Horizontal oil and gas drilling has become one of the most valuable technologies ever introduced in the business. It is an enhanced oil recovery (EOR) or gas recovery method that is becoming more and more popular as the price per barrel of oil gets higher.
Unlike a directional well that is drilled to position a reservoir entry point, a horizontal well is commonly defined as any well in which the lower part of the well bore parallels the oil zone. The angle of inclination used to drill the well does not have to reach 90° for the well to be considered a horizontal well. Applications for horizontal wells include the exploitation of thin oil-rim reservoirs, avoidance of draw down-related problems such as water/gas coning, and extension of wells by means of multiple drain holes.
Unlike a directional well that is drilled to position a reservoir entry point, a horizontal well is commonly defined as any well in which the lower part of the well bore parallels the oil zone. The angle of inclination used to drill the well does not have to reach 90° for the well to be considered a horizontal well. Applications for horizontal wells include the exploitation of thin oil-rim reservoirs, avoidance of draw down-related problems such as water/gas coning, and extension of wells by means of multiple drain holes.
Cost experts have agreed that horizontal wells have become a preferred method of recovering oil and gas from reservoirs in which these fluids occupy strata that are horizontal, or nearly so, because they offer greater contact area with the productive layer than vertical wells. While the cost factor for a horizontal well may be as much as two or three times that of a vertical well, the production factor can be enhanced as much as 15 or 20 times, making it very attractive.
Purposes of Directional Drilling
Inaccessible Locations - Quite often, a target payzone lies vertically beneath a surface location that is impractical as a rig site.
Multiple wells drilling from a single site - perhaps the most common application for drilling is associated with offshore production platforms. It is more economical, in most cases, to drill a number of directional wells from a single platform than to build individual platforms for vertical wells.
Sidetracking - the primary purpose is to deviate the wellbore around and away from an obstruction in the original wellbore such as a stuck drillstring.
Relief Wells - possible the most spectacular applications of directional drilling a relief well to intersect a blowout well near the bottom so that mud and water can be pumped into the blowout well.
Multiple targets - geologists may define multiple targets for a prospect that cannot be drilled with a vertical well. It may be necessary to drill through one target and alter the direction of the well to reach the next target, at a greater depth.
Multiple wells drilling from a single site - perhaps the most common application for drilling is associated with offshore production platforms. It is more economical, in most cases, to drill a number of directional wells from a single platform than to build individual platforms for vertical wells.
Sidetracking - the primary purpose is to deviate the wellbore around and away from an obstruction in the original wellbore such as a stuck drillstring.
Relief Wells - possible the most spectacular applications of directional drilling a relief well to intersect a blowout well near the bottom so that mud and water can be pumped into the blowout well.
Multiple targets - geologists may define multiple targets for a prospect that cannot be drilled with a vertical well. It may be necessary to drill through one target and alter the direction of the well to reach the next target, at a greater depth.
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