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Cementless Geothermal Well Construction
Elvin ALLAHVERDIYEV, Khizar ABID, Catalin TEODORIU
[University of Oklahoma, USA]
Geothermal wells are by default subjected to thermal cycles that impose demanding loads on the casing strings and cement. Historically, well construction relied on cement to provide annular zonal isolation, structural support, casing protection, and wellbore stability. However, the cement sheath is prone to mechanical failures (e.g., cracking, debonding, strength degradation, etc.) under high cyclic thermal stresses. In addition to violating environmental and safety standards, these failures can lead to inelastic buckling, sustained casing pressure, and cross-flow between communicating formations. This work proposes a novel cementless well construction methodology to overcome the well design and integrity limitations in geothermal environments, specifically. However, the concept can be applied to any type of well application, including oil and gas, CO2 sequestration, enhanced oil recovery (EOR), and/or underground storage wells with thorough well design and planning. The concept proposed in this work utilizes hydraulically-set metal expandable packer (MEP) systems as an alternative to cement for the annular zonal isolation. These packers need to be set at competent formations for a long-lasting metal-to-rock and metal-to-metal seal. This work presents a model with the key design considerations for a successful application using a commercial well design software that also has finite element analysis (FEA) features. In order to eliminate packer failures, certain pre-tension is applied to the strings after each packer set. The concept offers very high potential to achieve maximum well integrity over a longer operational life-of-well, even post-plug and abandonment, neglecting the corrosion damage, which needs further solution development. The metallic packer technology already has a proven track record in the oil and gas wells with back-up cement in place.
Topic: Drilling