Improved Method for Underbalanced Perforating With Coiled Tubing in the South China Sea
- Graeme Rae (Talisman Malaysia Ltd) | Mohd Bakri Yusof (Talisman Malaysia Ltd) | Juanih Ghani (Helix RDS Malaysia Sdn Bhd) | Shahril Ridzauddin Mohd Mokhtar (Dowell Schlumberger) | Jock Munro
- Document ID
- Society of Petroleum Engineers
- SPE/ICoTA Coiled Tubing and Well Intervention Conference and Exhibition, 1-2 April, The Woodlands, Texas, USA
- Publication Date
- Document Type
- Conference Paper
- 2008. Society of Petroleum Engineers
- 4.2.3 Materials and Corrosion, 1.6 Drilling Operations, 1.6.9 Coring, Fishing, 4.1.5 Processing Equipment, 4.1.2 Separation and Treating, 2.2.2 Perforating, 3 Production and Well Operations, 5.6.1 Open hole/cased hole log analysis, 1.10 Drilling Equipment
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In Malaysia, coiled tubing (CT) conveyance is used to optimize underbalanced perforating, especially for rig-related operations. Well trajectory, temperatures and fluids can create uncertainties on both depth control, and the accuracy of hydrostatic cushion before firing the guns. The conventional method of correlating the CT on depth involves two CT runs the first to run a memory gamma ray (GR) and casing collar locator (CCL) and the second run for the actual perforation. The underbalanced condition calculated based on wellbore fluid displacement is often deemed insufficient to create effective cleanup of the perforations.
This paper outlines a solution to these challenges. For a CT perforation campaign in the South China Sea, a CT string equipped with fiber optic cable inside was used, coupled with a bottomhole assembly capable of measuring both bottomhole temperature, internal and external CT pressure, and in addition casing collar locator. The primary objective of the job was to ensure that the perforation was performed with maximum under-balance but not exceeding a safe drawdown on the formation and risking collapse of the perforation tunnels. With 1,000 psi initial underbalance, to remove perforation damage the well would then remain balanced to avoid fluid invasion on the new perforations. The secondary objective was to avoid an additional CT run for correlation, thus saving rig time.
The objectives were met and this new approach to coiled tubing operations was found to be effective. Not only was there significant saving of rig time, the wells performed superior to existing wells and were brought into production sooner than planned. This technology has elevated CT standard operation onto a higher level in Malaysia.
Talisman Malaysia Ltd. (TML) operates more than 130 wells in South China Sea. Previous perforating techniques on these oil, gas producers and water injectors did not produce to their full potential. Studies indicated that the main cause for the high skins was the perforation damage and/or the overbalanced condition inducing losses of damaging fluid to the formation.
Coiled tubing has been used as a conveyer to perform underbalance perforating for many years. CT allows:
- Ability to displace the wellbore fluid with nitrogen gas to create the underbalance required
- Faster running in hole and pulling out hole compared to drill pipe
- Cheaper daily rate compared to perforating with the rig.
There are two conventional types of CT perforation methods;
- Wired CT, in which an electric cable will be injected into the CT reel.
- Standard CT, in which a pressure activated firing mechanism will be used as part of the toolstring
Although these conventional methods are deemed efficient in the industry, incidents that have a high impact on cost deliverability include
- Perforating off depth due to inaccurate depth control
- Guns not fired due to pressure discrepancies, discovered only after CT was retrieved to surface with an additional run being required.
- Well does not perform as expected due to insufficient underbalance condition.
- Guns sanded in due to higher than expected underbalance
- Premature firing of guns due to pressure surges.
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