Conceptual Casing Design for a HPHT Carbonate Development Project with High CO2 and H2S Contaminants

Abstract

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.