Technical Paper: Improved Method for Underbalanced Perforating With Coiled Tubing in the South China Sea

Society: SPE
Paper Number: 113698
Presentation Date: 2008
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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.