Abstract
The growing demand for maximizing hydrocarbon recovery from challenging reservoirs has a major influence on propelling the coiled tubing (CT) market to provide effective rigless intervention solutions. Among those challenges, the combination of acid stimulation of extremely sour wells in addition to high reservoir temperature while protecting the coiled tubing against corrosion and sulfide cracking is tenuous balance of design. This paper examines guidelines for successful implementation of coiled tubing intervention in extreme sour environment as high as 40% mol of H2S and 11% mol of CO2, with reservoir pressure of 6,000 psi and a bottomhole temperature of approximately 300°F while controlling risks of failure due to acid and H2S corrosions.
Those conditions triggered a combination of a custom-fit engineered pipe management and chemical protection designs provides a comprehensive precedent to operate CT in a harsh sour environment while maximizing coil life. Engineered pipe management provides a continuous update to the CT operational envelope limit, monitor wall thickness, pipe deformation characterization. Additionally, evaluate the pipe integrity by identifying the pipe anomalies in compliance with API RP 5C8 such as pitting, deformation and corrosion damage throughout the job. The analysis of mass data of CT pipe integrity parameters enables monitor coil life in a real time and update to the CT operating envelope limit, accordingly, identifies a new defect occurs after a series of jobs and support pro-active decisions. Chemical protection with unique scavengers and appropriate fatigue derating to inhibit the corrosive environment in combination with appropriate engineered pipe management is primarily evaluated in this study. The paper summarizes the application of improvised practices with continuous monitoring of defect evolution throughout the CT string's service life can ensure pipe reliability and enable making the required changes to CT operating envelope on the fly while controlling risks of tubing failures. Case histories will be discussed to emphasize the guidelines practices that should be considered for establishing the best protection and yield lessons for design and execution for CT intervention for similar unforgiving environments
