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M.Ing. / Please refer to full text to view abstract

M.Ing. / This dissertation provides a review of the most notable papers published with regard to the specific performance characteristics of Tunnel Boring Machines (TBM's) during the past twenty years. It is a literature study of a Bibliography of 57 publications, which were screened from an original list of 970 documents ...

A Thesis Submitted to the Faculty of Engineering University of Witwatersrand, Johannesburg for the Degree of Doctor of Philosophy. Johannesburg 1977 / No abstract

This study investigated the performance of the biomass Eichhornia crassipes plant (ECP) as an additive in water-based drilling-mud. ECP is an invasive plant of fresh water ecosystems, so its use in drilling operations provides a low-cost, sustainable option that has off-site environmental benefits. Mechanical tests were conducted on ECP fibres to determine their stiffness under dried and water-wet conditions. Initial tensile tests on nylon fibre determined potential experimental artefacts with the experimental approach. The dried fibres had a water content of 8.163 wt. % (SE 0.636), whereas the wet fibres were 93.43 wt.% (SE 0.294). Water wet fibres had a lower modulus of elasticity than dried fibres and therefore, dried fibres have less tensile strength than wet fibres (Mean = 45.16 MPa; SE = 5.023; N = 41). Rheological properties of bentonite-based drilling muds amended with ECP at different concentrations were also studied. These muds were prepared by mixing ECP fragments at various concentrations (%w/w) with bentonite-water solutions and aged under ambient conditions. Mud viscosity gradually decreased with increasing shear rate, showing characteristic shear-thinning behaviour. Lost circulation of bentonite-water solutions mixed with ECP fragments were assessed with static filtration experiments. Slots and single perforated discs were designed to mimic fractures surrounding drilled boreholes. From a broad range of testing conditions, it was found that ECP fibres significantly decrease lost circulation by bridging fractures. An optimal concentration of 0.83 % by weight of ground plant stalks mixed with 6.28% bentonite in water improved rheology and filtration properties. A bridging gap model for a single fibre showed that ground stalk was less deflected than dried fibre when bridged an opening fissure. The findings of this research create an alternative to use ECP as lost circulation material in oil and gas drilling operations.

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