Page 114 - Drilling Technology in Nontechnical Language

Chapter 4 – PLANNING AND DRILLING A DEVELOPMENT WELL OFFSHORE 105

the formations above the reservoir are just a few feet thicker or thinner, or
if their dip angle is just a little bit different from what is expected, the well
might end up in the wrong place.

Fig. 4–15. Identifying the second kickoff point

To guarantee accurate knowledge of the downhole geology, the
well continues straight past the planned second kickoff point and into

the reservoir. Logs are then run, and the real situation can be identified.
The drilling assembly is pulled out, and plain pipe is run in (without a
bottomhole assembly). Cement is pumped to the bottom of the well so that
the top of the cement is above the required kickoff point and the pipe is
pulled out of the hole. Now a steerable motor assembly is run in, and the
cement is drilled to the point where the kickoff should start. During this
time, the drillstring is rotated so that the steerable motor drills straight.
It is important that the cement is designed with a higher compressive

strength than the formation. If the cement were weaker, it would be difficult
or impossible to leave the old wellbore and start a new one.
Once the kickoff point is reached, the steerable motor tool face is
aligned in the proper direction, and the well starts to deviate away from
the original wellbore.
The steerable drilling assembly will include both an MWD tool

(to measure directional parameters) and an LWD tool (to confirm the
geological position). The well is drilled to become horizontal at the exact
TVD (to within four or five feet, possibly less) that is required by the

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