We’ve summed up this report below with our top takeaways, along with insights you can apply to your own completion program.
Project Background
Chevron recently began production operations in the Denver-Julesburg (DJ) basin. This is a fairly new venture, so the company was looking to improve the completion design, perforating strategies, and overall productivity of the well. More specifically, they wanted to know whether they’d see better stimulation performance using internally oriented perforating systems, dissolvable versus composite plugs, and varied perforation phasing and orientation.
Chevron used high-resolution acoustic imaging to test the impact of these three variables in three distinct test phases across multiple wells, using a limited-entry completion design:
- Phase 1: Testing the performance of weight bar and internally oriented perforating systems versus standard designs
- Phase 2: Imaging wells isolated with dissolvable and composite plugs
- Phase 3: Assessing the effects of orientation on uniformity index and cluster efficiency
READ MORE: Frac plug forensics: our takeaways from Darkvision’s latest report
Phase 1 - Perforating Phasing
To ensure consistency of shot perforation hole size and plug depth, Chevron completed three wells with perforations at different phases and orientations:
- Well 1: 90° phased perforations (control; company’s standard design)
- Well 2: 0° perforations with weight bars oriented toward the high side
- Well 3: 0° perforations with an internal orientation assembly
Calibration perforations were shot in the heel of each well after stimulation to measure hole size. When these perforations were measured, Chevron found that exit holes were uniform but measured around 0.4 inches on average—larger than the manufacturer-specified diameter of 0.37 inches. This is 20% larger than expected and represents a significant drop in perf friction.
High-resolution acoustic imaging also visualized the plug to show how well it isolated each stage. Well 3 saw the most consistent orientation, with 100% of perforations shot within +/- 45° of the high side.
That said, the three wells also experienced casing damage or breaches at a combined 33% of plug set locations. The wells had poor uniformity and saw either 1) low erosion due to incomplete isolation, or 2) high erosion (over 300% in some cases) and casing damage in areas with full isolation. Results from this phase weren’t conclusive, so Chevron moved on to Phase 2 to assess plug performance.
Phase 2 - Plug Type
Chevron suspected that their dissolvable plugs weren’t maintaining downhole integrity and were allowing proppant erosion. The company tested a four-well pad, using dissolvable plugs in two wells and composite plugs in the other two wells. These tests found that composite plugs saw 6% average uplift in the pressure-normalized rate, meaning stage isolation improved with this plug type.
Based on this phase data, Chevron completed an analysis of over 3,000 composite plugs in 75 different wells, using seven different designs. For these composite plugs, the company noted pressure-normalized rates that were 5–10% higher than the rates for stages that used dissolvable plugs. While total cleanout time increased by roughly 4 minutes per stage with the highest-performing plugs, the increase didn’t have a major impact on the completion schedule.
Chevron also assessed two of the wells in this phase using acoustic imaging. This imaging showed heel-side stage bias, likely due to perforation holes that were larger than expected. Collar-shot perforations also had a tendency to grow into outlier perforations, increasing erosion and affecting the well’s uniformity index.
READ MORE: Why we changed our minds about dissolvable plugs
Phase 3 - Perforation Orientation
In Phase 3, three perforation orientations were assessed in a single well to see which orientation saw the highest uniformity and cluster efficiency. This well had a unique design where the cluster design changed from one orientation to another (moving from 90° non-oriented to 0° to 120/240°) every five stages, which made it ideal for this assessment.
Chevron deployed designs using an internal orienting perforating gun. Here’s what they found for each stage:
- Non-oriented: 62% cluster efficiency, 0.73/1 uniformity index
- 0° oriented: 78% cluster efficiency, 0.80/1 uniformity index
- 120°/240° oriented: 62% cluster efficiency, 0.67/1 uniformity index
Top Takeaways for Industry
- Systematically testing design changes within a well can lead to major efficiency improvements. Just make sure you test one factor at a time so you know what worked and what didn’t.
- Chevron noted major increases in cluster efficiency (+15%) and uniformity index (+13%) as a result of using the internal orienting perforating gun system.
- New assessment techniques make it easier to optimize horizontal well completion designs and stimulation techniques. This is improving efficiency and ensuring even stage stimulation in longer reservoir laterals.
- 0° oriented perforations were more uniform and saw less erosion than the non-oriented and 120°/240° oriented designs.
- Composite plugs tend to perform much better than dissolvable plugs in terms of stage isolation, downhole integrity, uniformity, and production rates. However, results can vary by well, depending on the specific plug used.
- Composite plugs can increase per-stage cleanout time by around four minutes per plug. But given improved performance and production, this time increase shouldn’t be a deal-breaker if you’re looking to switch from dissolvable to composite plugs. (Personally, we recommend switching to PurpleSeal™ frac plugs.)
- Identifying the locations where frac plugs are failing can help uncover failure rates for specific frac plug types and models. This makes it easier to discontinue low-performing products and improve downhole plug performance.
Want to add the industry’s favorite perf gun to your completion? Contact us today and learn more about PinPoint self-orienting perforating guns.
