Comparison of Hydraulic and Tracer Tomography for Discrete Fracture Network Inversion

• Main Authors: Lisa Maria Ringel, Márk Somogyvári, Mohammadreza Jalali, Peter Bayer
• Format: Article
• Language: English
• Published: MDPI AG 2019-06-01
• Series: Geosciences
• Subjects: hydraulic tomography; tracer tomography; DFN; Bayesian inversion; heterogeneity; fracture; hydrogeophysics
• Online Access: https://www.mdpi.com/2076-3263/9/6/274

Fractures serve as highly conductive preferential flow paths for fluids in rocks, which are difficult to exactly reconstruct in numerical models. Especially, in low-conductive rocks, fractures are often the only pathways for advection of solutes and heat. The presented study compares the results from hydraulic and tracer tomography applied to invert a theoretical discrete fracture network (DFN) that is based on data from synthetic cross-well testing. For hydraulic tomography, pressure pulses in various injection intervals are induced and the pressure responses in the monitoring intervals of a nearby observation well are recorded. For tracer tomography, a conservative tracer is injected in different well levels and the depth-dependent breakthrough of the tracer is monitored. A recently introduced transdimensional Bayesian inversion procedure is applied for both tomographical methods, which adjusts the fracture positions, orientations, and numbers based on given geometrical fracture statistics. The used Metropolis-Hastings-Green algorithm is refined by the simultaneous estimation of the measurement error’s variance, that is, the measurement noise. Based on the presented application to invert the two-dimensional cross-section between source and the receiver well, the hydraulic tomography reveals itself to be more suitable for reconstructing the original DFN. This is based on a probabilistic representation of the inverted results by means of fracture probabilities.