Zwitterionic Dipicolinic Acid-Based Tracers for Reservoir Surveillance Application

Abstract

Chemical tracing within oil reservoirs enables the determination of fluid allocation and interwell flow characteristics for improving injection fluid sweep efficiency and reservoir management, and thus novel instrument-readable, independently distinguishable tracers with ultralow sensitivity and detectability are highly desired. We present a series of dipicolinic acid (DPA)-based molecules as a new class of water tracers for reservoir surveillance applications, demonstrating the design and synthesis of three novel DPA-based molecules confirmed and characterized via NMR and mass spectroscopy. Further installation of zwitterionic functional groups onto the structure of these DPA-based tracer candidates leads to marked reductions in their dynamic rock retention, as demonstrated via core flooding experiments. From an optical detection standpoint, all synthesized DPA derivatives exhibit strong chelation with rare earth ions such as terbium (Tb3+) and emit long-lived fluorescence characteristic of lanthanide chelates, making them detectable using time-resolved fluorescence spectroscopy down to the parts-per-trillion (ppt) level. The time-resolution component is critical for their application as water tracers in reservoir fluids, enabling bypassing of background fluorescence from crude oil and other interferents present in brine. Results show that the stepwise derivatization of native DPA and its analogues generates a suite of molecular structures that can be effectively separated and identified using high-performance liquid chromatography (HPLC). Studies on long-term thermal stability at 100 °C and orthogonal detection by optical and chromatographic methods have demonstrated that the newly developed DPA-based ligands described herein have great potential to serve as highly traceable interwell oilfield tracers.