Earth’s Cryosphere, 2018, Vol. XXII, No. 2, p. 44-53
METHOD OF CALCULATION OF AXIAL LOAD ON THE WELLBORE CASING DURING THAWING OF FROZEN HOST SEDIMENTS
J.B. Gorelik, P.V. Soldatov
Earth Cryosphere Institute, Tyumen Scientific Centre SB RAS,
P/O box 1230, Tyumen, 625000, Russia; gorelik@ikz.ru
The paper presents data on casing deformations reported from high-latitude hydrocarbon production fields, and results of their comparison with laboratory simulations of a casing subjected to axial compression leading to deformations, such as buckling, similar to those occurring under operation conditions. The frozen soils in regions of well placements with reported buckled casings include epigenetically frozen clayey layers. In the thawed state, such layers have better mechanical properties and may retain their integrity under significant loads. As such, the thawed part of the layer comprises three supporting elements: wellbore casing; its own extension into the frozen soils; and the underlying thawed soils. A method for calculating axial loads on the casing depending on the thawed area size and thawing soils properties is proposed. The axial load exerted on casing tends to grow reaching its maximum at the initial stages of well operation, and then decreases to the asymptotically constant value (regardless of thaw radius). Early years of well operations appear to be most hazardous for the constructions, which agrees well with the known practical results.
Frozen soils, thawed soils, casing, axial loads, wellbore casing buckling