Multi-zone isolation in complex geology

In the complex subsurface environment of offshore Australia’s Bonaparte Basin, maintaining long-term well integrity while optimizing gas production presented multiple challenges to one of our clients. 

A well drilled in order to maintain/enhance production came with the potential for sustained casing pressure (SCP) in large-diameter casing strings, uncertain depth correlation between closely spaced production zones, and the threat of water ingress from lower formations compromising production efficiency. 

With these layered geological and operational uncertainties, ensuring robust, verifiable isolation throughout the wellbore was critical.  A reliable, expandable barrier system would need to perform across multiple casing and open hole environments, mitigate long-term risks, and allow for efficient future production from the reservoir intervals.

Requirements included:

• B Annulus protection: Risk of sustained casing pressure (SCP) in the 20” casing.
  
  
• Zonal isolation: Thin shale layer separating two production zones (upper and lower) posed risks for crossflow.
  
  
• Water zone isolation: A lower water-bearing zone threatened production from the upper reservoir.

Welltec® proposed a multi-barrier solution using three different metal expandable products, each tailored to the challenges presented in specific well sections:

• 16 WAB: Installed on 13-5/8” casing and expanded into the 20” casing at 868.2 m MD to provide a V0-rated life-of-well (LoW) seal, mitigating SCP risk in the B annulus.
  
  
• 1214 WAI: A 7.5-meter long Welltec® Annular Isolation (WAI) sleeve was deployed on 9-5/8” casing and expanded into the 12-1/4” open hole at 2,339.32 m MD, ensuring zonal isolation between the two production zones, across the thing shale layer. 
  
  
• 812 WAB: Run on a 7” liner and set at 3,068 m MD in the 8-1/2” open hole, the 812WAB effectively isolated the lower water zone, preserving the upper production zone.
  
  

Operation

Each solution/product/packer was deployed and expanded after cement placement and plug bump, with successful pressure tests confirming isolation:

• 16 WAB: Expanded with 4,200 psi after cement bump; simultaneously tested shoe integrity.
   
• 1214 WAI: Cemented and expanded with 5,300 psi; liner hanger set, and tool released. 
  
  
• 812 WAB: Set after cement bump and expanded with 5,300 psi; operation completed without issues.

Had there been any depth issues, the design of the WAI allowed for selective perforation without compromising zonal isolation.  However, all MEPs were successfully run in hole and expanded without issue, reaching target depths as planned—confirmed through caliper log validation.

This deployment represents the first-ever well, anywhere across the globe, to feature three different-sized Welltec metal expandable packers.  A flexible approach and engineering precision enabled successful deployment ensured:

• SCP Mitigation: Long-term annular seal using the 16 WAB.
   
• Zonal isolation: Effective separation of production intervals via the 1214 WAI.
   
• Water control: Isolation of non-productive water-bearing formations via 812 WAB.

Complex completion challenges were resolved without issue and on schedule—demonstrating Welltec’s reliability in delivering high-value isolation solutions.