The Role of
Faults in Turbidite Compartmentalization at the Bed-scale
Manzocchi, Tom1, John J. Walsh2,
Mark Tomasso3, Julian Strand2, Conrad Childs2,
Peter Haughton4 (1) University College Dublin, Dublin, 4, Ireland
(2) University College Dublin, Dublin 4, Ireland (3) The University of Texas at
Austin, Austin, TX (4) University College Dublin, Dublin, Ireland
Sandstone connectivity has been measured
in a comprehensive suite of faulted and unfaulted bed-scale turbidite models
assuming permeable sands and impermeable shales and shale smears.
Sedimentologically the sheet-like geometries are characterized by differences
in net: gross ratio, amalgamation ratio and the shape, size and orientation
distributions of the beds. Fault-system variables include fault frequency,
length, maximum throw and orientation distributions.
Shale smears have been modeled using either cut-off values of deterministic
fault-surface proxy-properties (e.g. SGR, SSF, CSP), or by explicitly modeling
stochastic smears associated with each shale horizon on the fault-surfaces.
Factor analysis is used to establish
sensitivities to connectivity and to connectivity changes in representative
models as a function of model parameters or, more usefully, dimensionless
ratios between sedimentological and fault-related parameters. If the size of
faults (maximum throw and length) are a few times smaller to a few time larger
than the bed sizes (thickness and length), we find that most variables
considered can be influential on the connectivity of the sequences, with
particular variables being more or less important depending on the values of
other fault-related or sedimentological variables. In general, however, systems
at these scales are rarely more compartmentalized in three dimensions than
their unfaulted counterparts, irrespective of whether and how fault rock
properties are modeled. Faults that are large in relation to the beds can,
however, have a significant positive or negative impact on connectivity
depending on the characteristics of the shale smears.
AAPG Search and Discover Article #90063©2007 AAPG Annual Convention, Long Beach, California