DATA PROCESSING & INTERPRETATION
significantly aid acquisition, interpretation, and reservoir characterisation. For example, if you were unsure about a feature
on the real seismic, you could run a model based on what you already know about a reservoir to see if the same feature appeared anyway, even though there was nothing there in your model. You could then be confident that it was an artefact. Te model can also indicate how best to process the
data. Since it can be hard to distinguish subtle features from artefacts, if you aggressively process the seismic you can end up interpreting noise. Knowing where the noise is likely to occur can help to indicate where the interesting features really are and where you need to pay more attention to filtering the noise.
Improving the reservoir model Most of the time the underlying geology is known well enough from previous surveys to make a good model that can be used to generate the seismic model. What is not known is the exact location of the oil and the faults which is the critical information you need. If the model is perfect, the seismic generated from it would be identical to the real seismic, but since it probably has some errors, comparing the two should give you a better idea of where those errors are. By feeding back the information gained from comparing the real with the synthetic data you can try and make the reservoir model match the actual geology better, improving on what you already know. Te model can be fine-tuned and a new seismic
prediction made to compare with the real seismic, then the process can be repeated iteratively until the two match more exactly, at which point the model will be a faithful representation of what the seismic data is telling you about the geology.
SEAM Te Society of Exploration Geophysicists Advanced Modeling Corporation (SEAM) has been working on a project for the past three years to “advance the science and technology of applied geophysics through a cooperative industry effort focused on subsurface model construction and generation of synthetic data sets for geophysical problems of importance to the resource extraction industry.” Phase I concentrated on a 3D geological and geophysical model for a deepwater region containing reservoirs at a range of depths, including around and below a massive salt body. It conducted complementary geophysical simulations including CSEM (controlled source electromagnetic), gravity, and magnetic modelling as well as seismic. Phase I brought together a consortium of twenty oil companies and four service companies who
contributed time and funds to the effort. According to a recent survey conducted by SEAM, the participants overwhelmingly agreed that the investment was worthwhile and 88 per cent agreed that the seismic earth model was of significant benefit to the future of sub-salt imaging research. Te original idea was to share the cost of the data processing which was prohibitively expensive for a
single company, but the cost has come down to such an extent that it is no longer a barrier. Also more efficient algorithms mean that less processing power is needed Te Society of Exploration Geophysicists is a not-
for-profit organization that promotes the science of applied geophysics and the education of geophysicists. SEG, founded in 1930, fosters the expert and ethical practice of geophysics in the exploration and development of natural resources, in characterising the near surface, and in mitigating earth hazards. Te Society, which has more than 33 000 members in 138 countries, fulfills its mission through its publications, conferences, forums, web sites, and educational opportunities.
Faster wave equation Tierra Geophysical, a small start-up company with three employees that was given the contract to calculate the seismic data set, spent two years optimising the wave equation to run faster. It estimates that with its algorithms the model can be run around twenty times faster, and the latest processers can raise the improvement to fifty times. Tierra Geophysical was sold to Landmark Graphics
in February, which was awarded the contract for storage and distribution of the Phase I data. Approximately 25TB of compressed data will be stored for up to 10 years.
Te SEAM Board of Directors has selected Land
Seismic Challenges for Phase II which will start in early 2011.
www.engineerlive.com 29
Fig.1. The errors introduced by multiple reflections and other sources of noise in seismic imaging. Image: Tierra Geophysical
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