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ABSTRACT: Fault and Stress Modeling of Alpine Field with Application to Drilling Difficulty Mitigation

Hennings, Peter H.1, Laurent Maerten2, Rico Ramos3, Milt B Enderlin3, Robert Krantz3, David Shafer3, Chip Alvord3, Cliff Crabtree3 
(1) ConocoPhillips, Houston, TX 
(2) Stanford University, Stanford, CA 
(3) ConocoPhillips, AK

ABSTRACT: Fault and Stress Modeling of Alpine Field with Application to Drilling Difficulty Mitigation

Alpine Field on Alaska’s North Slope is being developed using horizontal drilling from central pads. The sandstone reservoir at a depth of 7,200 ft hosts a complex array of normal faults that form drilling-fluid loss-hazards that can impede operations. Detailed 3D interpretation and boundary-value elastic stress modeling of the fault network was conducted to investigate the mechanisms controlling faulting and the development of fluid-conducting damage zones. 

Alpine contains a complex but well-organized network of normal faults that formed in two stages: a NNW-striking set forms a graben through the center of the field and a younger NW-striking set formed adjacent to and abuts NNW-striking faults. The NW-striking faults formed in regions of stress concentration during subsequent oblique-extension. Characterization of drilling fluid loss data suggests that dilatent damage zones surround all the faults but are more thoroughly developed adjacent to NW-striking faults. Present-day subsurface stress magnitudes are calculated to occur in the ratio 1:0.86:0.73 (SV:SH:Sh) with SH trending 45°. This stress condition is consistent with the formation of the NNW-striking fault set. We interpret SH to have rotated slightly CCW since the formation of the NW-striking faults. 

We find that elevated fluid losses occur in regions of anomalously low mean stress in the hanging-walls of the larger normal faults. We interpret these regions to be structurally unstable and have elevated fluid conductance capacities. An empirical relationship has been derived relating fluid loss, fault geometry, and stress perturbation to produce a risking scheme for future drilling which is critical to arctic operations. 



AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004