Managing Uncertainties and Surprises in Carbonate Gas Reservoir through Lower Completion Design Optimisation

There are three (3) requirements of any completion in common; safe, economical efficient and reliable. 76% of PETRONAS CarigaliSdnBhd's wells in Sarawak Gas are completed in porous, heterogeneous and complex carbonate reservoirs. Four (4) types of lower completions are implemented for carbonatereservoir: barefoot, open hole Pre-Drilled Liner (PDL) with isolation packer, open hole blank liner with isolation packer with post perforation and cemented cased hole. This paper shares the best practices, lessons learnt, risks and performance from recent experiences at field FX, FY and N which are used to support the proposed lower completion design and selection criteria workflow. Other than risk of wellbore collapse, early water breakthrough and fluid losses to formation, the provision for zonal isolation, cost, well productivity and complexity of operation have been part of the critical elements to be considered in the proposed process workflow from planning to execution phase. Dedicated studies such as wellbore stability analysis, critical drawdown requirement over time and well modeling are also being carried out to provide enhancment of lower completion design. This selection criteria and lower completion design process flow has been applied in recent FY field development campaign which resulted 32% of cost saving in 3 horizontal wells and met the production gas target with zero Lost Time Injury (LTI). The other particular merit of this paper is to share some the best practices and lessons learnt from FX, FY and N field case histories and the approaches taken to manage the risks.