Parameter Sensitive Inter-Well Tracers to Map Reservoir Conditions
Authors: Maddinelli Giuseppe , Bartosek Martin , Bonoldi Lucia , Moghadasi Leili , Renna Dario , Moscatelli Davide 
Published: October 2022

Abstract
The use of tracers as a diagnostic tool, represent a valid method, widely applied during waterflooding operations in the oil and gas industry, to gather information on the reservoir salient features. The main purpose of this work is the investigation of novel molecules, potentially applicable as inter-well tracers, with peculiar properties compared to standard products, such as the presence of fluorescence units which allows a more efficient detection. Moreover, the combined presence of chemical units sensitive to oil or other features of the formation, could allow the estimation of hydrocarbon content and porous media structure.
The different tracer molecules under testing have been evaluated through a series of coreflooding tests on core plugs saturated with brine and at residual oil saturation, resembling reservoir conditions. The detection of the chemical species was performed by use of fluorescence spectroscopy directly on the fluids flushed out of the core, avoiding any complex handling of the solution. The method is potentially applicable to on-line detection directly on site.
Different low molecular weight polymeric products with fluorescent properties were prepared for testing with the aim to evaluate their performance compared to standard tracers. In a preliminary screening procedure, the possible adsorption of the molecules on rock powder surface was evaluated. Only molecules showing a negligible adsorption were selected for the full testing. Then the products were solubilized in brine and injected in Berea core plugs or slim tubing at different fluid saturation (fully brine and at residual oil saturation). The production curves obtained were compared to a passive tracer (NaI) previously injected and the retention time difference was evaluated. Consistent differences in the production curves were observed among the products, revealing their potential use in formation characterization. The method allowed the evaluation of the travelling performance inside the cores of the different potential tracers. In particular, the different affinity to oil presence, correlated to the peculiar molecular lipophilicity revealed a potential application as partitioning tracers. The measurement of the bulk partition coefficients, represented by the concentration of the tracers between the two phases (K = Coil/Cwater) allowed estimation of the oil present and results were in reasonable agreement with the experimentally measured oil content (Sor). A limit observed in proper application of the tracer procedures is often associated to the efficiency in detection in production fluids. The classes of products applied show a more efficient detection phase, which is critical in tracers’ campaign, allowing a more precise evaluation of the production curves suitable for better modelling and parameter estimation. The conditions of application (e.g fluids, temperature, and lithology) should be nevertheless carefully evaluated in a lab examination before use in the field.