INTEGRATED CASING DESIGN METHODOLOGY FOR PERMAFROST WELL INTEGRITY

With the growing demand for oil and gas resources, the development of northern fields located in permafrost regions becomes increasingly critical. Well construction in the cryolithozone requires careful consideration of thermal interaction and permafrost freezeback to ensure casing string integrity. In this paper, a casing design methodology has been developed and scientifically substantiated to eliminate the limitations and drawbacks of the approaches employed by North American (USA/Canada) and Russian engineering schools. The North American approach was established in Alaska (Prudhoe Bay), where sandy soils predominate; these soils are highly susceptible to rapid thaw subsidence, while freezeback pressures remain relatively low at around 13.8 MPa. In contrast, the Siberian region is dominated by high-ice and ice-rich clay soils that retain free water during freezeback, expanding to generate extreme collapse loads (Pcollapse≈10–50 MPa). Consequently, the Russian school relies heavily on analytical calculations of freezeback loads during well shut-in for workover or suspension. Conversely, the North American school utilizes three-dimensional finite volume (or finite element) modeling to predict axial and bending deformations during permafrost thawing.As a case study, a comparative well design calculation was performed for the Kuparuk field (Alaska). The results demonstrate fundamental discrepancies: according to the Russian methodology, the well design successfully withstands freezeback loads, allocating the safety margin in favor of the production casing. Meanwhile, US-based FEM analysis focuses on increasing the steel grade of the surface casing, while the production casing is omitted from the structural load path evaluation. To resolve these contradictions, an original methodology has been developed. It harmonizes the regulatory requirements of both engineering schools and incorporates finite volume modeling of the casing–cement–rock stress-strain state under both permafrost thawing and subsequent freezeback conditions. The obtained results confirm that the new methodology enhances the accuracy of engineering decisions, optimizes the structural safety margins of wells, and ensures integrity across all stages of the well lifecycle.