Travel-time-based thermal tracer tomography

Abstract

Abstract. Active thermal tracer testing is a technique to get information about the flow and transport properties of an aquifer. In this paper we propose an innovative methodology using active thermal tracers in a tomographic setup to reconstruct cross-well hydraulic conductivity profiles. This is facilitated by assuming that the propagation of the injected thermal tracer is mainly controlled by advection. To reduce the effects of density and viscosity changes and thermal diffusion, early-time diagnostics are used and specific travel times of the tracer breakthrough curves are extracted. These travel times are inverted with an eikonal solver using the staggered grid method to reduce constraints from the predefined grid geometry and to improve the resolution. Finally, non-reliable pixels are removed from the derived hydraulic conductivity tomograms. The method is applied to successfully reconstruct cross-well profiles as well as a 3-D block of a high-resolution fluvio-aeolian aquifer analog data set. Sensitivity analysis reveals a negligible role of the injection temperature, but more attention has to be drawn to other technical parameters such as the injection rate. This is investigated in more detail through model-based testing using diverse hydraulic and thermal conditions in order to delineate the feasible range of applications for the new tomographic approach.

Field validation of thermal tracer tomography for reconstruction of aquifer heterogeneity

“…This layer is also visible in the tomogram at the same depth but is thicker. The cause of this difference may be that thermal tracer tomography tends to reduce high-K and increase low-K zones [Somogyv ari et al, 2016]. The inversion by Jim enez et al [2016] was also performed jointly with slug tests, and the slug test profile indicated a very thin sand layer at 390 m (see Figure 8).…”

“…As a result, the mean tracer velocity distribution (velocity tomogram) is obtained, which can then be converted to a K-field (K-tomogram) according to equation (1). Instead of solving the problem over a regular grid, the staggered grid method is applied in this study [Vesnaver and Bo€hm, 2000] in line with related travel time-based hydraulic tomography applications [Jim enez et al, 2013;Hu et al, 2015;Somogyv ari et al, 2016]. The inverse problem is solved over multiple coarse grids, shifted horizontally and vertically.…”

Characterizing CO2 plumes in deep saline formations: Comparison and joint evaluation of time-lapse pressure and seismic tomography

“…A staggering technique is applied to the inversion procedure for improving the resolution of the final tomogram, and to weaken the effect of positioning (Vesnaver and Böhm, 2000;Somogyvári et al, 2016). The base model used for the inversion is discretized by five columns and four rows.…”

Comparison of Hydraulic and Tracer Tomography for Discrete Fracture Network Inversion

“…They are based on the inversion of signals that are recorded among multiple sources and receivers, which are employed to infer two-dimensional (2D) or three-dimensional (3D) images of the spatial hydraulic parameter distribution. For identifying those structural characteristics that are relevant for groundwater flow, solute, and heat transport, invasive concepts are available that apply hydraulic [1][2][3][4][5][6] or pneumatic pressure [7][8][9][10], or that use tracers, such as dye [11][12][13], salt [14][15][16][17], or heat tracers [18][19][20][21]. In comparison to many alternative near-surface geophysical applications, these signals are rarely introduced from the ground surface.…”