Institute of Geophysics and Tectonics (IGT) PhD Projects
Simultaneous measurement of Q and AVO from seismic reflection amplitudes
Supervisors: Dr Roger Clark and Dr Linda Hodgson (BP, Aberdeen)
Only UK/EU candidates are eligible.
SUMMARY
This BP-funded PhD is about measuring seismic attenuation (Q) from surface seismic reflection surveys, and using it in the context of hydrocarbon exploration and other applications. It would draw together outcomes from recent developments by the Leeds group, produce a new ‘best-practice’ workflow for analysis of anelastic attenuation simultaneously with AVO, and apply it to real industry and academic dataset(s).
WHY?
The background. Seismic anelastic attenuation (quantified as Q, Seismic Quality Factor) is caused by the conversion of seismic wave energy to other forms, such as frictional heat and fluid transport. It’s a valuable petrophysical property (carrying information on pore fluid saturation and pressure), but it preferentially damps high frequency components of a wave over lower ones, and causes dispersion (frequency-dependent velocity). Together, these modify amplitude, phase, and waveform of a seismic wave as it propagates: the reasons why Q is usually regarded as a nuisance, and signal-processing tools exist to mitigate as far as is possible the detrimental effects it has. Despite this, Q (normally found from comparing wavelet spectra) is not routinely determined in resource exploration. First, only borehole-based surveys (Kaderali et al. 2007: Figure 1) have easy experimental geometries – but give expensive results at just one place. Then, algorithm limitations conspire with geophysical factors (e.g. scattering, interfering arrivals) to prevent capture of representative wavelet spectra. Hence, instead, corrections for Q effects are typically applied with only approximate values, and reservoir evaluation makes no quantitative use of Q. These are major shortcomings in how reflection seismic is utilised, especially for hydrocarbons exploration and production.
WHAT?
The project aims. To address this gap, the applied geophysics group at Leeds has been working towards finding accurate and precise Q values from surface seismic CMP gathers, to give cost-effective spatial coverage at the same time as facilitating deterministically correct Q compensation, and assessment of reservoir characteristics. Our ‘prototype’ method (Dasgputa & Clark 1998), critically assessed by e.g. Carter (2003), has evolved through a number of specific applications and generic signal-processing improvements (e.g. Clark et al. 2009, Reine et al. 2009a; Blanchard et al. 2010a,b; Moffat et al. 2010). In particular, an algorithm designed by Reine et al. (2009b: Figure 2) now offers reliable analysis of an individual depth interval. This PhD would build on that new capability, and extend the inversion approach to deliver more information. The first, principal, aim will be for the first time make an integrated quantitative analysis of reflection amplitudes in terms of Q and AVO simultaneously. Further methodology aims will include quantifying the anisotropy of Q, and the frequency-dependence of the Q value itself, within a target interval. As well as validation with synthetics, applications to real data will be an important and necessary part of the PhD: probably a UK North Sea field initially, then further BP and/or other datasets (perhaps even in other geological settings e.g. cryosphere, near-surface) as appropriate to the evolution of the project.
Correctly characterising Q interval-by-interval down the seismic section offers many direct and indirect benefits for seismic reflection analysis as applied to hydrocarbon exploration. If reliable field measurements of interval Q become more widely available, and are linked to current, progressively more realistic, rock physics models (e.g. Müller et al. 2010) a more confident prediction of pore fluids in porous rocks becomes possible. Better interval Q measurements will also be welcome in “Q compensation” (e.g. Wang, 2006) and encourage confidence in its outcome. Restoration of high-frequency wavelet components, and thereby improved time resolution of reflection images, will be deterministically correct: and applying the right compensation for dispersive velocity will eliminate Q as a cause of any difficulty in zero-phasing of the wavelet, a pivotal conditioning step in many interpretation processes.
Dr Roger Clark would supervise it at Leeds, in conjunction with Linda Hodgson at BP Aberdeen. It will be fully funded by BP. Its annual stipend will match research-council rates, and it will have a significant extra budget for necessary and desirable items (e.g. high-specification computer resources, publication costs, conference attendance).
WHERE?
The School of Earth & Environment at Leeds. The project will be hosted in the Institute of Geophysics & Tectonics (IGT), School of Earth & Environment (SoEE), University of Leeds. SoEE has a large and thriving PhD and Master’s community, delivering training across a wide range of subjects, including industry-facing geology and geophysics. This area is also drawn together in a cross-campus institute, the Centre for Integrated Petroleum Engineering & Geoscience (CiPEG). Applied geophysics within IGT/SoEE is well-known in industry, and exceptionally well-resourced, with an extensive suite of industry-standard software and field geophysical equipment. SoEE itself is housed in a newly refurbished and extended building, and offers an excellent work environment for PhD students. It’s expected that the student would also spend several periods of time at BP Aberdeen and/or Sunbury (London).
WHO?
Who would be a good applicant? Applicants need to be UK or EU nationals, and should hold, or expect to obtain, an Upper Second or First BSc degree in geophysics, physics, or a related discipline (or its equivalent from the EU). A relevant Master’s degree and/or industry experience would be welcome, but are not necessary. Strengths/interests in numerical methods (signal processing, inverse theory) and computer literacy (Linux environments and programming) will be needed: for EU nationals, minimum standards in IELTS/TOEFL results may be required also. Informal enquiries about the PhD itself may be made to Roger Clark (r.clark(at)see.leeds.ac.uk, +44(0)113-343-5221). Formal applications should be made through the process shown on the SoEE web pages, by to 17:00 on Friday 2 March 2012 at the latest: informal enquiries about the application process can be made to Michelle Lesnianski, m.lesnianski(at)see.leeds.ac.uk.
