The use of equilibrium adsorptive-desorptive or ion-exchanging (alongside with conservative, including contrasting-diffusivity) liquid-phase tracers for characterizing a single, large-area hydrofrac created at a pilot unconventional-reservoir site in the NW-German Sedimentary Basin is examined prospectively by numerical simulations. The purpose of the exercise is twofold: (I) to assist in the process of tracer species selection for upcoming tests at this particular site, and (II) to derive more general recommendations for the early-stage use of tracers in unconventional-reservoir development, from the S[ource] and P[athway] characterization perspective adopted within the EU-H2020 project FracRisk (grant no. 636811). In terms of S and P compartments [cf. fig. 5 in McDermott et al. 2014], the take-away from our scoping simulations can be summarized qualitatively: (i) overall tracer recovery ratios correlate with transmissivity ratios between hydraulically competing P, S compartments; (ii) tracer arrival times correlate with the effective aperture or porosity of the critical (spill-controlling) P compartment; (iii) mid-/late-time tracer signal slope changes may indicate geomechanical effects within P or S compartments. The pilot unconventional-reservoir site in the NW-German Sedimentary Basin offers the unique advantage of well-steerable forced-gradient flow conditions, thereby enabling to more reliably estimate in-situ adsorption-desorption properties for a number of tracer species currently regarded as promising candidates for reservoir stimulation applications. On the other hand, processes like tracer adsorption-desorption and/or matrix diffusion need not make a major difference for frac characterization from short-term tracer signals.

Press the Back button in your browser, or search again.

Copyright 2018, Stanford Geothermal Program: Readers who download papers from this site should honor the copyright of the original authors and may not copy or distribute the work further without the permission of the original publisher.