Compaction of sedimentary rocks

Burial compaction of sedimentary lithotypes results in changes to rock densities. For any pure lithotype, these changes are described and modelled by a porosity function: rho(b)(z) = rho(Fr) + (rho(eta) - rho(Fr))phi(z) Porosity varies in response to changes in maximum effective stress, generally as an exponential decay function. This porosity function may be modified to incorporate thermo-kinetic and chemical processes. In recent years, various workers have developed and published porosity functions describing compaction in several major lithotypes. Most rock sequences consist of mixtures of lithotypes. The volumetric proportions of principal lithotypes can be estimated from wireline log data. In mixed lithology sequences, the volumetric and density consequences of burial compaction are estimated by weighted summation of changes to each lithotype present: rho(b)(z) = Sigma(i=1)(n+m)[nu(i)rho(i)(z) + phi(i)(z)rho(eta)] Systematic variations in rock density computed in this manner are used as a key to detailed analysis and prediction of other sequence attributes which may be of great technical and commercial interest. These include acoustic performance prediction, hydrocarbon generation prediction and primary migration modelling, and sedimentary basin and hydrocarbon system geometric modelling..