Secondary Application of Low Salinity Waterflooding to Forties Sandstone Reservoirs

Law, Stuart (Senergy Ltd) | Sutcliffe, Philip Graham (Senergy Ltd) | Fellows, Susan Alison (Computer Modelling Group Ltd.)

OnePetro 

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.

Introduction

Low salinity waterflooding (LSWF) is an enhanced oil recovery (EOR) technique which is of growing interest,as it represents a low cost and flexible form of EOR. The technique involves the injection of water at of a significantly lower salinity, compared to the natural salinity of the reservoir connate water. Until recently, although it was known that the ionic composition of a fluid flowing in a porous medium does influence the measured permeability ( Schleidegger 1974), the manipulation of this effect to improve oil recovery by injecting water of a different salinity and ionic composition to that of the natural formation water, had not been considered.  As compared to the normal method of injecting seawater ( HSWF), LSWF is seen as a viable EOR technique.   Further, LSWF offers the potential to increase recoverable oil without the need for re-engineering of the field, as it can use the existing infrastructure and wells, provided that facilities space exists topsides for installation of a reverse osmosis plant.

  Country: North America > United States (0.94)
  Industry: Energy > Oil & Gas > Upstream (1.00)
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