High-density cesium formate brine for upper completions and well cleanup provided Brunei Shell Petroleum (BSP) with outstanding HSE protection and significant time savings, including elimination of non-productive time (NPT). Effective fluid management kept losses to a minimum over an eight-well campaign, while in-country recycling enabled rapid fluid turnaround to streamline operations, reduce inventory, cut shipping costs and lower environmental impact.
Challenges
To provide effective well control and cleanup of multiple high-pressure wells in a remote location, while minimising operational costs and environmental impact.
Solution
A flexible and cost-effective high-density cesium/potassium formate brine system with in-country reclamation.
Results
Completions ran trouble free with clear time savings across all wells, including no NPT. Fluids were quickly recycled locally to provide operational, financial and environmental benefits.
(424–631 bar)
(14.6–17.4 lb/gal)
Discovered in 1970, the complex Champion oil and gas field is situated 40 kilometres north-northwest of Bandar Seri Begawan, Brunei in water depths of 10 to 45 metres. It is highly compartmentalised and consists of several areas, including Champion West and Champion Deep.
Formate fluids have the upper hand
With BSP’s lower completion strategy incorporating swell packers to isolate zones of interest, it was natural to consider solids-laden oil-based muds (OBMs) or high-density bromide brines for setting upper completions. However, these fluids are unsuitable due to discharge restrictions, high solids content, formation water compatibility and HSE risk.
Building on its successful record of running upper completions in lower pressure wells with sodium/potassium formate brine, BSP selected heavy cesium/potassium formate brine for its high-pressure Champion West and Champion Deep wells.
The solids-free brine from 1.75 to 2.09 g/cm3 (14.6 to 17.4 lb/gal) delivered a minimum 200-psi overbalance to form an effective primary barrier in live-well upper completion runs. This high-density well control barrier allowed BSP to access higher pressured oil and gas zones with confidence, whilst saving time by running upper completions in clear brine. Furthermore, its superior HSE profile eased operations and raised safety and environmental standards across the eight wells.
A versatile solution
Final reservoir pressures were unknown until drilling ceased, giving little time for completion fluid preparation. The versatility of cesium/potassium formate, coupled with local reclamation, meant final density adjustments were carried out quickly, which reduced fluid lead time and eliminated shipping-related NPT.
With cesium formate as the primary well control barrier, there are far fewer slickline packers required, which means upper completions can be run in live wells. Even with typical hole angles in excess of 50° at upper-completion setting depth and temperatures of 90–101°C (194–214°F), solids-free cesium/potassium formate brine delivered the wells quickly with no NPT. In fact, completion time reduced from ten to three days over the campaign, which represents a 70% improvement over competing fluids.
Cesium formate cleans up
Due to a narrow hydrostatic window, BSP also used cesium formate to build two types of spacer volume at the rig site for safety and control purposes during well cleanup. One was a high-viscosity polymer-based laminar-flow push-pill and the second, a wash-pill containing powerful surfactants and mutual solvents to change the well from an oil-wet to a water-wet state and remove OBM residue in preparation for running upper completions. Both pills performed exactly as expected to ensure smooth cleanup of all eight wells.
Keeping it close to home
Sinomine Specialty Fluids’ brine-leasing business model is dependent on effective reclamation of cesium formate. The more brine reclaimed the less the client has to pay. With in-country recycling, reclamation costs and fluid turnaround time are drastically cut. In Brunei, Sinomine partnered with BSP’s fluid services contractor, Halliburton, to reclaim the formate using standard filtration equipment at Halliburton’s local mud plant. Under the supervision of Sinomine engineers, average recovery rates were 98.8% for the completion brine and 85.1% for the cleanup pills, against budgeted recovery rates of 90% and 60% respectively. The completion brine was filtered and ready for reuse after only two days of processing. Recycling the fluid in Brunei reduced environmental impact and saved BSP considerable transportation costs.
Conclusions
High-density cesium/potassium formate brine helped BSP successfully complete and clean up multiple wells faster than competitive fluids, with higher levels of operational effectiveness and lower environmental impact. Key benefits are:
- Stable primary well control on live high-pressure wells for trouble-free upper completions delivered in up to 70% of the time used in earlier operations
- Greater control and safety during cleanup
- Reduced transport and inventory costs with lower environmental impact from effective in-country brine reclamation
- A versatile fluid coupled with in-country facilities mean fluid densities can be adjusted at short notice, which is ideal when final reservoir pressures are unknown before drilling is completed
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