Abstract

During a recent revisit (October 1999) to Duyong Field, Offshore Peninsular Malaysia, the operator Petronas Carigali Sdn Bhd (PCSB) was able to drill through the troublesome Terengganu Shale and successfully completed a well in the productive Tapis Gas Sands. The well, Duyong A-4 STR4D (DYA-4STR4D) was drilled and completed under approved budget with minimal lost time. DYA-4STR4D was the first 3–1/2" monobore completion by PCSB in Peninsular Malaysia, paving the way for future application of the technology especially for the development of marginal oil and gas fields. This paper will summarize the design, planning and execution of this milestone achievement for PCSB.

Background

Duyong Gas Field located about 236 km southeast of Kuala Terengganu in Block PM-12 and was discovered by Conoco in 1970. The field development was started in 1983 by PCSB and a total of 13 wells were drilled by 1985 from the 3 platforms; DYDP-A, B and C using the jack-up rig Parameswara in water depths of about 76-78 meters (Fig.1, 2, 3). All these wells were completed in the "S" reservoir sands located between 1650 to 1827 mss.

Out of these 13 wells, well DY-A4 was initially planned to develop the "T" reservoir sands which require penetrating the approximately 250 meters thick highly reactive Terengganu Shale overlying it. This well was drilled down to the top of the Terengganu Shale without problems and the 9-5/8" production casing was set and cemented casing-off the "S" sands. Several attempts were made below the 9-5/8" casing to pass the Terengganu Shale failed. Severe bore hole problems were encountered resulting the well to be sidetracked three times without success. A water based sea water polymer mud used failed to inhibit the Terengganu Shale. Finally, further drilling into the "T" sands was terminated and the well was completed as a single gas producer in the "S" sands. A new 9-5/8 inches casing string had to be run inside a sidetrack hole due to a leak in the old casing string resulting from extended drilling below it.

In 1995, during the Revisit-I Campaign, another attempt was made to develop the "T" sands from a new well DY-A7 drilled from the Duyong-A platform. This well also failed to be drilled to the objective "T" sands. This time the failure was due to the differential pipe sticking problems encountered in the depleted "S" sands which was further aggravated by the higher equivalent mud weight required to drill through the shallower "R" sands ("R" sands are being produced from the Duyong B & C platforms). Like in the DY-A4 well, a water based mud was used. This well failed even to penetrate the Terengganu Shale. After premature running of the 13–3/8" casing set at shallower depth, the well was plugged and abandoned. Further attempts to make progress in drilling to the "S" sands failed, due to the repeated differential pipe stuck problems encountered.

With potential viable reserves still remaining untapped at this location, a third attempt was planned to develop the "T" sands during the Revisit-II Campaign from Duyong-A platform in Q4, 1999. For this Revisit-II campaign, the jack-up rig Harvey H. Ward owned and operated by R & B Falcon was contracted for the project.

Operation Planning
Side-scan Sonar.

Suspecting poor primary cementing as observed from the high annuli pressures in all the wells, a shallow seismic survey was conducted prior to the Revisit - I campaign in 1993 / 1994. The results showed severe gas migration resulting from channeling effects in most of the shallow unconsolidated sandy layers beneath the platforms to be gas charged. For safety in using the jack-up rig, a shallow seismic survey was run again prior to this campaign. As part of the procedure in positioning a jack-up at a platform, a ROV survey will be conducted to check for any seabed construction debris. An opportunity will be taken to check for any gas breaking to the seabed which also indicated no active gas bubbling at the seabed.

Side-scan Sonar.

Suspecting poor primary cementing as observed from the high annuli pressures in all the wells, a shallow seismic survey was conducted prior to the Revisit - I campaign in 1993 / 1994. The results showed severe gas migration resulting from channeling effects in most of the shallow unconsolidated sandy layers beneath the platforms to be gas charged. For safety in using the jack-up rig, a shallow seismic survey was run again prior to this campaign. As part of the procedure in positioning a jack-up at a platform, a ROV survey will be conducted to check for any seabed construction debris. An opportunity will be taken to check for any gas breaking to the seabed which also indicated no active gas bubbling at the seabed.

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