Effects of Underbalance and Effective Stress on Perforation Damage in Weak Sandstone: Initial Results

Abstract

Effects of Underbalance and Effective Stress on Perforation Damage in Weak Sandstone: Initial Results L.A. Behrmann; L.A. Behrmann Schlumberger Perforating and Testing Center Search for other works by this author on: This Site Google Scholar J.K. Pucknell; J.K. Pucknell BP Research Search for other works by this author on: This Site Google Scholar S.R. Bishop S.R. Bishop BP Research Search for other works by this author on: This Site Google Scholar Paper presented at the SPE Annual Technical Conference and Exhibition, Washington, D.C., October 1992. Paper Number: SPE-24770-MS https://doi.org/10.2118/24770-MS Published: October 04 1992 Cite View This Citation Add to Citation Manager Share Icon Share Twitter LinkedIn Get Permissions Search Site Citation Behrmann, L.A., Pucknell, J.K., and S.R. Bishop. "Effects of Underbalance and Effective Stress on Perforation Damage in Weak Sandstone: Initial Results." Paper presented at the SPE Annual Technical Conference and Exhibition, Washington, D.C., October 1992. doi: https://doi.org/10.2118/24770-MS Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentAll ProceedingsSociety of Petroleum Engineers (SPE)SPE Annual Technical Conference and Exhibition Search Advanced Search AbstractSingle-shot laboratory flow tests were performed on six Castlegate sandstone cores to determine the effect of perforating a weak sandstone (approximately 1600-psi mean unconfined uniaxial compressive strength). Experiments were performed at two effective stress levels and various underbalances.The Castlegate was perforated under simulated downhole conditions as described in API RP 43, 5th Edition. Radial flow tests were performed immediately after perforating to establish perforation productivity. These tests gave no information on the distribution of permeability damage; therefore, a radial flow permeameter was used to measure the permeability distribution.As anticipated, the total perforation length in the Castlegate sandstone was greater than in stronger sandstones; however, the shape of the perforations, the amount of debris left inside the perforation tunnel and the effect on productivity due To the level of underbalance were unexpected. Although the number of experiments was limited, the following observations were made:At all conditions the rock around the initial perforation tunnel failed;At low effective confining stress, the failed rock was expelled into the "wellbore," creating a large, asymmetric cavity/tunnel;At higher effective confining stress, the failed rock remained in the perforation, filling the tunnel;Perforation productivity appeared to decrease at higher underbalances; andExperimental artifacts may affect measured productivities when testing softer sandstones.IntroductionWell performance computer models require input of both drilling and perforation damage to calculate productivities. The literature suggests 0.5 in. of depth of perforation damage and a 0.1 to 0.2 permeability reduction factor based on the core flow efficiency (CFE) values from the API RP 43, 4th Edition tests. To determine the cost benefit of underbalance tubing-conveyed perforating (TCP) versus high shot density wireline overbalance perforating, a more definitive answer is required with respect to perforation damage versus rock properties and underbalance levels.API RP 43 5th Edition, published January 1991, includes a new Section 4 single-shot test in Berea sandstone under simulated downhole conditions. The experimental results presented in this paper utilized the basic procedures given in Section 4 and are a continuation of previously published work.The purpose of these experiments was to determine the effect of perforating on the productivity of a weak sandstone formation. Impairment to well productivity is normally defined in terms of a "skin." Perforation productivity generally improves as the flowing differential applied after perforating is increased, an effect believed to be due to minor amounts of debris being "washed" out of the perforation. To obtain a skin closely related to the original state of the perforation, all flow testing after perforating was performed at a fixed, relatively low pressure differential of 20 psi. Keywords: underbalance, effective stress, spe 24770, perforation, diameter, perforation damage, weak sandstone, permeability, perforation damage zone, upstream oil & gas Subjects: Perforating, Completion Installation and Operations, Completion Operations This content is only available via PDF. 1992. Society of Petroleum Engineers You can access this article if you purchase or spend a download.