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Title: Passive microseismic monitoring of a hydrofracture field trial
Author: Bishop, Ian
Awarding Body: Cardiff University
Current Institution: Cardiff University
Date of Award: 1994
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A sandstone formation, part of the reservoir rock comprising the Beckingham Oilfield, Nottinghamshire, was fractured by the injection of water under pressure through perforated casing, at depths of 1 km. The formation breakdown, and the repeated injection of water over a period of two weeks, was monitored by five triaxial sondes situated about the injection interval and several surface mounted geophones. Four of these sondes were situated in the treatment borehole, the fifth, in an observation borehole, approximately 280 m away. No seismicity was observed in the observation well or on the surface. The repeated cycling of the induced fracture system (closed, open, closed) over a 2 week period, was also monitored by Hydraulic Impedance Tests. Prior to examining the data, this thesis reviews the history of hydrofracture, both planned and inadvertent, and the use of microseismic monitoring techniques that attempt to man the dimensions of the induced fracture. Due to high noise levels during injection, only the shut-in periods of the data set were analysed in detail. The thesis examines the larger picture first: continuous microseismic acoustic emission, event rates, b-values and spectral averageograms, prior to concentrating on the discrete microseismic events generated by the fracture during the decay of the well head injection pressure. There is also an examination of tube waves generated by changes in pressure in the cased borehole during shut-in. The work finds that there is little guidance for events that can be described as containing clear P and S wave phases but instead finds events known as crack waves that are thought to be generated by resonances in the fluid filled conduits of the induced fracture system. Typically, these events have waveforms dominated by high frequency content near their onset superimposed on lower frequency information. The spectra of these events ranges from a single narrow band peak to examples with many sharp peaks. Prior to considering a model, these events are compared with crack waves from other systems, eg volcanic tremor, glacial quakes (including events recorded by the author during a visit to a surging glacier in Spitzbergen), gas outbursts and hydrofracture.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available