Page 170 - Introduction to Petroleum Engineering

TYPES OF WELLS 157
Directional wells can be drilled to follow the orientation of a geologic
formation. This improves access to the formation when production tubing is
perforated within the formation. Horizontal wells are examples of this. The portion
of a horizontal well nearest the vertical section of the well is the heel, and the
end of the horizontal well is the toe. The horizontal section is often called the
lateral or reach.
A sidetrack diverts the direction of the well. This can be done for many reasons,
such as avoiding a piece of broken drill pipe or to reach a different reservoir.
A multilateral well has multiple segments branching from the original well. The
original well is called the trunk, and the segments are called laterals or branches.
Multilateral wells are used in offshore environments where the number of well slots
is limited by the amount of space available on a platform. They are also used to
produce fluids from reservoirs that have many compartments. A compartment in a
reservoir is a volume that is isolated from other parts of the reservoir by barriers to
fluid flow such as sealing faults. Before modern directional drilling, a reservoir that
was broken up into several compartments required a large number of vertical wells to
drain each section. Today, a smaller number of wells can be used to intersect separate
reservoir compartments.
Technology for drilling directional wells has advanced rapidly in the last 30 years.
One key advance is MWD technology. MWD technology transmits directional
information from the BHA by creating pressure pulses that travel through the drilling
mud to the surface and are decoded there. The front portion of the BHA typically
includes directional sensors, mud‐pulsing controls, a mud motor, a bend of 0–4°, and
a drill bit. MWD gives the drilling team frequent updates about the inclination from
vertical and the azimuth or direction in the horizontal plane of the BHA. With this
information, the team can adjust the drilling direction, often referred to as geosteer-
ing. When geosteering, there are three angle choices: build angle orients the well
toward the horizontal, drop angle orients it toward the vertical, and maintain angle
continues the existing well trajectory.
With an appropriately instrumented BHA, MWD also can provide rotational
speed and rotational speed variations, the type and severity of BHA vibrations,
temperature, torque and weight on the bit, and the mud flow rate. Drillers use this
information to adjust operations to maximize the ROP and to decrease wear on the
bit. The BHA can also include formation logging tools that provide data in a process
called logging while drilling (LWD). LWD tools work with the MWD system to
transmit information to the surface.

example 8.7 Drill Time
The top of a formation of interest is at a depth of 5000 ft and the ROP of the
drill bit is 250 ft/day. How long will it take to drill to the top of the formation?
Answer
Time to drill = 5000ft / (250ft/day ) = 20days