WILLIS, B. J., C. D. WHITE, S. L. GABEL, and J. P. BHATTACHARYA
Bureau of Economic Geology, The University of Texas at Austin, Austin, TX

Abstract: Documenting Deltaic Bedding Architecture in Outcrop for Reservoir Simulation

Delta deposits have complex internal architecture related to facies changes up the delta front, varying rates of delta progradation, grain sorting during migration of a hierarchy of bedforms, and the distribution of shales formed during depositional pauses. These internal complexities can strongly influence patterns of subsurface fluid flow during the development of analog reservoirs. Reservoir simulation based on high-resolution outcrop data is a method to understand the influence of different types of geologic variability on subsurface flow. Unfortunately few sedimentologic studies generate data that can be easily incorporated into reservoir simulation models, and similarly methods of gridding and data interpolation used in the construction of simulation models can obscure important geologic details.

A sedimentologic data base, collected specifically as a basis for reservoir simulation models, documents complexity within an outcropping tide-influenced delta in the Frontier Formation of central Wyoming, USA. The data set is digital in contrast to standard sedimentologic data presented as graphic bedding traces and logs. The focus is on documenting stratal geometry and the spatial distribution of internal rock properties rather than simply tracing bedding. Facies are mapped as polygons. Shales are defined by line segments associated with the top of specific strata. Numerical data of sedimentologic parameters and permeability are used to estimate rock property variations within mapped strata. Finer scale data sets document variations within individual facies types. These geologic data can be incorporated into a counterpoint simulation grid with minimal loss of detail.

AAPG Search and Discovery Article #90928©1999 AAPG Annual Convention, San Antonio, Texas