The paper presents different design solutions for prevention of casing strings deformation in wells of Komsomolskoye field. The world experience of solving casing strings deformation problems has been surveyed. The deformation is related to Earth surface sagging. Radio positioning satellite data has been processed in order to investigate the reasons of casing and oil well tubing deformation in producing wells of Komsomolskoye field oil production infrastructure, where sufficient local sagging of Earth surface has been identified. The evidences of Earth surface sagging have been presented. The information on problem wells in Komsomolskoye field has been additionally processed and the fragments of retrieved tubing have been examined in order to identify nature and reasons of strings collapse. The assumptions for casing strings deformation reasons have been presented. The different methods for the recovery of casing string internal drift diameter, including the isolation of problem section using running and cementation of integral joint casing string with high pipe grade. Intermediate casing pipes with K55 pipe grade and maximum possible wall thickness have been recommended for problem section isolation. Problem section enlargement or the washout of cavern with maximum possible diameter has been recommended, which would sufficiently improve cementation quality and decrease the risk of casing string buckling.
The authors have developed the design sketch of a special spool for wellhead equipment. The spool allows the hoisting of production string in case of rock sagging. The authors recommended additional scientific research, including geomechanical modelling, hole stability modelling overtime and rock pressure specification.
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