Monobore wells have been a staple of the oil and gas industry for many years due to their simplicity and flexibility for common intervention techniques. One downside comes when a producing interval or intervals start depleting, compromising lift performance. Velocity strings have been successfully deployed in monobore gas wells to improve lift performance. Retrofitting oil wells, such as presented here, with a gas lift string can significantly enhance the productive life of a well. Performing this retrofit rig less offers additional opportunities in maintaining field production from more marginal wells not especially suited to full work over operations.
Retrofitting completions rig less presents a number of technical and operational challenges. Gas lift utilizing a coiled tubing (CT) dip tube and the associated valve sizing, setting depths, and lift gas optimization are discussed in the context of the reservoir conditions and well parameters. The mechanical aspects associated with the hanging of the dip tube, thermal effects, and corrosion inhibition present specific challenges similar to conventional completions, but with the complexity of deployment under live well conditions.
Well control aspects associated with deployment, retrieval, and production are important considerations both technically and operationally. The Pressure Control Equipment (PCE) stack must be suited to the dip tube completion components, while providing effective barriers to secure well during deployment and emergency scenarios. The ability to connect, test, and deploy several gas lift mandrels suitably spaced with coil tubing "tubing" are operationally challenging. The deployment aspects are thus fundamental to the success of the concept.
During a job in Thailand, a corrosive, high-CO2, nonproducing monobore oil well was revived using a corrosion-resistant CT dip-tube gas lift completion. The project successfully restored well production from zero flow to 900 B/D. Conceptual design, tool selections, key technical decisions, and operational aspects are discussed.