Investigation of chemical effects of long-term water flooding on reservoir rocks

In carbonate reservoirs, the rock surface is of particular importance for recovery mechanisms. The polar compounds contained in oil are capable of adhering to the surface of the reservoir rock in competition with water molecules. Depending on the composition of the oil and reservoir conditions, the resulting surface has different properties, denoted in petroleum engineering as oil- or water-wet.

The polar molecules form strong bonds with the surface of the calcite crystals, leaving their hydrocarbon structure facing away from the surface, where they can interact with other compounds in oil through hydrogen bonding or van der Waals forces, forming a thick immobile layer of crude oil on the rock surface.

The effective application of water-injection methods requires considering the interplay of brine, oil and surface in order to optimize solutions for a particular reservoir. Due to the complex nature of the phenomena the composition of the crude oil has a pivotal impact. Infrared (IR) spectroscopy has been used to perform chemical fingerprinting of the adsorbed oil to observe how properties of the surface may change in response to changing conditions.

This information can then be used when designing injection strategies or to anticipate the reservoir response to production chemicals.