Characterization of Fluid Dynamics in Carbonate Reservoirs using 4-D GPR: Assessment of Stratigraphic and Structural Controls on Flow and Comparison with Dynamic Modeling

Marchesini, Pierpaolo; Grasmueck, Mark; Eberli, Gregor; Weger, Ralf J.

Time-lapse 3-D Ground Penetrating Radar (4-D GPR) was used to track fluid flow in two carbonate reservoir analogues: the fracture-controlled Madonna della Mazza grainstone quarry (Southern Italy) and the structurally undisturbed oolitic limestone of Ingraham Park (Miami, FL). The goals of this study are: 1) to assess the role of stratigraphic versus structural heterogeneities and to characterize fluid dynamics in gravity flow experiments; 2) to compare 4-D GPR results with dynamic flow simulation.

In Madonna della Mazza (MdM) 2952 liters of water were infiltrated from the quarry surface into the host matrix (poro/perm, 35%/630mD) in a location with deformation bands and open faults. At Ingraham Park 3200 liters were infiltrated in 5 hours (poro/perm, 60%/1500mD). Both infiltrations were performed using 4 m-diameter, temporary ponds. Water decreases the speed of electromagnetic waves and, as a consequence, increases the traveltime of subsurface reflections. Timeshifts are extracted between pairs of time-lapse surveys with 3-D cross-correlation. The timeshifts volumes are converted to water content changes by applying the Topp petrophysical transfer function. Such 3-D water content change volumes provide snapshots of fluid flow over an observation period up to 15 hours after the end of the infiltration.

At the MdM quarry, the undisturbed matrix experiences higher water content changes (peak of 4%) than the deformation bands area (2%) indicating their active role in compartmentalizing fluids. In addition, the infiltrated water bulb shows a pronounced up-dip asymmetry along a fault plane due to preferential flow. At Ingraham, water content changes peak is 9% across the pond infiltration area. Here, higher porosity and permeability values of the host rock facilitate more rapid fluid migration compared to MdM. The upper water bulb boundary is within the pond perimeter while the lower boundary is shifted down-dip as fluid migration follows stratigraphy.

For dynamic flow modeling in Eclipse the detailed stratigraphic and structural interpretation of MdM 3-D GPR survey had to be simplified and downsampled for computational reasons. The dynamic model fails to capture and visualize the role of structural heterogeneities: the effect of deformation bands on the fluid migration is completely lost. Simplification and downsampling prevent dynamic modeling from reproducing realistic flow conditions observed in the 4-D GPR experiments.

AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013