Introduction
Directional drilling is a unique drilling technique used to deviate from the established borehole trajectory in order to reach a target that would otherwise not be accessible from the surface. It can be used in oil, natural gas and other industries to reach subsurface resources, install or repair underground pipelines or for other subterranean projects. The technique has been successfully used for many years and continues to improve.
A Brief History of Directional Drilling
The history of directional drilling dates back to the nineteenth century. The first practical application of directional drilling was used to build the Blackpool Marine railway tunnel in England in 1845. After its initial use, directional drilling was increasingly employed to meet the engineering demands of creating underground power lines, sewers and pipelines. The development of directional drilling technology is credited with the introduction of the rotary drill in the early twentieth century. This allowed for much more accurate directional control of drilling and enabled companies to create longer and more complex directional curves.
The introduction of electronic instrumentation in the 1970s further improved directional drilling capabilities. With the development of better logistics and improved engineering capabilities, directional drilling was used increasingly in the exploration of energy, natural gas and oil reserves all around the world.
Description of the Directional Drilling Process
The directional drilling process begins at the surface with the placement of a “kicking-off” or “kick-off” point. This is a fixed point and is set depending on the type of drilling required. Drilling is started using a rotating drill bit and steady pull from the surface; however, smooth rotation and a steady pull are difficult to maintain at angles beyond a few degrees. In order to control the angle of the drill string and the direction of drilling, a range of specialised equipment and techniques are used.
Directional drilling is normally performed with a drill bit specially designed to create a curved path surrounding the “kick-off” point. These drill bits are usually composed of rotating cutters, usually tungsten carbide, and are positioned on the end of the drill string to create a rounded bottom-hole pattern. Specialised drill-bits are often used depending on the type and amount of material to be drilled. Once the target depth is reached, a tool known as a “measuring-while-drilling-tool” (MWD) is used to measure the angle of the wellbore. The MWD tool is placed directly on the drill-bit and is capable of tracking changes in the drilling angle.
The ability to accurately control the drill string angle and target point is also known as “steerability”, and is achieved using a variety of techniques. These include using either a deflection motor or a downhole drilling motor to steer the drill bit. The deflection motor allows for continuous directional monitoring by using either a bent sub or a drill pipe to bend the wellbore trajectory. Downhole drilling motors, on the other hand, are more accurate yet require more power since they need to rotate the drill bit. Both techniques require expertise, skill and precision in order to successfully steer the drill bit through rocks and other subsurface materials.
Conclusion
Directional drilling is a vital tool used in the exploration and production of energy reserves and in many modern construction projects. The development of sophisticated equipment, techniques and logistic capabilities has enabled greater flexibility and accuracy when drilling in complex and inaccessible areas. It is a process that requires specialised techniques and expertise in order to guarantee success and safely reach a desired target. Directional drilling is a unique and important technique that is continuously developing and improving.
