A major step in the recognition of the contribution of 4D, time lapse seismics, was announced at the annual meeting of the Society of Exploration Geophysicists (SEG), held in San Antonio, Texas this month. Speaking during a technical session, David Whitcombe explained why BP is so keen on 4D.
BP’s initial 4D successes were won on oilfields west of Shetland. The Foinaven project significantly reduced the uncertainty of the 15 wells drilled (at a cost of £25 million each) and improved the production/injection strategy. Next, in 1995, the UK North Sea Forties field had run out of economic targets for infill drilling. 4D technology halted, and even reversed this decline.
BP investigated the overall robustness of the 4D method by comparing oil/brine reflection coefficients over all of its NW European oilfields. The magnitude of this reflection coefficient turned out to be of the same order as the seismic limit of resolution.
Until recently that is. What has gone almost unnoticed in the last decade is a spectacular across-the-board improvement in the seismic method, driving down the signal to noise threshold by a full order of magnitude. As Whitcombe observes - “the seismic method gets better the more it is pushed.” See this month’s editorial for more technical background.
This timely technological breakthrough is set to address BP’s fundamental business challenge - that of maintaining around 5% production growth in the face of an underlying 15% decline of existing fields, assuming ‘status-quo’ development. In 2000 4D surveys were acquired on Forties, West of Shetlands, Harding, Montrose and Marnock. A significant success was a new well on the Arbroath field, where a ‘no-change’ area on the 4D survey located a good dry-oil producer down-dip from several watered out wells.
Today, for BP, 4D has come out of the R&D closet. You no longer have to justify a 4D survey. But you will have to explain ‘why not’ if you opt not to acquire 4D.
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