Impact of laboratory-induced damage on the permeability of coquinas with variable texture

Coquina carbonate rock reservoirs are characterized by challenging pore systems due to a range of textures and diagenetic processes. Such complexities can result in highly variable permeability values within the reservoir with deformation leading to further permeability changes. This work explores the impact of laboratory-induced deformation on the permeability of coquina samples containing distinct textural heterogeneities.
Here, a block of coquina, a carbonate rock consisting of calcite-cemented shelly fragments with porosity of approximately 20% and somewhat diffuse and discontinuous layering, was cored to produce four cylindrical samples, 78mm long and 38mm diameter where C12 and C13 were perpendicular and C22 and C2 )were parallel to bedding. Initial vertical permeability was 49, 37, 362 and 56 mD for samples C12, C13, C22 and C24 respectively. All samples were deformed in triaxial compression (2.5MPa confining pressure). Laboratory-induced deformation resulted in an increase in vertical permeability to 54, 89, 386 and 98 mD respectively.
The broader project uses Neutron Tomography to investigate both pore-network state via water distribution pattern and water front evolution within samples, using deuterated and normal water for the latter where their contrasting response to neutrons provides a marker for flow rate indicators. The same procedure was followed before and after the laboratory-induced deformation of the samples to see the impact of deformation on saturation and flow. This study reports only the pore-network state.
The bulk permeability measurements show some post-deformation increase in all cases. The Neutron Tomography identifies significant new connections in sample C13 specifically in the distinct axis-normal layer that was previously only poorly connected to the adjacent rock. The same layer when parallel to the flow direction (C24) shows a reduced flux enhancement. Samples with no obvious contained layer (C12 and C22) show neither the focusing of deformation into a specific lower permeability layer nor a noticeable pore connectivity enhancement.