Evolution of Ball/Baffle Milling in Karachaganak Field Using Tractor Milling Technology from 2011 to Date

Abstract

New wells in KPO are completed as multistage frac completions utilizing up to ten stimulation sleeves activated by a ball landed in a respective seat (called a baffle) installed inside the sleeves. The objective since the beginning was to mill balls and baffles in the horizontal section improving the safety of the operation while minimizing volume of fluid injected, execution time, costs, and clean-up time. The initial approach was to use coiled tubing. Using coil to mill balls and baffles was not optimal, as the milling performances were difficult to replicate well after well. Additionally a significant amount of fluid was injected into formation together with some debris causing formation damage and making clean-up a long and costly process. An alternative option of milling utilizing robotic technologies was investigated as a viable solution for improving our performance. Therefore, the experience gained by KPO on milling with tractor in multistage frac completion is unique worldwide, and did add a lot of value to the wells delivered to production. This paper describes the evolution and modification done to tractor milling approach, particularly: Yard tests performed before implementing the operation in the field. No field deployment application took place before yard test outcomes were completely satisfactory.Results of the tests and modifications done to the tools as a result of the tests performed in the yard.Performance during field job execution, lessons learnt during each application, and how those lessons learnt influenced design modification of the tools and milling methodology. Thanks to a close collaboration established between KPO and Welltec, all objectives were accomplished with repeatable performance. Recently, up to nine balls and baffles corresponding to the entire horizontal section have been milled with a tangible benefit in terms of production, reducing clean-up time and emissions and improving safety. Even though the initial target was achieved, KPO believes there is still room for improvement and optimization. This will be done in the near future following further dedicated yard tests with positive results.