In the Sabriyah oil field, one of the largest in northern Kuwait, water production has become an increasing problem for Kuwait Oil Company (KOC). In some wells this problem has drastically reduced oil production. Most wells in this field produce oil from multiple layers open to production in limestone reservoirs. This simultaneous
production from frequently numerous intervals creates a complex challenge to any water shutoff solution. Adding to these difficulties are the non-productive time because of downhole tool reliability, harsh high-pressure/high-temperature (HP/HT) downhole environment, and well-completion configurations imposing considerable restrictions on tool size and packer inflation ratios.
The use of through-tubing inflatable packers conveyed with coiled tubing (CT) became an attractive alternative to applications needing a workover rig for zonal isolations where accurate, selective fluid placement is critical for job success. Schlumberger teamed up with KOC to implement a new solution for this water production problem.
KOC and service company team selected and applied a through-tubing inflatable packer solution to achieve a successful zonal isolation and water shutoff in a pilot Sabriyah producing well. The solution, in which two packers were used to straddle the target zone, employed the CoilFLATE HPHT system. It marked the first use of this technology in Kuwait.
The pilot project resulted in a large reduction in water production, while proving the reliability of this system and providing a safe and cost-efficient solution to KOC. This application became the preferred solution to the water production problems throughout the Sabriyah field.
Well intervention tool design
The new downhole isolation system is a single, through-tubing inflatable anchoring packer designed to extend critical through-tubing zonal isolation capability to previously inaccessible, chemically harsh and high-temperature environments. Robust component design enables this system to operate at downhole temperatures up to 375°F (190°C) and perform under large pressure differentials and at high inflation ratios. With an inflation ratio of 3 to 1 while maintaining 2,000 psi differential pressure across the packer elements, it is unique among inflatable packer systems on the market. The system eliminates the need for a workover rig, as it can be run on CT or jointed pipe into vertical, deviated or horizontal well bores. Another major economic benefit is the ability to perform remedial operations in live well conditions.
The system enables temporary isolation of wellbore sections or permanent abandonment of selected zones. Chemically resistant sealing components make this technology especially suited for selective placement of different treating fluids, such as those required for water shut-off, acid stimulation and other fluid systems.
Sabriyah shutoff solution
The first treated well was producing at around 2,100 b/d of fluids but had experienced a water-cut increase that had grown to 36% in 2003 from a 10% level only 2 years earlier.
The success of the treatment depended on accurate, selective fluid placement in a zone requiring isolation between two oil-producing intervals, all in an HP/HT environment. The selected tool string and packer elements needed to be run through the production tubing minimum inside diameter, while providing an inflation ratio to seal against the large inside diameter of the production casing.
A dedicated, computer-based optimization program was used to accurately predict hydraulic conditions, calculate the inflation pressure and maximize the packer's performance. A unique, real-time depth-correlation system was employed as part of the bottomhole assembly to provide accurate depth measurements.
The cornerstone of the solution was the setting of two single inflatable packers to straddle and isolate the middle water-producing zone using a special cement slurry. The packers were then deflated and removed.
Results and future impact
The immediate treatment highlights included:
• A 70% water-cut reduction in the target zone, confirmed by post-job wireline logs;
• Successful implementation of the new solution allowed the use of this application in other Sabriyah field wells; and
• Substantial operation cost savings achieved by avoiding the need to use a workover rig and pull production tubing.
The post-treatment production data obtained from this well provided valuable information for KOC in their efforts to reduce the water production in the Sabriyah field. Furthermore, the successful application proved to be a reliable alternative to workover-rig techniques for numerous types of well interventions requiring through-tubing zonal isolation.
These include water and gas shut-offs, acid stimulations and other chemical treatments, and zonal production evaluations.
Conclusion
Use of the through-tubing inflatable packer technology enabled KOC to isolate a rapidly growing water-cut zone between oil intervals in a well in northern Kuwait's Sabriyah field. This successful, complex HP/HT isolation enabled a shutoff treatment reducing water production by 70% in the target interval. In addition, the process achieved six-figure savings by eliminating the need for a work-over rig and removal of the production string. More broadly, the achievement has expanded KOC's options for a variety of potential well-intervention needs, providing solutions that avoid the complexity and expense of traditional workover operations.

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