Lee, Keumsuk1, M. Royhan Gani1, Xiaoxian Zeng1, George A
McMechan1, Willliam R. Griffin1, D. Nahid Sultana1, Janok P.
Bhattacharya1, Carlos L. V. Aiken1, Xueming Xu1
(1) University of Texas at Dallas, Richardson, TX
ABSTRACT: GPR Survey of a Delta Front Reservoir Analog, The Wall Creek Member, Frontier Formation, Wyoming, U.S.A
Ground penetrating radar (GPR) surveys, outcrop sedimentology and shallow coring were done at a reservoir analog in the Turonian Wall Creek Member in Wyoming. The objective was to image decimeter-scale 3D bedding geometry of a top-truncated lowstand delta front containing low-permeability concretions that are hypothesized to influence fluid flow.
Two 3-D surveys cover surface areas of 30 m x 80 m and 12 m x 12 m at frequencies of 50 MHz and 200 MHz, respectively, and image detailed bedding structure. Two 2-D GPR grids (100x300 m and 160x200 m) contain orthogonal lines 20 m apart, use 50 MHz antennas, are aligned to depositional strike and dip, and image larger-scale bedding geometries. GPR processing involves dewowing, time-zero adjustment, airwave/average elimination, and prestack Kirchhoff migration. Migration velocities were controlled by ten cores that also provide independent sedimentologic information behind the cliff faces.
Two radar facies (RF) were identified: RF1 corresponds to the sand body and RF2, to the underlying mudstones. RF1 contains offlapping clinoforms with high-amplitude, high-continuity reflections. RF2 is characterized by short, complex, irregular, low-to-high amplitude reflections. RF1 thickens, while RF2 thins, seaward. These facies match well with geometries observed in the adjacent cliff-faces. Concretions within RF1 are recognized throughout the GPR data. Instantaneous GPR amplitudes and frequencies calibrated with the core data are used to translate the GPR volumes into 3D permeability volumes. Correlation of beds throughout the volumes provide the geometrical framework of the 3-D stratigraphic surfaces that are the basis for 3-D fluid flow modeling.
AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004.