Geological Drilling

Abstract

Perhaps no other field in the oil industry has seen as much progress in the last decade as directional drilling. It was initially developed as a technique to reach reservoir targets not accessible with vertical wells, for example fields — or parts of fields — situated offshore but close to the coastline where a drill rig could be placed. Several fields offshore California and in the Caspian Sea around Baku (Azerbaijan) were developed in the 1930s and 1940s with deviated drilling. With the rapid growth of offshore drilling from platforms, directional drilling became common as a large number of wells were drilled from the same platform into a field. Although geology dictated what objective the wells were targeting, the well trajectory was usually defined in strictly geometric terms. After an initial vertical or steep section of the well, deviation was built up at a prescribed depth and build-up angle, and once the desired deviation was reached the well was on its target, perhaps with a vertical drop-off in its last section where it penetrated the reservoir.