Implementation of PMCD to Explore Carbonate Reservoirs from SemiSubmersible Rigs in Malaysia results in Safe and Economical Drilling Operations

Abstract

Abstract PETRONAS has been drilling carbonate reservoirs offshore Sarawak since the 90's. However, with more prospects being explored, the challenges have escalated as the company has embarked into exploring the remaining carbonate pinnacles where the primary objective is to identify the gas or oil water contacts of the prospects. Some of these carbonate reservoirs are characterized by the presence of large karsts and fractures, leading to a frequent scenario of total mud losses and kicks. Conventional drilling practices are not considered a safe or economical option to drill the carbonate sections. Additional problems associated with the drilling operation in these zones includes poor hole cleaning, low ROP, high vibrations and stuck pipe events. Implementing the Managed Pressure Drilling (MPD) variant called Pressurized Mud Cap Drilling (PMCD) allowed the drilling team to reach targeted total depths on several wells. Upon encountering unsustainable losses the wells were converted over to PMCD. Light Annular Mud (LAM) was injected into the annulus and a sacrificial fluid (SAC) was pumped down the drillstring allowing drilling to continue to total depth. By successfully implementing the PMCD technique, the operator was able to reduce risk and reach the exploration targets successfully. Lessons learned surrounding operational techniques, pressure limitations of the drilling system and continuous training and development of the operating team have expanded the application for the operator. The authors present lessons learned of wells drilled to date and key lessons learned as the Operator evolves to improve execution of PMCD.