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).Civil Engineering and Geoscience

Reservoir characterisation using process-response simulations: The Lower Cretaceous Rijn Field, West Netherlands Basin

Petroleum geologists always need to deal with large gaps in data resolution and coverage during reservoir characterisation. Seismic data shows only large geological structures, whereas small-scale structures and reservoir properties can be observed only at well locations. In the area between wells, these properties are often estimated by means of geostatistics. Numerical simulations of sedimentary processes offer an alternative method to predict these properties and can improve the understanding of the controls on reservoir heterogeneity. Although this kind of modelling is widely used on basin scale in exploration geology, its application on field scale in production geology is virtually non-existent. We have assessed whether the recent developments in numerical modelling can also aid petroleum geologists in the interpretation of the reservoir geology. Seismic data, well data and a process-response model for coastal environments were used to characterise the Lower Cretaceous oil-bearing Rijn Field. Interpretation of seismic and well data led to a definition of the structural setting and the depositional model of the Rijn Member in the area. From the sedimentological interpretation the sea-level history could be estimated, which is the one of the most important input parameters for the process-response model. Application of the process-response simulator to the Rijn Field resulted in approval of the depositional model. The output was presented in a 2-dimensional north-south profile, which corresponds very well to the well logs along this section. The results demonstrate that numerical simulations of geological processes can be very useful as a tool to explore many likely geological scenarios. While it cannot be used to supply a unique solution in many cases, it forms a helpful guide during reservoir characterisations to find an optimal scenario of the controls on deposition of the Rijn Member, which contributes to the understanding of the inter-well reservoir heterogeneityCivil Engineering and Geoscience