Abstract Low permeability reservoirs contain a large volume of the world's oil resource. Often these fields are characterised by low waterflood injectivity, poor sweep and low productivity. A substantial number of these fields are initially, or during production become, fractured. Improved oil recovery and EOR for these fields is an attractive goal, although many conventional EOR applications present major challenges.
We present results on how wettability alteration, together with physical and chemical modifications of the waterflood, can improve oil recovery. From high precision adsorption experiments, together with wettability measurements on model systems, we present conclusions on the inter-relationship of adsorption behaviour and wettability of reservoirs.
Laboratory measurements are presented confirming how:
Wettability can be modified through changes in salinity, hardness and temperature.
In waterflooding there is a direct, measurable relationship between wettability (contact angle) and adsorption at the solid / liquid and liquid / liquid interfaces. These inter-relationships can be expressed in basic thermodynamic concepts.
Adsorption at solid / liquid interfaces can be directly related to the existence and nature of thin aqueous films in water wet and mixed wet reservoirs. Dynamic effects resulting from brines of different chemical and physical properties can be highly important in terms of displacement efficiency during waterflooding.
We demonstrate the significance of these results for waterflooding and EOR in lower permeability fields. Approaches such as wettability alteration, low salinity (including brine compositional modification) waterflooding, and variation of injection brine temperature all show potential. This is in contrast to more traditional chemical and immiscible gas injection, which are often technically difficult in these fields. We further conclude that these approaches can be beneficially applied fields with substantial fracturing and faulting.