posted on 2021-12-02, 12:34authored byRena Shi, Hooisweng Ow, Gawain M. Thomas, Sehoon Chang, Hsieh Chen, Wei Wang, Bora Yoon
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.