Recovery mechanism due to brine injection (Dynamic Water, Low Salinity, etc.) in carbonate remains a point of discussion and widely open for research. As wettability alteration is heavily suggested as the main driver for recovery, this study focuses on the in-situ evaluation of wettability alteration due to multiple successive dynamic water flooding of carbonate cores plugs.
Five different core flooding with Nuclear Magnetic Resonance (NMR) T2 monitoring were performed on three different carbonate core plugs. These plugs were fully characterized in terms of petrophysical parameters and petrography. NMR T2 measurements were performed throughout the core flooding experiment including the heat up, brine injection, soaking and cooling down.
Initial results on two samples that are of similar T2 distribution showed relatively different irreducible water saturation (10.7 and 14.9 %) after centrifugation and an NMR T2 inverted wettability after ageing of (-0.15 and -0.04). in the first case, the core was flooded with Gulf sea water. NMR showed clear trend towards increasing water wetness as a result of subjecting the cores with soaking periods, this accompanied with a clear additional recovery following the soaking. In the second case, the core was flooded with Gulf sea water followed by 10 times diluted sea water. Despite a high similarity with the previous core plug, recovery with sea water flooding alone resulted in 57% recovery without further recovery when the other brines were injected. In this case, where most of the effects seems to be happening during the first flooding, NMR, consistently with the production data, did not detect any clear wettability change during the soaking periods.
The results clearly indicate, for the first time, an in-situ wettability alteration due to Dynamic Water injection as demonstrated by NMR T2 distribution analysis.