Department of Geology &
BASINAL FLUIDS AND
APPLIED GEOPHYSICS GROUP
[this web page dates from mid 1997]
Professor David Smythe and Drs Gary Couples, Ben Doody, Stuart Haszeldine, Orla McLaughlin, Doyle Watts and Mark Wilkinson
Glasgow is now the leading UK University researching on deep subsurface hydrogeology in the North Sea petroleum basin. Stuart Haszeldine's group blend a unique mix of stable and radiogenic isotope measurements with predictions from computer simulations using industry-class computer software to quantify fluid flow, overpressure, and geochemical interations, all within a well-constrained understanding of the sedimentological, sequence stratigraphic and structural geological setting. Close collaboration with, and funding from, leading major oil companies is important, as this assists both partners with the supply of data, and two views of the same problems. The group have built up a unique suite of case studies and regional expertise on the North sea rift basins. Cementation and fluid studies on these basins are acting as type examples for rift basins worldwide This enables the testing of models of cementation and hydrogeological flow using progressively larger data sets and focused studies in a known context. The group are concerned to unravel the processes of interaction of fluid movement, organic contribution, and mineral interaction all within the geological setting of temperature increase, fluid geopressure, and sedimentological control. Results of such work provide new intellectual insights into the processes of fluid flow and mass-transfer in sedimentary basins, and also provide important models of direct use to the petroleum industry in exploration and production. The approaches and techniques used in this work are also transferable to shallower hydrogeology and environmental research.
Robbie Stewart, with Stuart Haszeldine and Tony Fallick (SURRC), demonstrated that cementation in Paleocene sandstones of the North Sea was controlled by the interation of regional flows of meteoric water, with depositional and compactional waters. Carbonate cements were sometimes derived from detrital chalk debris, but the volumetrically most important cements were formed by the oxidation of vertically migrating oil to form calcite within the flowing meteoric aquifers. Such vertical leakage is positioned above deep Jurassic structures. Thus this can act as a regional exploration tool to confirm the timing of hydrocarbon migration, and to locate deeper hydrocarbon accumulations.
David Darby, with Stuart Haszeldine and Gary Couples demonstrated that overpressure in the Central North Sea is a dynamic system. This overpressure is being generated today by lack of compaction following rapid subsidence in the last 2 Ma, and by active generation of hydrocarbons and their cracking to condensate and gas. Lateral movement of fluids has caused growth of the clay mineral illite (dated by K-Ar) at different times in different parts of the basin. This is the first demonstration of the spatial prediction of diagenesis being matched with measured dates. In extreme overpressured settings the leakage of compactional fluids is vertical. Mark Wilkinson and David Darby also developed the concept of Maximum Potential Porosity to investigate the development of porosity during burial. For the first time Stuart Haszeldine, Campbell Fleming and Gary Couples have mapped overpressure potentials in the deep subsurface to identify such "leak points", and confirmed that by independent identification of the same leak points from the first quantitative 2-D simulation of present day heat transfer in the subsurface by moving fluids. The strength of this approach is supported by Mark Wilkinson's work with Stuart Haszeldine showing that secondary porosity is forming today in sandstones at these leak points; this results in economically important porosity of more tha 20% at 6 km. They have demonstrated that feldspar in the original sandstones is systematically lost during deep burial, changing the rock from an arkose to a diagenetic quartzite. This extreme mobility of aluminium in the deep subsurface had previously been unrecognised, and necessitates revision of laboratory geochemical simulations and of simplistic provenance studies on sandstones or psammites.
Orla McLaughlin and Stuart Haszeldine have shown that economically important secondary porosity has formed at the faulted edge of the Viking Graben. This is due to the focused release of deep compaction waters derived from mudrocks rich in organic acids. This forms a new model to explore for excellent porosity "fairways" in sandstones, produced diagenetically.
Mark Wilkinson studied siderite zonation and showed that previous views that this was related to porewater changes as result of transgression-regression variation is not correct and biochemical zonation within shallowly buried sediments is now thought to be the cause of the zonation. Studies with J.P. Hendry (Queen's University, Belfast) of dolomite-ankerite cements have enabled the importance of cross-formational flow in the transport of large volumes of carbonates.
Mark Osborne, with Stuart Haszeldine, has produced a definitive compilation of fluid inclusion data, which suggests that quartz cementation in deep sandstones is not due to hot hydrothermal circulation, but to subsidence-related increases in temperature and pressure. Our proposal that fluid inclusion data is progressively reset during burial, has since been confirmed experimentally by USA workers, and has caused a worldwide upset to this paradigm.
Collaboration between Stuart Haszeldine and Tony Fallick at SURRC has resulted in Calum Macaulay's construction of laser-based isotope analytical facilities for Sulphur Carbon and Oxygen in carbonates, and Oxygen in silicates. Precision and reproducability of these analyses are now closely comparable to conventional methods of isotopic analysis. The laser systems offer much less preparation time, smaller sample sizes, and a spatial resolution in situ down to 50mm. The laser system developed by British Petroleum Research has been acquired by Tony Fallick at SURRC as a result of this work, and places SURRC in a leading UK position (probably a leading world position) in the diversity and quality of laser- based technique now available.
New collaboration was instigated with Dr Rudy Swennen at Leuven Geology Dept., Belgium. This Belgian-funded project will examine the use of non-destructive CAT-scan X-ray imaging of porosity in oilfield core samples. Collaboration with Prof. Steve Larter at Newcastle UK, Professor Grant Garven at John Hopkins, Prof Jim Boles at Santa Barbara continues.
Gary Couples leads an active group of collaborators using both computer simulation and spatial analysis techniques to better understand a range of processes operative in basins and their basements - especially the role of fluids. Several types of hydrogeologic systems have been studied. In the North Sea, the process of overpressure buildup, and then the thermal structural, and diagenetic consequences of its escape, have been the focus of work mentioned above in collaboration with Stuart Haszeldine, Mark Wilkinson Dave Darby, Campbell Fleming, and Helen Lewis. Convective flow systems have been investigated in the North Sea (with Haszeldine and students) and in Ireland (with Mike Russell and Helen Lewis). Topographically-driven flows have been considered in studies undertaken of the proposed waste repository at Sellafield (with Haszeldine and McKeown), and in Ireland (with Russell and Lewis).
The depositional history of the Palaeozoic North American intracratonic basins has been studied by Gary Couples in collaboration with Rich Lane (Amoco, Houston Texas) and Mark Frye (KPMG Environmental Group, San Antonio, Texas). This study has established a need to reconsider current geodynamic paradigms of basin formation and evolution, and work continues on this topic. A separate study of the depositional history of the Irish Carboniferous (Helen Lewis PhD thesis) has revealed similar stratigraphic patterns, opening a research direction considering the causes and consequences of depositional discontinuties.
Funding continued from Greenpeace Environmental Trust for Chris McKeown. Stuart Haszeldine appeared as an expert witness in the Planning Enquiry relating to Nirex's proposal to build a Rock Characterisation Facility near Sellafield.
Computer simulations of modern subsurface water flows around Sellafield, West Cumbria, by Chris McKeown, Stuart Haszeldine and Gary Couples have shown that water flow paths are regionally upwards towards the surface after passing through the proposed radioactive waste Repository zone. Rates of flow could return radionuclides to the surface within 10,000yr. The regional permeability of the host rock formation (Borrowdale Volcanic Group) is up to 40x too great to be declared safe at this stage of investigation. Pathways of fluid flow carrying radionuclides indicate that discharge could be onshore, with negative safety implications. Investigations have been made of the neotectonics of the NW England area; an historically active fault zone along the coastal strip can be demonstrated, with some evidence that groundwater has been seismically pumped to the surface. Geochemical investigations of fracture mineralogy within the host rock have shown that no reduced sulphide minerals are present, in contrast to the claims of Nirex. Computer simulations of water-rock geochemistry have shown that the natural groundwater is oxidising, will remain so, and is likely to be unsuitable to retain uranium in a subsurface Repository. Geophysical work undertaken by the Department on the Sellafield site is reported elsewhere in this account.
Alistair Fraser in association with Stuart Haszeldine completed his work on the hydrocarbon evolution of Carboniferous basins of onshore northern England. This has led to several benchmark modern syntheses, and a definitive atlas of tectonic styles is in preparation.
Stuart Haszeldine and Allan Hall, working with Scottish Power (one of Britain's largest generating companies) and Fife police, established new methods of assessing and controlling the quality of coal delivered to power stations from opencast coal mines. This led to a doubling of coal quality, a re-orientation of suppliers contracted to Scottish Power, and the termination of long term contracts, with a substantial business benefit to the generating company.
The common interest of the three academic staff (Dave Smythe, Ben Doody and Doyle Watts) is high resolution crustal seismology at all scales. Most projects and proposals involve at least two of the three staff, as seismology is a complex and technically demanding field. Most research involves national and international collaboration. Current and recent projects involve colleagues from Greece, Norway, Russia, Austria, Iceland, Lithuania and the USA, as well as from elsewhere in the UK.
Since its inception in 1988, the Group has built up from scratch an unusual niche as one of the few groups worldwide (and unique in the UK) in being able to mount full-scale seismic reflection experiments. The value of the obsolescent equipment donated to date by the geophysical industry would originally have been at least $5M in the mid 1980s. It requires a lot of technical hands-on maintenance, a task undertaken mainly by Doyle Watts and a specialist technician. Costs of upkeep are self-funded through outside hire and small contract jobs.
Although the Group has undertaken some major crustal seismic projects in the last few years, the recent Sellafield nuclear waste repository experiment discussed below exemplifies the Group's strategy of moving towards new methods of high resolution small-scale seismic imaging, with applications to environmental protection and waste disposal.
An anomaly in our understanding of upper continental crustal structure is that near-surface structure in metamorphic terrain is frequently steeply dipping or vertical, whereas seimic reflection images tend to display flat-lying reflectors below depths of a few kilometres. The seismic image of the topmost 2-3 km is usually blank. Calibration by a crustal drill hole is required to solve this paradox. The Kola SG-3 superdeep well, Russia, is one of only two possible sites currently in existence where hypotheses on the sources of crustal reflections might be directly tested against in situ geological and fluid samples. However, until recently this borehole lacked the deep crustal seismic section required for the correlation . In 1992 Dave Smythe led the Kola international field expedition to collect the necessary seismic data. Despite several political, weather and funding problems, the acquisition phase of the experiment was successful. Preliminary reports of the experiment have been published. The seismic data, which are currently being processed, will address the conflict between the steep lithological dips seen at outcrop and the deeper flat-lying reflectors commonly observed wherever deep seismic reflection profiles are shot.
The Kola vibroseis data were recorded in unsummed and uncorrelated mode. This has permitted Shuang Qin and Dave Smythe to develop new vibroseis processing methods for application in the pre-correlation domain. These new methods successfully remove some of the noise contaminating such data.
In 1994 Dave Smythe proposed and carried out the world's first 3-D seismic survey of a potential nuclear waste repository, in an experiment for UK Nirex Ltd near Sellafield, West Cumbria, to see whether the vibroseis technique can produce high resolution information from the shallowest levels of the upper crust. The survey was highly successful, disproving prior industry reservations about the feasibility of the method for addressing such a problem. Although the 3-D seismic reflection method is now standard within the oil exploration industry, such data have never before been recorded at such a high density of data per unit volume of rock. About one cubic kilometre of rock has been imaged at an average 130- fold of coverage - about five to ten times denser than normal. However, the geological information presented to the 1995 Public Planning Inquiry by Nirex relied on its earlier 2-D Seismic survey. Dave Smythe demonstrated, in his capacity as an Expert Witness appearing for the Objectors, that Nirex does not yet understand the geology of its proposed underground site, and that further 3-D work (inter alia) will be required. Other departmental work relevant to radioactive waste disposal at this site, is dealt with above in this report.
Dave Smythe has identified geophysically the offshore continuation into the North Sea of the Late Carboniferous quartz-dolerites of northern Britain. The newly-extended swarm may well be the largest suite of continental dykes in the world discovered to date. Together with Mike Russell he has related this swarm to North Atlantic rifting processes, in a quantitative test of their previously published ideas.
Dave Smythe has processed data from two high-resolution shallow seismic reflection lines acquired by Austrian colleagues over high-grade crystalline crust in the Bohemian Massif, to show that reflections from as deep as 1 km can be imaged using a portable impulsive source. The dataset had previously only been used successfully to define the thick Quaternary overlying the crystalline rocks, by using refracted arrivals. Geological interpretation has been carried out by combining the seismic results with coincident audiomagnetotelluric profiles acquired subsequently.
Andrew Deighan and Doyle Watts developed applications of the 1-D wavelet transform to seismic reflection processing. The technique appears to successfully remove ground roll and air-blast noise from vibroseis, dynamite, and engineering data supplied by industry and gathered by our own seismic recording systems. The 2-D wavelet transform removed guided wave energy from vibroseis shot records acquired in Northern Ireland and appears very promising for processing data from areas covered with volcanic rocks. They are presently organizing a consortium of industry partners to investigate this promising new method of processing seismic data.
Belgasim El-Saiti and Doyle Watts processed seismic data from the Serpent Mound crypto-explosion structure in south-western Ohio, USA, supplied by the Ohio Geological Survey. Application of the wavelet transform enabled imaging of shallow reflectors, much improving previous commercial processing of these data. Belgasim El-Saiti modelled sonic well log data to interpret the processed lines. They demonstrated a correlation between vertical breakups of the reflectors, which may be faults and/or zones of mineralization which corespond to magnetic anomalies. This led to Royal Society funding of a project for further magnetic surveying of the structure and a detailed examination of two deep cores drilled from the complex central uplifted portion of the structure. They will be working with Ohio Geological Survey scientists Mark Baronoski and Greg Schumacher.
Mohamed Boulfoul and Doyle Watts demonstrated that random shear wave splitting in the near surface was the main cause of data degradation on the BIRPS WISPA shear wave section. They published one method to reduce this effect.
Doyle Watts continues to help maintain the Glasgow University seismic reflection facility. Pelton Corporation donated a Mark 5, Advance I controller for our vibroseis facility. Doyle operated a Failing Y-1100 truck for Dave Smythe's Kola Project, and designed the patch panels for the 270 channel three component 4.5 kilometer spread that was used in that experiment and rebuilt the MDS-10's that were used in the Glasgow Doghouse (a seismic recording truck). Ben Doody continues to investigate crustal structure using seismic techniques at all scales, but with particular emphasis on regional structure and character of the deep crust.
In 1992 he collaborated with the BGS on a regional seismic refraction traverse of the Welsh Basin, later supplemented by a wide-angle air gun profile along its offshore extension through Cardigan Bay. Based on initially simple models, raytrace modelling was carried out using the SEIS83 and RAY84 packages to obtain complex models of upper crustal P-wave velocity structure based upon direct, refracted and reflected arrivals, the last from near-normal to wide-angle incidence. Principal regionally significant layers with P-wave velocities of approximately 5.0, 5.7 and 6.1 km/s define large scale upper crustal features. Basin fill is up to a maximum of 8-10 km, in agreement with estimates from onshore geology, deepening from onshore to offshore. Anticlinal features within the topmost (Palaeozoic) seismic layer at depths of 2-3 km near to the SE margin of the basin are spatially related to the Tywi Anticline structure. The model is broadly consistent with regional gravity and magnetic observations and detailed comparisons will permit final model refinement.
Ben Doody coordinated the land acquisition of the SWABS experiment undertaken with BIRPS. A 192-channel, 3 km static spread in Berwickshire recorded air gun sources out to offsets of 200 km. The objective is to produce high resolution images of deep crust using the approach of high density offend, wide angle recording. Such data offer the possibility of better determination of velocities than possible with traditional near-normal incidence acquisition. Demultiplexing, a major task, has been carried out in house, followed by bandpass and notch filtering, gain recovery and application of field statics. To date efforts have concentrated on obtaining receiver gathers, including "Super Common Offset Stacks" with a stacked trace interval of 10 metres. This lateral resolution is similar to earlier experiments (e.g. BABEL), but the higher acquisition density of onshore SWABS permits stacking and consequent significant improvement of signal-to-noise ratio. The crust consists of an Upper Palaeozoic layer of P-wave velocities up to about 5.5 km/s, underlain by crystalline crust with apparent velocities increasing from 5.8 to about 6.3 km/s. The mid and lower crust produces very strong reflections in line with previous offshore normal incidence lines.
Ben Doody has also recorded a deep seismic sounding (DSS) profile across Lithuania in 1995, in conjunction with the Lithuanian Geological Survey, GeoForschungsZentrum Potsdam, Warsaw Institute of Geophysics and Oulu University. The NW-SE profile crosses several NE-SW trending subunits (terranes?) of the East European Craton (EEC). This work is part of EUROBRIDGE, an international multidisciplinary programme (under the auspices of EUROPROBE) to investigate Proterozoic cratons with particular reference to the processes involved in their formation. The EEC is being used as a typical example of Proterozoic craton. The EUROBRIDGE research is directed to a transect between the major, exposed parts of the EEC - the Baltic and Ukraine shields. The fulcrum of the work is a series of DSS profiles along the transect. The 1995 experiment is the first major phase of DSS acquisition. The regional DSS model serves as a framework for petrological and tectonic studies. An excellent data set was acquired. Initial interpretations suggest a three layer crystalline crust with P- wave velocities increasing with depth from about 6.0 to over 6.5 km/s. Crustal thickness seems to be on average about 45 km. Further data processing and modelling, particularly using ray tracing techniques, is in progress.
Near normal incidence seismic reflection land surveys in the Baltic
Shield have not revealed the Moho as an easily mapped, first order discontinuity.
To improve imaging of the Moho, Ben Doody has cooperated in 1995 with Uppsala
and Oslo universities and GEON (Russia) to conduct the CABLES (Caledonian
And Bothnian Lithosphere Elucidated by Seismics) wide-angle seismic experiment.
The profile trends W-E from Trondheim (Norway) to the Bothnian Sea, near
Sundsvall (Sweden). Data processing is currently at a very initial stage.
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Last change: Jul 2 1997