Predicting Depth of Penetration of Downhole Perforators

Abstract

Productivity of a cased-and-perforated well depends on completion parameters (charge, shot density and phasing), formation properties (lithology, anisotropy, permeability, fluid properties and saturations), and environmental conditions (pressure and temperature). A shaped charge produces a jet of dense, typically solid material traveling at very high velocity which penetrates casing, cement, and formation. This penetration process creates a tunnel in the rock connecting the reservoir and the wellbore. Stress waves generated during penetration damage the rock around the tunnel, creating a complex zone of mechanically deformed rock material. Explosive and metallic debris may mix with damaged rock material. Depending on the specific conditions (mechanical rock properties, permeability, fluid viscosities, interfacial tensions, pressures and fluid storage volumes), reverse surge flow following the jet penetration partially or completely clears the tunnel of the charge and rock debris. The resulting tunnel is a rugose, tapered cylinder roughly characterized by its diameter and total depth of penetration. The degree of cleanup and total depth of penetration are two of the most critical parameters influencing flow performance of a perforated well. This work focuses on predicting penetration depth and providing a summary of recent progress and advances in this area. A review of industry penetration prediction methods is presented, including relationships based on surface perforation tests in concrete targets, as well as correlations of penetration depth with properties that could be measured by downhole logging tools. Despite a variety of available methods and published experimental data, penetration depth results are often inconsistent with each other and of questionable use in predicting actual downhole penetration. Moreover, most studies have concentrated on the influence of a single penetration variable. There have been no systematic studies of the interaction of parameters on perforation penetration. This paper emphasizes the critical need for such a study, given the difficulty of downhole measurements of penetration depth to finally achieve reliable penetration predictions, and suggests future directions and conditions necessary for such a study. Introduction Prior to the adoption of perforation technology in the oilfield industry, wells were completed "open hole" or "shot hole" (barefoot), sometimes employing liners. The perforated-casing completion was an important and necessary development as wells got deeper, and reservoir conditions became more complex. Early gun perforators were "bullet" devices, using actual projectiles (usually steel bullets) to penetrate the well casing. Prior to the introduction of lined shaped-charge perforators, almost all research emphasis was placed on increasing the depth of bullet penetration. Shaped-charge perforators were adapted for oilfield industry from the military in the 1950s (Pugh et al. 1952; Eichelberger and Pugh 1952; Turechek and Lindsay 1953; Eichelberger 1956) and have displaced the old bullet perforators (nearly to extinction) since then. This paper is focused on depth of penetration (DOP) of downhole shaped-charge perforators and summarizes recent progress and advances in understanding and predicting this important parameter. Productivity of cased-and-perforated wells is influenced by many different factors, including completion (charge characteristics, shot density and phasing), formation properties (lithology, anisotropy, permeability, fluid properties and saturations), and environmental conditions (pressure and temperature). The main goal of natural-perforation completion is to optimize production flow by re-establishing connectivity between wellbore and reservoir, and maximizing the effective wellbore diameter. Drilling and completion operations result in various types of formation damage, including drilling damage (mechanical damage, mud filtrate invasion, and fines migration), perforation damage (crushed zone of reduced permeability around perforating tunnels), partial penetration, well deviation, etc.

New Predictive Model of Penetration Depth for Oilwell-Perforating Shaped Charges

“…Other researchers (i.e. [18]) have come to similar conclusions. The fact that alternative penetration models have recently been introduced ([20]) is further testimony to the industry-recognized need for improvements over the conventional models.…”

“…1) API Section I concrete Berea sandstone (normalized to 7000 psi UCS) 2) Berea rock of different UCS (rock strength effect) 3) Unstressed rock stressed rock (influence of effective stress) 4) Effects of cement, casing, and wellbore fluid Recent surveys [17,18] have summarized some of these historical correlations.…”

New Insights into Optimizing Perforation Clean Up and Enhancing Productivity with Zinc-Case Shaped Charges

“…1997, Brooks et al 2011 to study perforation systems and their flow effectiveness in more detail (using API-RP 19B Section II and IV). A perforating flow laboratory can be a valuable engineering simulation tool to provide insight into the following: -Perforation tunnel geometry (shape, penetration, damaged zones, hole size) (Brooks et al 2011) -Damaged zone around the perforation tunnel -Tunnel cleanup mechanisms -Underbalance optimization (Walton et al 2001, Manalu et al 2005) -Productivity analysis (Halleck 1997) -Development and validation of numerical models (Sun et al 2012, Sun et al 2013, Gladkikh et al 2009) -Selection of gun systems -Deployment techniques Reduction and management of perforating debris (in particular, charge case debris) is a critical aspect that determines the success of a perforating job in complex well completions. It is well known that steel and zinc-case charges are commonly used shaped charges for perforating, with the zinc case charge being the low-debris option as it yields smaller (powdered) debris which can easily be flowed back, and is acid soluble, avoiding significant operational issues that often result from the larger debris of steel cases.…”

Discrete Element Simulation of Induced Damaged Zones in Perforation of Deep Gas Reservoirs

“…First perforation devices that employ a bullet as a shooting tool for breaking the rock, were replaced by shaped charge perforation around 50 year ago (Gladkikh 2009). This new device has continuously been developed during this period by experimental studies which showed that many factors including the formation porosity (Behrmann and Halleck 1988a), ultimate strength (Thompson 1962;Behrmann and Halleck 1988a;Behrmann et al 1992;Ott et al 1994), acoustic velocities and bulk modulus (Venghiattis 1963;Halleck et al 1988;Halleck et al 1991), grain size (Brooks et al 1998), lithology (Aseltine 1985;Halleck et al 1991;Smith et al 1997;Halleck et al 2004;Snider et al 2006), fluid type, saturation, and pore pressure (Aseltine 1985;Behrmann and Halleck 1988b;Halleck et al 1988;Bird and Block 1996;Karacan et al 2001 ;Grove et al 2008), heterogeneity (Smith et al 1997), confining and effective stresses (Saucier and Lands 1978;Halleck et al 1988;Henderson and Navarette 1990;Ott et al 1994;Grove et al 2008), and wellbore pressure (Behrmann and Halleck 1988b) are the important parameters affecting the perforation quality.…”