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Abstract
Chapter from: M
61: Basin Compartments and Seals
Edited by
Peter J. OrtolevaAuthors:
C. Qin and Peter J. Ortoleva Methodology and Concepts
Published 1994 as
part of Memoir 61
Copyright © 1994 The American Association of Petroleum
Geologists. All Rights Reserved. |
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Chapter 25
*
Banded Diagenetic
Pressure Seals:
Types, Mechanisms,
and Homogenized Basin
DynamicsC. Qin
Peter J. Ortoleva
Indiana University
Bloomington, Indiana,
U.S.A.
*
ABSTRACT
The structure, mechanisms
of formation, and key role of diagenetically banded pressure seals are
reviewed. A difficulty in predicting the genesis time and location of these
seals is that they are apparently affected by local stresses and fluid
pressures, but, in turn, they affect the basin-scale distri-bution of these
factors. We show that this very formidable multiple-scale basin modeling
problem can be solved via a computational homogenization technique.
Banded pressure seals are classified in
two complementary ways. First we distinguish those generated through self-organization
from those directly of sedimentary origin. They are then classified according
to the specific processes (pressure solution, nucleation, diffusion, flow,
coupled mineral reactions, and grain comminution) by which they emerge.
The argument is made that feedback in the network of reaction, transport,
and mechanical processes underlies the development of many diagenetic seals.
The technical problem of the need to simulate
submeter-scale banding phenomena in basin-scale models is introduced and
addressed. A computational homogenization scheme is shown to simultaneously
capture phenomena on these two scales by treating them both in a way that
preserves their characteristics. We believe that this approach is a great
advance in basin modeling more generally in that it allows one to capture
phenomena on multiple spatial scales arising from complex sedimentary features
and their reworking through diagenesis.
The following are demonstrated by simulations
carried out for pure quartz sandstones undergoing stress-induced reactions,
diffusion, and fluid flow. Seals are very likely to form within finer grain
beds or at some specific depth within macroscopically uniform grain-size
sediments. The depth and the time needed to form a seal depend upon the
intensity of overpressure, fluid flow, geothermal gradient, subsidence
velocity, grain size, the sediment sequence, and tectonic environment.
High overpressure or higher geothermal
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