Improved/Enhanced Oil Recovery from Carbonate Reservoirs by Tuning Injection Water Salinity and Ionic Content

Abstract

Improved/enhanced oil recovery by tuning the ionic composition of the injection water is currently deemed as new emerging recovery method. In the recent years, extensive research on oil/brine/rock systems has shown that injecting low salinity brines has a significant impact on oil recovery from sandstone reservoirs. Although, the potential for carbonates has not been carefully investigated, some reported studies have excluded carbonates from this effect. In view of research results for the last three years, we demonstrated in previous reports (SPE 137634; SPEREE Journal, vol. 14(5), pp. 578-593, SPE 143550, SPE 141082) that substantial oil recovery beyond conventional waterflooding from carbonates can be achieved by optimizing ionic composition of field injection brine. Also, research confirmed that the driving mechanism is wettability alteration. In this paper, we present the results of new reservoir condition laboratory coreflooding studies, conducted using composite rock samples from different carbonate reservoir, to investigate the impact of ionic content on oil recovery at both secondary and tertiary recovery modes. Also, we report a broad range of laboratory studies addressing role of water ions. In addition, we briefly disclose the results of first-ever field application conducted in a carbonate reservoir to demonstrate the SmartWater Flood potential. The experimental results revealed that substantial tertiary oil recovery beyond conventional waterflooding can be achieved by altering the ionic content of field injection water. Similar potential has been confirmed also in the secondary recovery mode. For recovery mechanisms, the new results confirmed that wettability alteration is the main cause for the substantial increase in oil recovery. Compared to previous reported work, the variation in oil recovery from two different carbonate reservoirs is attributed to the variations in reservoir temperature and also the chemistry of initial formation water. For field application, two field trials confirmed that injection of SmartWater achieved ∼7 saturation units reductions in residual oil beyond conventional seawater flooding. Considering these field trials are the first-ever applications in carbonate reservoirs, they further provided another confirmation that SmartWater Flood is emerging recovery method targeting carbonate reservoirs.

Thin liquid films in improved oil recovery from low-salinity brine

“…However, carbonate rocks are not always positively charged in the presence of CaCl 2 and MgCl 2 . Chen et al have measured the zeta potential of TP powder, which is 82% calcite but also contains some quartz and clays, in 0.1 weight percent CaCl 2 over a pH range of 5 to 11. They find that the zeta potential monotonically decreases from about 5 mV at pH = 5 to − 23 mV at pH = 11 [47].…”

Effect of Ca2+, Mg2+ and SO42− ions on the zeta potential of calcite and dolomite particles aged with stearic acid

“…Yousef et al [26,27] studied the effect of using diluted seawater on the oil recovery from carbonate, and found that diluted seawater increased the magnitude of the negative surface charges of carbonate rock particles. Very recently, Mahani et al [28] investigated the underlying mechanism for improved oil recovery from carbonates during low salinity water flooding using contact angle measurements, geochemical modeling and zeta potential measurements.…”

Geochemical Investigation of the Combined Effect of Injecting Low Salinity Water and Carbon Dioxide on Carbonate Reservoirs

“…Based on the latter finding, we proposed several models for the LSWI effect on oil recovery from carbonates [27,28]. Moreover, we proposed that both dissolution and changing surface charge of the rock are the reasons for wettability alteration and incremental oil recovery by LSWI for corefloods of Yousef et al [5,6] from a geochemical point of view [29].…”

“…Wettability alteration in carbonate rocks using LSWI can be achieved by injecting water containing SO 4 2-and either Ca 2+ or Mg 2+ or both of them at high temperatures (>90 o C) [11]. Yousef et al [6] demonstrated that wettability alteration is the reason behind LSWI through NMR, contact angle, and zeta potential studies. Nevertheless, work is progressing on understanding the chemical interactions between crude oil/brine/rock (COBR) system.…”