Natural hydraulic fractures (NHFs) are fractures whose growths are driven by fluid loading. The fluid flow properties of the host rock have a primary, but hitherto little appreciated control on the NHF propagation rates. This study focuses on investigating the impacts of host rock fluid flow on the propagation and pattern development of multiple NHF in a poroelastic media. A realistic geomechanical model is developed to combine both the fluid flow and mechanical interactions between multiple fractures. The natural hydraulic fracture propagation is observed to consist of a series of crack-seal processes indicating incremental stop-start growth. Growth timing is on the scale of millions of years based on recent natural fracture growth reconstructions. These time scales are compatible with some model scenarios. My newly developed numerical model captures the crack-seal process for multiple NHF propagation. A sensitivity study conducted to investigate the impacts of different fluid flow properties on NHF propagation shows that permeability is a predominate influence on the timescale of NHF development. In low-permeability rocks, fractures have more stable initiation and much longer propagation timing compared to those in high-permeability rocks. Another aspect of great interest is the influence of fluid flow on fracture spacing and pattern development for multiple NHFs propagation in a poroelastic environment. My new poroelastic geomechanial model combines the natural hydraulic fracturing mechanism with the mechanical interactions between fractures. The numerical results show that as host rock permeability decreases, more fractures can propagate and a much smaller spacing is reached for a given fracture set. The low permeability slows down the propagation of long fractures and prevents them from dominating the fracture pattern. As a result, more fractures are able to grow at a similar speed and a more closely spaced fracture pattern is achieved for either regularly spaced or randomly distributed multiple fractures in low-permeability rocks. Investigation is also conducted in analyzing the distributions of fracture attributes (length, aperture and spacing) in low- and high-permeability rocks. For shales with high subcritical index, low permeability helps the fractures propagate more closely spaced instead of clustering. Meanwhile, in low-permeability rocks, factures have relatively smaller apertures, which lead to a slower fracture opening rate. The competition between the slow fracture opening rate and quartz precipitation rate will affect the effective permeability and porosity of the naturally fractured reservoir. However, the competition is trivial in high-permeability rocks. Other factors, such as reservoir boundary condition, layer thickness, subcritical index and pattern development stage, all have considerable impact on fracture pattern development and attribute distribution in a poroelastic media. / text

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The evolution and development of eyespot and non-eyespot colour pattern elements was studied in Vanessa butterflies using a phylogenetic approach. A Bayesian phylogeny of the genus Vanessa was reconstructed from 7750 DNA base pairs from 10 genes. Twenty-four non-eyespot and forty-four eyespot color pattern elements from the Nymphalid ground plan were defined and studied and their evolutionary history was traced on the Vanessa phylogeny. Ancestral character states were predicted and the direction of evolutionary changes was inferred for all characters. Five serially arranged eyespots were predicted for the ancestral Vanessa on all wing surfaces. Homologous eyespot and non-eyespot characters on the surfaces of the forewing were more similar than those on the surfaces of the hindwing. Homologous eyespot characters on the dorsal surfaces of fore and hindwings show more similarities than the ventral surfaces, in contrast to what was found for non-eyespot characters. Independent Contrast analysis was also used to study correlations between eyespot characters. Independent Contrast analysis revealed significant correlations between eyespots 2 and 5 and eyespots 3 and 4 on all wing surfaces. This consistency among highly variable eyespot characters suggested a structural hypothesis: the existence of a Far-Posterior (F-P) compartment boundary and organizer could be responsible for the observed correlations. This hypothesis was tested in several ways. First, examination of wing patterns across species from all families of butterflies revealed correspondence between wing cells 1 and 4 and between cells 2 and 3. Second, evaluation of spontaneous mitotic clones in butterflies and moths reveals a peak abundance of clonal boundaries along the vein dividing wing cells 2 and 3. Finally, experimentally generated FLP/FRT mitotic wing clones produced in Drosophila, reveal a clonal boundary posterior to the L5 wing vein, which is homologous to the vein dividing wing cells 3 and 4 in butterflies. Collectively, this suggests the existence of an additional compartment boundary associated with an organizer in wing cell 3 responsible for patterning the posterior portion of insect wings. A model is proposed that predicts that the wing developmental compartment boundaries produce unique combinations of gene expression for each wing sector, permitting eyespot individuation. / February 2016