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Fine grained siliciclastic lithologies commonly act as sealing caprocks to both petroleum fields and host reservoirs for CO2 sequestration, and are of great importance in controlling fluid flow and storage. Despite this, they are rarely characterised in terms of sedimentology, diagenesis, or how these relate to caprock quality. This thesis aims to improve our understanding of caprocks through petrological study using standard techniques to analyse caprocks in terms of paragenetic sequences and sequential processes and then use this to find out the key intrinsic and extrinsic controls on porosity, and thus caprock quality. Subsequently, direct experimental measurement of permeability and its relation to petrological and other petrophysical data is used to test the quality of the caprock and the controls on caprock quality.

It is becoming increasingly common practise to model the impact of faults on fluid flow within petroleum reservoirs by applying transmissibility multipliers, calculated from the single-phase permeability of fault rocks, to the grid-blocks adjacent to faults in produc- tion simulations. The multi-phase flow properties (e.g. relative permeability and capillary pressure) of fault rocks are not considered because special core analysis has never previ- ously been conducted on fault rock samples. The principle aim of this thesis is to fill this knowledge gap. Two distinct approaches have been adopted. First, a considerable num- ber of experiments have been conducted to measure the multi-phase flow properties of faults. The measurements represent different type of fault rocks: cataclastic fault rocks, and fault rocks in impure sandstone; significant amount of effort was needed to evaluate and design new experimental methods. Second, an attempt has also been made to numer- ically model the multi-phase flow behaviour of fault rocks; several numerical techniques (lattice Boltzmann method, pore scale network modelling) have been used. In addition, production simulation modelling has been conducted to investigate the implications of the results. The relative permeability measurements were made using a gas pulse-decay technique on samples whose water saturation was varied using vapour chambers. The measurements indicate that if the same cataclastic fault rocks were present in gas reservoirs from the southern Permian Basin they would have k,.g values of < 0.02. Such large reduction in gas effective permeability was also seen for tight gas sandstones and siltstones. However, the steady-state oil relative permeability measurements for a kaolin rich sample which represents an analogue to fault in impure sandstone was found to be higher then those for the cataclastic fault rocks. The samples studied show also different sensitivity to effective stress. The gas relative permeability measurements proved far more stress sensitive than the single phase permeability values. Pore scale network models have a strong capability in modelling the relative permeability and capillary pressure curves for such low permeability rocks. The predicted results by the model were in good agreement with the experimental data presented in this work. Similarly, lattice Boltzmann method found to have a strong capability for modelling the multi-phase fluid flow in a variety of situation.