Field Trial to Enhance Open-Hole Coiled Tubing Accessibility with the Use of a Special Coiled Tubing Lubricant

Use of metal-on-metal lubricants is a common way to enhance coiled tubing (CT) accessibility in extended reach (ER) wells. However, there is less data available on the effect of lubricants in open-hole applications. Historically, there is only a laboratory study (Sharma and Silviu 2020) that evaluated the effect of lubricants in an open-hole environment. This paper will discuss methodology and results from a 2-in CT field trial where a special CT metal-on-metal lubricant was utilized inside an open-hole completion to enhance accessibility to perform acid stimulation. The wells have measured depth over 17,000-ft with about 7,000-ft of 6-in open-hole lateral, requiring CT acid stimulation. The open-hole formation type is carbonate with permeability values ranging up to 10 mD. The operator requires CT to reach maximum possible depth, providing maximum coverage for acid stimulation. Proprietary CT software is used to model CT accessibility with sensitivity analysis performed with possible coefficient of frictions (CoF) expected from the laboratory research mentioned earlier. The methodology of applying the special CT lubricant is based on filling the entire well with the lubricant solution to maximize CT accessibility. These field trials were executed in October and November 2022. The plan was to run CT to the maximum possible depth in the absence of lubricant. Upon attaining friction lock, base CoF will be analyzed, and CT will be picked up to a certain depth. Special CT lubricant then will be applied at 2% concentration mixed in fresh water by pumping across the CT tubing annulus and via CT in the open-hole while running inside the hole. The special CT lubricant used in this case study was field proven to provide up 40-60% reduction in metal-on-metal CoF based on previous applications in cased completions. The open-hole effectiveness was predicted and modelled based on previous laboratory studies conducted (Sharma and Silviu 2020), which was observed to be in the range of 20 – 40% reduction in CoF for limestone samples. The actual CoF analyzed on one of the field trials was 17%. Being a first-time application of special CT lubricant in open-hole environment, the methodology and results from this field trial will enable application in open-hole wells with similar formations, globally. With more applications of metal-on-non-metal lubricants, it will provide better understanding to the industry on their behaviors downhole.