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.

This paper will discuss the key focus areas in successfully delivering a slim well design as a Proof Of Concept (POC) for marginal fields and well cost optimization. Well Tall-A is a Near Field Exploration (NFE) well targeting marginal reservoir which utilize the slim well concept; a 2-hole section well with 9-5/8" as the conductor. For a successful well execution, three (3) key focus areas were identified which are successful operation of 9-5/8" Casing While Drilling (CWD) to section TD, sustainability of 9-5/8" casing as conductor for the whole well life cycle and achievement of well objectives. Tall-A recorded the longest and successful 9-5/8" CWD Level 2 (non-directional) for Asia Pacific with 1168m drilled footage as of year 2020. Lessons learnt from previous PCSB 9-5/8" CWD operation were incorporated for casing bit selection hence a heavy-set casing bit (8 bladed) which has been proven in drilling long hole interval in the Middle East (>1000m) was utilized. Continuous monitoring during execution is essential in ensuring the casing is set at the desired setting depth. Sustainability of the 9-5/8" casing as conductor for the whole well life cycle is critical for a slim well design concept. Several studies and extensive discussions between multiple parties has been incorporated to enable utilization of the 9-5/8" as conductor with required sufficient tension to sustain the exploration well lifecycle. A conductor study was performed which incorporated the Metocean data, rig data and connection Stress Concentration Fatigue (SCF) to qualify the 9-5/8" as conductor. To meet the primary and secondary targets; the 8-1/2" hole needs to be kicked-off early and build up to maximum 44 deg before maintain tangent to final TD at 2752m MDDF. Due to the long open hole (1475m) and well inclination within the avalanche hole cleaning regime (30 to 60 deg), the well is prone to hole cleaning problem and wellbore instability. Hence, it is critical to have good drilling practices and precise mud weight selection to ensure no hole problem encountered. The well was successfully drilled to TD, completed the well testing and P&A. In summary, well Tall-A successfully maneuvered all challenges to deliver the well safely that resulted in Best In Class (BIC) performance. The slim well design concept has been proven achievable and serve as base design for future marginal wells.

This paper presents the success story of an exploration well in Malaysia evaluating the conventional approach of stacked cement plugs against the use of sacrificial tubing with a hydraulic disconnect sub system. Plug and Abandonment (P&A) is the process where the well is sealed permanently, and permanent well barrier must extend across the full cross section prior rig move. It is vital to ensure that plugged wells do not leak after abandonment, as there could be several potential leak paths or channeling from microannulus. Thus, well integrity shall be the utmost priority in designing the P&A strategy. Conventional P&A requires multiple cement plugs of a given length to be set and pressure tested, which could however be quite time-consuming and thus costly. The number of cement plugs will be based on the length of the open hole section, hydrocarbon zones presence or caprock to meet the P&A guidelines. The guidelines require that cement plugs be placed and tested across any open hydrocarbon-bearing formations, across all casing shoes, across freshwater aquifers, and perhaps several other areas near the surface. The thought process, design requirement both for the hardware and cement slurry, and execution follow through of a P&A approach with a sacrificial tubing method, driving for cost savings and operational efficiency will be elaborated. Some of the key points for replication based on lessons learnt are P&A with sacrificial tubing is economical justified for well scenario. As for the design, tubing centralizers or rotation is required in deviated hole for proper cement placement. Rotation of tubing during cementing is recommended for effective mud removal and cement placement for the case of no centralizer placement. This paper provides the novelty of the extensive planning, execution and improvement methods that will aid the project team to save cost and time in plug and abandonment (P&A) the well.