Functionalized Polysaccharides as Transient Markers for Subsurface Monitoring

Abstract

Tracers, or ″markers″, have extensive applications in monitoring the subsurface and environment. Oil and gas fields apply a series of molecular tracers for interwell monitoring to support reservoir management. In near wellbore applications, tracers help to identify zonal flow allocation. Continuous monitoring using a series of different tracers is particularly appealing for mud logging operations that require precise and real-time assessment of the formation. Mineral particles (cuttings), generated during drilling, can provide valuable petrophysical and lithological information about the formation. In recent studies, polymeric nanoparticles (tracers) have shown promising results in labeling the cuttings at the depth of their origin. However, nondegradable tracers, such as polymeric nanoparticles, accumulate in the downhole/drilling fluids during continuous operation, which increase background noise at the time of detection and therefore reduce the detectability of the tracers over time. Thus, the application of a tracer-based technology demands the development of many different costly tracers to overcome the background noise in detection caused by tracer accumulation. Here we present the development of the first generation of transient markers that perform their ″marker″ function for a short period of time before degrading to undetectable molecules in the environment. These markers are conjugates of inexpensive polysaccharides with aromatic halides (tracers), which are synthesized via a simple esterification method. We have demonstrated that these markers can label mineral particles and then release the tracer molecules during pyrolysis-GCMS (Py-GCMS) analysis. The Py-GCMS results show distinct retention times and mass patterns that unambiguously identify the marker on the mineral particles. Additionally, we have characterized the hydrolysis of the marker at elevated temperatures in basic fluids using NMR, double-shot Py-GCMS analysis, and HPLC and determined the first-order rate constant of the marker’s hydrolysis using quantitative Py-GCMS analysis. The results have demonstrated the potential for the transient application of these markers in subsurface environments.