Challenges of a HPHT Completion Design with Extreme H2S and CO2 in a Carbonate Gas Development

Abstract

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.