3-D Variability of the Upper Permian Capitan Carbonate Platform: New Insights from Subsurface and Outcrop Data

Hunt, David W.¹; Blendinger, Wolfgang ²; Labrana, Gemma ^3
1 StatoilHydro ASA, Bergen, Norway.
² Petroleum Geology, University of Clausthal, Clausthal, Germany.
³ Geochemistry and Petrology, Universitat de Barcelona, Barcelona, Spain.

The Upper Permian Capitan platform is cut by syndepositional fault and fracture systems that localized paleokarst development. Such features are an important source of heterogeneity in carbonate reservoirs. However, most are sub-seismic in scale and so will only be detected from borehole data. In order to assess the density of well data required to identify synepositional fault and fracture systems, a 40x30 km 3D subsurface model of the Upper Permian Capitan carbonate platform has been constructed. The initial stratigraphic framework is constructed in IRAP-RMS and uses well log data from 45 commercially available wells, core and log data from the PDB-04 research well, published 2D correlations and available formation tops as constraints. The modelled stratigraphic interval ranges from the Bell Canyon through the Capitan, Seven Rivers, Yates and Tansill formations.

From the well picks the key stratigraphic horizons were modelled by interpolation. The resulting 3D model shows some important features:

- Dramatic thickness variation along depositional strike. Thicknesses appear almost 2 times higher in the western part of the model as compared to the eastern part. The thickness change appears to be controlled by a northerly-trending fault or a flexure.

- Despite the dramatic lateral thickness changes the amount of basinward progradation is nearly constant.

- Contour maps suggest several anomalies superimposed onto an otherwise consistent, low angle eastward structural dip. Based on outcrop analog data, these anomalies could indicate faulting and/or flexures oriented parallel to the platform margin.

- The siliciclastic intercalations of the Yates and Tansill formations appear concentrated in localized “lows”. Outcrop analog data suggest these are either small grabens and/or fault-controlled synclines.

Outstanding questions concerning the structural setting and the 3D distribution of the intercalated clastics are refined by the incorporation of additional well data in ‘problematic’ areas. The results hold important implications for the density of borehole data required to resolve syndepositional fault and fracture and any associated paleokarst systems within the subsurface.

AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009