Thesis (M. Phil.)--University of Hong Kong, 2000. / Includes bibliographical references (leaves 119-125).

No description available.

A major problem faced by the petroleum industry is the deposition of wax during the pumping of waxy crude oils. This precipitation occurs at “normal” temperature, typically 20-30°C in Libya. It could occur during the journey from well to terminal through hundreds of miles of pipelines. This kind of transportation is expensive in terms of pumping costs. The pumping has to be continuous; otherwise wax can build up in the pipeline, reducing the pumping or even stopping it. The property that defines this characteristic is the yield stress which depends on wax concentration and cooling rate. The build-up of paraffin and asphaltenes can lead to serious problems in formation, tanks, and pipelines. Blockages can be expensive and time-consuming to deal with; this is precisely the topic of this research. For this research, model and real waxy crude oils are formulated and their rheology systematically measured under various cooling rates to determine the yield stress. A pipeline loop has been designed to measure the start-up pressure of stagnant oil which has been allowed to precipitate wax. The start-up pressure and the thickness of deposited wax are used in a simple mathematical model to calculate the yield stress. This research thus provides two independent means of predicting the yield stress. This research studied three different waxy crude oils. An MCR-301 Anton Paar rheometer was used to measure the rheology of the oils, and a pipeline rig was used to obtain the start-up pressure to calculate the yield stress of each type of oil after different stoppage times. Also, the thickness of the precipitated wax is measured to calculate the yield stress precisely. The data show that the layer thickness has significant effect on the yield stress and start-up pressures and corresponding yield flow stresses have been found to underpin the crystallisation process of the wax and slow cooling rate produce stronger structures requiring higher stresses to fracture and induce flow. Also, longer shutdown times make these structures even stronger and therefore require even larger stresses for flow to commence.

The Lower Tertiary Balder Formation in the Beryl Embayment, North Sea, consists of sands interbedded with claystones and tuffs. The sands are massive and well sorted and can be up to 400 feet (122 m) thick, and are highly porous and permeable hydrocarbon reservoirs. The sands form large lobate and circular bodies of sands a few kilometres in diameter, with steep sides that are sometimes controlled by fault planes. The margins of the sands sometimes display thick sand wings extending up along fault planes. The sands display dewatering structures such as sills and dykes have a complex geometrical relationship with the surrounding sediments. Hydrothermal mineralisation is displayed as nodules, concretions and cementation of the sands within the Balder interval. The concept of seismic pumping, which postulates the rapid upward migration of deep fluids as the result of fault movement, was introduced to the literature some eighteen years ago, but fell into disrepute. However, it is argued here that re-shear of normal faults in the reverse direction can under certain critical physical conditions cause seismic pumping and can transport large quantities of deep seated fluids rapidly. This gives rise to the expulsion of fluid from depth into conventionally deposited massive sands of submarine fan environments, belonging to the Balder Formation, and thus in the fluidisation of the sediments. These sands have been intruded into the surrounding rocks and along fault planes forming a complex distribution of in situ and remobilised sands, thereby giving rise to the observed sand geometries and structures.

This dissertation describes a proof-of-principle experiment demonstrating a technique for stable isotope enrichment called Magnetically Activated and Guided Isotope Separation (MAGIS) (1). Over the past century a large number of enriched isotopes have become available, thanks largely to electromagnetic separators called calutrons that were developed during World War II. These isotopes have found applications across an array of fields including medicine, basic science, and energy. Due to substantial maintenance and operating costs, the United States decommissioned the last of its calutrons in 1998, leading to demand for alternative methods of isotope separation. Our experiment suggests the promise for MAGIS as a viable alternative for replenishing stockpiles previously provided by calutrons. Our apparatus combines optical pumping with a scalable magnetic field gradient to enrich lithium-7 (Li-7) by suppressing lithium-6 (Li-6) throughput in a lithium atomic beam. We first evaporate lithium metal in a crucible in order to generate thermal, high flux beam. We then perform optical pumping on Li-6 atoms, magnetically polarizing a substantial fraction of Li-6 atoms into the entirely high-field seeking 2²S₁/₂, F = 1/2 ground state. The resultant beam then samples a magnetic field gradient produced by a 1.5 m long array of rare-earth permanent magnets bent over its length by 20 mrad. This geometry prevents high-field seeking lithium atoms from reaching the plane beyond the magnets, while efficiently deflecting low-field seeking atoms. We measured Li-6 suppression – using independent techniques – along the plane after the magnets beyond a factor of 200, corresponding to Li-7 enrichment to better than 99.95%. As apparatus-specific hindrances appeared to limit this suppression, we believe that we should achieve better enrichment on a commercial apparatus. We also measured both the absolute flux beyond the single, 1.5 in tall magnet array and the efficiency for guiding feedstock material to the collection plane. Given the planar configuration for the field gradient, the flux that we measured should scale linearly with both magnet height and the number of arrays surrounding the source. Our measurements therefore indicate that – at source temperatures that we actually investigated – a commercial apparatus fitting within a volume of just several cubic meters should yield hundreds of grams of enriched (to beyond 99.95%) Li-7 per year. In addition, we observed a competitive ratio between collected material and feedstock with greater than 20% of lithium incident upon the magnet array reaching beyond the magnets. Benchmarking our work against the calutron, we demonstrated comparable enrichment in a manner that should scale to the production of similar quantities. In contrast, however, MAGIS should require vastly less energy input. While calutrons required massive currents for maintaining a static magnetic field over a substantial area, the only non-shared energy expense for MAGIS is the cost for running the low power lasers for optical pumping. Via additional analysis, we have supplemented this proof-of-principle experiment with schemes for applying MAGIS to over half of the stable isotopes in the periodic table. Due to the success of this demonstration and the broad applicability of the principles, we believe that MAGIS will play an important role in the future of stable isotope enrichment. / text

No description available.

No description available.

Silty soils are a common occurrence and can exhibit low strengths, and minimal bearing capacity, causing widespread construction and performance problems. These soils are highly moisture-sensitive and their stability is greatly influenced by the degree of densification achieved during compaction. The strength and stiffness of silty-subgrade soils is also greatly reduced when moisture infiltrates the compacted soil during post construction period. This investigation concentrated on further developing the description of the pumping problem for soils with high silt content and the development of guidelines for stabilization of problematic silts. Using documented field experiences of the DOTD districts, the study presents a testing program to investigate the nature of the problem, the character of the silt materials, and their performance with modifying/stabilizing agents. Seven representative silt soil samples were used in the laboratory program. The unique characteristics that identify a soil with a high potential to pump were determined with standard laboratory tests. The response and stability of the silts under compaction and loading with various moisture levels and compaction efforts was also tested. The susceptibility to pumping of the different samples was reviewed in terms of their physical characteristics. In addition to the silt content percentage, the plasticity character was noted as being significant. The potential for the modification/stabilization of the problem silt soils was also studied. The laboratory tests were selected with respect to construction needs and possible post construction conditions. A limited number of specific additives were proposed with consideration for their ability to dry the subgrade silts sufficiently to be compacted and with the strength to provide a "working table" for the construction of the base and pavement. The additives selected included hydrated lime, portland cement, and class c fly ash. A unitary set of guidelines for stabilizing problematic silts is proposed.

Thesis. 1978. B.S.--Massachusetts Institute of Technology. Dept. of Mechanical Engineering. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING. / Bibliography: leaves 61-62. / by Charles B. Fly. / B.S.

Thesis. 1978. Ph.D.--Massachusetts Institute of Technology. Dept. of Physics. / This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE. / Vita. / Includes bibliographical references. / by Zbigniew M. Drozdowicz. / Ph.D.