Qiang Zhang

Casing deformation in horizontal wells reduces the effective drift diameter of the wellbore and may interrupt workover and hydraulic fracturing operations. Accurate prediction of reshaping load is therefore important for deformed-casing repair and wellbore integrity management. In this study, the mechanical response of C110-grade elliptically deformed casing restored by a pear-shaped expander was investigated without cement-sheath constraint. Two analytical reshaping-force models based on curved beam theory and thick-walled cylinder theory were established, and a three-dimensional finite element model was developed to simulate nonlinear tool–casing contact and elastoplastic deformation. Five expander outer diameters of 122–130 mm were analyzed, and a 1:8 similarity-scaled experiment was conducted for validation. The results show that the reshaping force increased from 50.2 t to 141.7 t as the expander outer diameter increased from 122 mm to 130 mm, whereas the improvement in minor-axis expansion was relatively limited. The finite element results agreed well with the experimental results, with average errors of 8.542% for reshaping force and 8.822% for minor-axis expansion. The thick-walled cylinder model showed better prediction accuracy than the curved beam model, with an average error of 4.11%. The proposed analytical–numerical–experimental framework provides a basis for reshaping-load estimation, expander selection, and stepwise restoration process design in deformed-casing repair.

To extract remaining reserves beneath the plugged sections of an abandoned well, a casing-outer sidetracking technique is proposed to connect a rescue well to the original well. Due to the short spacing and high curvature, an ultra-short-radius drilling method with an articulated double-layer flexible drill string is adopted. However, random contact during drilling introduces nonlinear mechanical challenges. To address this, a transient dynamic modeling strategy is developed: the drill string is discretized into spatial beam elements, with articulation modeled by universal joints and contact described using gap elements. A transient dynamic model is established, along with criteria for contact state identification and convergence. An iterative solution procedure for multiple contact scenarios is proposed. Validation using a single-layer case confirms model reliability. Results show that the outer casing provides guidance and experiences increasing fluctuating contact forces in curved sections, while the inner flexible drill string transmits weight on bit (WOB), producing high contact forces near the bit that increase with WOB. The maximum deformation of the flexible drill string reaches 2.12[ ]m, with an average WOB loss of 2[ ]kN. This paper offers theoretical guidance for safe and efficient sidetracking operations.

Carbon fiber composite sucker rods represent a technological innovation in oil production systems, exhibiting excellent performance. This sucker rod not only improves oil production efficiency and reduces accidents, but also saves energy and lowers the operating costs of oil wells. However, the working conditions of the carbon fiber composite sucker rod oil extraction system are relatively complex. The carbon fiber composite sucker rod body adopts a symmetrical structure formed by one-time solidification of three layers of fiber (carbon/glass fiber) materials, requiring the use of steel sucker rods in combination, and the impact of various system parameters is not fully understood. This paper focuses on the carbon fiber composite sucker rod as the research object, analyzing the external loads of the carbon fiber composite sucker rod oil extraction system. It also establishes a mechanical model of carbon fiber composite sucker rods, adopts a new finite element modeling method for sucker rod pumping systems, conducts transient dynamic analysis on the lifting motion of carbon fiber composite sucker rods in oil wells, and optimizes system parameters. The example verifies the rationality and feasibility of the finite element model. The results show that the higher the dynamic viscosity of crude oil, the more polished rod dynamometer cars tend to approach a “parallelogram”, and the polished rod load becomes more stable during the lifting process. With larger strokes, the maximum polished rod load increases, the longitudinal vibration amplitude of the carbon fiber composite sucker rod increases, and the load variation becomes more unstable. As the number of strokes increases, the maximum polished rod load and the pump plunger stroke length both increase, leading to higher pump efficiency, but the fluctuation amplitude of the polished rod dynamometer cars also increases, which affects the stability of the sucker rod’s lifting motion. When the carbon fiber sucker rod ratio exceeds 0.5, the difference between the self-weight and polished rod load initially decreases, then increases. As the carbon fiber sucker rod ratio increases, the pump plunger stroke length gradually decreases, and pump efficiency declines.

For the sake of realizing the safety detection of natural gas and petroleum pipeline welds, this paper designs a ferromagnetic pipeline weld magnetic flux leakage detector based on the calculation of the magnetic circuit of the detection probe, with the magnetization direction perpendicular to the traveling direction. The traditional pipeline magnetic flux leakage detection device uses a detection system mode in which the magnetization direction is parallel to the direction of travel. However, due to the structural characteristics of the weld, the traditional detection system mode is not applicable. Since the weld magnetic flux leakage detector needs to travel along the direction of the weld, the detector designed in this paper rotates the magnetizer 90 degrees along the direction of the weld seam so that the magnetization direction is perpendicular to the direction of travel, breaking through the technical barrier that make traditional magnetic flux leakage detection devices unsuitable for weld detection. The detection device includes a magnetizing structure, a data sampling device, and a driving and traveling device. The magnetic flux leakage signal collected by the detector is converted into a digital image in the form of a grayscale matrix. Using mathematical morphology and chain code algorithms in image processing technology, a pipeline weld defect inversion software system is developed, and a preliminary quantitative analysis of pipeline weld defects is achieved. The application of this technology enables the inspection and protection of oil and gas pipeline welds throughout their life cycle, broadens the scope of existing inspection objects, and is of great safety significance for ensuring national public security.

In pipelines for transporting oil and gas, multiple cracks often exist in weld joints. The interaction among the cracks should be considered as it directly affects the life span of the pipeline structures. In the current investigation, based on the fluid–solid magnetic coupling model, the virtual crack-closure technique (VCCT) is applied to systematically study the multi-crack dynamic interaction effect on pipeline welds during the crack propagation process. The results show that the existence of an auxiliary crack accelerates the main crack’s propagation. When the auxiliary crack is nearer to the main crack tip, the enhancement effect of the auxiliary crack on the main crack increases. Further, when the initial length of the auxiliary crack increases, the main crack becomes easier to propagate. Two important parameters, the distance between the two interacting crack tips and the initial size of the auxiliary crack, are studied in detail. Their interference effect on the main crack has been quantified, which is very user-friendly for engineers to conduct failure assessment and prevention for oil and gas pipes with multiple cracks at weld joints.