Field-X is a large offshore gas structure located 50 nautical miles from Miri City, Malaysia. The reservoir is a High-Pressure High-Temperature (HPHT) carbonate formation with high contaminants i.e., 1.8% mol of Hydrogen Sulfide (H2S) and 18% mol of Carbon Dioxide (CO2). This paper dwells on the completion design for the high-rate wells planned for this development. Exploration and appraisal wells showed severe reservoir properties that are "unique" as compared to other HPHT developments around the world. A multidisciplinary engineering team including HPHT drilling and completion specialists, production technologists, reservoir engineers, external specialist consultants, and facilities engineers are all working with a One Team One Goal mindset to address the challenges of completing this carbonate reservoir. Some of the completion design challenges addressed in this paper are Annular Pressure Management (APM) systems, perforation strategy for long intervals, well intervention philosophy, compaction and subsidence loading, thermal well interference due to the proximity of the platform well slots, HPHT monobore completion equipment design, qualification, and availability due to a very limited number of suppliers with long lead times. Another critical challenge addressed in this paper is an extensive material selection process to withstand the extremely corrosive well fluids, high temperature, and potential material cracking that historically has led to catastrophic consequences. As a result of the environment, exotic tubular materials are proposed based on intensive laboratory tests and computer simulations. Three-dimensional time history geomechanical and reservoir models explicitly detail the displacement compaction field which the downhole tubulars will be exposed in their lifetimes. Any annular pressure build-up will be handled by an APM system addressing the A, B, and C annuli with a permanent downhole gauge (PDG) installed for pressure and temperature monitoring tubing and annuli. These are some examples of the well design challenges tackled and resolved. The project is currently at the design phase, and all the thought process and design philosophies would be tested in this field. The authors wish that the lessons learned, engineering approaches, and design results will be useful in future sour HPHT completion developments.
HPHT wells are typically associated with high complexity, technically challenging, long duration, high risk and high NPT as many things could go wrong especially when any of the critical nitty-gritty details are overlooked. The complexity of this project is amplified with very high level of contaminants compounded by high pressure and high temperature environment. In the conceptual planning phase for the upcoming development of such project where its scale and severity are unprecedented in the country/region, a fit for purpose casing and tubing design is critically important to ensure the well integrity over its design life is assured. At the same time, cost optimization can be achieved utilizing industry practices, testing and qualification of materials and vast learning from incidents and failures occurred in similar HPHT projects over the last three decades scattered around the world. This paper intends to outline the challenges and optimization of casing design philosophy which is drawn upon various perspectives such as long term well integrity, drilling operations, working stress design, effect of compaction and subsidence, probability of failure analysis, multi-well thermal analysis, downhole material corrosion performance, connection performance and a combination of all the above in a holistic manner. A particular focus would be discussing the delicate balancing act between satisfying the working stress design of downhole tubular versus the complexity of downhole material selection work. With the given challenging environmental condition, this points towards exotic type of CRA materials which require certain magnitude of yield strength deration attributed to the given environmental condition and their respective manufacturing processes.
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