Отправлено: 11.12.13 03:20. Заголовок: Geometric models of porosity reduction by ductile grain compaction and cementation

Geometric models of porosity reduction by ductile grain compaction and cementation
Maryam A. Mousavi and Steven L. Bryant

AAPG Bulletin, v. 97, no. 12 (December 2013), pp. 2129–2148

ABSTRACT
Pore-volume reduction of sediments by plastic deformation during compaction and by cementation of grains has been
evaluated for different proportions of ductile and hard grains.
We represent the compaction behavior of grains with a purely geometric model, which uses the cooperative rearrangement
algorithm to produce dense, random packings of partly inter penetrating spheres. We varied the fraction of grains assumed
to be ductile and the radius of the rigid core of the ductile grains.

The predicted relationship between the fraction of ductile grains in the sediment and the porosity after compaction
agrees well with previously published experimental data in the literature.

The radius of the rigid core of the ductile grains is an effective way to represent different kinds of ductile material, ranging from
brittle (rigid radius >0.9) to extremely ductile (rigid radius <0.7).
We simulated quartz cementation in our compacted rock by adding isopachous cement.
Cement thickness was reduced on the smaller grains and increased on the larger grains to account for presumed export of pressure
dissolved material from finer grained regions and the import of material into coarser grained regions.
These simulations yield descriptions of pore-scale geometry resulting from processes common in sandstones.
Modeled pore geometry provides in sight into transport properties of such rocks. For example, the models predict,
to within a factor of five, the permeability of samples of tight-gas sandstones having little intragranular porosity.