An experimental and numerical investigation on the hydromechanical behaviour of carbonate fault zones upon reactivation: the impact of carbonate mud sealing layers and overall research outcomes
Published:July 17, 2020
M. Nogueira Kiewiet, C. Lima, A. Giwelli, C. Delle Piane, V. Lemiale, L. Esteban, F. Falcao, M. B. Clennell, J. Dautriat, L. Kiewiet, J. Raimon, S. Kager, D. Dewhurst, 2020. "An experimental and numerical investigation on the hydromechanical behaviour of carbonate fault zones upon reactivation: the impact of carbonate mud sealing layers and overall research outcomes", Integrated Fault Seal Analysis, S. R. Ogilvie, S. J. Dee, R. W. Wilson, W. R. Bailey
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To contribute to the understanding of the impacts of fault reactivation induced by reservoir exploitation, we describe the final series of laboratory experiments, numerical simulations and microstructural analysis conducted during the ‘Fault Reactivation in Carbonates’ research project. In the project, the structure and hydromechanical properties of carbonate-hosted fault zones were investigated. For the analyses here reported, faults were artificially generated by direct shearing composite blocks made of layers of reservoir analogue rocks (outcrop travertine or synthetic grainstone) intercalated with one layer of a sealing analogue rock (synthetic carbonate mudstone). Post-direct shearing, cylindrical plugs containing the fault zone and parts of intact rock were cored out from the blocks and tested in a triaxial test rig, simulating fault reactivation. Varied stress paths and pore-pressure conditions representative of fluid depletion and injection were considered. In parallel, two-dimensional mechanical models representative of the direct shear experiments were developed using smoothed particle hydrodynamics (SPH). We observed a continuous reduction in fault transmissibility during direct shearing, followed by a permeability reduction of 50–80% with increasing mean effective stress in the subsequent fault reactivation tests. Experimental fault zone geometries produced during direct shear were broadly reproduced by the two-dimensional modelling approach. We also detected that the inclusion of the carbonate mud sealing rock into the fault zone caused greater compaction of the fault materials when compared to experiments conducted without carbonate mud layers. We conclude that with fault displacement, increasing incorporation of carbonate mud sealing material into the fault zone and the concomitant development of gouge results in the continuous reduction of fault transmissibility/permeability. This occurs in the two very different limestone host-rock types and for all the stress configurations investigated. Discussions on these results and also on the outcomes of the research project as a whole are presented in the paper.
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Faults commonly trap fluids such as hydrocarbons and water and therefore are of economic significance. During hydrocarbon field development, smaller faults can provide baffles and/or conduits to flow. There are relatively simple, well established workflows to carry out a fault seal analysis for siliciclastic rocks based primarily on clay content. There are, however, outstanding challenges related to other rock types, to calibrating fault seal models (with static and dynamic data) and to handling uncertainty.
The variety of studies presented here demonstrate the types of data required and workflows followed in today's environment in order to understand the uncertainties, risks and upsides associated with fault-related fluid flow. These studies span all parts of the hydrocarbon value chain from exploration to production but are also of relevance for other industries such as radioactive waste and CO2 containment.