Pegaga Development Drilling Operations with PMCD and CDIV Applications

Abstract

This paper describes the implementation of Pressurized Mud Cap Drilling (PMCD) and Casing Downhole Isolation Valve (CDIV) technology for the Pegaga Development Project to mitigate heavy fluid losses, allowing safe and effective drilling operations to reach well TD. The project consists of seven gas producers (deviated wells), drilled using a jack-up rig from a 10-slot wellhead deck. This paper also describes the planning and operational challenges met to ensure the smooth application of PMCD, starting with selection of the rig and supply vessels, challenges related to adverse weather conditions, long distances between the supply base and drilling location, sufficient mud tank capacity, continuous supply of Light Annular Mud (LAM) for PMCD operations and pandemic related personnel movement restrictions. A continuous learning process was applied for the drilling team where challenges experienced in drilling the first well in PMCD mode and lessons learned were captured and applied to the subsequent wells to improve drilling results. A comprehensive decision tree was established and refined to help the offshore team to make quick decisions when needed to switch to PMCD mode. The Pegaga gas field is located in Block SK320 in the Central Luconia Province, off the coast of Sarawak, offshore Malaysia. The main reservoir is a Pinnacle Carbonate reservoir, which is made up of vugular/karstified carbonates that are likely to cause severe or total losses. The top-hole sections for all seven wells were batched drilled before the PMCD system was rigged up prior to commencing the 12-1/4" intermediate and 8-1/2" reservoir hole sections. The 12-1/4" sections were drilled to above the target gas reservoir carbonate formations, with the PMCD system on standby in case the carbonate formations and severe losses were encountered shallower than prognosed. A single 9-5/8" CDIV (NACE standard) was run with the 9-5/8" × 10-3/4" casing string and permanently set (cemented) in the 12-1/4" open hole, which was the first time this had been done in Malaysia. The CDIVs were set in the open hole to reduce the potential volume of gas below the CDIV and reduce the mud volume required for tripping in PMCD conditions, while increasing the safety and efficiency of PMCD operations. Seven wells were drilled to TD, five in PMCD mode, two conventionally. The lower and upper completions were run and set on six wells, with four of the lower completions run and set in PMCD mode. The CDIV was used to isolate the open hole for tripping out the BHA and running in the lower completion on two of the PMCD wells, while the other three used the top kill method.