Initial porosity of random packing: Computer simulation of grain rearrangement

The initial porosity of clastic sediments is poorly defined. In spite of this, it is an important parameter in many models that describe the diagenetic processes taking place during the burial of sediments and which are responsible for the transition from sand to sandstone. Diagenetic models are of importance to predict the sub-seismic heterogeneity of reservoir rock. Also, initial porosity is an important parameter for decompaction routines to reconstruct the burial history of rock used to determine the maturation of oil source rock. Measurement of initial porosity is usually difficult, because unconsolidated sediments are easily disturbed during sampling and because sediments close to the surface already have been subjected to varying degrees of compaction. Neither is it possible to observe the processes that take place during compaction, since these take place over geological time scales. Laboratory experiments do not allow us to accurately mimic these processes due to the relatively short time span available. For these reasons, no analytical methods exist to quantify the relation between the grain-size distribution, grain shape and the (initial) porosity. Therefore, these parameters are ignored in many models that describe porosity loss, despite the knowledge that they have a large influence on the heterogeneities inside a sand body. In this thesis an object-based simulation model is presented that is used to improve our insight into the relation between the parameters of the grain-size distribution, the initial porosity of sandy sediments, and the evolution of porosity decrease during the initial phase of compaction. The model is capable of simulating all different types of disordered packing in a proces-based approach without significant boundary effects. The possibility to simulate all kinds of packings of different size distributions offers also many opportunities to study the effect of different depositional mechanisms of sediments on rockproperties (such as porosity)