Perforation performance evaluation has come under scrutiny in several recent publications. For most shaped charge perforators sold, performance is evaluated in cement targets, from which downhole performance is extrapolated. This method has been shown to generally over-predict downhole performance, with broad implications for perforating systems and shaped charge design, and well completion design.
Advanced test methodologies are an order of magnitude more complex than the simplified cement penetration tests. This paper details a set of experimental shaped charge development programs with specific geometry and/or flow performance requirements and examples of their corresponding field performance. Tests have been performed with full simulation of single shot perforation, and simplified perforating simulations into stressed rock. Results are reported for shale, sandstone, and high permeability sandstone targets. Designs tested include both conventional and reactive shaped charges.
In one example from 2008-2009, CNX completed fourteen wells using both conventional and reactive perforating systems to evaluate any impact on completion performance. Stimulation and production data have been analyzed for 81 stimulation stages. When comparing wells perforated with reactive shaped charges to conventionally perforated offsets, a reduction in breakdown pressure gradient of between 13% and 29% is observed. Subsequent treating pressures are reduced by 6% to 15%. The wells perforated with reactive shaped charges have also exhibited significantly slower productivity decline over the first nine months.
In addition, near-perforation permeability has been mapped using advanced digital imaging techniques. This allows the grain structure and permeability distribution of a perforated rock target to be accurately measured as a function of radial distance away from the perforation wall and longitudinal position along the perforation tunnel. The paper describes important improvements in our understanding of perforation damage distribution, and provides techniques for use in conjunction with API RP 19B Section 2 and 4 tests to design perforating shaped charges and systems.