Combination of Light Annular-Mud Drilling and Downhole Isolation Valve for Drilling in Fractured Gas Reservoir, A Case Study

Abstract

The South Sumatra Field in Indonesia produces from a high deliverability gas reservoir with the gas rate of each well around 50 to 200 MMSCFD. The primary target is the fractured network present in the Pre- tertiary Granite/Andesite while the secondary target is the Tertiary carbonate. In the past decade, Light Annular Mud Cap Drilling (LAMCD) is one of Manage Pressure Drilling (MPD) methods that has been frequently applied to drill in the surrounding areas of South Sumatra's oil and gas fields. The LAMCD method allows drilling to continue despite experiencing total loss of circulation in the fractured reservoir. Sacrificial fluid, usually fresh water, is injected down into the wellbore through the drill pipe. Viscous fluid with the density slightly lower than the pore pressure is injected intermittently into the annulus. The challenge occurs prior to tripping out where the well needs to be balanced. The killing operation contributes additional cost from the lost circulation materials, additional operation days or non-productive time (NPT) and inflicts damage into the reservoir due to the injected LCM. The downhole isolation valve (DIV) system is integrated into the 9-5/8″ casing string to cope with the challenge. By using this system, the requirement to kill the well while tripping out is eliminated. The successful utilization of LAMCD and DIV is elaborated in this paper as part of the drilling program and the combination of the two principles are applied. This paper focuses on the utilization of LAMCD and DIV in a case study of Drilling Well X which was drilled in the South Sumatra Field.