Xiaoguang Huang

A downhole emergency packer is prepared to seal the drill pipe-casing annulus when the high-pressure overflow and kicks occur during offshore drilling. When there exists fluid in the annulus, the increase in fluid pressure during setting increases the difficulty of working and even results in sealing failure. The primary objective of this research is to investigate the influence mechanism of downhole fluid on the setting efficiency, and provide theoretical support for solving such problems under hydrodynamic conditions. In this work, the hyperelastic constitutive model of the rubber cylinder was established through uniaxial tension and uniaxial compression tests. The fluid-structure coupling model was developed by finite element method, to simulate the setting process of the downhole emergency packer and quantitatively evaluate the impact of downhole fluids on setting efficacy. The results revealed that the fluid velocity and pressure increased throughout the setting process while the annular area shrank, raising the setting difficulty. The existence of fluid flow considerably diminished the setting efficacy of the rubber cylinders. The sealing coefficient, K decreased by 7.15%, 11.06%, and 14.41% when the flow velocities from the inlet were 5 m/s, 6 m/s, and 7 m/s, respectively. Therefore, the setting pressure could be increased according to the actual downhole conditions to achieve the actual setting effect safely.

The blowout during shallow oil‐gas exploitation always increases the failure risk of the offshore platforms and equipment on them. The thermo‐solid dynamic response of offshore structures in blowout accidents is significant for the process safety evaluation and post‐disaster recovery. A new safety evaluation method was proposed using blowout scenario modeling on the offshore platform and the structural safety evaluation of wellhead devices through the fluid‐thermal‐solid coupling analysis and reduced yield strength method. The results indicated that the blowout flame was significantly affected by the blowout gas velocity, and environmental wind strength, low blowout gas velocity, and high wind speed can lower the flame height and aggravate the safety conditions of the wellhead devices. The proposed method can be applied to the process safety evaluation of offshore structures in blowout accidents.

In this work, a finite-element welding model of the X80 pipeline is established, and the residual stress is calculated using a direct thermal–mechanical coupling method through the User Material (UMAT) subroutine of the double-ellipsoid moving heat source. The effects of process parameters on the welding residual stress of the X80 pipelines are discussed. The ultrasonic longitudinal critical refraction (LCR) wave-detecting method is adopted to verify the simulation results. The results show that the residual stress at the inner surface is higher than that at the outer surface, and the peak Mises stress at the welding seam approaches the yield stress. With the increase in welding groove angle and heat input, the peak Mises stress increases at the inner surface and decreases at the outer surface, but the high-stress zone at the outer surface broadens. The residual stresses at the outer surface are more sensitive to the welding parameters. The comparison between the simulated results and ultrasonic LCR detection indicates that the finite-element method is feasible, and the simulation results are credible.

In the drilling process of offshore exploration wells and high-risk wells, the possibility of high-pressure overflow and kick increases greatly when encountering unknown or inaccurate formation conditions. If it is not handled properly, it may cause catastrophic accidents. Overflow and kick are the early warnings of blowout accidents, and the wellhead blowout preventer can be shut off first to cope with such emergency conditions. However, once the bottom hole high pressure spreads to the wellhead, it may bring safety risks to the wellhead emergency disposal. In this work, a new type of downhole packer while drilling was designed to quickly seal the annulus when high-pressure fluid appears underground. ABAQUS software is also used to simulate the sealing performance of the rubber cylinder, and analyze the stress changes of the rubber cylinder during the setting process. When the working stress is 10MPa, the maximum Mises stress of the rubber cylinder is 14.3MPa, and the contact stress of the rubber cylinder presents a "shoulder protrusion" distribution. By comparing the stress changes in the rubber cylinder with or without a metal skeleton, it was found that the overall contact stress with a metal skeleton will increase, which has a good impact on the sealing of the rubber cylinder.

Based on the continuum damage mechanics theory, a frequency‐dependent high‐cycle fatigue damage evolution model was established. According to the fatigue results of API X80 steel, the frequency‐dependent damage evolution parameters were regressed. Using the available riser mechanical model, the user subroutine of high‐cycle fatigue damage evolution was compiled, and the accelerating effect of corrosion pits on fatigue crack initiation of the marine riser was analyzed. The results show that a single corrosion pit at the surface can reduce crack nucleation life by more than 80%. In a double corrosion pits' case, the stress interference between pits significantly affects the crack nucleation. Circumferential double pits can produce a fatigue crack earlier than the single pit, but the effect of axial double pits is just the opposite. When the spacing reaches a certain distance, the stress interference disappears, and the crack nucleation life approaches that of a single pit case.

Based on the elasto‐plastic damage constitutive model, a continuum nonlinear damage evolution model for the high‐cycle corrosion fatigue of the API X65 pipeline steel is proposed. Firstly, a series of experiments are carried out to determine the corrosion fatigue damage parameters of X65 steel in the artificial seawater, then the corrosion fatigue damage model is used in the finite element (FE) analysis to predict the crack nucleation life of high‐cycle corrosion fatigue. In order to consider the influence of corrosion pit on the crack nucleation of corrosion fatigue, a user‐subroutine UMESHMOTION provided by the general software ABAQUS is used to construct a numerical model of damage evolution with the corrosion pit effect considered on the API X65 steel. Numerical results show that the numerical model considering the effect of damage and corrosion pit can better predict the crack nucleation life of the API X65 steel than that considering only the damage effect.

To meet the design requirements, different types of defects are often machined on the surface of fatigue components. Local stress concentration formed at the notch accelerate the initiation of fatigue crack, therefore greatly shorten the service lives of such components. Based on the theory of continuous damage mechanics and the principle of irreversible thermodynamics, the damage evolution model of low cycle fatigue is investigated. By programming the damage evolution model as UMAT subroutine and coupling it to ABAQUS, the fatigue damage and crack initiation life of notched P92 steel samples under specific loads are simulated, and the crack initiation location is determined. Furthermore, the damage evolution and crack initiation sensitivity of notch morphology are considered. The results show that the crack initiation occurs easily in the notch root where the damage is greatest and the plastic strain accumulates fastest under cyclic loading. The fatigue damage accumulates slowly at the initial stage, but the damage accumulates rapidly after the cumulative damage reaches a critical value. The fatigue damage evolution and fatigue initiation life are very sensitive to the notch morphology parameters. The notch morphology need to be carefully analyzed, to improve the fatigue life of the notched samples.

BP neural network in predicting thermal fatigue life of microelectronic chip