Multimineralic Mechano-Chemical Model of Compaction, Pressure Solution, and Fracture Nucleation Infilling

Julie L. Boyd, Anthony J. Park, Peter J. Ortoleva

We have developed a pressure solution contact rate law of the diffusion-limited type that is valid for cases where the diffusion coefficient of a solute along the contact can be different for each solute. Accounting for different mineralogies at each grain-grain contact is especially important because of the interaction of minerals changes the mechano-chemical properties of the contact environment which in turn affects the pressure solution of both minerals. A statistical account is made of the fact that the behavior of the contact between any two grains may differ significantly with the mineral identity of each of the two grains.

Fractures play a central role in many diagenetic processes. They may comprise the major component of the matrix permeability. Fractures and healing of seals can determine limits on overpressures and the leakage of petroleum from overpressured compartments or the injection of petroleum into underpressured ones. To account for both complex multi-mineralic pressure solution and fracture nucleation growth and cement infilling a coupled kinetics model has been developed.

The simulator CIRF.B is used to test the ideas presented here. The program simulates chemical compaction behavior in a variety of rock types to demonstrate the effects of composition, mineralogy and textural variations on the extent of pressure solution in sediments, the frequency and rates of fracturing and healing, and the degree and composition of fracture in filling. Simulations are performed to compare the differing effects that like and dissimilar mineral grain-grain contacts generate in systems that include quartz, calcite, feldspar and muscovite.

AAPG Search and Discovery Article #91020©1995 AAPG Annual Convention, Houston, Texas, May 5-8, 1995