Well Test Tomography for Rock Hydraulic Characterization

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Responding to the demand for quantitative characterization of rock hydraulic properties in large-scale utilization of ground/underground space, we developed a system of hardware/software for multi-well interference testing named 'Hydropulse Tomography (HT)', by which the distribution of rock permeability in 3-D space can be detected using small number of boreholes. HT uses pressure pulses generated by fluid injection/production/shut-in operations at a packered interval of a well, and transient pressure responses caused by the pulses are received at multiple wells and multiple points. For the transient pressure data obtained through this type of operation, fully 3-D numerical inversion analysis is done to determine the spatial heterogeneity of permeability in rock around observation site.We developed a numerical inversion system for transient data, which consists of 3-D one-phase flow simulator, quasi-Newton scheme for non-linear minimization with optimal control algorithm, and schemes for practical well-modeling, time-dependent weighting, arbitrary zoning, and smoothing. The code was validated using 1-D,2-D,and 3-D problems by checking performances of reconstructivity, convergence, and so on. Laboratory experiments for multi-hole HT were done using 1-D and 2-D heterogeneous media, and the obtained data were successfully inverted to the permeability distributions that coincide with the ones set in media. Field testing and 3-D large-scale inversion analysis was done, and the determined permeability distribution was consistent with the geological description, observation of borehole TV and the data of Lugeon test, which were available at the site.