Laboratory Experiments Provide New Insights into Underbalanced Perforating

Abstract

Laboratory Experiments Provide New Insights into Underbalanced Perforating Ian C. Walton; Ian C. Walton Schlumberger Search for other works by this author on: This Site Google Scholar Ashley B. Johnson; Ashley B. Johnson Schlumberger Search for other works by this author on: This Site Google Scholar Larry A. Behrmann; Larry A. Behrmann Schlumberger Search for other works by this author on: This Site Google Scholar David C. Atwood David C. Atwood Schlumberger Search for other works by this author on: This Site Google Scholar Paper presented at the SPE Annual Technical Conference and Exhibition, New Orleans, Louisiana, September 2001. Paper Number: SPE-71642-MS https://doi.org/10.2118/71642-MS Published: September 30 2001 Cite View This Citation Add to Citation Manager Share Icon Share Twitter LinkedIn Get Permissions Search Site Citation Walton, Ian C., Johnson, Ashley B., Behrmann, Larry A., and David C. Atwood. "Laboratory Experiments Provide New Insights into Underbalanced Perforating." Paper presented at the SPE Annual Technical Conference and Exhibition, New Orleans, Louisiana, September 2001. doi: https://doi.org/10.2118/71642-MS Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex Search nav search search input Search input auto suggest search filter All ContentAll ProceedingsSociety of Petroleum Engineers (SPE)SPE Annual Technical Conference and Exhibition Search Advanced Search AbstractPerforating underbalanced has become the primary means of removing perforation damage and maximizing productivity through a cased and perforated completion. The level of static underbalance (wellbore to pore pressure difference prior to perforating), considered the critical parameter in achieving acceptable productivity, has been investigated theoretically and experimentally through testing on outcrop and reservoir cores under laboratory conditions.We now report on a new series of laboratory experiments conducted on outcrop cores under more representative downhole conditions. Investigation of previously neglected parameters produced profound differences in perforation productivity. In some circumstances static overbalanced perforating proved to be as effective as static underbalanced perforating. The surprising results on underbalanced and overbalanced tests suggest a new approach to minimize perforating damage. Not only do these results impact our understanding of the mechanism of perforation damage removal, but they also have important implications for future design of perforating jobs.IntroductionUnderbalanced perforating is the most widely accepted method for minimizing perforation damage in oil- and gas- well completions. In conventional underbalanced perforating the wellbore pressure is set below reservoir pressure before firing the guns. Here, we consider this as the static underbalance. The reduction in near-perforation pore pressure and the induced surge flow that occur immediately after formation of the perforation tunnel serve to break down the crushed zone responsible for perforation damage. The surge flow also sweeps some or all of the loose debris from the tunnel, though this contributes little to productivity impairment. A good summary of early work in this area can be found in Ref. 1. Underbalanced perforating has evolved with recent studies focused on predicting underbalance pressure criteria for obtaining minimum perforation damage.2,3 On the other hand, overbalanced perforating has fallen into decline, except for a niche application of extreme overbalanced perforating. It is believed that injection of fluids into the perforation tunnel carries with it solid material, which blocks the pores, subsequently impairing productivity. However, the under- versus over-balanced issue is not quite as clear cut as this description would suggest. Reports from field jobs suggest that sometimes the productivity from underbalanced perforating is disappointing, while that from overbalanced perforating is on occasion surprisingly good. Considering the impact perforation performance can have on well productivity and the role played by underbalanced perforating in particular, it is essential that we understand the physics and flow dynamics behind these techniques.The emphasis in underbalanced perforating has been on the degree of underbalance needed to remove perforation damage and minimize productivity impairment. The assumption was that the wellbore pressure remained approximately constant throughout the perforation cleanup process and the static underbalance set prior to the detonation was seen across the perforation tunnel. Little attention has been given to the delicate issue of exactly how the wellbore pressure varies through the perforation operation and hence how much underbalance is actually experienced by the perforating tunnel. Keywords: wellbore pressure, walton, productivity, tunnel, behrmann, upstream oil & gas, pore pressure, johnson, underbalance, completion installation and operations Subjects: Perforating, Completion Installation and Operations, Completion Operations This content is only available via PDF. 2001. Society of Petroleum Engineers You can access this article if you purchase or spend a download.