Coiled Tubing Material Selection for Velocity Strings in Sour Brine Service
Why this work is in the frame
A frame that forgets how it found something cannot be audited. These are the routes that admitted this work.
Bibliographic record
Abstract
Abstract Installing coiled tubing velocity strings is a common deliquification strategy used in gas wells in which the flowrate has dropped below the critical rate required to remove produced liquids from the well. Initially in Shell’s Groundbirch unconventional gas development, a standard carbon steel coiled tubing grade was used for these applications. Due to elevated levels of chlorides, carbon dioxide and in some cases H2S, a long-term inhibition schedule was then needed to minimize corrosion. Recently, however, a special CRA material has been employed, that Shell had previously helped develop for subsea applications (Li et al, 2002), which has eliminated the need for costly long term inhibition. This paper outlines the selection process and implementation of this material change. Standard 13Cr alloys are well known in the industry but could not be used in the Groundbirch fields due to the high chlorides levels of the produced water as well as H2S levels sometimes above NACE thresholds. On this basis, higher chromium coiled tubing materials were evaluated based on their ability to resist corrosion, sulphide and chloride stress cracking, as well as their mechanical properties. A fit for purpose material testing program was used, combining standard NACE test protocols with unconventional specimen shapes and crevice corrosion assessments in simulated well environments. Factors such as the direction of primary loading stresses, mechanical deformation during installation, as well as coiled tubing manufacturing characteristics such as the longitudinal seam, bias welds, and orbital (butt) welds were also considered. From this fit-for-purpose testing, not only was the preferred corrosion-resistant material, Nitronic 19D duplex-steel, selected for the coiled tubing strings, but an operating envelope has been developed for it, as well as manufacturing specifications have been defined for the strings for optimum performance. Installation guidelines to reduce the mechanical damage inflicted on the strings have also been created. Although the campaign startup was delayed due to manufacturing issues, once the campaign did start, the installations have been efficient, with future campaigns planned. By selecting a single, robust material grade for CT Velocity String material for a variety of potential conditions (high salinity, CO2, H2S), and also developing some guidelines for their use, installations can be done efficiently in Groundbirch in large campaigns, with long term cost savings from eliminating the need for continuous inhibition. Furthermore, the long term integrity of the strings should benefit, ultimately leading to longer completion life, less production deferment, and less intervention issues due to corroded and failed CT strings.
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Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from it