Measuring
Autogenic Noise Superimposed on Idealized, Long-Term Distributary
Dynamics
Sheets, Benjamin1, David Hoyal1,
Tao Sun1 (1) ExxonMobil Upstream Research
Company,
The long-term average behavior of
distributive depositional systems is relatively predictable and linear. The
deposits tend to be monotonous, recording slow system re-equilibration via a
gradual increase in slope to some regional ‘grade,' and in plan view, the front
of the growing deposits will tend towards a radially-symmetric
form. Most distributary systems, however, are noisy,
producing intrinsic oscillations around the equilibrium trend. Though these
oscillations can occur on a variety of time-scales (from minutes to many
millennia), this paper is focused on autogenic noise associated with channelization, levee formation, and local overextension of
the depositional front beyond the long-term trend. The channelization
process leads to a type of ‘landscape inertia,' which is related to both the
momentum of channelized flow and a pseudo-inertia
associated with depositional landforms such as levees that confine flow to
particular courses.
Analysis of experimental and numerical
simulations of deep water and shallow marine distributive depositional systems
indicate that this noisiness is clearly related to autogenic cycles in channel
mouth bar formation and distribution. The period and magnitude of the cycles is
related to the parameters controlling basin evolution, such as sediment and
water discharges, sediment cohesiveness, and accommodation rates. An
understanding of distributive autocyclic noise,
therefore, has important implications for reservoir characterization and
prediction, particularly as deposits associated with this scale of autocyclic behavior are commonly below seismic resolution.
AAPG Search and Discover Article #90063©2007 AAPG Annual Convention, Long Beach, California