FIELD BRINE COMPOSITION IMPACT ON TERTIARY OIL RECOVERY FROM CARBONATE RESERVOIRS AN EXPERIMENTAL STUDY

The impact of brine salinity and ion composition on oil recovery has been an area of research in the last years. Evidence from laboratory studies supported by some field tests has distinctly shown that oil recovery depends on the injected water salinity and ion composition. This paper presents the results of laboratory coreflooding study conducted using composite cores from a Saudi Arabian carbonate reservoir to investigate the impact of salinity and ionic content on oil/brine/rock interactions and eventually on oil recovery. The experimental parameters and procedures were well‑designed to reflect the reservoir conditions and current field injection practices, including reservoir pressure, reservoir temperature, salinity and ionic content of initial formation water and current types of injected water. Two systematic coreflood experiments‑each with a type of field injection water‑‑ were deliberately conducted using the same rock samples to neutralize the discrepancies that appear from variation in rock properties, and eventually to assess accurately the impact of salinity and ion composition on oil recovery. The experimental results revealed that substantial tertiary oil recovery beyond conventional waterflooding can be achieved by altering the salinity and ionic content of one type of field injected water. The new emerged trend is distinct from what have been addressed in previous reported studies on topics of low salinity waterflooding for sandstones, or seawater injection into high temperature chalk reservoirs; also it is considered by all measures a significant achievement in terms of large incremental recovery, application to carbonate reservoirs, and unique coreflooding experimental parameters and procedures.