.5% OOIP. Average peak oil cut response was an increase of 3.2%. Differential pressure measurements showed injectivity loss when lower salinity waters were injected. Injection of 500 mg/L water and sea water (50,000 mg/L) following produced water resulted in a 6-fold reduction of injectivity. As each respective water injection continued injectivity was restored as the injected water and core ion balance reached equilibrium. In the graded salinity coreflood, injection loss was observed with injection of each subsequent lower-salinity solution until the final water of 500 mg/L. Injection of produced water after the low saline waters re-established the original ion balance and increased injectivity values to prior to low saline water injection or greater.

Correlating ion balance between core and injected water with injectivity loss and subsequent increase in injectivity as a new ion equilibrium is established but has not been reported. Ramifications for injection of low salinity waters into carbonate reservoirs is that injectivity could be restored if sufficient volume of the low saline water is injected to establish a new rock-water equilibrium near well bore.