Print this pagetoward Predictive Models of Early-Formed Fractures in Steep-Sloped Carbonate Systems
Early-formed fractures may contribute significantly to permeability and porosity in steep-sloped, microbial-boundstone, carbonate systems. These structures may therefore play an important role in charging, storage capacity, and production of reservoirs within these systems. We integrate 3D outcrop analog studies from the Guadalupe Mountains of New Mexico and West Texas with elastic finite element models to gain insights into the processes that drive synsedimentary fracturing. Our ultimate goal is the ability to predict the occurrence and distribution of early-formed structures within steep-sloped carbonate systems.
We have selected two regions of the Guadalupe Mountains to construct our outcrop analog models - the Slaughter Canyon, and McKittrick-Big canyon regions. We integrate geologic field mapping, digital photogrammetry, and Global Positioning System (GPS) surveying to construct 3D models of structural and stratal geometry. Geologic field mapping provides the stratigraphic and structural framework, including quantification of structural densities using scanline methods. Digital photogrammetry is used to convert field interpretations to a 3D structural model with ~1 m precision. GPS surveying (cm to m precision) provides the means to accurately tie field interpretations including key stratal boundaries and structures to the 3D model.
In Slaughter Canyon systems of platform-margin-parallel synsedimentary faults with up to ~30 m of throw extend for several kilometers along strike. These faults initiated 500-1400 meters shelfward of the active margin, and several remained active throughout the deposition of the carbonate platform. This pattern of faulting is consistent with patterns of stress predicted from stepwise-elastic models of a prograding steep-sloped margin. In McKittrick Canyon, synsedimentary faults are also present, however their throw is an order of magnitude smaller. We propose that the platform margin geometry may be a factor in this significant change along strike. Axisymmetric elastic models predict less compressive margin perpendicular stresses for convex margins than for concave margins. Convex platform margins, such as the region around Slaughter Canyon, may therefore be more prone to synsedimentary faulting and jointing.
AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009