Inverse modeling of flow tomography experiments in fractured media

Abstract

[1] The accurate characterization of the location, hydraulic properties, and connectivity of major fracture zones is essential to model flow and solute transport in fractured media. Cross-borehole flowmeter tests, which consist of measuring changes in vertical borehole flows when pumping a neighboring borehole, were shown to be an efficient technique to provide information on the properties of the flow zones that connect borehole pairs. The interpretation of such experiments may, however, be quite uncertain when multiple connections exist. In this study, we explore the potential of flow tomography (i.e., sequential cross-borehole flowmeter tests) for characterizing aquifer heterogeneity. We propose a framework for inverting flow and drawdown data to infer fracture connectivity and transmissivities. We demonstrate that successively exchanging the roles of pumping and observation boreholes improves the quality of available information and reduces the under-determination of the problem. The inverse method is validated for several synthetic flow scenarios. It is shown to provide a good estimation of connectivity patterns and transmissivities of main flow paths. It also allows the estimation of the transmissivity of fractures that connect the flow paths but do not cross the boreholes, although the associated uncertainty may be high for some geometries.

Hydraulic Tomography: 3D Hydraulic Conductivity, Fracture Network, and Connectivity in Mudstone

“…Recently, Hochstetler et al (2016) used HT to investigate a highly heterogeneous (K range of 10 −7 to 10 −1 m/s) unconsolidated sedimentary aquifer at HRFS with highquality results. For HT in fractured aquifers, synthetic and field studies using drawdown, tracer, and temperature data have been conducted in 2D (e.g., Hao et al 2008;Klepikova et al 2014;Trottier et al 2014;Wang et al 2016;Somogyvári et al 2017;Fischer et al 2018), and 3D (e.g., Klepikova et al 2013) but we are only aware of distributed-parameter 3D HT field studies at the Mizunami research site in Japan (Illman et al 2009;Zha et al 2015). The Mizunami studies were at the scale of >0.5 km lateral and vertical extent, or considerably larger than the HRFS focus of this paper and in situ remediation.…”

Estimating hydraulic conductivity of fractured rocks from high‐pressure packer tests with an Izbash's law‐based empirical model

“…This technique was first proposed by Londe and Sabarly [] and has been extensively employed to examine the pressure‐sensitive permeability of fractured rocks [ Cornet and Morin , ; Cornet et al ., ; Cappa et al ., ; Derode et al ., ]. In a complete HPPT, however, the flow in the tested rocks is particularly prone to become non‐Darcy as a result of high flow velocities and hydraulic gradients in the cracks or fractures [ Derode et al ., ; Klepikova et al ., ], and the interpretation of the experimental data becomes quite difficult because the flow path geometry is in nature complex and full of uncertainties, even being altered under high fluid pressures due to hydraulic fracturing [ Doe and Geier , ]. Hydraulic fracturing is an effective stimulation technique for oil and gas production in low‐permeability reservoirs [ Yang et al ., ; Adachi et al ., ; Gu and Mohanty , ], but this process should generally be avoided in hydraulic engineering for reducing the risks of cracking, tensile failure, permeability enhancement, and leakage in rocks [ Fehler et al ., ; Rubin , ; Jiang et al ., ].…”

What does hydraulic tomography tell us about fractured geological media? A field study and synthetic experiments

“…Zha et al (2014), through synthetic simulations, found that the joint inversion of steady-state head and flux data induced by pumping can lead to a better characterization of hydraulic properties in a synthetic fractured medium. Generally, flux or flow rate data are more sensitive to fracture connectivity, and thus can provide complementary information about fracture properties with respect to traditional head data (Klepikova et al, 2013).…”