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.
Testing Setup and Procedure
Because API RP 19B lacks specific guidelines for multitubular systems (although it is currently being reviewed to establish procedures for testing multiple tubulars), the operator and service provider developed a modified procedure following the general recommendations of Sections II and IV (SPE 191526).
The program was executed in five primary steps.
Step 1: Finalizing Parameters and Charges
The team analyzed historical data to establish a representative baseline for the testing. Most past jobs used 19⁄16-, 2-, and 2⅜-in. gun systems within 3½×9⅝-in. configurations. Key parameters were standardized: a reservoir unconfined compressive strength (UCS) of 3,000 to 5,000 psi, reservoir pressure of 1,500 psi, overburden stress of 5,000 psi, and wellbore pressure of 1,200 psi.
A critical addition was the eccentricity parameter, which simulated the tubing being offset within the casing—a common scenario in offshore deviated wells. This configuration allowed the team to study the impact of thicker cement sheaths on penetration. The operator selected 10 charge types, with two shots per charge to ensure repeatability, totaling 20 tests.
Step 2: Pre-Test Simulations
Before the physical testing, coupon tests were done to gain understanding of charge performance across multiple tubulars. Also, all the test cases were simulated in a commercially available simulator to obtain downhole performance data and establish a baseline to compare predicted and actual performance.
Key simulation findings included:
- 2-in., 6.5-g charges: Predicted 12- to 15-in. tunnels.
- 2⅜-in., 11-g charges: Predicted about 18-in. tunnels.
- 19⁄16 in., 3.5-g charges: Predicted about 5-in. tunnels.
- Eccentricity: The simulator suggested minimal impact on rock penetration regardless of tubing position.
- Charge type: No significant difference in penetration was predicted between ultradeep-penetrating (UDP) and reactive liner charges of the same weight.
Step 3: Modified Test Setup
The experimental setup was designed to replicate the complex geometry of a cement-packer completion. The perforation jet had to penetrate a tubing plate, a first cement layer (i.e., tubing-casing annulus), a casing plate, and a second cement layer (i.e., casing-borehole annulus) before entering the core.
The core was housed in an elastomer sleeve within a pressure vessel to maintain overburden and pore pressures, while the shaped charge was subjected to wellbore pressure (Fig. 1).
Step 4: Sample and Core Preparation
AISI 4140 steel plates were used to replicate L80 tubing and casing, using specific holders to simulate both centric and eccentric cement sheaths.
For rock targets, Trebgaster and Bentheimer sandstones were selected to represent 3,000- to 5,000-psi reservoirs. After cleaning, oven drying, and vacuum saturation, each core's UCS was verified via the scratch method to ensure consistency (SPE 78157). Simultaneously, cement recipes were cured for up to 3 weeks to match the 2,000- to 3,000-psi strength typically found in field operations. The cement UCS was verified using a crush-test procedure.
Step 5: Test Execution
Testing was conducted in a modified Section IV vessel, where real-time sensors recorded overburden, pore, and wellbore pressures. Each setup replicated the full multitubular completion, including the gun scallop and annular cement layers. Upon detonation, the apparatus was disassembled, and the rock cores were cut in half and analyzed according to API RP 19B Section II standards to measure precise penetration and entry-hole geometry at each interface (Fig. 2).
Key Findings and Recommendations
The testing program provided unique, laboratory-validated insights into perforation performance in complex multitubular environments. The following sections detail these key findings and the resulting strategic recommendations.
Finding 1: Prediction of perforation simulators
The test results revealed that industry-standard simulators significantly over-predict tunnel lengths in multitubular completions. Actual penetration was significantly lower than modeled in all 20 test shots, with differences ranging from 60 to 100%. The 19⁄16-in. charges and charges in eccentric configurations failed to reach the core entirely. Larger 11-g charges showed the least deviation but still underperformed by 60%.
As a recommendation from this testing, the operator now mandates that gun selection and skin calculations for cement-packer jobs align with these modified API RP 19B Section II results rather than on simulations alone. Future designs must incorporate a greater than 50% risk factor to ensure realistic production forecasting.
Finding 2: Poor small charge performance
Tests confirmed that 19⁄16-in. charges are ineffective for multitubular completions. In all cases, the jet terminated at the casing before reaching the core, despite simulators predicting 5-in. of penetration. Based on this result, the operator has now discontinued the use of 19⁄16-in. charges for cement-packer jobs. Strip guns or fragmented guns must be evaluated for small tubulars.
Finding 3: Reactive vs. ultradeep penetrating charges
While reactive charges aim to "self clean" the tunnels, they underperformed deep penetrating charges by over 50% in multitubular setups. Further deliberations on this finding are required.
However, it is possible that the lighter reactive liners used in the charges being tested produce a less-stable jet that struggles with the concentric tubulars. Consequently, the operator will prioritize conventional deep penetrating charges for cement-packer perforation jobs until further data is available.
Finding 4: Impact of eccentricity
Eccentric tubing creates thicker cement sheaths that attenuate jet energy. Only 11-g UDP charges successfully reached the core in eccentric tests; reactive and smaller charges failed entirely. Simulators failed to predict this charge behavior in eccentric cases. The operator now recommends 11-g or larger charges and, where eccentricity is suspected, magnetic orientation combined with higher shot density to ensure reservoir connectivity.
Finding 5: Recommended charges for multitubular perforation cases
Tests showed 2⅜-in., 11-g UDP charges provide the best results, yielding tunnels greater than 6 in. For smaller 2⅞-in. completions, where 11-g guns cannot be deployed, a new 2-in., 8-g UDP outperformed historical 6.5-g versions. Based on these testing results, the operator mandates use of the bigger charges for all cement-packer or similar completions.
Conclusion
This industry-first testing provides lab-validated insights into multitubular perforation performance, addressing simulator inaccuracies for complex configurations and suboptimal charge selection. The findings are now integrated into the operator’s gun selection and design guidelines. The operator’s future plans include reperforating underperforming wells, collaborating with suppliers on specialized gun systems, and expanding testing to other complex environments.
For Further Reading
SPE 78157 Continuous Scratch Testing on Core Allows Effective Calibration of Log-Derived Mechanical Properties for Use in Sanding Prediction Evaluation by R. Suárez-Rivera and J. Stenebråten, TerraTek; and F. Dagrain, Faculté Polytechnique de Mons.
SPE 193964 Perforation Performance Simulation in Complex Multicasing Scenarios by T. Burky; G.G. Craddock and J. Lavery, Halliburton.
SPE 191526 Shaped-Charge Perforation Depth at Full Downhole Conditions: New Understandings by B. Grove and D. Manning, Halliburton Jet Research Center.
SPE 220664 Unlocking Brown Field Opportunities—An Operator’s Insights and Recommendations for Maximizing Shallow-Zone Monetisation Through Rigless Cement Packers by S. Anand; I.S. Husin, B.B. Madon, R.L. Kai; M. Shahnizam, and B. Khairuddin, Petronas.
Saurabh Anand, SPE, is a principal petroleum engineer with more than 18 years of experience in field development, production enhancement, well completions, stimulation, and artificial lift systems across onshore, offshore, and unconventional assets. His career includes operational and technical leadership roles supporting assets in Malaysia, Iraq, Indonesia, Turkmenistan, and India. He is recognized as a Petronas subject-matter expert in stimulation and artificial lift and has authored and coauthored more than 30 SPE technical publications. He holds an MSc in petroleum engineering from Heriot-Watt University and a BTech in petroleum engineering from the Indian School of Mines.
Aisyah Borhan, SPE, is a senior manager currently leading the production-enhancement unit. With 19 years of industry experience, she brings strong technical expertise in production technology and petroleum engineering, including field development planning (FDP), workover, and production surveillance. She is experienced in leading multidisciplinary FDP teams and specialized studies, with hands on involvement in major FDPs, infill drilling, compression projects, and overall production-sharing contracts, and asset management. She has held diverse operational and strategic roles across Malaysia and international assets, including Vietnam, Egypt, and South Sudan, covering brownfield, subsea gas, late life assets, and resource-development portfolios.
Mohd Shahnizam, SPE, holds a BSc degree in petroleum engineering and is a production technologist with over 13 years of experience in production enhancement, field development planning, well optimization, and offshore production operations within the oil and gas industry. He has extensive technical and operational experience supporting offshore assets and reservoir development projects with Petronas across Malaysia fields. Shahnizam’s career includes broad experience in production enhancement (perforation, cement packer, stimulation, etc.), production surveillance, well performance analysis, gas lift optimization, production modelling, field governance, reserves management, and well intervention activities.
Hanaey Ibrahim is currently the DynaEnergetics global technical advisor following 33 years’ experience in operating companies including Gulf of Suez Petroleum Company, American Oil Company, BP, Zakum Development Company, Abu Dhabi National Oil Company, Shell Global, and Petroleum Development of Oman (PDO). He was perforation subject-matter expert with Shell Global for 10 years and with PDO for 8 years. Ibrahim has served at the voting level on the API RP-19B and RP-67 committees since 2011 and RP-19PT since 2018. He also holds the position of the International Safety Director of the International Perforating Forum Committee in Houston. Most recently, during 2020 to 2023, he served as an approved perforation training instructor for 3 API-U perforation training courses.