The use of coiled tubing (CT) in wells containing hydrogen sulfide gas (H2S) has associated problems because of the potential for sulfide stress cracking (SSC) of the CT material. Carbon dioxide (CO2) can also contribute to general corrosion or intensify any H2S-related corrosion because of chemical reactions resulting in acid. However, with the right precautions, equipment, and procedures, this type of operation can be carried out safely and successfully.
The various problems associated with working with CT in H2S and CO2 wells are discussed and a general best practice taken from locations working regularly with H2S and CO2 is presented. This paper shows the equipment, chemical inhibitor, quantity and method of inhibitor application, and other precautions taken to carry out the work safely and successfully. An alternative approach is also highlighted for some situations whereby any H2S is bullheaded into the well before coiled-tubing intervention. This alternative approach avoids any contact of H2S with CT to prevent corrosion. A number of case histories are shown for different H2S and/or CO2 locations around the world, which detail the type of operations, quantity of H2S and CO2, procedures used, frequency of operations, and the overall success of these methods in ongoing operations.
This paper presents a review of methods and equipment currently being used around the world to work in potentially corrosive and dangerous H2S and/or CO2 wells.