New Insights on the Role of Multivalent Ions in Water-Carbonate Rock Interactions

Kwak, Hyung Tae (Saudi Aramco) | Yousef, Ali A. (Saudi Aramco) | Al-Saleh, Salah (Saudi Aramco)

OnePetro 

Since the first introduction of Smart Waterflooding in carbonates rocks by Saudi Aramco in 2010 (Yousef et al., 2010), tuning the salinity and ionic composition of injecting water in carbonate reservoir has been considered as one of the most promising economical IOR/EOR method. Thanks to the numerous efforts in this field of researches for last a few decades, it is quite clear rock wettability alteration is one of the key mechanisms for increasing oil recovery. So far, most studies related to low salinity effects and Smart Waterflooding focused on the physical and chemical pore system alterations with multi-phase fluid system, which includes water and oil in either sandstone or carbonates. Without, however, fundamental understanding of single-phase fluid (water) - rock interaction, there will always be unanswered questions lying behind the study related to the IOR/EOR by controlling water chemistry.
The current study is focused on individual key ions (Ca2+, Mg2+, (SO4)2-) effects on carbonate rock by only injecting water with controlled amount of separate or combined key ions into the selected carbonate rock. A recently proposed MR-CT microscopy (Kwak et al., 2012) has been a tool of choice for the current research work since it can monitor the physical and chemical alteration of rock surface after interacting with fluids with specific types and amount of ions. In addition, since MR-CT microscopy is non-destructive measurement, the effect of various types of fluids with the identical rock sample before, during, and after core flooding test repeatedly.
NMR results indicate that the magnitude of water-rock interaction changes when injecting different types of ions. These results provide more insight on how key ions interact with carbonate rock surface. In addition, the different reactivities of rock surfaces with different mineralogy have been monitored when specific types of ions are injected. The fundamental understanding acquired by the current study, effects of key ions in carbonate rock with single-phase fluid will be a very important stepping stone to build 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.