Directional drilling is the method of drilling the non-vertical well by controlling the deviation and direction of a well to reach to a predetermined point.
Applications of directional drilling
The major applications of directional drilling are listed in the following:
Multiple wells from a single location
In areas like offshore or Arctic, where the drilling site condition, costs and environmental issues enforce drilling the optimum number of wells from a single rig, directional drilling is the best option.
The sidetrack is a technique used to make a lateral from the well. When there is an obstruction in the well like lost drill string or part of bottom hole assembly (BHA) and is not drillable the sidetracking must be accomplished. This technique may be employed in depleted wells to redirect from the existing well for entering to another pay zone. Geological problems are other issues which cause changing the path of the well.
Horizontal wells are highly inclined (inclination > 85deg) wells to increase the rate of production and improve the performance of the reservoir. Directional drilling is the most common practice to drill the horizontal wells.
Multiple target zones
A single wellbore can be used as a base line to approach to the multiple target zones, using multiple completions and deliver the high production of hydrocarbon. Only one drilling rig, wellhead and surface equipment is needed and the total length of casing, tubing and drill string is less than drilling several wells.
Inaccessible surface locations
In a case that a pay zone is not accessible by drilling a vertical well, directional drilling has helped us greatly. The drilling team plan and design the drilling site location, well trajectory and entry point in the reservoir. Extended reach drilling (ERD) wells are the examples of these applications.
Fault drilling is another application of directional drilling. Drilling a vertical well into a fault plane to reach an underlying pay zone is problematic. To solve this problem, the well is drilled perpendicular or parallel to the fault to enhance the production rate.
When a well is not controllable the relief well should be directionally drilled and intersected near the wild well with extreme precision, then the killing mud is pumped into the relief well to kill the wild one.
Hydrocarbons like oil or natural gas can be trapped under a dome-shaped structure of salt column (Salt-dome). Drilling a well vertically through a salt-dome leads facing serious problems such as, corrosion of casing or tubing, lost circulation of drilling/completion fluid or washout.