Page 49 - Petroleum and Gas Field Processing

such operations that are performed to resolve specific problems that are
found after production has started. Some of the important and common
operations are briefly described in the following subsections.

Perforating Operation
For cased hole completions, perforations are made through the casing and
cement and into the formation to establish communication between the
formation and the wellbore. It is essential to have clean perforations with
relatively large diameters and deep penetrations to achieve high well
productivity. Further, perforating should be done only through the clean
and productive zones within the formation, as determined from the
formation evaluation logs. Therefore, extreme care is taken in locating the
perforating gun at the right locations. The selection of the type of
perforating gun, explosive charges, and completion fluid and the control of
the pressure in the well at the time of perforating are very important
elements in achieving effective and productive perforations.
Perforations are made by detonating specially shaped explosive
charges. The shaped charge consists of a body called the case, a linear that
is made of a powder alloy of lead, copper, and tungsten, the explosive
material that is contained between the case and the liner, and a detonating
cord. Figure 19 shows a schematic cross section of a shaped charge. Upon
explosion, the case expands and ruptures and the liner collapses into a
carrot-shaped jet consisting of lead, copper, and tungsten particles. The jet
travels at very high velocity and impacts upon the casing with an
extremely high pressure. The high energy of the jet causes the jet to
penetrate through the casing, cement, and formation, thus creating the
perforation.

Figure 19 Shaped charge (cutaway).

Copyright 2003 by Marcel Dekker, Inc. All Rights Reserved.