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installation of equipment required for production. At this stage, the operator
may have limited information about the geological characteristics of the reservoir
and surrounding formations. Such information, including data about the
surrounding formations, pore pressures, reservoir configuration and reservoir
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volumes, is developed during the exploratory drilling operation and may lead to
changes in the drilling plan and well design as the operation proceeds.

Once an operator finishes drilling an exploratory well and performing its
initial evaluation of the well, it typically seals the well by pumping cement and
installing mechanical plugs. This procedure is commonly referred to as
“plugging and abandoning” the well. If the operator believes that it eventually
will be able to produce hydrocarbons from the exploratory well, it may choose to
perform “temporary abandonment” procedures, which are procedures that allow
the drilling rig to move off of the well so that the operator can return at a later
date to complete the well and prepare it for production.

A typical deepwater well is drilled using the following process:

 A drilling rig moves on the location of the well. Many rigs operating in
deepwater are “dynamically‐positioned,” which means that they are not
moored to the seafloor but instead hold their position over the well
through a combination of satellite technology and directional thruster
activity. The Deepwater Horizon was a dynamically‐positioned rig.

 The rig lowers drill pipe (also known as a drill string) with a drill bit
attached to its end. The drill bit bores into the sea floor and the subsea
formation to make a hole. That hole is referred to as the wellbore.

 The rig installs, or “sets,” a large‐diameter pipe known as “casing” into
the wellbore to establish a barrier between the wellbore and the
surrounding formation and to ensure that continued drilling does not
result in the collapse of the wellbore. The initial casing that is set in the
wellbore is called “conductor” casing.

 The rig then uses the “marine riser” or “riser,” which is a large pipe that
surrounds the drill pipe, to lower the subsea BOP stack onto the well.
The subsea BOP is latched to the wellhead on the conductor casing.

14 “Pore pressure” is the pressure of fluids within the pores of a reservoir.

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