Case Study: An Industry-First Comprehensive Perforation-Testing Program To Evaluate Perforation-Charge Performance Across Multiple Tubulars
Saurabh Anand, Aisyah Borhan, Mohd Shahnizam, Hanaey Ibrahim_
Perforation tunnel geometry is critical to well deliverability. While downhole performance is traditionally predicted using commercial simulators based on API RP 19B Section I, the industry is increasingly adopting Section II testing data for more-reliable simulation output. Historically, modified Section II testing has been preferred for complex, nonroutine cases where Section I- and Section II-based standard simulations are not reliable.
The operator manages numerous offshore cement-packer completions, which involve through-tubing perforations across multiple tubulars and cement sheaths. These are typically used for shallower targets where workovers are cost prohibitive. However, these jobs have encountered high failure rates (SPE 220664).
Detailed investigations identified poor perforation performance as one of the primary causes for many such poor-performing wells. Note that the small-diameter charges, which are suitable for 3½-in. and smaller tubing sizes, must penetrate two layers of steel and cement, often resulting in high skin values and, in some cases, failing to establish reservoir communication.
To address this, the operator in this case study, Petronas, conducted modified API RP 19B Section II tests at a specialized facility, replicating the specific downhole completion, reservoir properties, and shaped charge types. A total of 10 charges were evaluated across various tubular and reservoir settings. The resulting data provided significant insights, which have now been integrated into the operator’s gun-selection guidelines to improve future completion success. This pioneering work represents the first exhaustive study to evaluate shaped-charge performance within such complex downhole configurations.
Background
A majority of clastic reservoirs offshore Malaysia consist of interbedded sandstone and shale layers, often requiring dual-string completions. However, even with dual strings, the smaller, shallower reservoirs located above the production packer are often not completed initially. A full workover is rarely economic for these low-reserve zones, hence requiring a cement-packer technique to monetize these zones. This rigless approach uses coiled tubing to place a cement barrier in the annulus, allowing the zone to be perforated through the existing tubing.
Over the past 15 years, the operator has performed many such jobs, but over 70% underperformed, including 30% of jobs that failed to produce at all (SPE 220664).
A 2024 study by the operator identified three main causes:
- Subsurface uncertainty
- Operational execution
- Perforation performance
While new workflows have improved subsurface and execution reliability, achieving robust perforations in cement-packer completions remains a significant technical challenge.
Efficient perforation tunnels must bypass the drilling-damaged zone (i.e., greater than 6 in.) and provide a sufficient entry hole to minimize pressure drops.
While large tubing-conveyed perforating guns easily achieve long tunnel lengths in standard wells, cement-packer completions are limited by small internal diameters, requiring small charges that struggle to penetrate through multiple strings.
Predicting perforation performance in such challenging configurations has been historically difficult (SPE 193964). Commercial simulators, which rely on API RP 19B Section I & Section II data, can be overly optimistic for such cases.
Considering these limitations, modified API RP 19B Section II perforating tests on actual rock under downhole stress and with multiple tubular configurations were planned to obtain realistic data. This case study details how the operator used these specialized tests to optimize gun selection and improve success rates for multitubular cement-packer completions.