Enhanced oil recovery in carbonate rocks using seawater spiked with copper chloride: Imbibition experiments

Abstract

It is widely accepted that oil recovery during waterflooding can be improved by modifying the composition of the injected brine, typically by depleting the total salinity or altering potential determining ions (PDI) such as: Ca2+, Mg2+, and SO42− concentration. Numerous laboratory experiments and field tests have demonstrated this effect in both clastic and carbonate rock Samples and reservoirs. However, some authors have found alternative ions, such as phosphate (PO42−) and borate (B(OH)4-) which, in some cases, presented additional recovery and have thus opened the discussion for potential alternative ions to enhanced oil recovery. With this in mind, copper ion's potential for enhanced oil recovery (EOR) was studied, combining different conditions usually employed on smart water experiments, such as depleting the total salinity and removing the PDI to highlight the real effect of copper on additional oil recovery. The investigation was carried out with Brazilian pre-salt reservoir Samples in imbibition experiments using Amott cells at ambient pressure and 63 °C. The evaluation of the copper effect on oil recovery for coreflooding was proved in a previous paper by Bernadinelli et al. (2021), however the analysis with imbibition experiments in this study aim to clarify the effect of copper on the capillary pressure, by analyzing the eventual additional oil production. These Samples were prepared and aged, and the oil production was monitored during the experimental time. The experiments were carried in four sequences to evaluate the effect of copper on oil recovery, consisting first of salinity reduction from 0% of sodium chloride to 100% of the original amount in the seawater (SW), followed by the removal of PDI salts, the study of the production mode (secondary or tertiary), and the analysis of the copper chloride concentration on the final recovery. The results using copper at the secondary recovery showed remarkable increases (from 6.3% to 10.0%) of the original oil in place (OOIP) compared to the oil recovered from the formation water (FW). In tertiary mode, the best recoveries occurred at salinities between 8 and 18 kppm and copper chloride (1 g/L), and presented increasing recoveries 3.9%, 5.8%, and 9.3% of OOIP. This work presents an initial investigation on the use of copper as an active ion for the smart water effect and sheds light on its effect on both secondary and tertiary modes for strategies of recovery that use soaking methods and also for fractured reservoirs.