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Development of Sucker Rods for Aggressive Environments

A Cr-Mo-B-Ti low alloyed steel, with a special quenched and tempered heat treatment, was designed. Corrosion fatigue resistance of the new material was evaluated at lab scale. Field tests are being carried out in 26 wells where sucker rods had failed for years.

Product Number: 51317--8944-SG
ISBN: 8944 2017 CP
Author: Martin Buhler
Publication Date: 2017
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Operating conditions for sucker-rods are becoming more aggressive as the water production and the CO2 and H2S presence increase. Additionally due to the increase of the fatigue loads higher mechanical properties are required.Under the combined effect of all those conditions sucker rod failures can take place due to the synergist effect of localized corrosion fatigue corrosion and in some cases the embrittling effect of H2S.Taking this scenario into account the development of a sucker rod with adequate performance in those environments was addressed.The steel composition and the heat treatment conditions are key parameters to optimize the obtained microstructure and the performance in aggressive environments.The first steps of the development were the steel design and the evaluation of the material corrosion fatigue resistance in CO2 y H2S environments at lab scale. Corrosion fatigue machines coupled to autoclaves were used for the testing program. Testing temperature and pressure as well as water chemistry pH and the concentration of the aggressive gases were changed.Considering the obtained results the steel design was optimized. After this optimization process sucker rods and couplings of a Cr-Mo-B-Ti low alloyed steel with a special quenched and tempered heat treatment were industrially produced and evaluated in field tests.The obtained product fulfilled the requirements of API 11B grade D special and additionally presents high toughness.The connection of the sucker rods is a region where corrosion fatigue can preferentially occur due to the mechanical stress conditions. Taking this into account the presented sucker rod design included the use of a premium connection to control stress concentration when the environmental conditions and fatigue loads are highly demanding..Field tests were carried out in wells where sucker rods had experienced a high rate of failure due to environmental attack. A working group was formed with field teams to select the more convenient wells and to prepare a protocol where the procedure for the running of the strings as well as the criteria to evaluate the performance of the tested rods were agreed.This paper presents the development experience from the steel design to the lab and filed tests results.

Key words: sucker rods, corrosion fatigue, H2S, CO2, aggressive environments

Operating conditions for sucker-rods are becoming more aggressive as the water production and the CO2 and H2S presence increase. Additionally due to the increase of the fatigue loads higher mechanical properties are required.Under the combined effect of all those conditions sucker rod failures can take place due to the synergist effect of localized corrosion fatigue corrosion and in some cases the embrittling effect of H2S.Taking this scenario into account the development of a sucker rod with adequate performance in those environments was addressed.The steel composition and the heat treatment conditions are key parameters to optimize the obtained microstructure and the performance in aggressive environments.The first steps of the development were the steel design and the evaluation of the material corrosion fatigue resistance in CO2 y H2S environments at lab scale. Corrosion fatigue machines coupled to autoclaves were used for the testing program. Testing temperature and pressure as well as water chemistry pH and the concentration of the aggressive gases were changed.Considering the obtained results the steel design was optimized. After this optimization process sucker rods and couplings of a Cr-Mo-B-Ti low alloyed steel with a special quenched and tempered heat treatment were industrially produced and evaluated in field tests.The obtained product fulfilled the requirements of API 11B grade D special and additionally presents high toughness.The connection of the sucker rods is a region where corrosion fatigue can preferentially occur due to the mechanical stress conditions. Taking this into account the presented sucker rod design included the use of a premium connection to control stress concentration when the environmental conditions and fatigue loads are highly demanding..Field tests were carried out in wells where sucker rods had experienced a high rate of failure due to environmental attack. A working group was formed with field teams to select the more convenient wells and to prepare a protocol where the procedure for the running of the strings as well as the criteria to evaluate the performance of the tested rods were agreed.This paper presents the development experience from the steel design to the lab and filed tests results.

Key words: sucker rods, corrosion fatigue, H2S, CO2, aggressive environments

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