The perforation of wellbore casing is a critical step in establishing communication between the wellbore and formations of interest. The effectiveness of this communication is dependent upon both the geometry of the perforations and the permeability distribution of altered material surrounding them. To date, our understanding and modeling of this geometry and permeability distribution has been limited to simple representations consisting of cone-shaped tunnels surrounded by a damaged layer exhibiting a constant, reduced permeability - typically of constant thickness. These models are based mainly on performance evaluations conducted in cement targets, and less frequently upon performance tests with stressed sandstone targets. This methodology influences our thinking regarding many post perforation process, including fracture completions, but breaks down when estimating perforation performance in shale formations.

This paper describes a body of experimental work with perforation simulation in a state of the art API RP-19B Section 4 facility. Tests are conducted in shale targets with a variety of shaped charge designs. The perforation tunnels are evaluated for geometry and performance using next generation CT scan imaging techniques. The results of this study show that perforation geometry produced in shale targets is significantly different from that produced in cement or sandstone targets commonly used to estimate perforation performance and that changes in shaped charge design can produce significant geometry improvements not recognizable by selection and evaluation in conventional targets.

In addition a field case comprised of 14 wells and 81 stimulation stages is presented demonstrating the potential improvement that can be obtained by using shaped charges designed for maximum performance in shale formations. When comparing wells perforated with improved 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%.

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