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    Adsorption and Degradation of Enhanced Oil Recovery Chemicals

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    The possible contamination of ground waters by injection of chemicals used for enhanced oil recovery was evaluated at the National Institute for Petroleum and Energy Research. The objective of the study was to delineate the nature of the reservoir rock/injected chemical interactions and the potential for ground-water contamination.

    As a preliminary step in the investigation, a method for determining the cation exchange behavior of consolidated sandstone specimens at in situ flow-through conditions as compared to a crushed specimen method at ambient conditions was developed. The flow-through method was tested in the laboratory on small core specimens (0.038 by 0.102 m) and was used as an indicator of the potential of chemicals to interact with the rock matrix.

    Results obtained provided individual concentration profiles for major and minor amounts of cations removed from the core after exchanging with lanthanum. The information obtained is valuable in assessing the potential compatibility of injected fluids with a reservoir formation. Upon comparing the cation exchange capacity (CEC) for specimen C071 (Parkman formation, sandstone) the values were 13.9 meq/kg for the crushed method versus 6.11 meq/kg for the flow-through method. This was a consistent finding for all the specimens tested; CECs determined on the crushed core specimens were higher than those determined by the lanthanum flood on the whole core. These displacement tests could also indicate prior chemical contamination by observation of the cations displaced by the flow-through method. This option is not available using the crushed core method.

    The whole core flow-through method was adapted to a larger (0.155 by 0.762 m) closed core system to evaluate the stability/degradability of enhanced oil recovery (EOR) chemicals: three surfactants, a co-surfactant, and a polymer. Seven separate tests were conducted with test periods ranging from 17 to 135 days. The tests were conducted at simulated reservoir conditions of temperature, pressure, and fluid flow rate. Specimens were taken periodically and analyzed using gas chromatography, liquid chromatography, ultraviolet spectroscopy, or colorimetric techniques of both. The chemicals were found to be stable for the conditions studied during the testing periods with no detectable amounts of degradation products. These tests indicate the stability of these EOR chemicals over extended time periods at in situ conditions and the potential of the chemicals to contaminate ground-water sources over a long time period.


    ion exchange, enhanced oil recovery, cation exchange capacity, aquifer, stability, degradation, toxicity, core tests

    Author Information:

    Crocker, ME
    Project leader and associate chemist, National Institute for Petroleum and Energy Research, Division of IIT Research Institute, Bartlesville, OK

    Marchin, LM
    Project leader and associate chemist, National Institute for Petroleum and Energy Research, Division of IIT Research Institute, Bartlesville, OK

    Committee/Subcommittee: D19.31

    DOI: 10.1520/STP44872S