Investigating the Dynamic Three-Dimensional Loading Effects on Perforating Guns Imposed by Shaped Charges
Authors: Craddock G. G. , Zhang Wei , Wight Jim , Rodgers John , Glenn Timothy S. , Serra Marco , Bettenmann Thomas 
Published: March 2015

Modern developments in shaped charge technology have resulted in greater explosive loads being used on perforating guns, which has stretched the capacity of perforating guns into uncharted territory. Traditional gun design approaches and standards use collapse pressure calculation and swell measurement with overloaded charges as design verification methods. The extremely complicated interactions between explosives, fragmented casings, and the gun wall are evaluated on an empirical basis, and the nature of these interactions is not well understood. In this paper, a new design model is presented that augments traditional design approaches and provides gun designers with better data on gun system structural performance, including the effects of phasing, shot density, and charge type.

The loads imposed on the gun body by the explosives are multidimensional because of the spiral arrangement of most shaped charges. The resulting dynamic response of the gun body is therefore quite complex and requires three-dimensional (3D) analysis. High-frequency bending, torsion, and tensile loads are expected. The casings are typically fragmented, and some of the larger fragments can impose high impact loads on the gun wall. A fully coupled computer model has been developed that incorporates the rapid explosion, casing fragmentation, and multidimensional structural responses.

Multiple instrumented surface tests were performed to validate the dynamic 3D model. Proprietary testing techniques were used to extract gun internal pressure history and gun stress history at multiple locations immediately following detonation. Redundant strain gauges were used, and shots were repeated to ensure the integrity of the data.

This paper presents the instrumented gun test setup and results, along with the newly developed 3D simulation model and shock hydro model results. This paper also presents validation of the newly developed 3D model through comparisons with test data.

Introduction

Critical to the understanding of perforating gun/charge dynamics is the undertaking of instrumented gun testing in a controlled environment. Accurate downhole data collection within the perforating string has historically been challenging or impossible within close proximity to the charges. Previous attempts have produced limited results, with indirect fluid communication between charges and the transducer (Schatz et al. 2004). Surface testing using instrumentation to capture fluid pressures and structural response can provide valuable input for the design of more robust gun systems. Unfortunately, it is difficult to locate sensors in close proximity to an explosive event and to have them survive and produce quality data (Han et al. 2010). New tools and testing methods are required to perform such measurements.

In this paper, a sensor sub solution is presented for accurately measuring the shock response of a detonating gun. This tool is used to characterize an array of charges and gun systems. The data are then used to calibrate a proprietary finite element analysis (FEA) -based software package developed for simulating the perforating event. A shock hydrodynamics code (CTH) is then used to better understand the dynamics of guns near the scallop. Three configurations are presented, with test data and comparisons to simulations: a small-diameter gun with a four small charges,a small-diameter gun with a full charge load, anda large-diameter gun with four large charges.

The discussion concludes with lessons learned about charge-gun dynamics. Section I is the introduction, Section II is the surface test setup, Section III is the presentation of the test data and comparison to the FEA simulation, Section IV is the shock hydro simulation results, and Section V is the discussion and conclusions.