Water flooding has long since been used to increase oil production from fractured carbonate reservoirs. More recently steam injection has also been applied specifically to enhance oil recovery from fractured carbonate reservoirs containing heavy oil. Production simulation modelling provides a method to optimise these processes. However, such models do not generally consider the impact of steam injection on fracture permeability due to the lack of a quantitative understanding of the impact of thermal and chemical processes on fracture deformation and fluid flow. To help fill : this knowledge gap, a series of flow, loading and unloading experiments were performed on fractured and un fractured samples between ambient and 90°C. Loading fractured samples resulted in non-linear fracture closure. Unloading showed that some of the deformation was permanent. Fracture permeability was reduced dramatically as temperature was increased even when an unreactive mineral oil was used as the permanent while the confining pressure was kept constant. CT images showed that fracture apertures were dramatically reduced and contact areas increased during heating. The results indicate that this was caused by temperature weakening. Recirculation of reactive and equilibrated water through the fractures also resulted in a large reduction in fracture aperture probably as a result of dissolution and water weakening of the chalk. These thermal and water weakening effects have a far bigger impact on fracture permeability than simply loading and unloading the samples but are not accounted for in industry standard production simulation models. Finite element models, incorporating an elastoplastic constitutive model, were generated with fracture geometries based on the CT images obtained during the experiments. These models were able to reproduce the general behaviour of the fracture deformation observed in the experiments including both the nonlinearity and partial irreversibility of the process. These features could not be reproduced using a purely elastic model. The results are consistent with the idea that the contact asperities deformed by plastic deformation. These results suggest that the elastoplastic constitutive relationship probably provides a better tool to model the controls on fracture behaviour. Coupling this model with reservoir production simulation has the potential to improve the prediction of fluid flow in fractured carbonate reservoirs during steam injection. Keywords: Enhanced oil recovery, steam injection geomechanics fractured carbonate reservoirs.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:551230 |
| Date | January 2011 |
| Creators | Al Zadjali, Ruqaiya Jan Mohammed |
| Publisher | University of Leeds |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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