(59j) Improved Oil Recovery with Viscoelastic Surfactant: Screening and Effectiveness of Formulations

Middle East carbonate reservoirs are usually characterized as high temperature and high saline (HTHS) reservoirs. In chemical enhanced oil recovery (cEOR), interfacial tension (IFT) and capillary number are the key parameters that alter the reservoir environment. Viscoelastic surfactant (VES) is introduced due to its dual capability of lowering the IFT and improving the sweep efficiency of the reservoir. In this work, the main objective is to screen out a novel VES for cEOR applications in HTHS carbonate reservoirs.

Novel VES solutions of 0.1 to 1 wt% concentrations were prepared with synthetic sea water and stirred until they attain equilibrium. Densities and IFT’s of VES solutions and oil at different temperatures (30^oC, 50^oC and 80^oC) were determined using density meter and spinning drop tensiometer (Kruss). Equilibrated solutions were used with heavy crude oil of 17^oAPI to determine the IFT. Both short term and long term thermal stability of VES was evaluated using an approach based on FTIR, NMR and TGA analyses. Aging of VES was performed for 30 days at two high temperatures of 90^oC and 120^oC.

IFT results showed considerable reduction in IFT with novel VES and heavy oil upto 10^-1 mN/m range. IFT decreased initially and then increased with increase in VES concentrations. Non-linear trend of IFT was obtained. IFT reduction usually depends on the concentration of solutions used. Results also indicate that ultralow IFT was obtained at 50^oC. Critical micelle measurements were performed and 3wt% was found as CMC. VES was evaluated for short term thermal stability using TGA analysis and found to be stable upto 250^oC. FTIR, ¹H NMR and ¹³C NMR before and after aging the VES samples were compared and structural changes were observed in the aliphatic region. The peaks were shifted away due to the presence of C-O bond in the sample. IFT for aged samples was determined and almost two folds of increase in IFT was observed. Depending upon the results of this investigation at high temperatures from FTIR, ¹H NMR and ¹³C NMR and IFT, this novel VES exhibit great potential to be used in cEOR applications when we have HTHS reservoirs.

Based on the ultralow IFT’s and thermal stability obtained with the viscoelastic surfactant, they are excellent additives that can be used in chemical EOR for HTHS conditions. They are also very efficient when we have heavy oil reservoirs and where IFT reduction is required in order to mobilize the oil and improve the sweep efficiency of the reservoir.