Wellbore perforation is a stage of oil well completion; it provides a direct link between
the wellbore and the oil formation through perforation tunnels and the surrounding cement sheath. The quality and quantity of the tunnels have a direct influence on well productivity. Therefore it is crucial that completion engineers should ensure that wellbore perforations are located in the right places, oriented correctly, deep, and clean. Effective perforation design and execution process facilitate natural flow and easy pumping of oil, exclude water from the overlying or underlying units, and keep formation rock particles out of the well.
In order for a wellbore to be productive, the casing and cement are perforated to allow the oil and gas to enter the wellstream. In case of cased-hole completions, casing is required to be run into the reservoir. Perforating equipment are transported to and operated at the site by a specialized crew. The tools are then assembled upon arrival to the site. A wireline, slickline, or coiled tubing runs a reservoir-locating device and a perforation gun into the wellbore. Upon reaching the perforation reservoir level, the gun shoots holes to the sides of the well to allow oil and gas to enter the wellstream. Perforations are created by either firing bullets into the sides of the casing or discharging jets/shaped charges into the casing.
Locations of perforations are determined previously using drilling logs, although intervals cannot be easily located through casing and cement. To solve this problem, a gamma ray collar – correlation log is implemented to correlate with the initial log run on the well and define the locations where perforation is needed.
Perforation almost always involves use of explosives, and surface detonation poses a great risk to the lives of drillers. Before starting the perforation, keep all non-essential personnel out of the site and post warning signs. Prohibit the use of communication gadgets or navigational systems, and shut down non-essential electrical systems during gun-arming operations. Operations involving explosives should only be performed under the direct supervision of the special services supervisor. Remnants of explosives should be reported to the aforementioned supervisor.
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“How Does Well Completion Work?” Rigzone. Dice Holdings, Inc., 1999. Web. 19 Dec. 2014. <https://www.rigzone.com/training/insight.asp?i_id=326>.
“Oil and Gas Well Drilling and Servicing ETool.” Occupational Safety & Health Administration. U.S. Department of Labor. Web. 22 Dec. 2014. <https://www.osha.gov/SLTC/etools/oilandgas/servicing/special_services.html>.