Two-phase flow in smooth and rough walled single fracture

Date
2012
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Abstract
The research documented in this thesis describes an experimental study of co-current flow of oil and water in neutrally wet smooth and rough-walled single fractures. The fracture is modelled as a thin gap as is used in a Hele-Shaw cell. The focus of the investigation is on the impact of fracture inclination angle and flow direction, phase flow rate ratios, flow regime, and fracture wall roughness on the interference of oil and water flow in the gap as measured by relative permeabilities for oil and water. Four inclination angles were examined: 0° (horizontal), 30°, 60°, and 90° (vertical); the non-zero ones were evaluated for both up-dip and down-dip flow directions making the total number of inclination-flow configurations equal to seven. For each of the fracture configurations considered, the flow rate ratios of oil and water were adjusted to determine impact on flow regime and phase interference. Another set of experiments was performed on artificially roughened single fractures to examine how oil and water phases respond and interact with the fracture walls. For the smooth-walled experiments, the nominal gaps studied were equal to 0.127, 0.254, and 0.381 mm. In the rough-walled experiments, the nominal gaps were equal to 0.381 and 1.25 mm. To examine the effect of the initial fluid filling the gap, a set of water-saturated smooth and rough-walled experiments were also conducted. In these experiments, the gap was nominally equal to 0.254 and 0.381 mm in the smooth-walled fractures, whereas it was 1.25 mm in the rough-walled fracture. In summary, the results of the experiments demonstrated that the relative permeability of oil and water exhibited variations in shape and extent indicating the effects of phase interference and phase saturation hysteresis. Roughness of the gap impacted the flow by amplifying phase interference and changing the shape and end-points of the relative permeability to oil and water. Fractal analysis of the flow patterns observed in the experiments revealed the complexity the flow of oil and water in a Hele-Shaw cell. The tortuosity, derived from the fractal analysis, showed that the channel tortuosity increases with increasing wall roughness and smaller fracture gaps. The computed tortuosity values are found to be much greater than unity. To better understand the nature of the two-phase flow in the gaps, two-phase relative permeability models (X-curve model, Corey, viscous coupling model, homogenous single-phase approach, and saturation exponent model) were fitted against the experimental relative permeability data. The fits to the models reveal that there is no single model that best fits the experimental data. However, reasonable fits were obtained with the saturation exponent model and homogeneous single-phase approach. In some cases, the viscous coupling model provided a good fit. The other models poorly fitted the experimental relative permeability data.
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Bibliography: p. 170-172
Most pages are in colour.
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Citation
Al-Turki, A. A. (2012). Two-phase flow in smooth and rough walled single fracture (Doctoral thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca. doi:10.11575/PRISM/5068
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