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Gold/Mining/Energy : Strictly: Drilling and oil-field services -- Ignore unavailable to you. Want to Upgrade?

To: bw who wrote (6725)	1/6/1998 2:02:00 PM
From: Teddy	Read Replies (1) \| Respond to of 95453

Something to read while we waite. One of the reasons why drilling continues even as crude prices have pulled back. "FOURTH DIMENSION" ADDED TO HUNT FOR OIL. By Sean Maguire LONDON - New seismic techniques, which add time as a fresh dimension, are paying off for companies trying to squeeze oil out of ageing North Sea fields. Norwegian oil producers have begun to rely on the fledgling science, which compares seismic surveys taken at different stages in a oilfield's lifetime to help spot pockets of hydrocarbons missed by the drilling teams. The development of seismic in four dimensions (4D) -- depth, width and length, plus time -- has helped Norway's state-owned Statoil to raise its forecast for oil recovery from the Gullfaks field by nine percent to 62 percent. That is a profitable extra 330 million barrels of oil. The global 4D market will top $500 million this year, an increasing slice of the total annual spend on seismic, for exploration and other purposes, of around $1.5-$2 billion, says Oslo-headquartered Petroleum Geo-Services. Take-up will be quickest in the North Sea and the Gulf of Mexico with rapid growth in 4D expected by 2000. High recovery rates have helped ease oil industry worries that the benefits of 4D were not worth the cost. The technology had developed slowly because of doubts about the compatability of surveys performed years apart, problems with analysing mountains of data and the interdisciplinary challenge it represents to oil companies. "Its got to the point that there are enough promising pilot results around for there to be quite widespread interest," said Bob Seymour, 4D manager at seismic giant Western Geophysical. "If it works it is extremely attractive economically," said Seymour. Clients convinced of the method expect to improve oil recovery by 10 percent at a marginal cost. Most oil industry seismic studies are still "shot" by boats trailing long lines of hydrophone arrays which record sound waves, generated by a compressed air gun, that are reflected back by rocks deep beneath the ocean floor. Companies are also testing Ocean Bottom Cable (OBC) systems, which can measure "shear" (transverse) waves as well as just pressure waves from sound. In simple "pressure" form OBC systems were originally used in areas cluttered with platforms and pipelines. Now the dual OBC systems are promoted as offering clearer resolution of complex sub-sea faults. However, the technology lags behind 4D techniques in general acceptance. Both systems are attractive to oil companies because they help in understanding how efficiently water or gas pumped into an oil reservoir flushes crude towards up-wells. Lessons from pioneering 4D work by Norsk Hydro on the Oseberg field in 1989 and 1991 will be used on the complex Njord field, which is due on stream in September. Norsk Hydro hopes to improve recovery from 30 to 36 percent to produce an extra 40 million barrels of oil. A pilot 4D seismic project on part of Gullfaks in 1995 helped Statoil so far to spot three new drilling targets. One well is producing 6,300 barrels of oil a day, from an area the company's model of the reservoir predicted would be empty, and the two other targets should yield oil this week. "Dissatisfaction with reservoir modelling and drainage simulation has driven the need for 4D seismic mapping," said Statoil's Lars Magnus Pedersen. "Previously we had just guesses of what was going on in the sub-surface." Pedersen expressed frustration that a lack of experts to integrate 4D seismic data with production records, well loggings and laboratory work on core samples was holding back improvements in Statoil's management of its reservoirs. "We can't just sit and wait, we don't have many years of life left on some of our fields," he said. Statoil ordered a new survey this summer over the large Statfjord field and contracted Western Geophysical to compare results with previous studies in 1980 and 1991. Statoil hopes the survey will help increase recovery from 65 to a mammoth 70 percent. British Petroleum has begun a 4D project at its Foinaven field off the west of Scotland which will compare the merits of repeated OBC and surface seismic surveys and help improve oil recovery. BP and Schlumberger seismic subsidiary Geco-Prakla have buried a seismic cable a metre under the ocean floor around a fifth of the Foinaven field in a $8 million joint project with Shell. First repeat surveys will be done nine to 12 months after oil starts flowing, which is now scheduled, after many delays, for the last quarter of this year. (c) Reuters Limited