AAPG ANNUAL CONFERENCE AND EXHIBITION
Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA
Tracking and Quantifying Fluid Flow in a Fractured Carbonate Reservoir with 4-D Ground Penetrating Radar (GPR)
(1) Comparative Sedimentology Laboratory, University of Miami, Miami, FL.
(2) Department of Geological Sciences, Michigan State University, East Lansing, MI.
Sixteen time-lapse Ground Penetrating Radar (GPR) surveys were used to characterize the parameters controlling fluid flow in a fractured carbonate reservoir. A novel 1-10m scale field experiment was conducted in the Madonna della Mazza former limestone quarry (Italy) where previously acquired 3D GPR datasets revealed the presence of a porous matrix, open faults, and sub-vertical oriented deformation bands. We injected a moving water mass of 3000 liters below the fractured quarry floor and quantified local water content changes, delineating flooding/drainage boundaries, and determining the influence of faults and deformation bands on fluid flow propagation rates. The sensitivity of GPR to subsurface water content changes allows to characterize the dynamics of wetting, saturation, and draining zones within a 20x20x12m GPR volume. Event timeshifts and amplitude differences between repeated surveys are related to subsurface water content changes. GPR reflection travel timeshifts from pairs of repeated surveys are extracted with a 3D warp algorithm. Quantitative fields of water content changes and total mass balance are generated by applying the Topp petrophysical transfer function. Results show that flow rates are higher and the momentary wetting and drainage fronts of the evolving waterbulb are more uniformly developed in the undisturbed strata compared to zones including deformation bands. In this portion of the volume, characterized by porous matrix, the volumetric water content changes are also higher experiencing peaks of 10%. Wetting and drainage fronts inferred from the GPR data and water content changes lower than 5% show that deformation bands reduce hydraulic conductivity in horizontal direction whereas vertical open faults represent preferential flow paths. However, we also observe how deformation bands seem to facilitate vertical water transport across stratigraphic boundaries in the following stages of the 5-days monitoring period. The results obtained from time-lapse 3D GPR processing are compared with sample plug measurements, small in-situ infiltration/evaporation experiments, and results from Eclipse fluid flow dynamic simulation.