Fault reactivation, leakage potential, seal integrity, and
hydrocarbon column heights
Speaker: Yen, Pei?chi
Abstract
The faults affect the migration of fluids in petroleum reservoirs; we need to evaluate the state
of stress and pore pressure acting on the major faults. Many of the faults bound hydrocarbon
reservoirs. We first test the hypothesis that faults are being reactivated in the current stress field
are permeable and thus tend to leak, in other situation faults that are inactive in the current stress field are likely to seal. By comparing the stress state resolved on each fault element and the reference pore?pressure, we can expect stress at failure (using a Coulomb failure criterion) and created color?shaded maps showing the proximity to fault slip along each fault. The leakage potential of reservoir?bounding faults appears to exert an important influence on potential hydrocarbon column heights. We then want to predict the potential risk of CO2 leakage along reservoir?bounding faults, take the Teapot Dome oil field, Wyoming, USA, for example. A preliminary geomechanical model has been developed to evaluate the potential for CO2 injection inducing slip on the S1 fault, the major fault at Teapot Dome, and thus threatening seal integrity. Uncertainties in the stress tensor and fault geometry have been incorporated into the analysis using Monte Carlo simulation. From the simulation, the authors find that we need ~10 MPa of excess pressure to cause the S1 fault to reactivate and provide a potential leakage pathway. This would correspond to a CO2 column height of ~1500 m, whereas the structural closure of the Tensleep Formation in the pilot injection area does not exceed 100 m. Better constraint of the least principal stress is needed to establish a more reliable estimate of the maximum reservoir pressure required to hydrofracture the caprock.
Reference
Chiaramonte, L., M. D. Zoback, J. Friedmann and V. Stamp, 2008. Seal integrity and feasibility of CO2 sequestration in the Teapot Dome EOR pilot: geomechanical site characterization. Environ Geol, 54, 1667?1675.
Wiprut, D. and M. D. Zoback, 2002. Fault reactivation, leakage potential, and hydrocarbon column heights in the northern North Sea. Norwegian Petroleum Society Special Publication, 11, 203?219.