Multiphase and non-Darcy flow effects in hydraulically fractured gas wells reduce effective fracture conductivity. Typical proppant pack laboratory experiments are oriented in such a way such that phase segregation is not possible, which results in mixed flow. Tidwell and Parker (1996), however, showed that in proppant packs, gravity segregation occurs for simultaneous gas and liquid injection at laboratory scale (1500 cm2). Although the impact of gravity on flow in natural fractures has been described, previous work has not fully described the effect of gravity on multiphase non-Darcy flow in hydraulic fractures. In this work, reservoir simulation modeling was used to determine the extent and impact of gravity segregation in a hydraulic fracture at field scale. I found that by ignoring segregation, effective fracture conductivity can be underestimated by up to a factor of two. An analytical solution was developed for uniform flux of water and gas into the fracture. The solution for pressures and saturations in the fracture agrees well with reservoir simulation. Gravity segregation occurs in moderate-to-high conductivity fractures. Gravity segregation impacts effective fracture conductivity when gas and liquid are being produced at all water-gas ratios modeled above 2 Bbls per MMscf. More realistic, non-uniform-flux models were also run with the hydraulic fracture connected to a gas reservoir producing water. For constant-gas-rate production, differences in pressure drop between segregated cases and mixed flow cases range up to a factor of two. As the pressure gradient in the fracture increases above 1 to 2 psi/ft, the amount of segregation decreases. Segregation is also less for fracture half-length-to-height ratios less than or close to two. When there is less segregation, the difference in effective conductivity between the segregated and mixed flow cases is reduced. I also modeled the water injection and cleanup phases for a typical slickwater fracture treatment both with and without gravity effects and found that for cases with segregation, effective fracture conductivity is significantly higher than the conductivity when mixed flow occurs. Gravity segregation is commonly ignored in design and analysis of hydraulically fractured gas wells. This work shows that segregation is an important physical process and it affects effective fracture conductivity significantly. Hydraulic fracture treatments can be designed more effectively if effective fracture conductivity is known more accurately.

No description available.

During the past decade, a new class of knowledge representation has emerged known as structured distributed representation (SDR). A number of schemes for encoding and manipulating such representations have been developed; e. g. Pollack's Recursive Auto-Associative Memory (RAAM), Kanerva's Binary Spatter Code (BSC), Gayler's MAP encoding, and Plate's Holographically Reduced Representations (HRR). All such schemes encode structural information throughout the elements of high dimensional vectors, and are manipulated with rudimentary algebraic operations. <br /><br /> Most SDRs are very compact; components and compositions of components are all represented as fixed-width vectors. However, such compact compositions are unavoidably noisy. As a result, resolving constituent components requires a cleanup memory. In its simplest form, cleanup is performed with a list of vectors that are sequentially compared using a similarity metric. The closest match is deemed the cleaned codevector. <br /><br /> While SDR schemes were originally designed to perform cognitive tasks, none of them have been demonstrated in a neurobiologically plausible substrate. Potentially, mathematically proven properties of these systems may not be neurally realistic. Using Eliasmith and Anderson's (2003) Neural Engineering Framework, I construct various spiking neural networks to simulate a general cleanup memory that is suitable for many schemes. <br /><br /> Importantly, previous work has not taken advantage of parallelization or the high-dimensional properties of neural networks. Nor have they considered the effect of noise within these systems. As well, additional improvements to the cleanup operation may be possible by more efficiently structuring the memory itself. In this thesis I address these lacuna, provide an analysis of systems accuracy, capacity, scalability, and robustness to noise, and explore ways to improve the search efficiency.

During the past decade, a new class of knowledge representation has emerged known as structured distributed representation (SDR). A number of schemes for encoding and manipulating such representations have been developed; e. g. Pollack's Recursive Auto-Associative Memory (RAAM), Kanerva's Binary Spatter Code (BSC), Gayler's MAP encoding, and Plate's Holographically Reduced Representations (HRR). All such schemes encode structural information throughout the elements of high dimensional vectors, and are manipulated with rudimentary algebraic operations. <br /><br /> Most SDRs are very compact; components and compositions of components are all represented as fixed-width vectors. However, such compact compositions are unavoidably noisy. As a result, resolving constituent components requires a cleanup memory. In its simplest form, cleanup is performed with a list of vectors that are sequentially compared using a similarity metric. The closest match is deemed the cleaned codevector. <br /><br /> While SDR schemes were originally designed to perform cognitive tasks, none of them have been demonstrated in a neurobiologically plausible substrate. Potentially, mathematically proven properties of these systems may not be neurally realistic. Using Eliasmith and Anderson's (2003) Neural Engineering Framework, I construct various spiking neural networks to simulate a general cleanup memory that is suitable for many schemes. <br /><br /> Importantly, previous work has not taken advantage of parallelization or the high-dimensional properties of neural networks. Nor have they considered the effect of noise within these systems. As well, additional improvements to the cleanup operation may be possible by more efficiently structuring the memory itself. In this thesis I address these lacuna, provide an analysis of systems accuracy, capacity, scalability, and robustness to noise, and explore ways to improve the search efficiency.

One of the major challenges in fracturing low permeability/tight/unconventional gas formations is the loss of frac water and well productivity due to fluid entrapment in the matrix or fracture. Field results have indicated that only 15-30% of the frac fluid is recovered at the surface after flow back is initiated. Past studies have suggested that this water is trapped in the rock matrix near the fracture face and remains trapped due to the high capillary pressure in the matrix. Significant efforts have been made in the past to understand the impact of liquid blocking in hydraulically fractured conventional gas wells. Numerous remediation measures such as huff and puff gas cycling, alcohol or surfactant based chemical treatments have been proposed to reduce fracture face damage. However, when considering hydraulic fractures in unconventional reservoirs horizontal wells, the fluid may also be trapped within the fracture itself and may impact the cleanup as well as productivity. This study shows that under typical gas flow rates in tight / shale gas formations, liquid loading within the fractures is likely to occur. Most of the previous simulation studies consider a 2D reservoir model and ignore gravity, considering the high vertical anisotropy (or extremely low vertical permeability) in these tight reservoirs matrix. However, this study presents the results of 3D simulations of liquid loading in hydraulic fractures in horizontal wells, including gravity and capillary pressure effects. Both CMG IMEX and GEM have been used to study this phenomenon in dry and wet gas cases. The impact of drawdown, fracture and reservoir properties on liquid loading and well productivity is presented. Results show that low drawdown, low matrix permeability or low initial gas rates aggravate the liquid loading problem inside the fracture and thereby impact the cleanup and gas productivity during initial production. A clear understanding of the phenomena could help in selection of optimal production facilities and well profile. / text

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The thesis is focused on design of industrial vacuum cleaner for use in workshops. The thesis includes design and technical reaserch of current vacuum cleaners. The main part contains original design solution with regard to technical and ergonomics requirements.

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Brominated flame retardants is a group of compounds present in numerous types of materials in our surroundings. Although their purpose is to slow the progression of a fire, many has been shown to be toxic to the environment. Novel brominated flame retardants have been introduced to the market as old ones have been removed. Reliable methods are crucial to be able to monitor how the novel brominated flame retardant spread and accumulate in the environment. To achieve this, a method validation of a cleanup method using multilayer silica followed by analysis by atmospheric pressure gas chromatography coupled to tandem mass spectroscopy was performed. This method had been previously used for polybrominated diphenyl ethers and the aim was to see if it could be used for analysis of novel brominated flame retardants as well. Spiking experiments showed generally good results, with recoveries of the native compound ranging from 40% to 174%. To apply the method on real matrix samples, eight samples of osprey eggs and five samples of adipose tissue of ringed seal was analyzed. Several novel brominated flame retardants were found, most abundant being the methoxylated polybrominated diphenyl ethers. Dominant congener was 2'-Methoxy-2,3',4,5'-tetrabromodiphenyl ether (2PMBDE#68) followed by 6-Methoxy-2,2',4,4'-tetrabromodiphenyl ether (6PMBDE#47), 5-Methoxy-2,2',4,4'-tetrabromodiphenyl ether (5PMBDE#47) and 5-Methoxy-2,2',4,4',6-pentabromodiphenyl ether (5PMBDE#100) with concentrations ranging from &lt;0,13-13 ng/g lipid weight in osprey eggs and &lt;0,003-249 ng/g lipid weight in ringed seal blubber. Also 1,2-Bis(2,4,6-tribromophenoxy)ethane and pentabromobenzene were found in both osprey eggs and ringed seal blubber. Hexabromobenzene was found in ringed seal blubber and 2,3,5,6-tetrabromo-p-xylene was identified in osprey eggs. / Bromerade flamskyddsmedel är en grupp ämnen närvarande i många olika typer av material i vår omgivning. Även om deras syfte är att bromsa förloppet vid en eldsvåda har många visat sig vara toxiska för miljön. Nya bromerade flamskyddsmedel har kommit ut på marknaden i takt med att gamla tagits bort. Pålitliga metoder är nödvändiga för att övervaka hur nya bromerade flamskyddsmedel sprids och ackumulerar i miljön. För att uppnå detta validerades en metod bestående av flerskiktskiseldioxid och analys med atmosfärstryck-gaskromatografi kopplat till tandem-masspektroskopi. Denna metod hade tidigare använts för analys av polybromerade difenyletrar och målet var att undersöka om samma metod kunde användas för analys ad nya bromerade flamskyddsmedel. Spikning gav generellt goda resultat - utbytet för de nativa ämnena var mellan 40% och 174%. För att pröva metoden på prov med riktigt matris analyserades åtta prov med fiskgjuseägg och fem prov med späck från vikare. Flera nya bromerade flamskyddsmedel hittades, mest förekommande var de metoxylerade polybromerade difenyletrarna. Dominerande kongen var 2'-metoxy-2,3',4,5'-tetrabromodifenyleter, följt av 6-metoxy-2,2',4,4'- tetrabromodifenyleter, 5-metoxy-2,2',4,4'- tetrabromodifenyleter och 5-metoxy-2,2',4,4',6- pentabromodifenyleter i koncentrationer från &lt;0,13-13 ng/g lipidvikt (fiskgjuseägg) och &lt;0,003-249 ng/g lipidvikt (sälspäck). Även 1,2-bis(2,4,6-tribromofenoxy)etan (fiskgjuseägg och sälspäck), pentabromobensen (fiskgjuseägg och sälspäck), hexabromobensen (sälspäck) och 2,3,5,6-tetrabromo-p-xylene (fiskgjuseägg) identifierades.

No description available.