In low-permeability gas reservoirs, horizontal wells have been used to increase the reservoir contact area, and hydraulic fracturing has been further extending the contact between wellbores and reservoirs. This thesis presents an approach to evaluate horizontal well performance for fractured or unfractured gas wells and a sensitivity study of gas well performance in a low permeability formation. A newly developed Distributed Volumetric Sources (DVS) method was used to calculate dimensionless productivity index for a defined source in a box-shaped domain. The unique features of the DVS method are that it can be applied to transient flow and pseudo-steady state flow with a smooth transition between the boundary conditions. In this study, I conducted well performance studies by applying the DVS method to typical tight sandstone gas wells in the US basins. The objective is to determine the best practice to produce horizontal gas wells. For fractured wells, well performance of a single fracture and multiple fractures are compared, and the effect of the number of fractures on productivity of the well is presented based on the well productivity. The results from this study show that every basin has a unique ideal set of fracture number and fracture length. Permeability plays an important role on dictating the location and the dimension of the fractures. This study indicated that in order to achieve optimum production, the lower the permeability of the formation, the higher the number of fractures.

In low-permeability gas reservoirs, horizontal wells have been used to increase the reservoir contact area, and hydraulic fracturing has been further extending the contact between wellbores and reservoirs. This thesis presents an approach to evaluate horizontal well performance for fractured or unfractured gas wells and a sensitivity study of gas well performance in a low permeability formation. A newly developed Distributed Volumetric Sources (DVS) method was used to calculate dimensionless productivity index for a defined source in a box-shaped domain. The unique features of the DVS method are that it can be applied to transient flow and pseudo-steady state flow with a smooth transition between the boundary conditions. In this study, I conducted well performance studies by applying the DVS method to typical tight sandstone gas wells in the US basins. The objective is to determine the best practice to produce horizontal gas wells. For fractured wells, well performance of a single fracture and multiple fractures are compared, and the effect of the number of fractures on productivity of the well is presented based on the well productivity. The results from this study show that every basin has a unique ideal set of fracture number and fracture length. Permeability plays an important role on dictating the location and the dimension of the fractures. This study indicated that in order to achieve optimum production, the lower the permeability of the formation, the higher the number of fractures.

In preparation for the upcoming all-sky data releases of the Gaia mission we compiled a catalog of known hot subdwarf stars and candidates drawn from the literature and yet unpublished databases. The catalog contains 5613 unique sources and provides multi-band photometry from the ultraviolet to the far infrared, ground based proper motions, classifications based on spectroscopy and colors, published atmospheric parameters, radial velocities and light curve variability information. Using several different techniques we removed outliers and misclassified objects. By matching this catalog with astrometric and photometric data from the Gaia mission, we will develop selection criteria to construct a homogeneous, magnitude-limited all-sky catalog of hot subdwarf stars based on Gaia data.

This dissertation is composed of three parts of major contributions: In Chapter II, we developed a new conceptual model and derived a new semi-analytical model for flow to a horizontal well beneath a water reservoir. Instead of treating the leakage from aquitard as a source term inside the aquifer which is called Hantush’s assumption (1964), we linked flows in aquitard and aquifer by the idea of continuity of flux and drawdown. The result in this chapter is compared with that of Zhan and Park in 2003 which Hantush’s assumption is adopted at various hydraulic and well configurations. It shows that Hantush’s assumption becomes inaccurate in regions where vertical velocity components are significant. In Chapter III, we deal with the interaction of an aquifer with two parallel surface water bodies such as two streams or canals. In this chapter, new closed-form analytical and semi-analytical solutions are acquired for the pumping induced dynamic interaction between two streams and ground water for two different cases. In the first case, the sediment layers separating the streams from the aquifer ground water do not exist. In the second case, the two low permeable layers are considered. The effect of aquitard and water right competition is addressed in this chapter. This model can be used for interpreting and deriving hydrologic parameters of aquitard and aquifer when pumping occurs between two channels. It can also be used to predict stream depletion which is essential for water management and ecology conservation. In Chapter IV, we investigated the three dimensional upconing due to a finite-length of horizontal well and its critical conditions. The results are compared with those of vertical wells. The critical condition which includes the critical rise and the critical time at a certain pumping rate depends on the well length, the initial interface location, the well location, and the pumping rate. Our results show that horizontal well might be a better tool for coastal groundwater resources development. In real field applications, installing long wells as shallow as possible is always desirable for sustaining long periods of pumping with significant rates.

In the Middle East, extended reach horizontal wells (on the order of 25,000 feet of horizontal displacement) are commonly acid stimulated by jetting acid out of drill pipe. The acid is jetted onto the face of the openhole wellbore as the drill pipe is withdrawn from the well. The jetting action helps to remove the drilling fluid filter cake and promote the acid to penetrate into the formation and form wormholes to stimulate the well. However, with very long sections of wellbore open to flow, the acid placement and subsequent wormhole distribution and penetration depths are uncertain. This study has modeled the acid jetting process using a comprehensive model of acid placement and wormhole propagation in a horizontal well. It is presumed that the acid jetting tool removes the drilling mud filter cake, so that no filter cake exists between the end of the drill pipe and the toe of the well. Correspondingly, the model also assumes that there is an intact, low-permeability filter cake on the borehole wall between the end of the drill pipe and the heel of the well. The drill pipe is modeled as being withdrawn from the well during the acid jetting treatment, as is done in practice. The acidizing simulator predicts the distribution of acid and the depths of wormholes formed as functions of time and position during the acid jetting treatment. The model shows that the acid jetting process as typically applied in these wells preferentially stimulates the toe region of the horizontal well. Comparisons of the simulation predictions with published data for acid jetting treatments in such wells showed good general agreement. Based on the simulation study, this study presents recommendations for improved acid jetting treatment procedures to improve the distribution of acid injected into the formation.

This dissertation is composed of three parts of major contributions: In Chapter II, we developed a new conceptual model and derived a new semi-analytical model for flow to a horizontal well beneath a water reservoir. Instead of treating the leakage from aquitard as a source term inside the aquifer which is called Hantush’s assumption (1964), we linked flows in aquitard and aquifer by the idea of continuity of flux and drawdown. The result in this chapter is compared with that of Zhan and Park in 2003 which Hantush’s assumption is adopted at various hydraulic and well configurations. It shows that Hantush’s assumption becomes inaccurate in regions where vertical velocity components are significant. In Chapter III, we deal with the interaction of an aquifer with two parallel surface water bodies such as two streams or canals. In this chapter, new closed-form analytical and semi-analytical solutions are acquired for the pumping induced dynamic interaction between two streams and ground water for two different cases. In the first case, the sediment layers separating the streams from the aquifer ground water do not exist. In the second case, the two low permeable layers are considered. The effect of aquitard and water right competition is addressed in this chapter. This model can be used for interpreting and deriving hydrologic parameters of aquitard and aquifer when pumping occurs between two channels. It can also be used to predict stream depletion which is essential for water management and ecology conservation. In Chapter IV, we investigated the three dimensional upconing due to a finite-length of horizontal well and its critical conditions. The results are compared with those of vertical wells. The critical condition which includes the critical rise and the critical time at a certain pumping rate depends on the well length, the initial interface location, the well location, and the pumping rate. Our results show that horizontal well might be a better tool for coastal groundwater resources development. In real field applications, installing long wells as shallow as possible is always desirable for sustaining long periods of pumping with significant rates.

Upon recognition of the pathogen, plants initiate defense responses that can include the production of antimicrobial compounds such as phytoalexins. Nectria haematococca mating population VI (MPVI) is a filamentous ascomycete that contains a cluster of genes known as the pea pathogenicity (PEP) cluster in which the pisatin demethylase (PDA) gene resides. PDA is responsible for the detoxification of the phytoalexin, pisatin, produced by the pea plant (Pisum sativum). Thus, PDA allows the fungus to colonize and become a pea pathogen. It has been proposed that the evolutionary origin of PDA and the PEP cluster is explained by a horizontal gene transfer (HGT) event. The observations supporting this hypothesis include the location of the PEP cluster on a conditionally dispensable (CD) chromosome, the phylogenetically discontinuous distribution of the cluster among closely related species, and bias in GC content and codon usage. This study used a three-pronged approach to test the hypothesis that PDA and the PEP cluster were inherited via HGT. Percent identities of conserved genes, along with GC content analysis and phylogenetics support vertical inheritance.

Os elementos transponíveis são conhecidos por possuírem a fascinante propriedade de mudarem de local dentro do genoma de suas espécies hospedeiras e mesmo de serem capazes de atravessar barreiras interespecíficas, invadindo novos genomas. Neste estudo, uma nova família de elementos transponíveis, denominada harrow, é descrita para a Superfamília hAT. Buscas por seqüências harrow foram realizadas em 65 espécies de Drosophilidae, sendo que a maior parte dessas espécies pertence a grupos Neotropicais do gênero Drosophila ou é cosmopolita. As seqüências harrow encontradas apresentam distribuições descontínuas ao longo do gênero Drosophila e apresentam altas similaridades entre si, inconsistentes com os tempos de divergência das espécies hospedeiras. Além disso, incongruências topológicas foram encontradas entre as filogenias de harrow e das espécies hospedeiras. Os resultados obtidos no presente estudo indicam que harrow provavelmente invadiu os genomas de seus hospedeiros por múltiplos eventos de transferência horizontal, os quais devem ter ocorrido entre espécies dos Trópicos do Novo Mundo. Estes resultados reforçam a visão de que eventos de transferências horizontais entre eucariotos são mais comuns do que se previa anteriormente. / Transposable elements are known for their amazing properties of moving from one place to another inside the genome of their host species, as well as, for their ability to cross species boundaries, invading new genomes. In this study, a new family of transposable elements, harrow, is described for the hAT Superfamily of DNA transposons. Searches for harrow sequences were conducted in 65 Drosophilidae species, mainly representing Neotropical and cosmopolitan group species from genus Drosophila. The obtained harrow sequences show a patchy distribution along the genus Drosophila and present high sequence similarities, which are inconsistent with the divergence times of the host species. Additionally, topological incongruities were found between harrow and host species phylogenies. The results obtained in this study indicate that harrow has probably invaded its host genomes through multiple horizontal transfer events, which should have occurred in Neotropical regions. These results support the growing view that horizontal transfers between eukaryotes are more common than they have been thought before.

Os elementos transponíveis são conhecidos por possuírem a fascinante propriedade de mudarem de local dentro do genoma de suas espécies hospedeiras e mesmo de serem capazes de atravessar barreiras interespecíficas, invadindo novos genomas. Neste estudo, uma nova família de elementos transponíveis, denominada harrow, é descrita para a Superfamília hAT. Buscas por seqüências harrow foram realizadas em 65 espécies de Drosophilidae, sendo que a maior parte dessas espécies pertence a grupos Neotropicais do gênero Drosophila ou é cosmopolita. As seqüências harrow encontradas apresentam distribuições descontínuas ao longo do gênero Drosophila e apresentam altas similaridades entre si, inconsistentes com os tempos de divergência das espécies hospedeiras. Além disso, incongruências topológicas foram encontradas entre as filogenias de harrow e das espécies hospedeiras. Os resultados obtidos no presente estudo indicam que harrow provavelmente invadiu os genomas de seus hospedeiros por múltiplos eventos de transferência horizontal, os quais devem ter ocorrido entre espécies dos Trópicos do Novo Mundo. Estes resultados reforçam a visão de que eventos de transferências horizontais entre eucariotos são mais comuns do que se previa anteriormente. / Transposable elements are known for their amazing properties of moving from one place to another inside the genome of their host species, as well as, for their ability to cross species boundaries, invading new genomes. In this study, a new family of transposable elements, harrow, is described for the hAT Superfamily of DNA transposons. Searches for harrow sequences were conducted in 65 Drosophilidae species, mainly representing Neotropical and cosmopolitan group species from genus Drosophila. The obtained harrow sequences show a patchy distribution along the genus Drosophila and present high sequence similarities, which are inconsistent with the divergence times of the host species. Additionally, topological incongruities were found between harrow and host species phylogenies. The results obtained in this study indicate that harrow has probably invaded its host genomes through multiple horizontal transfer events, which should have occurred in Neotropical regions. These results support the growing view that horizontal transfers between eukaryotes are more common than they have been thought before.

Os elementos transponíveis são conhecidos por possuírem a fascinante propriedade de mudarem de local dentro do genoma de suas espécies hospedeiras e mesmo de serem capazes de atravessar barreiras interespecíficas, invadindo novos genomas. Neste estudo, uma nova família de elementos transponíveis, denominada harrow, é descrita para a Superfamília hAT. Buscas por seqüências harrow foram realizadas em 65 espécies de Drosophilidae, sendo que a maior parte dessas espécies pertence a grupos Neotropicais do gênero Drosophila ou é cosmopolita. As seqüências harrow encontradas apresentam distribuições descontínuas ao longo do gênero Drosophila e apresentam altas similaridades entre si, inconsistentes com os tempos de divergência das espécies hospedeiras. Além disso, incongruências topológicas foram encontradas entre as filogenias de harrow e das espécies hospedeiras. Os resultados obtidos no presente estudo indicam que harrow provavelmente invadiu os genomas de seus hospedeiros por múltiplos eventos de transferência horizontal, os quais devem ter ocorrido entre espécies dos Trópicos do Novo Mundo. Estes resultados reforçam a visão de que eventos de transferências horizontais entre eucariotos são mais comuns do que se previa anteriormente. / Transposable elements are known for their amazing properties of moving from one place to another inside the genome of their host species, as well as, for their ability to cross species boundaries, invading new genomes. In this study, a new family of transposable elements, harrow, is described for the hAT Superfamily of DNA transposons. Searches for harrow sequences were conducted in 65 Drosophilidae species, mainly representing Neotropical and cosmopolitan group species from genus Drosophila. The obtained harrow sequences show a patchy distribution along the genus Drosophila and present high sequence similarities, which are inconsistent with the divergence times of the host species. Additionally, topological incongruities were found between harrow and host species phylogenies. The results obtained in this study indicate that harrow has probably invaded its host genomes through multiple horizontal transfer events, which should have occurred in Neotropical regions. These results support the growing view that horizontal transfers between eukaryotes are more common than they have been thought before.