Abstract:
Low Salinity Waterflooding (LSWF) is one of Enhanced Oil Recovery (EOR) techniques that are often mentioned nowadays. Several studies showed that injecting low salinity water leads to Multi-component Ion Exchange (MIE) which is one of oil recovery mechanisms provided by this technique. This study was performed to investigate the effects of specific clay mineral in rock and ion in injected water.
First, representative clays were analytically tested to ensure their mineral compositions and the selected representative clays were tested by filtration with different water formulations to identify ionic capacities in MIE for each clay. Results obtained from filtration test and clay content of core were gathered to identify low salinity water formulations to use in second part performed by coreflooding test. During the coreflooding, oil recovery factor and pressure difference were detected and effluent from coreflood test was collected for ion analysis to accompany the explanation.
From the study, calcium ion was found to be the most powerful ion in MIE for all clays as it can replace magnesium ion at high magnitude. Potassium ion was the second powerful ion and it can replace calcium ion. High concentration of low salinity water (5,000 ppm) had more effect on clays with lower Cation Exchange Capacity (CEC) which are illite and kaolinite. Calcium ion and potassium ion were chosen to generate low salinity water formulation. From coreflood test, 1,000-ppm low salinity water was more favorable than 5,000 ppm. At lower concentration, magnesium ion bridging between oil and rock surface was broken from high salnity contrast, resulting in liberation of oil drops and pressure difference increases strikingly. Illite clay was favorable for MIE than kaolinite, which is lower in CEC. For cases that positively response to selected water formulations, and increment of oil recovery was in the range of 0.07 to 0.14 after conventional waterflooding.
