Ease Extraction Resistance of Spudcan by Adding an Extra Layer of Sand above Clay

Abstract

Jack-up rig, supported by a number of movable and independent legs with a footing at the bottom called spudcan, is a type of oil rig platform which is used in self-elevating system to support offshore platforms in shallow to moderate waters. Being different from the normal gravity structures, jack-up rigs can be mobilized to other sites after the exploration of oil and gas reserve is completed by extracting the legs with spudcans. However, extraction of the spudcan can be difficult and time consuming. In this paper, the spudcan penetration and extraction process is simulated using the finite element method. The research concentrates on the nonuniform clay that the shear strength profiles increase with the depth of clay, and ignores the shaft friction. In order to ensure that the effects of sand property on the bearing capacity and extraction resistance, three models for different dilation angles of sand were built. Furthermore, considering the influence of sand thickness, five models with different sand thicknesses were generated, in which the penetration depth is one time the diameter of the spudcan. In addition, the spudcan penetration depths are extended to twice and half of the spudcan diameter to verify the effect of penetration depth. Results obtained from these model analyses reveal that the required extraction force of the spudcan with a thin sand layer above clay is lower than that without the sand layer. Moreover, the results also show that thick sand layers can produce better effect of reducing extraction resistance of spudcan.