Perforations are required to establish effective hydraulic communication between the wellbore and the surrounding formation. An often considered key attribute is to achieve maximum penetration, providing an effective flow path by extending through the near-wellbore damaged region, penetrating undamaged reservoir beyond.
The challenge is always to design the perforation system to maximise flow efficiency. In the majority of instances deeper penetration is a key design parameter, but penetration is affected not only by the shaped charge, but also critically by rock strength and stress effects. Therefore, perhaps of greater importance are perforations that are both clean and less damaged, providing a more effective connection to the reservoir, whilst maintaining maximum penetration.
Much has been done to enhance perforation efficiency through the development of dynamic underbalance systems and, where appropriate, the application of reactive charge technology. However, little has been done to explore possible benefits resulting from significant changes in perforation geometry, beyond conventional premium system design.
This paper provides a detailed insight into a comprehensive research and development study, following the conclusions obtained for a new convergent perforation system. The system is optimised through harnessed shock-wave energy, achieved by focusing charge groups at a fixed point within the reservoir.
A rigorous section IV test programme was conducted to evaluate the potential flow performance enhancement for such a perforation system. Lab results highlighted a >15% increase in the tested productivity ratio, compared directly to standard system shots, executed under identical conditions.
API-19b Section IV test data validation was carried out using Computation Fluid Dynamics (CFD). A key objective was to match the lab flow performance data, replicating boundary conditions and perforation geometry within each model. CFD modelling enabled further detailed assessment of key relevant parameters influencing improved flow performance, i.e. crushed zone damage and improved channel geometry effects.
Furthermore, CFD was used effectively to model a series of short radial well models, using each matched perforation geometry, comparing the convergent perforation system against the standard HSD system. These models provided further evaluation of key performance influencing factors such as shot arrangement and phasing effects.
In conclusion, the study has shown, through various levels of verification, adopting a convergent perforation approach to gun system design, can enhance perforation flow efficiency through geometry improvement. CFD modelling also showing, within a radial wellbore arrangement, such a system is capable of improving flow performance by as much as 50%.