Uranine as a Tracer in the Oil and Gas Industry: Determination in Formation Waters with High-Performance Liquid Chromatography

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.

Fluorescent Based Tracers for Oil and Gas Downhole Applications: Between Conventional and Innovative Approaches

“…Uranine, Fluorescein (520 nm) [9] HPLC/FLD (0.03 μg/L); HPLC/LIF (40 fg/mL) [1]; colorimetry (mg/mL level) [6];…”

“…UV (0.1-10 mg/mL) [1] Very low Eosin Y (545 nm) [10] Solid phase spectrophotometry (1.20 mg/L) [11]; digital color analysis (DCA) (1.32 mg/L) [11] Low Rhodamine B (625 nm) [10] Solid phase spectrophotometry (0.06 mg/L) [11]; DCA (0.6 mg/L) [11] Strong Rhodamine WT 555 nm [10] visual/UV < 100 ppb [12] Low-Medium Sodium Naphthionate (420 nm) [13] HPLC/FLD (pg/mL level) [14] Low HPLC/FLD (0.03 µg/L); HPLC/LIF (40 fg/mL) [1]; colorimetry (mg/mL level) [6];…”

“…Moreover, fluorescent tracers are relatively inexpensive, readily available at the commercial scale, relatively nontoxic at low concentrations, and able to be monitored and quantified via simple, portative, and cost-efficient analytical techniques that include spectrofluorimetry, UV-Vis spectroscopy, and digital color analysis. Most well-known fluorescent molecules commonly tested in oilfield applications include fluorescein/uranine [3][4][5][6], rhodamine [1,4,7], eosin [8], and polyaromatic sulfonic acids (Table 1).…”

In Situ Downhole Fluid Analysis Systems Using LED, Laser-Induced Fluorescence, and Uranine-Traced Drilling Water

“…8 Later, the uranine tracer was adapted in the oil industry in inter-well analysis. 9 The employed methods are based on detecting and measuring the concentration of uranine in the samples in the laboratory using chromatography. Now, adding tracers into the water-based drilling mud has become a common practice during the drilling processes.…”

“…The applied fluorescence methods for the analysis of crude oils are based on the correlation of different fluorescence parameters with chemical or physical characteristics of the sample. 13 The proposed instruments for the fluorescence behavior of oil include spectrophotometric 14,15 and chromatographic methods 9,16 for the laboratory investigations, and filter spectrometers 17 for the downhole setups.…”