Search

Unbonded flexible risers (UFRs) connect surface production platforms to subsea production systems, and are therefore vital for tasks such as the transportation of oil and gas and the injection of water. The tensile armor layer is the main load layer of UFRs. Once this layer is partially broken, the safety of offshore oil and gas gathering and transportation is seriously threatened. In this study, an 8-layer UFR model is developed to calculate the effects of damaged inner and outer armor wires and boundary conditions on the tensile stiffness, ultimate load capacity, and stress distribution and load ratio of the inner and outer tensile armor layers. Broken inner tensile armor wires are found to have a greater impact on the tensile properties and produce the same torsional buckling failure mode as observed in the field. The influence of the pressure load on the ultimate load capacity of the UFRs is analyzed, and the results demonstrate that the outermost pressure increases the interlayer action between the tensile armor layers and the adjacent layers, thereby reducing the torsional angle of the UFRs under the ultimate tension. Additionally, the innermost pressure is found to have a negligible effect on the ultimate load. • A finite element modeling method for ultimate tensile finite elements of unbonded flexible risers that takes into account efficiency and accuracy is proposed. • The torsional buckling failure mechanism under the ultimate tensile load of the unbonded flexible riser was revealed. • The influence of the fracture number of tensile armor wires, internal and external pressure on the ultimate tensile of unbonded flexible risers were analyzed. [ABSTRACT FROM AUTHOR]

[Display omitted] • Nano SiO 2 layer was produced by laser texture-deposition (LTD) technology. • SiO 2 layer can delay the oxidation of Cu surface during boiling. • Superior capillary wicking and durability improve the heat transfer. • The CHF of LTD is 2.8 times that of the original copper surface. To improve the durability of pool boiling, laser texture-deposition technology was introduced to produce massive area of micro/nano structures on copper surface without any chemical treatment. The XPS analysis and the SEM images revealed that the two-tier micro/nano structure was formed on the micron protrusions, where villous cluster nano SiO 2 layer was deposited on copper oxide nanoburrs. Subcooled pool boiling experiments indicated that villous cluster nano SiO 2 structure delayed the oxidation of Cu, and thus enhanced the durability (capillary wicking/superhydrophilicity). Furthermore, the CHF and HTC of the laser texture-deposition surface reached 2805.8 kW/m2 and 111.8 kW/(m2·K). The CHF and HTC are 2.8 times and 2.1 times that of the original copper surface, respectively. Laser texture-deposition technology proves to be a promising green processing technology for the heat transfer of pool boiling. [ABSTRACT FROM AUTHOR]

• Revealed the inherent mechanism of casing shear deformation. • Proposed measures to add a wellbore annulus buffer layer to reduce casing shear deformation. • Through experiments, it has been confirmed that adding a buffer layer can effectively reduce the shear deformation of the casing. • Optimized the structural parameters of the buffer layer through finite element method. In the process of exploiting shale gas, wells experience casing deformation at rates reaching 40%, leading to the failure of setting tools such as bridge plugs during completion operations. This failure results in cessation of fracturing operations, seriously affecting productivity. To reduce and reveal the mechanism of casing deformation, in this work, casing shear deformation experiments were designed and carried out simulating an 8.5-inch wellbore, which verified that the casing deformation was shear deformation caused by formation slip. Based on the mechanism of casing shear deformation, the measure of adding a wellbore annulus buffer layer to reduce casing shear deformation is proposed, and the finite-element method is used to verify that increasing the compressible space of the buffer layer and reducing the compression stiffness can further reduce the casing deformation. Finally, a casing shear deformation experiment with an added buffer layer was developed. The casing generated a few shear deformations under 40-mm formation slip, which verified the effectiveness of the measures proposed in this paper to reduce the shear deformation of the casing. [ABSTRACT FROM AUTHOR]

During the process of deep-sea oil and gas exploitation, unbonded flexible risers (UFRs) are corroded by CO 2 and other media over long periods of time, which causes serious damage to the tensile armor layers and threatens the safety of the UFRs in service. To study the effects of torsional response, ultimate loading, and failure mode on UFRs after corrosion, and to reveal the torsional failure mechanism of the UFR while considering corrosion defects, an 8-layer UFR torsional response model is established in this paper. Local bending of the UFR and lateral buckling failure of the inner tensile armor layer occur under counterclockwise ultimate torsion, whereas strength failure of the inner tensile armor layer occurs under clockwise torsion. When the degree of corrosion is 0.4 mm, the counterclockwise torsional stiffness of thickness corrosion, width corrosion, and combined corrosion decreases by 27.6%, 10.8%, and 28.4%, and the ultimate loading of counterclockwise torsion for thickness corrosion, width corrosion, and combined corrosion decreases by 37%, 13.4%, and 39.3%, respectively. Therefore, the influence of thickness corrosion and combined corrosion on the torsional response of UFRs is worthy of further attention. • Established a theoretical and numerical model for unbonded flexible risers, and compared and verified the correctness of the model. • Studied the influence of corrosion of the tensile armor layer on the torsional response of unbonded flexible risers. • Revealed the ultimate torsional failure mechanism of unbonded flexible risers. • Restored the lateral buckling failure mode of unbonded flexible risers. [ABSTRACT FROM AUTHOR]