Published by the DTI Oil & Gas Directorate for the reservoir engineering and IOR community in the UK.
Send comments on this issue and contributions for next issue to iornewsletter@senergyltd.com by 15 August 2002.

Geophysics Group, University of Reading, UK

Clive McCann of the Geophysics Group, University of Reading presents details of the research programme and research capabilities of the Group aimed at improving the seismic characterisation of hydrocarbon reservoirs (c.mccann@reading.ac.uk)

The Geophysics Group of the University of Reading, UK undertakes research into fundamental controls on the propagation of seismic (acoustic) waves through sedimentary rocks and applies this knowledge to the improvement of seismic characterisation of hydrocarbon reservoirs. Understanding the mineralogical and petrophysical controls on seismic energy loss is a particular focus of the research.

The Group currently consists of three members of academic staff, two Post-Doctoral Research Fellows and two PhD research students. The Rev. Dr. Timothy Astin heads the Group.

Research progress is achieved by a combination of laboratory experimental studies, numerical analysis of data from (mainly commercial) surveys and mathematical analysis of laboratory and field data leading to widely applicable predictive models. The research strategy of the Group is to investigate the fundamental science underlying seismic propagation in reservoir rocks and to develop ideas and techniques which are applicable and relevant to the practising geophysicist and reservoir engineer.

Laboratory experiments combine acoustic measurements under in situ conditions over a broad frequency band, on texturally well-characterised materials. The Group has developed very accurate methods for measuring the velocity and attenuation of compressional- and shear-waves over a frequency range from 3 kHz to 45 kHz and at 1 MHz in reservoir rock samples under simulated in-situ pressure conditions. In the sonic frequency range the measurements are undertaken on samples of about 30 cm length and 2.5 cm diameter by accurate observation of the sample resonances In the ultrasonic frequency range the measurements are undertaken on 5 cm diameter samples using propagating compressional- and shear-waves. The samples can be measured under dry, fully- and partially-saturated conditions with appropriate pore fluids. The poro-perm, mineralogical and pore-structures of the samples are fully characterised using a wide range of equipment in Reading University and at other research centres.

The Group has developed algorithms within the Landmark ProMax™ seismic processing suite for the accurate determination of the attenuation of compressional- and shear-waves from full-waveform sonic and VSP data. The algorithms are used in conjunction with the standard processing routines for investigating the seismic properties of reservoir rocks in the hertz to kilohertz frequency range for well-characterised materials, and developing techniques for the interpretation of rock properties from seismic data.

The research of the Group is well-supported by industry contracts and research grants. Amongst other current projects, the Group is undertaking a collaborative research programme, PEGASUS 2, with Heriot-Watt University, Imperial College and Newcastle University on reservoir characterisation, funded by the Engineering and Physical Sciences Research Council and an industry consortium. Other recent research collaborations have been with the University of Bergen, the University of Adelaide and the University of Tehran.

Example applications of the research include the improved spatial interpretation of rock- and fluid-properties in the monitoring of hydrocarbon reservoirs from time-lapse seismic images.

As an example of the data from the geophysics laboratory, Figure 1 shows compressional- and shear-wave velocities versus porosity for a suite of reservoir limestones. The open circles show the measured compressional wave data, the closed circles show the compressional wave data corrected for the effects of pore-shape in the limestones. The corrections have been determined by analysing the correlated deviations of the compressional- and shear-wave velocities from the linear velocity/porosity relationships. The corrected data enable a significantly better prediction of porosity to be made from the compressional wave velocities and hence are valuable in the interpretation of downhole sonic logs. (Data from Assefa, S.B., McCann, C. and Sothcott, J., 2002, Velocities of compressional waves and shear waves in limestones. Geophysical Prospecting, in the press.)

Figure 1. Compressional- and shear-wave velocities versus porosity for limestones

Experimental techniques under development include the design of equipment for the accurate measurement of velocity and attenuation of compressional- and shear-waves in samples of poorly consolidated sediments under simulated in-situ conditions of temperature and pressure. The Group is seeking industry sponsorship for the development of equipment capable of accurately analysing the seismic properties of large rock samples under simulated in situ conditions of pressure and temperature, to investigate the spatial scaling of these properties.

With the approval of sponsors, research results are published in the open scientific literature and presented at appropriate conferences by the members of the Group. Examples of recent papers and presentations are given below.

Recent publications and conference presentations:

Jones, S., Astin, T.R., McCann, C., and Sothcott, J., 1998, The effects of pore fluid salinity on ultrasonic wave propagation in sandstones. Geophysics, 63, 928-934.
Dasios, A., McCann, C., Astin, T.R., McCann, D.M. and Fenning, P., 1999, Seismic imaging of the shallow sub-surface: shear wave case histories. Geophysical Prospecting, 47, 565-592.
Dasios, A., Astin, T.R. & McCann, C. 1998. Compressional wave-attenuation from full-waveform sonic data. Tech. Proc. 60th Ann. Mtg. European Assoc. Geoscientists & Engineers, Leipzig. Paper 10-44, 1998, 391-392.
Dasios, A., Astin, T.R. & McCann, C. Increasing confidence in seismic Q measurements: a comparison of estimates from sonic and surface seismic data. 68th Annual Meeting SEG, New Orleans, 1998.
Assefa, S.B., McCann, C. and Sothcott, J., 1999, Compressional wave and shear wave attenuation in oolitic limestones of Southern England. Geophysical Prospecting, 47, 359 - 392.
Khaksar, A., McCann, C., and Griffiths, C., 1999, Compressional- and shear- wave velocities as a function of confining stress in dry sandstones. Geophysical Prospecting, 47, 487-508.
Khazanehdari, J., McCann, C., Sothcott, J. and Astin, T.R., 1999, Up-scaling laboratory velocity data to field measurements. Technical Extended Abstract of paper presented at the 10th European Symposium on Improved Oil Recovery, Brighton, UK, August 1999.
Khazanehdari, J., McCann, C., Sothcott, J. and Astin, T.R., 1999, Stress sensitivity of seismic velocity. Technical Proceedings of the 61st Annual meeting of the European Association of Geoscientists and Engineers, Helsinki. Paper No P182, 2pp.
Domnesteanu, P., Domnesteanu, R. and McCann, C., 2002, Modelling the seismic attributes of overpressured siliclastic rocks, with a genetic annealing (GAN) algorithm. Geophysical Prospecting, 50, 169-182

For further details of the research programme, the research capabilities of the Geophysics Group and reprints of our published papers please contact either: t.r.astin@reading.ac.uk or Clive McCann, Part-time Professor of Geophysics, Geophysics Group, The University of Reading, PO Box 227,Whiteknights, Reading RG6 6AB,UK., Telephone: 44 (0) 118 9318796, c.mccann@reading.ac.uk

Disclaimer: The material available on this website is designed to provide general information only. Whilst every effort has been made to ensure that the information provided is accurate, it does not constitute legal or other professional advice.
Please note: The Department of Trade and Industry cannot be held responsible for the contents of any pages referenced by an external link.