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The AAPG/Datapages Combined Publications Database

Houston Geological Society Bulletin


Houston Geological Society Bulletin, Volume 49, No. 2, October 2006. Pages 21-21.

Abstract: Applying Deltaic and Shallow Marine Outcrop Analogs to the Subsurface


Janok P. Bhattacharya

A fundamental problem in subsurface reservoir characterization is determining the continuity of flow units and flow barriers. Flow units and barriers exist on a variety of scales from field-wide to interwell to wellbore.

Outcrop analog studies and databases are used to develop Previous HitmodelsNext Hit for

  • regional and field-scale reservoir and nonreservoir elements associated with shallow marine, deltaic reservoir types
  • detailed 3D facies architecture of small-scale, intrawell heterogeneity (cements and “stochastic” shales) in specific depositional subenvironments (e.g., delta front facies) that may be incorporated into reservoir Previous HitmodelsNext Hit
  • conceptual reevaluations of shoreline and deltaic facies that may be applied by geologists interpreting or correlating seismic, well log or core data.

The subsurface geologist must use facies Previous HitmodelsNext Hit and sequence stratigraphy concepts to correlate well data. Several examples of deltaic reservoirs that consist of Previous HithorizontalNext Hit Previous HitlayersNext Hit are described. Outcrop examples suggest that delta front sandstones are not Previous HithorizontalNext Hit but dip seaward. This recognition challenges many current reservoir Previous HitmodelsNext Hit that assume flat-lying beds and affects how we correlate core and well log data. On the regional scale, the analogs suggest very different exploration Previous HitmodelsNext Hit are required to search for basin-distal reservoir sandstones.

From the perspective of general facies Previous HitmodelsTop, historically shorefaces have been assumed to form homogenous, uniform reservoirs that require little effort to produce. Production histories, however, show that this assumption is not valid for many so-called shoreface-type reservoirs. Many reservoir units identified as wave-dominated shorefaces are actually delta front deposits. This new model for wave-influenced coastlines suggests a distinct facies asymmetry, with homogenous beach and shoreface sands accumulating on the updrift side of the river mouth and significantly more heterogeneous facies on the downdrift side. The new model was used to reinterpret Cretaceous “shoreface” deposits in Wyoming, New Mexico and Utah and should be applicable to subsurface deltaic reservoirs elsewhere.

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