Maximum Differential Pressure Perforating

Abstract

Laboratory data and field results have shown that casing perforations are plugged when there is a pressure differential toward the formation at the time of perforating. As a result, there has been a trend toward thru-tubing completions so that the wells can be perforated with a pressure differential toward the wellbore. However, there has been an accompanying sacrifice in depth of penetration because of the smaller charge size, especially in the thru-tubing hollow carrier guns. Also, when the encapsulated charges are used, the casing has to absorb the shock when the gun is fired. Recently, a perforating system has been developed whereby the deep penetration of the larger charges in casing guns can be combined with the efficient clean-out of the negative differential perforating. In this system each perforation is sealed perforating. In this system each perforation is sealed off from hydrostatic pressure as the gun is fired. The volume inside the gun at atmospheric pressure is sufficient to contain the products of combustion and still give essentially full formation pressure as a differential into the gun. The resulting implosion into the gun insures that each perforation will have maximum capacity for flow or injection. Laboratory and field data are presented showing the benefits of this new perforator. Full allowable wells are being obtained through natural production in many cases. In others lower breakdown pressures, higher injection rates, and more efficient well treatments and sand consolidation jobs are the result. Introduction The effectiveness of perforations in oil and gas well casing has been the subject of a number of papers since the introduction of bullet guns in 1932 and of jet guns in 1948. In 1956 Allen and Worzell and Krueger reported the results of perforating Berea sandstone targets with various perforating Berea sandstone targets with various wellbore fluids and pressure differentials. Their data indicated that serious perforating plugging occurred whenever there was a differential pressure to the formation at the time of perforating, especially with mud in the well bore. These plugs consisted of crushed formation, liner particles, jet charge particles and mud. Pressure differentials as high particles and mud. Pressure differentials as high as 430 psi were required to initiate backflow on some of these tests.