Holistic Analysis, Diagnostics and Operating Philosophy for Wellhead Leak Issue for Gas Producer, Offshore Malaysia

Abstract

Since the beginning of production, well NA2 and NA3 wells had issues with wellhead integrity due to thermal growth and wellhead tilting. Seepage was observed from wellhead and based on gas chromatography test, the seepage is Synthetic Based Mud (SBM), possibly from B and C annulus (intermediate and surface casing). For well NA3, seepage was observed coming out from the connection of Casing Head and Drive Pipe Housing House (DPHH) while for Well A2, seepage was found between DPHH and conductor. The issues arise from the failed elastomer seals found at the connections of leak of each well suspected due to well growth/shrink and tilting which caused the wear and tear of the seals. The seepage of both wells was rectified by injecting the failed elastomer seals with pressure activated sealant to the P-seal and grease to the elastomer. Both wells managed to produce at the capped production rate without seepage as of today. Another main issue at Field N is the leaking of metal-to-metal seal at Xmas Tree which led to production deferment. Due to the failed barrier at surface, interim philosophy was established to operate the field and rectification plan was implemented to ensure the well is producing safely at the calculated risk. This paper describes the analysis and diagnosis, operating philosophy outline by operator which led to the well safely producing at the desired rate: (1) Standing Instruction (SI) for Well Production Ramp Up and Down based on trending of production and temperature to ensure wellhead growth and tilting will not affecting the integrity of sealant, (2) Finite Element Analysis (FEA) and Wellhead Growth Study to develop operating limit and maximum allowable growth, correlated with well production and temperature, (3) logging and survey for well leak detection and echometer survey, (4) Wellhead Seal Injection for corrective maintenance upon seepage observed, (5) manual measurement of growth and tilting and utilizing laser sensor for automation, (6) External Slip Lock Brace Support (ESBS) Installation to mitigate abnormal relative growth and (7) risk assessment for well integrity. The holistic approach in diagnostic, monitoring and operating philosophy enabled the well to be ramped up to higher production despite the threat of losing the gas production. PCSB also avoided the utilization of rig to rectify the well which resulted in cost avoidance for the company.