Cross-well Imaging in the SACROC Unit

Michael A. Raines and Brad Bryans, KinderMorgan, Midland, Texas

   Crosswell seismic images were recorded in the Cisco and Canyon Formations along the eastern side of the Pennsylvanian Horseshoe Atoll at the SACROC Unit in Scurry County, Texas.  “Reef top” geometry here is very extreme, with some portions of the interval composed of bioherm mound type growth, while other sections are formed by grain-type deposition.  Post-depositional changes (including karsting and mass wasting processes) have further altered the original geometry of the area and modified flow paths. 

Cross-well data includes images taken in strike and dip directions.  In both directions, wireline data indicates rather flat layering in the lower half of the interval.  In the strike direction, cross-well data indicates sub-horizontal layering.  However, in the dip direction, cross-well data indicates a complex stacking pattern characterized by sudden variations in depositional style, including some intervals with mound-like dip reversals.

Outcrops of the Holder Formation (Cisco-equivalent) in Behman and Dry Canyons of the Sacramento Mountains of New Mexico reveal a variety of depositional styles associated with mound development, including sharp contacts and transitional deposits, both in vertical and lateral directions.

The range of shapes seen in the upper portions of the Cisco deposits at SACROC via cross-well imaging have geometric equivalents in outcrop.  The implication of apparent seismic equivalents to outcrop is that log-based flow unit interpretations may not adequately define internal boundaries and therefore may not accurately predict flow paths, especially in the dip direction.