Breakthrough Integration of 3-1/2? Tubing in 8-1/2? Hole Cemented Monobore for Successful Tubing Stem Test TST

Abstract

This paper presents the success story of an exploration well in Malaysia which exemplary applied a breakthrough integration of 3-1/2″ tubing in 8-1/2″ hole cemented monobore utilizing a new well testing concept of Tubing Stem Test (TST) to save cost and rig time. The Tubing Stem Test (TST) concept which is the new approach of testing a well that integrates both completion and well test technology into a single system compared to conventional Drill Stem Test (DST). The cemented monobore technology was successfully implemented by smooth and flawless planning and execution. A comprehensive planning and collaboration of multiple disciplines in Wells and Subsurface team had ensured a successful delivery of the first Tubing Stem Test (TST) with 3-1/2″ Tubing Cemented Monobore in a near-field exploration well targeting marginal reservoir in Malaysia. During planning stage, the challenges were to ensure that the cementing design concept suits TST application to be executed smoothly by incorporating multiple of risk assessments, lessons learnt, best practices review, feasibility studies and multiple design challenge sessions. This is to ensure that the well integrity is not jeopardized by achieving good cement bond across 3.5″ × 8.5″ annulus section with exclusion of WAB (Welltec Annular Barrier) packer. During execution stage, main concern in cementing operation pushed project team to re-design the fit-for-purpose cementing slurry and multiple cement tests were performed to ensure cementing objectives were achieved. Project team optimized the design by using G Cement Silica blend which has been proven to eliminate fluid migration and provide good compressive strength (UCS). This has allowed additional perforation zone for the new target as CBL/VDL shown good cement bonding to targeted top of cement. Some of the good practices includes good tubing standoff, efficient pre-flush, spacer & cement slurry design with fast compressive strength development, good displacement efficiency and effective plug bump strategy. The thought process, design requirement both for the hardware and cement slurry, and execution follow through of cemented monobore operation in driving for cost savings and operational efficiency will be elaborated. This collaborative initiative has resulted significant cost savings by eliminating cost of wellbore clean-up (WBCU), eliminate 7″ Casing or Liner for reservoir section, DST package, DST tubing rental, simpler completion accessories and 5 days of rig operation days. Despite facing with challenging cement issue with challenging cement batch used, well has achieved good CBL/VDL result and 100% zonal isolation which has enabled perforation of planned and additional target hydrocarbon zones. Simultaneously, formation damage risk was reduced by eliminating the time the formation is exposed to overbalance brine This paper presents the planning and operational execution of 3-1/2″ Tubing in 8-1/2″ Hole Cemented Monobore to realize the feasibility of Tubing Stem Test (TST) as new approach of well testing operation to save cost and rig time.