When replacing the sealing element and lifting the oil production spool in a certain oilfield in Xinjiang, it was found that the casing at the clamping point of the wellhead hanger slip was broken. Based on the Ф232.5 mm W-type slip hanger structure used in the X1 well on site, a three-dimensional finite element model of the casing’s grip by the slip hanger was established. Firstly, based on the third and fourth strength theories, the calculation formula for the ultimate load of the casing under the slip effect was derived. Furthermore, tensile experiments, chemical composition measurements, and microstructure analysis were conducted on the 155 V casing samples used, and it was found that the performance of the 155 V casing material meets the standard requirements, the data suggests that the slip may contribute to casing fracture, warranting further investigation. Therefore, based on the mechanical finite element analysis model, it is calculated that the maximum stress on the outer wall of the casing reaches 1146 MPa, which is higher than the yield strength of the 155 V casing. This will lead to the damage of the casing used on site. Therefore, the structure of the slip is optimized, and the analysis shows that the top of the slip tooth is optimized to have a long axis of 400 mm, the one-fourth elliptical distribution with a short axis of 1 mm and the optimization of the top angle of the slip teeth to 60°–70° will significantly decrease the maximum stress on the outer wall of the casing. However, the optimization scheme of changing the inclination angle of the slip teeth and increasing the clearance of the slip back cone angle cannot effectively improve the stress distribution and maximum value on the outer wall of the casing.

As the casing undergoes bending deformation along the well trajectory, the contact position and state between the casing and wellbore exhibit dynamic variations during casing running operations in extended-reach wells. Assessing random contact between the casing and wellbore becomes critical for studying the mechanical properties of running casings. Hence, we utilized the Universal Mechanical Tester (UMT) pin-on-disk friction system to assess the kinetic and static friction coefficients of casing with surface casing and formation rock in mud environments, and employed the stochastic contact approach to develop a 3D dynamic finite element model incorporating the actual well trajectory. We conducted an analysis of the mechanical characteristics of running casings and discussed how factors such as wall thickness, friction coefficients, running speeds, and wellbore fluid density affect the mechanical distribution of casing. Numerical results indicate that the substantial frictional contact between the casing and the wellbore wall appears in the positive inclined and horizontal sections, and the casing initiates buckling behavior at a running depth of 3000 m. With the increase in running depth, the casings buckling behavior gradually transitions from sinusoidal to helical, causing a sharp increase in additional resistance against casing running. Finally, the casing cannot continue running beyond 4022 m. In comparison to the effect of wellbore roughness, the wall thickness of the casing and the fluid density primarily influence the horizontal well section. Furthermore, higher running speeds exacerbate buckling behavior by delaying the efficient release of the casings accumulated elastic energy.

During deep and ultra-deep well drilling operations, the throttling performance of the hydraulic-while-drilling jar is significantly affected by the combined influence of temperature-induced differential thermal expansion among components and changes in the rheological properties of hydraulic oil. These effects often lead to unstable jarring behavior or even complete failure to trigger jarring during stuck pipe events. Here, we propose a high-temperature degradation evaluation model for the throttling performance of the throttle valve in an HWD jar based on thermal expansion testing of individual components and high-temperature rheological experiments of hydraulic oil. By using the variation characteristics of the throttling passage geometry as a linkage, this model integrates the thermo-mechanical coupling of the valve body with flow field simulation. Numerical results reveal that fluid pressure decreases progressively along the flow path through the throttle valve, while flow velocity increases sharply at the channel entrance and exhibits mild fluctuations within the throttling region. Under fluid compression, the throttling areas of both the upper and lower valves expand to some extent, with their spatial distributions closely following the pressure gradient and decreasing gradually along the flow direction. Compared with ambient conditions, thermal expansion under elevated temperatures causes a more pronounced increase in throttling area. Additionally, as hydraulic oil viscosity decreases with increasing temperature, flow velocities and mass flow rates rise significantly, leading to a marked deterioration in the throttling performance of the drilling jar under high-temperature downhole conditions.