Coiled-Tubing Perforation and Zonal Isolation in Harsh Wellbore Conditions

Abstract

Coiled tubing has been widely used worldwide to perform perforating and zonal isolation operation due to the ability in intervening highly deviated and long section of horizontal wells under live condition, where slickline and E-line have difficulties. This paper presents case history of coiled tubing perforating and zonal isolation evolution in infill well at Resak field, one of the gas field operated by Malaysia National E&P Company, Petronas Carigali Sdn Bhd. Since the beginning of Resak Field production, coiled tubing has been used to perforate numbers of infill wells with low success ratio. The reservoir characteristics with high formation pressure and BHT followed by high CO2, H2S production and improper well clean up contributed in the increase of operational risks and challenges. Several failures reported in the past was carefully analyzed to determine the actual root cause prior to coming up with the proper job design and operational procedures. CTU with 1.5″ CT reel was used to convey 140 ft of 2–7/8″ gun due to crane and platform deck loading limitation. The small CT size and large gun conveyance required extra precaution since the presence of gun shock during perforation may affect the CT integrity. Therefore supporting perforating software was run in advanced to optimize gun selection where both operational risks and production objectives were taken into consideration. Coiled tubing forces simulation was also used to determine the ability of the gun assemblies to be safely conveyed into the target sands. In addition to that, one of the unique features from the gun assemblies was the selection of electronic firing head over a conventional or standard drop ball mechanism. This tool utilized coded sequence created fromvariation of surface pump rate to generate its firing command, providing reliable gun activation where as the drop ball mechanism in the past was found to have some operational difficulties. Lastly, this paper also mentions the proper selection of zonal isolation method that can withstand the wellbore condition, providing adequate isolation whilst able to be retrieved for future production requirements. The result of those engineering studies managed to overcome the operational failures in the past and at the same time was able to meet the production objective. Project Result After performing the coiled tubing operation by isolating J10.2 with inflatable bridge plug and perforating J10.1 with deep penetration gun, the well managed to be produced at 22.7 MMSCF/D & stabilized at 48 MMCSF/D (23 % choke size) with total gain of 41MMSCF/D which was higher than the expected gain of 35 MMSCF/day (Figure 1). Currently the well is the highest producing well in Resak field with stable production at 49.8 MMSCCF/D. Introduction This gas producer well was drilled in March 2004 and completed in 4–1/2″ monobore completion by penetrating the reservoir of J-10.2 & J-10.1, with J-10.2 being perforated leaving J-10.1 un-perforated (Figure 2). Based on the log analysis, J-10.2 sand has 6.8m TVD net pay with average effective porosity of 15% and permeability of 26md followed by water saturation of 37.7%. After 2 years of production, gas rates started to decline from 18 MMSCF/D down to 7 MMSCF/D with gradual increase in water gas ratio up to 10 BBL/MMSCF. This phenomenon was also supported by adjacent well performance which was shut in due to high water production. Nitrogen lift operation was performed on adjacent wells, but failed to sustain the production. Despite the decline trend, remaining gas reserves are still attractive and having potential to be produced in the future at 85% recovery factor.

An Evolved Approach to Performing Underbalanced Perforating Interventions in Mexico: A Step-Change Improvement in Efficiency, Reliability, and Safety

“…CT not only provides an economical solution, but it also allows intervening the many highly deviated and horizontal wells of the region. Perforating with CT is typically done by using perforating heads that are actuated either hydraulically (Omar et al 2006;Molero et al 2007)-when creating a pressure pulse signature by varying the injection rate through the CT string, which remotely activates an electronic firing head-or mechanically-by displacing a ball through the tubing to create a pressure differential across the perforating head once the ball reached its seat at the bottomhole assembly (BHA). Whichever the method, a fluid is always required to detonate the charges downhole.…”