Engineering Design Solutions of Drilling Fluid and Cement Slurry for a Challenging Deep HPHT Carbonate Appraisal Well in Malaysia

Abstract

Well construction in deep high-pressure, high-temperature (HPHT) carbonate wells typically impose the most restrictive restraints and essential requirements for drilling fluid and cementing design and application. This type of well presents specific challenges and difficult technical concerns that must be addressed not only in the drilling phase of the well but also on the long term well integrity. Drilling exploration or an appraisal well accentuates these challenges as formation details may not be fully understood. A recent appraisal well located in offshore Malaysia, presents many challenges especially on the drilling and cementing into its carbonate formation. Among the challenges of completing this HPHT well are high CO2 and H2S exposure, tight equivalent circulating density (ECD) concerns during drilling and cementing, losses from weak interbedded sands and severe losses concerns across its carbonate sections (Karst formation). In the HPHT section of this well, HPHT non-aqueous fluid (NAF) system was designed to meet the criteria for drilling and well test. Also, specially designed self-healing, high temperature flexible and expandable cement was engineered due to concerns of formation subsidence. This set cement design provides flexible properties to cater stress induced by formation movements, coupled with self-healing properties ensuring long term well integrity with its self-repair capabilities. A comprehensive and collaborative approach between drilling fluid and cementing design was among the pivotal factor ensuring the successful well construction of this appraisal well. This paper presents the complete engineering process from coherent well construction planning, drilling fluids and cement slurries design, rigorous laboratory validation, drilling and cementing hydraulic modeling, preventive and collective loss circulation control to successful well drilling execution. It also summarizes the lessons learnt from the operation and recommendations to drill and construct future wells under HPHT environment in this field.