Nontoxic low-cost amines as wettability alteration chemicals in carbonates

It is possible to improve the oil recovery from low temperature, oil-wet/neutral-wet, fractured carbonate reservoirs by spontaneous imbibition of water using nontoxic low-cost primary amines, R–NH2, as wettability alteration chemicals added to the injection water. The present paper discusses possible limitations in the performance of the chemicals such as solubility, pH, carbonate dissolution, and temperature effects. It was observed that C10-amine was compatible with high salinity brine at pH<7 in the temperature range of 20–70 °C, but C12-amine was insolvable at similar conditions. C10-amine (1.0 wt.%) was dissolved in brine at pH=6.5 and imbibed spontaneously into oil-wet reservoir dolomite cores at 20 and 40 °C. The oil recovery varied between 50% and 75% of original-oil-in-place (OOIP) depending on the core properties. The mechanism for the wettability alteration using C10-amine is believed to be similar to the previously studied C12TAB system, i.e., desorption of strongly adsorbed carboxylates from the carbonate surface by the formation of ion-pairs. At 70 °C, C10-amine appeared to fail as a wettability-modifying chemical, probably due to the dissolution of carbonate rock. The concentration of the active component C10NH3+ in the aqueous phase of the pores decreases in this dissolution process. Advancing contact angle measurements on oil-treated calcite crystals confirmed the potential of the C10-amine solution to make the surface strongly water-wet at pH=6.5 in the temperature range of 20–90 °C.