sidetrack

A sidetrack is a wellbore that branches away from an existing well at an angle, rather than continuing straight down the main hole. It is drilled by deviating the drill string laterally from the original well path, using specialized directional drilling techniques and tools. The sidetrack typically originates from a kickoff point deeper than the surface, allowing operators to reach new reservoir zones, bypass geological hazards, or exploit multiple pay zones from a single surface location.

The practical reasons for sidetracks are economic and technical. A sidetrack avoids the cost and time of drilling a completely new well from surface, which may also be impossible if surface location is occupied or restricted. They are commonly used to reach around underground obstacles such as salt domes, lost circulation zones, or unstable formations that damaged the original well. In multi-zone fields, a sidetrack from the same casing string can access different productive horizons at different depths and angles.

Setting up a sidetrack requires building angle gradually from the deviated kickoff point, typically using bent-housing assemblies, rotary steerable systems, or whipstock tools. The angle may range from gentle deviations of 10 to 15 degrees in moderate sidetracks, to 45 to 60 degrees or steeper in more aggressive wells. The sidetrack is normally sealed from the original wellbore using a cement plug or mechanical isolation tool at the kickoff point, creating a hydraulic barrier between the two bores.

Common failure modes include loss of angle control during buildup, which causes the sidetrack to rejoin the original well path or intersect it unintentionally. Keyseating (gouging of the wellbore wall by rotation) at the kickoff point can weaken the casing or isolate the sidetrack. Stuck pipe is also frequent in high-angle sidetracks due to increased friction and uneven hole cleaning in deviated sections.

The term reflects the branching nature of the well geometry: the sidetrack is literally a track off to the side of the main bore. In mining applications, the concept is similar but applied to underground development tunnels, where a sidetrack drifts laterally from the main shaft or adit to access ore bodies or provide ventilation routes. The name has remained consistent across both industries for over a century.