Development of a rapid and accurate method for determining partition coefficients of chemical tracers between oils and brines (for single well tracer tests). Final report

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Abstract
The objective of this work was as follows: (a) To develop a rapid and accurate method for determining chemical tracer partition coefficients (K-Values). (b) To study how common reservoir parameters (brine salinity, temperature, crude oil characteristics, gas-to-oil ratio and chemical tracer concentration) effect chemical tracer partition coefficients. We have developed a high pressure (up to 5000 psig), high temperature (up to 220/sup 0/F) system for rapidly and accurately determining chemical tracer partition coefficients for an oil/brine system. Reservoir brine is circulated in a closed system of known volume. This system is comprised of an equilibrium cell in which a known volume of oil is held stationary and a brine circulating loop. Known aliquots of chemical tracer are added to the system and the concentration of the chemical tracer in the brine phase is analyzed via gas chromatograph. A tracer mass balance is used to determine the concentration of the chemical tracer in the oil phase and hence, the partition coefficient is determined. Ethyl acetate partition coefficients were studied over a wide range of ethyl acetate concentrations, reservoir temperatures and brine salinities for a highly naphthenic crude oil. Some experiments were also conducted to determine the effect of gas-to-oil ratio andmore » crude oil type on the partition coefficients. In general, the ethyl acetate partition coefficients increased with an increase in temperature, ethyl acetate concentration and brine salinity while a slight decrease was observed for an increase in the gas-to-oil ratio. We have correlated the experimentally determined ethyl acetate partition coefficients with the ethyl acetate concentrate, temperature, brine salinity and the gas-to-oil ratio. This correlation can predict K-Values to within +- 10%. 5 figures, 3 tables. « less

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