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Satavisa Sarkar1, Sankar K Muhuri1, Thomas Dewers1
(1) University of Oklahoma, Norman, OK

Abstract: Experimental constraints on modeling of time dependent pore collapse

Time, temperature, effective stress, and rock texture all influence porosity loss to some degree during burial of sediments. Predictive models do not agree, however, on the relative importance of these parameters. We investigate constraints on such models made by experimental investigations of time-dependent pore volume loss (creep). Examination of experimental data from our laboratory, together with data sets from other workers, show that volumetric creep in porous aggregates of a variety of mineralogies occurs by the same mechanism, as evidenced by the same functional dependence on grain size, volume strain (or porosity), and effective pressure. Creep strain always accumulates as the logarithm of time, but can occur by a host of mechanisms. For example, pressure solution and microcrack growth are competitive processes, with pressure solution dominating at lower stresses, higher temperatures, finer grain sizes, and lower porosities. Parameterized creep laws are derived which govern the loss of pore volume in these systems. With the addition of temperature, triaxial stresses and poroelastic effects, numerical models predicting subsurface porosity loss within a given burial scenario based on these creep laws are constructed and compared to literature porosity-depth profiles.

In addition to the above, limited experimental data demonstrate the influence of the shape of the aggregate particle size distribution, intergranular cement, and clay content on compaction rates. Methods for including these effects in models for porosity loss are discussed. Preliminary numerical simulations of these models bear on present knowledge of rates of subsidence associated with reservoir drawdown, fault zone sealing, and porosity prediction.

AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana