AAPG Middle East Region, Second EAGE/AAPG Hydrocarbon Seals of the Middle East Workshop

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Improving the Understanding of Fault Sealing Properties and Minimizing Fault Reactivation

Abstract

During reservoir activity (production/injection), compaction/dilation can lead to ground surface displacements (e.g. subsidence, heave) and can also induce fault reactivation/seismicity. We propose a nontraditional closed-loop reservoir management workflow for first integrating ground surface displacements as a probe of fault sealing properties (blue loop) and second optimizing reservoir production while minimizing seismicity risks (red loop). In many cases considerable uncertainties are associated with reservoir flow simulations, which are based on very local well production information. These uncertainties are of diverse origins and can be attached to several parameters. One of those is the fault transmissibility for compartmented reservoir. In the first step of the workflow (blue loop) we propose to use measurements of ground surface displacements in a geophysical inversion scheme to connect to the global reservoir behavior in time and space and thus be able to better constrain reservoir. Compartmentalization (fault sealing). During reservoir activity (production/injection), pressure and temperature changes can lead to stress changes in the reservoir and in the caprock. These can potentially be large enough to reactivate pre-existing fractures and/or to generate new ones. In the case of small caprock thicknesses, slip on faults in the caprock can cause leakage and contamination of the overlying aquifer. This must be prevented. The second step of our workflow (red loop) thus consists in finding optimized production/injection strategies that take into account the risk of fault reactivation/induced seismicity. The performance of the workflow is demonstrated in a series of experiments representative of production scenarios in a highly faulted/compartmentalized gas field. The results of these experiments demonstrate the (1) improvement of fault transport properties(sealing) knowledges using ground surface displacements, and (2) the potential of model-based reservoir management workflows to contribute to safe production of hydrocarbon resources.