New and simple methods of determination partition coefficient and degree hydrolysis of tracer for estimating residual oil saturation by SWCTT technologies

SWCTT (Single-Well Chemical Tracer Test) actively used to determine the reservoir oil saturation as cost effective and quick method. To use this technology, the partition coefficients K and hydrolysis degree H of the tracer which determined experimentally in laboratories are essential for calculation of residual oil and estimation shut-off period of the well. In this paper, FTIR-spectroscopy and pH-metry were proposed for determination of partition coefficient of chemical tracer (ethyl acetate) and hydrolysis degree. Results obtained by these methods showed good correspondence with the data obtained by standard gas chromatographic analysis that confirms its applicability. All of these methods were used for the study of SWCTT parameters for four oilfields with different formation temperatures in the range 27–70 °C and formation water salinities up to 215,015 ppm. It was shown that oil-water partition coefficient of partitioning tracer increases with the rise of salinity. The apparent activation parameters of the hydrolysis reaction were determined by data on the degree of hydrolysis (pH-metry) and the concentration changes of tracer (head space gas chromatography analysis)