Toward the Creation of Models to Predict Static and Dynamic Fault Seal Potential in Carbonates

Abstract

In contrast to faults in clastic reservoirs, rules to predict fault-seal potential on an exploration and/or production timescale in carbonates are lacking. This makes it difficult to accurately risk fault-defined carbonate prospects or to identify infill drilling targets in more mature carbonate fields. Production timescale sealing behavior is better-constrained than exploration time scale behavior. There are a number of carbonate reservoirs with cross-fault column height differences that represent examples of apparent static fault seal but verification of these examples requires understanding of lithological/diagenetic patterns in the reservoir, variations in fluid properties and reservoir pressures and the charge and deformation histories of the traps. There are examples of better-constrained production time scale fault seal in carbonate reservoirs and aquifers. These include cross-fault differences in water table depths across carbonate–carbonate juxtapositions, cross-fault pressure differences in carbonate aquifers separated by faults, production-induced cross-fault pressure differences in carbonate hydrocarbon reservoirs, sealing behavior of faults in carbonate reservoirs inferred from well tests, and examples of low fault transmissibilities from history-matching exercises from carbonate reservoirs. Modelling indicates the time needed for re-equilibration of production-induced cross-fault pressure differences using a realistic range of carbonate fault permeabilities can exceed 100,000 years. This indicates that at least some faults in carbonates are sufficiently sealing to create infill drilling targets and lends support to the idea that faults in carbonates are capable of sealing on a geological time scale. With that said, the purpose of this presentation is not to argue that every fault in a carbonate reservoir will seal or will even be capable of sealing. This study shows, however, that there are enough examples of faults in carbonates that are sealing in either a static or dynamic sense that predictions of carbonate fault seal potential are needed.

AAPG Datapages/Search and Discovery Article #90291 ©2017 AAPG Annual Convention and Exhibition, Houston, Texas, April 2-5, 2017