Secondary Application of Low Salinity Waterflooding to Forties Sandstone Reservoirs

Abstract

Low salinity waterflooding (LSWF), versus high salinity waterflooding (HSWF) has been the focus of significant research at various centres around the world, yet there is still considerable debate over the exact mechanism that provides incremental oil recovery. The use of the LSWF technique is not widespread in the United Kingdom continental shelf (UKCS). However, it has been announced that the Clair Ridge development will deploy low salinity waterflooding (LSWF) in secondary mode from the start of field life, and a number of companies are currently assessing the applicability of the technique through high level screening and core flooding. Forecasting the potential oil recovery under LSWF is heavily influenced by the simulation technique that is used. Presently the most widely discussed approach is the use of a weighting table with relative permeabilities representing the high and low salinity cases. As the grid block falls below threshold salinity, the simulator utilises the weighting table to assign an interpolated value of salinity. This value of salinity is utilised to represent a change in wettability. While this approach approximates the net effect of LSWF, it does not capture the oil/rock/brine interaction. This study examines the modelling approach to LSWF utilising an in-house generic Forties Palaeocene model in CMG's STARS simulator. The conventional approach of modelling LSWF using high and low salinity relative permeabilities is compared to the latest Multi-component Ion Exchange (MIE) methods by numerical simulation to assess the impact on incremental oil recovery. A sensitivity analysis is then carried out on the effects of specific parameters on incremental oil recovery, utilising published data from fields in the Forties Palaeocene fan system. A discussion is provided. The impact on secondary recovery was accessed with respect to wettability alteration; injection salinity (LSWF versus HSWF); oil viscosity and aquifer influx. The application of LSWF in secondary mode to the Forties Palaeocene Sandstones was found to be favourable for the case of mixed-wet reservoirs.

From Mineral Surfaces and Coreflood Experiments to Reservoir Implementations: Comprehensive Review of Low-Salinity Water Flooding (LSWF)

“…Reservoir simulation modeling results showing percentage incremental oil recovery observed by multiple researchers in recent years. At the reservoir scale, fines migration, MIE, geochemistry, and wettability modification have been identified as major drivers of LSWF. ,,,,,, The volume of produced formation water has also affected the impact of LSWF, even in the presence of other mechanisms . With a general positive LSWF outlook, the only exception has been heavy oil reservoirs, which are normally characterized with low recovery factors due to high viscosity and heavy-metal contents. , Orange bars represent oil recovery by high-salinity water, while gray bars represent incremental oil recovery by LSWF.…”

“…Using reservoir simulation, a majority of incremental recovery observed were attributed to influence of capillary forces leading to wettability alteration, i.e., an increase in relative permeability of rock to water and corresponding decrease in oil relative permeability as a driver of wettability improvement. ,,, Other researchers such as Law et al discovered that the association of low salinity with intra-aqueous and mineral reactions, in addition to clay content and acid number, are evidence of better EOR performance.…”

Comprehensive investigation of low-salinity waterflooding in sandstone reservoirs

“…However, Shell applied the LSWF with 500 ppm in Omar oil field in Syria due to operational requirements. The analysis indicated that there was a decrease in the wettability from the original, which may be responsible for an expected incremental recovery of about 5-15% from the OOIP (Law et al 2014).…”