Abstract
In the oil and gas industry, tracers are used to estimate residual oil saturation, to indicate the location and orientation of fractures in tight reservoirs, to identify and mark the direction of fluid flow in fractured deposits, to locate faults and discontinuities, and to measure fluid movement in injection wells during drilling. The tracers should behave in a mechanically similar manner to the tested substance, e.g., formation waters, oil or gas, and, on the other hand, they should significantly differ from them in terms of chemical properties so that it is possible to identify them. One of the fluorescent tracers used in the oil and gas industry, e.g., for inter-well tests during secondary or tertiary production methods (especially during reservoir hydration), is uranine. In order to assess the effectiveness of fluid movement measurements, it is necessary to determine the uranine content in formation waters. In this study, a method was developed to determine uranine in formation water samples using high-performance liquid chromatography with fluorescence detection (HPLC/FLD). The initial step in preparing samples for chromatographic analysis would be solid phase extraction (SPE). The method was validated and allows for the determination of uranine in formation water samples in the concentration range from 0.030 to 2.80 µg/L. The validation of the method included the analysis of factors influencing the measurement result (sources of uncertainty), determination of the linearity range of the standard curve, determination of the quantification limit of the method, and verification of the reproducibility, selectivity, stability and correctness achieved. The method developed within the study can be successfully applied in the case of the determination of uranine content in formation water samples from the oil and gas mining industry, which are often unstable and characterized by a relatively complex matrix. After validation, the method will also be applicable to the determination of uranine in matrices with a similar physicochemical composition, e.g., to assess groundwater flow in deformed carbonate aquifers or to characterize faults that act as barriers to horizontal groundwater flow.
Highlights
This paper presents the optimization and validation results of a method for the determination of uranine in formation water samples
This study shows that the volume of formation water sample affects the determination of uranine
Uranine is usually determined using spectrophotometric methods; in specific matrices such as highly saline formation waters, a more specific method of sample purification and separation must be applied. Such a method is the method of liquid chromatography with fluorescence detection, developed and validated within the framework of conducted studies, preceded by the separation of analyte by means of solid phase extraction (SPE)
Summary
The development of modern technologies used in industry as well as the growth in the number of transport pipelines for liquid and gaseous media has resulted in an increase in the number of potential entry points for environmentally hazardous substances. Tracers can be a fast and highly sensitive way of detecting leaks. They are substances that are used to identify a process and gain information related to its nature. They should behave in a similar way to the substance being tested, e.g., formation water, gas or oil, but, at the same time, have different chemical properties in order to be identified
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