RIASSUNTO
Abstract
Qatargas North Field wells are typically 7 inch monobore medium to high deviation wells and are designed to handle high pressure sour gas containing of H2S and CO2. An extensive rigless well intervention program is carried out with 0.23 inch electric line and with 0.125 inch slickline for data acquisition, and for other downhole wireline jobs.
During a rigless PLT operation with 0.23 inch e-line, an accidental closure of the TRSCSSV resulted in cutting of the e-line. This necessitated a rigless heavy duty wireline intervention resulting in a successful, safe and a cost effective fishing operation in recovering 11,414 ft of 0.23 inch braided e-line.
This paper describes the approach and the technique applied in the fishing operation considering the limitations of a rigless operation. It also outlines the extensive workshop trials carried out during the preparatory phase for developing an acceptable double block and bleed barrier arrangement on the PCE for a safe well intervention. It also describes the planning considerations, the procedures developed, the high level Risk Assessment carried out, and the elaborate Load Assessment Study for working with a 90 ft mast and 0.23 inch braided line on a remote un-manned offshore platform.
Introduction:
Qatargas North Field is located offshore, northeast of Qatar in the Arabian Gulf and is the world's largest non-associated gas field. The sour, slightly over-pressured natural gas is contained in the Khuff carbonate formation. Majority of the offshore wells are 7 inch monobore design completed with 7 inch CRA tubing and liner sections. Wells deviations range from vertical to about 70 degrees.
An extensive rigless e-line program is carried out for data acquisition. This comprises of baseline logging program carried out just after PST, followed by a surveillance logging program carried out at a specified interval to study the changes in the reservoir, production and well parameters. The logging program generally comprises of production logging & pressure build-up (PLT-PBU), reservoir saturation survey (RST), and electromagnetic imaging survey (EMIT) and PS Platform Multifinger Imaging Survey (PMIT). The surveys are conducted in shut-in condition as well as in flowing condition at different rates. A drift run is generally conducted prior to any of these intervention jobs to ensure there is no obstruction inside the tubing or casing.
A 70 ft mast is used to rig up the required lengths of lubricators and the Pressure Control equipment. The wells are vertically equipped with a manual Swab Valve (SV), a hydraulically controlled Upper Master Valve (UMV), and a manual Lower Master Valve (LMV). A big bore tubing retrievable surface controlled sub-surface safety valve (TRSCSSV) is a part of the completion. During the well intervention jobs, the hydraulic controls for TRSCSSV and UMV are switched over to a Wireline Panel. This Panel has two remote Emergency Shut Down (ESD) system located at two strategic places to close TRSCSSV and UMV in case of exigency, when approach to the Wireline Panel is not possible.