An introduction to directional drilling
At one time, it was assumed all oil wells were essentially vertical or the bottom of the hole was directly under the drilling rig. The petroleum industry did not become fully aware of deviated well problems until the development of the Seminole, Oklahoma field. The wells in this field were drilled very close together and as a result wells were drilling into one another, and ones which were already producing. Deviations as high as 46º from vertical were measured in the Seminole wells. The average deviation from vertical was approximately 13°. Directional drilling began emerging in the late 1920’s when curvey instruments were developed that could measure both inclination and azimuth.
The first controlled directional drilling well was drilled in California in 1930 to tap offshore oil reserves. Unfortunately, operators were drilling across lease lines in order to drain oil owned by another individual, resulting in legal problems. In the 1930’s, wells were directionally drilled to tap oil reserves that would otherwise be inaccessible. In one case, directional drilling was employed to produce oil from under a cemetery. Oil was produced from under the ocean by placing the rig on the shore and directionally drilling into the offshore oil deposits.
Little attention was paid to directional drilling until a relief well was drilled to kill a blowout near Conroe, Texas. The relief well was drilled near the surface location of the blowout. Directional drilling techniques were used to intersect the producing formation near the blowout, and the blowout was killed by pumping fluid down the relief well and into the blowout well. Since then, directional drilling has been widely accepted. Today, the on-going research and development of new tools and techniques are making directional drilling more accurate and economical.
Directional drilling is now common from platform and offshore locations. The expense of placing production equipment off shore, or in the arctic, requires that wells be produced into a common area. The well heads can be located on one platform instead of several if wells are drilled directionally from one location. The drainage area for a platform may be extended with extended reach drilling (ERD) so that fewer wells and platforms may be needed. This will also minimize the environmental impact of the operations and maximize the economics of hydrocarbon production.
Platforms such as the one shown below may be taller than the tallest buildings in the world. Most of the structure will be below sea level and not visible. These platforms may be larger than three football fields. The structural loading is crucial to the cost of these tall structures. Each ton of material on the decks will add significantly to the costs, so space is at a premium. However, the cost of a structure this big makes it imperative that as many wells as possible be drilled from this one location. Directional drilling has permitted development of many subsea production intervals in an economic manner even though these platforms are expensive. The investment for these platforms, before a single drop of oil or cubic foot of gas is produced, is frequently in the hundreds of millions or billions of US dollars. Every effort is made to decrease drilling costs for these production platforms.