A sizable amount of literature exists analyzing the effect of confining stress on fracture conductivity in sandstones. This thesis attempts to answer similar questions with regard to shale formations. The low Young’s Moduli and Brinell hardness values characteristic of many prospective shale formations may lead to a great deal of embedment and fines production which can drastically reduce fracture conductivity. Furthermore, shales exhibit sensitivity to aqueous fluids which may cause them to be weakened in the presence of certain fracturing fluids. Previous work analyzing shale fluid sensitivity has failed to preserve the shales’ formation properties by allowing the shale to dry out. This paper presents a study of propped fracture conductivity experiments at reservoir temperature and pressure using various North American shale reservoir cores. Exposure to the atmosphere can alter the mechanical properties of the shale by either drying or hydrating the samples, so care was taken to preserve these shales in their native state by maintaining constant water activity (relative humidity). Variations in applied closure stress and aqueous fluid exposure were analyzed and in certain cases altered the propped fracture conductivity by crushing proppant, embedding the proppant into the fracture face, and producing fines. The damage to fracture conductivity is correlated to mineralogy for the various shale samples. These findings show that a one-size-fits-all frac design will not work in every shale formation, rather a tailored approach to each shale is necessary. In the future, the results of this work will be analyzed alongside easier to perform Brinell hardness tests, swelling tests, and other characterization techniques incorporated into the UT Shale Characterization Protocol. Correlations were developed to relate the simpler tests to the fracture conductivity experiments which yield a straight forward method to determine the role embedment and fluid sensitivity have on post treatment fracture conductivity in shales. The UT Shale characterization Protocol can then be used to optimize the design and execution of fracing treatments. / text

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A systematic study of structure-property relations has been carried out on a range of polymers, both with and without mesogenic moieties. These materials have been characterised using various thermal techniques, including DSC and DMTA. These polymers have been complexed with LiClO₄ and the effects of the salt on thermal characteristics have been investigated. In addition, AC impedance spectroscopy has been employed to determine the temperature dependence of the conductivity of these complexes. Results suggest that polymers with mesogenic side groups have the potential to exhibit a conduction mechanism which is independent of both the glass transition temperature of the complex as determined by DSC and the corresponding structural relaxation detected using DMTA. It is found that the glass transition temperature of these materials is determined primarily by the side groups, and not by the polymer backbone. A model is thereby proposed in which ionic motion is decoupled from Tg, but still dependent on the local viscosity of the ionic environment. Appreciable conductivity is therefore observed below the glass transition temperature of the complex, thus resulting in dimensionally stable polymeric complexes with possible applications as solid state electrolytes in batteries.

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The persistent photoconductivity (PPC) effect in the diluted magnetic semiconductor Cd(_1-x)Mn(_x)Te:In has been studied in detail. Electrical transport measurements have been made on a large number of samples to build up an understanding of the phototransport properties of this material. In particular, the compositional dependence of the phototransport parameters has been measured up to x ≈ 0.2. Several samples exhibit an elevated temperature PPC effect which has been interpreted in terms of the formation of multiple DX centres. These samples can have a quenching temperature of up to 190 K, suggestmg that Cd(_1-x)Mn(_x)Te:In could be an interesting material in terms of applications of room temperature persistent photoconductors. The low field magnetoresistance has been measured and analysed quantitatively in order to attempt to identify the origin of the magnetoresistive effects in insulating and metallic samples. The positive magnetoresistance has been found to be linked with the magnetization of the sample. An anomalous negative magnetoresistance has been observed tinder certain experimental conditions. This negative magnetoresistance has been interpreted in terms of the formation of bound magnetic polarons and their contribution to spin-disorder scattering. The main body of this thesis is concerned with the study of the Metal-Insulator Transition (MIT). The PPC effect allows us to study the MIT in a continuous fashion by fine timing the carrier density by illumuiation. In this way we have made the first zero magnetic field study of the MIT in a magnetic semiconductor. The critical behaviour has been found to be consistent with the scaling theory of electron localization, which predicts a critical form σ = σ(_0)(n/n(_c) – 1)(^v). The critical conductivity exponent, v was determined to be close to one, while the critical carrier density, n(_e), was found to be ~ 2 x 10(^17) cm(^-3), for x = 0.08. The temperature dependence of the conductivity has been quantitatively analysed m both the metallic and insulating phases. On the insulating side of the transition, variable range hopping (VRH) conduction has been observed at low temperatures (down to 300 mK). The temperature dependence is consistent with VRH conduction with electron-electron interaction effects taken into account. In the metallic phase the temperature dependence of the conductivity (up to ~ 1 K) is consistent with a model where the zero temperature value of the conductivity is corrected by electron-electroninteraction effects, and the effects of weak localization. The magnitudes of these corrections are found to be in reasonable agreement with theoretical predictions. The electrical transport has also been studied in the weakly localized regime in Cd(_1-x)Mn(_x)Te:In and Cd(_1-x)Mn(_x)Te:In, Al. A rapid decrease in the conductivity occurs at low temperatures ( < 1.5 K). This is interpreted in terms of the effect of the s-d exchange interaction, which leads to the formation of bound magnetic polarons. It is suggested that this drop in conductivity can only be observed in the paramagnetic phase, and that spinglassordering has a significant effect on the temperature dependence of the conductivity at low temperatures.