Abstract

In the early days of 3D seismic (in the late 70's through to the early 90's) it was always difficult to justify using this "new technology" -- the industry tends to be conservative, and commercial case history successes attributed to 3D seismic technology were slow in being published. By the early 2000's, however, if proposing a 2D seismic survey, then during the approvals process one would expect to have to justify not acquiring 3D seismic data.

4D seismic has had a slightly faster take-up. We should ask ourselves why approximately 80% of all seismic work in the North Sea is shot and processed for time-lapse (4D) purposes — in fact for the major oil companies in the North Sea, 4D represents over 90% of their work program in that area.

We should also ask ourselves why this situation came to pass in the late 90's, even when the oil price was below $25 per barrel.

The answers should be no surprise — most of the reservoirs in the North Sea were in decline by the late 90's, and those people who were charged with maximizing the flow rates and/or the reservoir recovery factors began to use technologies such as 4D which was beginning to make a significant impact.

At about the same time, it gradually became apparent that 4D could probably make a greater contribution if applied early in the life of a field -- even extended well-tests produced useful 4D results over periods of just a few months, and these could show up some of the important architecture of the reservoir.

Commercial case histories for 4D appeared relatively quickly compared to 3D and assisted the take-up of the method. Several of these will be presented in detail, together with a review of the current state of the science including "life of field" systems which are producing several "pictures" of the reservoir in a 12 month period, almost allowing a "movie" of the changes in the reservoir. The technology is evolving but its directions are clear and will be described in this paper.

Presented at: 2007 South East Asia Petroleum Exploration Society (SEAPEX) Conference, Singapore, 2007