A laboratory study on the impact of alkali on the performance of smart water flooding in carbonate reservoir cores

  • Nithin Chacko Thomas

    Student thesis: Master's Thesis


    Smart water flooding has generated tremendous interest in the recent years because of its unparalleled cost/benefit aspect as well as attractive HSE parameters. However the smart water prepared by dilution and alteration of active ion composition has limitations which can be improved by pH modulation. This aspect has not yet been investigated systematically, which is the objective of this study. In addition to this, understanding the inherent mechanism of how Smart water works and the impact of alkali on different smart water compositions is also analyzed. High potential smart waters are tested for their alkalinity and pH tolerance, using different alkalis and subjected to preliminary screening such as instant and delayed precipitation, IFT, contact angle measurement at higher temperature and zeta potential of the COBR (crude oil-brine-rock) system. Dissolution study is performed to find extent of rock dissolution when in contact with low pH brines. The selected brine pairs are used for reservoir condition core flooding on carbonate core plugs from one of the ADNOC fields for recovery analysis under secondary and tertiary flood conditions. Effluent samples collected at pre-defined pore volume injection intervals are analyzed in sub-ppm level using ICP-MS, to aid result interpretations. Furthermore, NMR studies are conducted on the cores before and after the flooding to identify any change in porosity distribution. Two alkalis (NaOH and Na2CO3) and three laboratory proven smart brines are evaluated for their mutual compatibility. Tolerance of the smart brines are seen to be more with NaOH compared to Na2CO 3. Solution pH are limited to 10 – 11 to avoid precipitation and pore blockage. Spinning drop IFT measurements suggested lowering of IFT for higher pH brines which indicates a potential higher recovery of residual oil, however desirable results were not obtained from micro-emulsion studies. Detailed Zeta Potential measurement of the oil/brine/rock and brine/rock interfaces indicated higher possibilities of electric double layer expansion for the higher pH smart brines compared to the normal pH smart brines and hence indicating wettability alteration towards water wetness. These are quantified through contact angle measurement at reservoir temperature. Considerable amount of residual oil was recovered in tertiary stage with high pH smart waters during the core flooding. With the three different smart brines used in the tertiary stage, around 1% to 6% of OOIP was additionally recovered after secondary water flooding with unaltered pH brines and further incremental oil recovery of 1 % to 6 % of OOIP with high pH brines. However, when high pH brines are directly used as a tertiary fluid, the recovery obtained is similar to that of combined recovery from unaltered pH and high pH brines in the previous tests and also this was achieved with 2 – 3 pore volume less brine, thus saving injection time and cost. Among the three different smart brines (0.1SW, 0.1SW4S and SW4S) studied to evaluate the effect of alkali, 0.1SW4S at pH 10.50 has the highest potential to recover residual oil from the carbonate core plugs. The additional recovery achieved through alkaline smart brine floods are mainly contributed by flow profile modification due to sulfate scale deposition, which is encouraged by enhancing brine pH, increase in zeta potential, and IFT reduction may also have minor contribution. Rock dissolution is seen to have minimum impact. In conclusion the study helps to understand the effects of changing the smart water properties by increasing the pH on recovery of residual oil during smart water flooding from heterogeneous carbonate core plugs. The pH modulated smart water flood EOR has not been investigated systematically as evidenced form the literature search.
    Date of Award2016
    Original languageAmerican English


    • Applied sciences
    • Alkaline flooding
    • Carbonate rocks
    • Hybrid EOR
    • Smart water flooding
    • Petroleum engineering
    • 0765:Petroleum engineering

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