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In the early days of land drilling most wells were drilled vertically, straight down into the reservoir.An operating company usually hires a directional drilling service company to: provide expertise in planning the well; supply special tools; and to provide onsite assistance when operating the tools.In this chapter we will discuss: the applications of directional well drilling; the design of these wells; and the techniques used to drill a well with controlled deviation from the vertical. The next chapter will discuss the tools and techniques used to survey the position of the well (determine the three dimensional position of all points in the wellbore relative to the wellhead).Although these wells were considered to be vertical, they rarely were.

In the early days of land drilling most wells were drilled vertically, straight down
into the reservoir. Although these wells were considered to be vertical, they rarely
were. Some deviation in a wellbore will always occur, due to formation effects and
bending of the drillstring. The first recorded instance of a well-being deliberately
drilled along a deviated course was in California in 1930. This well was drilled to
exploit a reservoir which was beyond the shoreline underneath the Pacific Ocean. It
had been the practise to build jetties out into the ocean and build the drilling rig on
the jetty. However, this became prohibitively expensive and the technique of drilling
deviated wells was developed. Since then many new techniques and special tools
have been introduced to control the path of the wellbore.
An operating company usually hires a directional drilling service company to:
provide expertise in planning the well; supply special tools; and to provide onsite
assistance when operating the tools. The operator may also hire a surveying
company to measure the inclination and direction of the well as drilling proceeds. In
this chapter we will discuss: the applications of directional well drilling; the design
of these wells; and the techniques used to drill a well with controlled deviation from
the vertical. The next chapter will discuss the tools and techniques used to survey
the position of the well (determine the three dimensional position of all points in the
wellbore relative to the wellhead).