Hennessy, John R.¹, Jory A. Pacht², Samir Ghazi³, H. Matt Pickrel³ 
(1) Consultant, Sugar Land, TX 
(2) Seis-Strat Services, Inc, Houston, TX 
(3) Conoco-Phillips, Houston, TX

ABSTRACT: A New Exploration Play Concept From the Idea to the Drill Bit – The Search for Reservoir Sands in Deep-Water Facies of the Late Cretaceous Olmos and San Miguel Formations, Webb County Texas

Evaluation of a large swath of 3D seismic data revealed the presence of slightly sinuous to meandering channel-form features in downdip facies of the Olmos and San Miguel formations where deep-water reservoir sands were not known to exist. Recognizing the economic potential borne out of these observations, a sequence stratigraphic study was initiated to determine likelihood of sand-fill in the channels. Strata were divided into sequences and systems tracts using well log, seismic, and biostratigraphic data. System tracts were evaluated relative to their seismic and well-log signatures in downdip areas and their relationship to up-dip intervals in producing fields. 
Well data suggest that possible sandy and silty crevasse-splays developed as coarse-grained sediment was transported through early lowstand erosional submarine canyons. Both onlap fill and accretionary channel fill began during “middle” early lowstand time and continued throughout development of this systems tract. Downdip well data show possible siltstone and silty sandstone channel-fill facies. These strata correlate with updip high gradient fluvial dominated deltas. Channel fill probably ceased during late lowstand time. Correlatable deltas updip are wave dominated. This suggests that wave and longshore currents moved much of the coarse-grained sediment along strike as opposed to downdip. 
Olmos deep-water channels were tested at two locations. The first well took a large gas kick and had to be sidetracked. As a result it probably intersected the channel at a sub-optimal location. Both wells were sub-commercial but penetrated gas-filled siltstones. Further work may result in location of reservoir sandstones which should produce at commercial rates.

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