|
Diagenetic Processes |
Department of Geological Sciences, South Road, University of Durham, Durham DH1 3LE, UK
Reservoir Technology Branch, BP Research Centre, Chertsey Road, Sunbury on Thames, Middlesex TW16 7LN, UK
Cementation patterns in modern reefs are inhomogeneous, even on the thin section scale. The concept of the microenvironment has been developed in order to explain this irregularity, this microenvironment being determined by both chemistry and permeability. Identification of the rate limiting step in carbonate cement growth has led to the suggestion that cementation patterns are controlled principally by the microenvironmental permeability. In order to test this hypothesis, modelling of the permeability characteristics of biogenic frameworks has been attempted. Representative matrix geometries were created mathematically and Poiseuille flow through these has produced cementation patterns similar to those observed in thin section. Visual comparison of the features of the real system and model results indicates that the conceptual model is realistic and permeability may indeed be the major control on cementation.
In the future, modelling of the matrix geometry will be controlled using the measured pore throat radius distribution of the rock. At that stage the model will be applicable not only to the prediction of cementation patterns but to many other problems involving fluid flow through porous media.
