published_or_final_version / Biochemistry / Doctoral / Doctor of Philosophy

The fold and thrust belt of the Subandean Ranges (central and southern Bolivia, and northern Argentina) contains both gas and condensate production and reserves in Devonian quartzose sandstones within deep structures. Reservoir sandstones present values of permeability close to 0.01 mD, implying that reservoir drainage must be controlled by a fracture system that enhances permeability. Hydrocarbon production in naturally fractured reservoirs is affected by fracture quality (degree of openness), spatial arrangement, size distribution (including aperture, height and length), fracture abundance, and arrangement with respect to stratigraphic and macro-structural features. Systematic study of fractures in the subsurface is complicated by the small probability that a well will intersect sufficient fractures for direct analysis of their attributes. Because of this fracture data obtained from logging and coring must be complemented with alternative methodologies. In my study I performed a workflow that includes geologic mapping of outcrop analogs of subsurface units, fracture characterization in outcrops and thin sections, the construction of kinematic structural model using algorithms for 3D analysis, petrographic description of composition and diagenesis, and statistical multivariate analyses in order to define how structural, lithologic and diagenetic features affect fracture distribution. From the construction of a structural model and the analyses of its properties, I generated semi-quantitative models of fracture attributes based on classic fold-related fracture concepts. This model was tested with direct fracture observations from core and outcrop, coupled with microstructural imaging using SEM-CL, to document fracture attributes. The models all show high curvature and strain values homogeneously distributed along the azimuth and close to the hinge of the anticline, which implies this domain should be most fractured. On the other hand, microfracture studies reveal that although highest strain values are found in the hinge, low strains also are found along the hinge even for samples with similar lithologies. The study of macro and microfractures in outcrop and core samples allowed me to clearly identify two opening mode fracture sets for the Devonian sandstones. These present an orthogonal arrangement and variable cross cutting relations. The dominant set (defined as Set I) has a WNW strike and is perpendicular to the structural trend of the Subandean Ranges; the subordinate set (defines as Set II) has a NNE strike, and is parallel to the previously mentioned structural trend. Set I has higher strain accumulation, log-normal spacing distribution, and is strongly controlled by the primary quartz content of the rocks. Set II also has a log-normal spacing distribution, and presents structural control. / text

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Aim: The aim of this retrospective study was to record the number and demographics of patients presenting with maxillofacial fractures at the Garankuwa Hospital, University of Limpopo, Medunsa Campus. In addition, the nature of these injuries and the aetiological factors involved were recorded and analysed. Materials and methods: The approach to this study was collection of data from records of patients who were treated at the Maxillofacial and Oral Surgery Department for injuries (fractures) to facial bones. All the records for the period January 2002 to December 2005 were analysed. Results: For the period (2002-2005) under review 4000 patient files were retrieved and analysed. These consisted of 1755 (43,88%) patients with mandibular or middle or upper third cranio-facial fractures who were included in this study and 2245 (56,13%) patients who had been treated as in or out patients for other oral and maxillo-facial procedures or pathology, who were excluded. The 1755 patients consisted of 232 (13.22%) females and 1519 (86.55%) males giving a male to female ratio of 6.55:1. Seventy percent of all the patients were in the age group 20-39 years with a peak frequency in the 3rd decade. The minimum age was two years and the maximum age was 88 years. A total of 2427 fractures were recorded. Of these 2077 (85.58%) occurred in the mandible where the most common sites were the angle (28.97%), the parasymphisis (17.43%) and the body (14.75%). Nearly 80% of the fractures were caused by personal assaults, 14.87% by motor vehicle accidents, 2.34% by gunshot wounds and 3.93 % by falls. Conclusion: In conclusion this study has shown that in a South African population being studied, the leading cause of fractures to the maxillofacial skeleton were interpersonal violence (assaults and gunshots) followed by motor vehicle accidents.

Thesis (M. Phil.)--University of Hong Kong, 2006. / Title proper from title frame. Also available in printed format.

Sequence stratigraphy relates changes in vertical and lateral facies distribution to relative changes in sea level. These relative changes in carbonates effect early diagenesis, types of pores, cementation and dissolution patterns. As a result, in carbonates, relative changes in sea level significantly impact the lithology, porosity, diagenesis, bed and bounding surfaces which are all factors that control fracture patterns. This study explores these relationships by integrating stratigraphy with fracture analysis and petrophysical properties. A special focus is given to the relationship between mechanical boundaries and sequence stratigraphic boundaries in three different settings: 1) Mississippian strata in Sheep Mountain Anticline, Wyoming, 2) Mississippian limestones in St. Louis, Missouri, and 3) Pennsylvanian limestones intermixed with clastics in the Paradox Basin, Utah. The analysis of these sections demonstrate that a fracture hierarchy exists in relation to the sequence stratigraphic hierarchy. The majority of fractures (80%) terminate at genetic unit boundaries or the internal flooding surface that separates the transgressive from regressive hemicycle. Fractures (20%) that do not terminate at genetic unit boundaries or their internal flooding surface terminate at lower order sequence stratigraphic boundaries or their internal flooding surfaces. Secondly, the fracture spacing relates well to bed thickness in mechanical units no greater than 0.5m in thickness but with increasing bed thickness a scatter from the linear trend is observed. In the Paradox Basin the influence of strain on fracture density is illustrated by two sections measured in different strain regimes. The folded strata at Raplee Anticline has higher fracture densities than the flat-lying beds at the Honaker Trail. Cemented low porosity rocks in the Paradox Basin do not show a correlation between fracture pattern and porosity. However velocity and rock stiffness moduli's display a slight correlation to fracture spacing. Furthermore, bed thickness is found to be only one factor in determining fracture density but with increasing strain, internal bedforms and rock petrophysical heterogeneities influence fracture density patterns. This study illustrates how integrating sedimentologic and sequence stratigraphic interpretations with data on structural kinematics can lead to refined predictive understanding of fracture attributes.

Azimuthal resistivity was performed at the King site, near Birsay, Saskatchewan to characterize the orientation and extent of fracturing in a glacial till. The target consisted of shallow (less than 4m deep) fractures in the upper oxidized portion of the Battleford Formation.<p> The fractures were visible in soil cores, but their orientation and extent were not known at the time of investigation. It was hoped that if the azimuthal resistivity method could be successfully applied at this site it could be used as an in situ fracture mapping tool at other sites. <p> Preliminary azimuthal resistivity surveys failed to detect a consistent anisotropic pattern that could be attributed to fracturing. A refined method of azimuthal resistivity was developed that built a 3D resistivity model of the site assuming a heterogeneous, isotropic earth. This model was used to predict and remove the effect of heterogeneity on the azimuthal resitivity observations. The results from the refined method also failed to detect a consistent anisotropic pattern. <p>Any single azimuthal resistivity observation from either the preliminary or refined surveys would have provided data that could have been interpreted as anisotropy due to fractures. It was only by comparing many azimuthal observations across the site that the lack of consistent azimuthal pattern became apparent. <p>It is recomended that an analysis of several observations be made before any interpretation of anisotropy is made for azimuthal resistivity sureveys in general.

Azimuthal resistivity was performed at the King site, near Birsay, Saskatchewan to characterize the orientation and extent of fracturing in a glacial till. The target consisted of shallow (less than 4m deep) fractures in the upper oxidized portion of the Battleford Formation.<p> The fractures were visible in soil cores, but their orientation and extent were not known at the time of investigation. It was hoped that if the azimuthal resistivity method could be successfully applied at this site it could be used as an in situ fracture mapping tool at other sites. <p> Preliminary azimuthal resistivity surveys failed to detect a consistent anisotropic pattern that could be attributed to fracturing. A refined method of azimuthal resistivity was developed that built a 3D resistivity model of the site assuming a heterogeneous, isotropic earth. This model was used to predict and remove the effect of heterogeneity on the azimuthal resitivity observations. The results from the refined method also failed to detect a consistent anisotropic pattern. <p>Any single azimuthal resistivity observation from either the preliminary or refined surveys would have provided data that could have been interpreted as anisotropy due to fractures. It was only by comparing many azimuthal observations across the site that the lack of consistent azimuthal pattern became apparent. <p>It is recomended that an analysis of several observations be made before any interpretation of anisotropy is made for azimuthal resistivity sureveys in general.