Microbial Fluid-Rock Interactions in Chalk Samples and Salinity Factor in Divalent Ca²⁺ ions Release for Microbial Enhanced Oil Recovery Purposes

In this study, laboratory experiments were performed on chalk samples from Danish sector of the North Sea to study microbial fluid-rock interactions with carbonate rock and to evaluate the dissolution of rock matrix (CaCO3). Result showed that the average concentration of Ca2+ ions after microbial fluid interactions with chalk samples in media of salinity 40-100g/l increased from initial average concentration of 203 mg/l at the start of the experiment to 1178 mg/l in 28 days. 3-D surface plot (salinity, Ca2+, pH) with time revealed delineation of the measured salinity into two groups with a boundary between 70 - 80 g/l. In the low salinity group (40, 50, 60, 70 g/l) pH increased but decreased in the high salinity group (80, 90, 100 g/l) at the end of the experiment. The highest Ca2+ ion concentrations was measured at highest salinities at the end of experiment which means that the dissolution rate of chalk increased with increase in salinity due to the lower values of pH as an indication that higher salt concentration facilitates more acid production by bacteria.