The Reciprocal Nature of Carbonate and Siliciclastic-Dominated Slope Channel Deposits

Prediction of reservoir sweet-spots in steep-slope systems for both conventional and unconventional production is frequently hindered by poor seismic resolution, sub-seismic and inter-well heterogeneity, and a lack of understanding of how slope systems respond to relative sea-level. Heterogeneity within the lower slope and basin in strike and dip results in highly-variable reservoir geometry and continuity that elevate uncertainty for exploration and production.

Measured stratigraphic sections, field mapping, high-resolution airborne lidar interpretation, and spectral image analysis were integrated into a 3-D GIS database and used to extract relationships between channel positions and fill types along Upper Permian (Guadalupian) paleoslopes between Pine and McKittrick Canyons in Guadalupe Mountains National Park. Exposures of the Bell Canyon/Capitan Formations offer multiple windows into the transition between proximal mid-to-lower slope carbonate debris and more distal siliciclastic slope-channel successions. Outcrop observations were used to reconstruct the slope profile and slope-channel geometry for the steep, high-relief Capitan shelf margin.

The turbidity flows responsible for channelization of the carbonate-dominated Capitan slope (clinothems) during lowstands bypassed siliciclastic material to the basin. After active channelization waned, slope channels were filled by amalgamated margin-derived carbonate debris with minimal siliciclastic preservation on the middle and lower slope. Progressively down-dip, siliciclastics in the lower part of the channel-fill succession were overlain by discrete carbonate breccia bodies. These breccias likely represent single depositional events compensationally stacked within the channels. In more distal positions siliciclastic-dominated gravity flows deposited meter-scale, margin-derived carbonate boulders within fine grained siliciclastic matrix.

Although precise toe-of-slope location has yet to be identified, relative positions and channel fill styles associated with very different flow rheology have been documented that highlight the transition from carbonate dominated slope facies and interfingering basinal clastics. Additionally, channel orientations mapped in the field may help estimate along-strike heterogeneity of the Capitan margin and aid in identification of relict margin outcrops preciously undocumented to better understand the complex composition of mixed carbonate and siliciclastic slope systems.  

AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California