Abstract
The current study is focused on the effects of the individual key ions (Ca2+, Mg2+, (SO4)2-) along with a few of other common ions (Na+ and Cl-) on carbonate rock by only injecting water with controlled amount of individual or combined ions into the selected carbonate rock at reservoir temperature. A low field NMR technique has been a tool of choice for the current work since it allows monitoring the physical and chemical alteration of rock surface after interacting with fluids which contain specific types and amount of ions. In addition, since NMR is non-destructive measurement, the effect of various types of fluids with the identical rock sample before, during, and after core flooding test can be monitored repeatedly.
NMR results indicate that the water-rock interaction changes when injecting different types of ions. The interaction a of key divalent key ions, Ca2+, Mg2+, and (SO4)2-, on the carbonate rock surface are observed with relatively weak reactivity of Ca2+ compare to the other two. At the reservoir temperature, 90°C, the reactivity of Mg2+ with the carbonate rock is greater than that of Ca2+. The reactivity of multivalent anion (SO4)2- is also significant with carbonate rock surface, but it will induce surprising behavior on NMR response. The fundamental understandings acquired by the current study, effects of key ions in carbonate rock with single-phase fluid will be one of the key building blocks to develop rigid understanding of more complicated multi-phase fluid interaction with various types of reservoir rocks, and eventually draw conclusions on how these ions change rock wettability.
