Deliquification of South Texas Gas Wells Using Corrosion Resistant Coiled Tubing: A 6-Year Case History
- Kelli Lyn Poppenhagen (ConocoPhillips) | Larry Keith Harms (ConocoPhillips Co) | Rock Wilkinson (ConocoPhillips Co) | Don E. Glover (ConocoPhillips Co)
- Document ID
- Society of Petroleum Engineers
- SPE/ICoTA Coiled Tubing and Well Intervention Conference and Exhibition, 23-24 March, The Woodlands, Texas, USA
- Publication Date
- Document Type
- Conference Paper
- 2010. Society of Petroleum Engineers
- 1.6.1 Drilling Operation Management, 2.2.2 Perforating, 4.3.4 Scale, 3 Production and Well Operations, 1.10.1 Drill string components and drilling tools (tubulars, jars, subs, stabilisers, reamers, etc), 3.1.5 Plunger lift, 2.7.1 Completion Fluids, 1.10 Drilling Equipment, 5.8.1 Tight Gas, 4.2.3 Materials and Corrosion, 3.2.2 Downhole intervention and remediation (including wireline and coiled tubing), 3.1 Artificial Lift Systems, 4.1.5 Processing Equipment, 2.4.3 Sand/Solids Control, 4.1.2 Separation and Treating
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Running coiled tubing can be an effective tool to deliquify gas wells, but this practice was discontinued in early 2000 in ConocoPhillips Lobo Field in South Texas because of problems experienced due to CO2 corrosion with standard coiled tubing metallurgy. Since 2004, ConocoPhillips has installed 90 corrosion resistant coiled tubing velocity strings as an alternative to conventional carbon steel coiled tubing. These installations have yielded 5 mmcfd in incremental gas rate and the change to a corrosion resistant metallurgy has drastically reduced the high failure rate and costly workovers that resulted from previous carbon steel installations. Various key learnings including candidate selection criteria and future application recommendations will be presented in addition to representative well types and production profiles. Metallurgy comparisons, post-use inspection findings and full-cycle cost implications will also be presented.
The Lobo Field in South Texas is a mature tight gas field with over 8 TCF produced to date. ConocoPhillips operates 1800 producing gas wells with characteristics that have been reported in previous papers (Harms 2004, Bui 2009).
The average production per well is about 150 MCFD with almost 80% of the wells flowing below the critical liquid unloading rate (Turner 1969, Coleman 1991).
Coiled tubing used for velocity strings to help aid liquid unloading was initiated in South Texas by ConocoPhillips in the late 1980s. By the late 1990s, over 90 coiled tubing installations had been installed in wells in Webb and Zapata Counties, Texas. These were mostly 1-1/4?? OD coiled tubing installed in 2-3/8?? or 2-7/8?? OD tubing or 2-7/8?? to 4-1/2?? OD casing at depths ranging from 6300 to 11,600'. The metallurgy was standard carbon steel used in the coiled tubing industry. A few strings of 1-1/2?? OD coiled tubing were also run during the 1990s.
Results indicated that many installations were successful in achieving gas well unloading and increasing production rates from the wells. Unfortunately, failure rates of the carbon steel were high with over 30 failures identified within 3 to 15 years after installation. CO2 corrosion resulted in holes in the tubing with strings actually parting prior to the well intervention work. In most cases it was evident the coiled tubing failure had probably occurred many months or even years prior to when it was identified by well intervention work. Fishing jobs performed to remove the damaged coil from the failed wells proved costly. Corrosion inhibitor treatment history for the failed coiled tubing strings is unknown prior to about 1998.
In 2004, stainless steel alloy coiled tubing became available (Martin 2003, Martin 2006) that was lower cost than many corrosion resistant alloys prior to that time. ConocoPhillips then reinitiated work to install the lower cost corrosion resistant coiled tubing (CRCT) velocity strings in South Texas candidate wells. This work program has been very successful and the use of CRCT velocity strings as an option to mitigate liquid loading is ongoing.
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