Justin L. Mason

Well Testing and Evaluation of Tubing-Conveyed Extreme Overbalanced Perforating

Traditionally, underbalance perforating has been the preferred perforation technique. Recently, however, a new extreme overbalance perforating (EOBP) that has the potential to improve the completion efficiency of a well without additional stimulation has been introduced. With this method a well with a fluid column is pressurized with nitrogen to above fracturing pressure of the formation before the gun is fired. Gas is then injected, with or without acid or proppants, to create short fractures that extend from the perforation tunnels. The presence of gas lowers the amount of liquid that contacts with the formation, facilitates the wells coming into production after perforation, and results in less formation damage. This new EOBP method creates highly conductive short fractures, the benefits of which outweigh any restriction that may be caused by perforating debris. The debris that exits the gun when it detonates will be pushed away from the wellbore during the pumping stage, and this will greatly diminish any adverse effects on productivity that overbalanced perforating could cause. This can be considered as a near-wellbore stimulation method that also improves the completion efficiency of a well by allowing perforating and stimulation to be accomplished in one operation. By performing two or more completion procedures during a single trip into the wellbore, service operators have been able to generate economical advantages. There are numerous ways in which EOBP may be performed. This paper will cover the design, planning techniques, and equipment that can be used to perform tubing-conveyed overbalance perforating. Examples and field cases will show scenarios in which wells with a variety of wellbore conditions such as open perforations and packerless and tubingless installations can be perforated in an extremely overbalanced condition. An analysis technique that can be applied to a short falloff test immediately following the perforation treatment as well as the standard well testing is also described in this paper. The method of analysis can be used to calculate skin damage, formation permeability, reservoir pressure, and if applicable, fracture parameters such as fracture half-length and conductivity. Several field cases are included to illustrate application of this method.