Research on the Buckling Mechanism and Optimization Design of Bohai Deep Well Tubing Considering the Cooling Effect of Drilling and Completion

In recent years, Bohai Oilfield has gradually commenced the development of buried hill formations with vertical depths exceeding 5000 m, where formation fluids exhibit notably high-temperature and high-pressure (HTHP) characteristics. Some production wells demonstrate wellhead and bottomhole temperatures as high as 100 ℃ and 180 ℃, respectively. Approximately half of these wells yield significantly higher production than anticipated, leading to rapid wellbore temperature escalation during production and inducing a series of tubing buckling issues. Field operation reports indicate that 50% of deep production wells experience excessive upper-string tension after tool deployment, a phenomenon recognized as a typical indicator of downhole tubing buckling. Conventional buckling analysis methods for shallow Bohai wells show marked discrepancies with actual measurements from deep wells, particularly in wellhead/bottomhole temperature mismatches and excessively rapid temperature rise trends. Comparative analysis reveals that low-temperature fluid invasion the formation during drilling and completion is the primary cause. Correcting the initial flowback temperature parameters of formation fluids enhances computational accuracy, yielding results that better align with field-monitored temperature trends. Furthermore, Landmark software simulations were employed to evaluate tubing stress under various production scenarios, assess buckling risks, and propose optimization measures. Key findings include: (1) Tubing buckling is prevalent in Bohai deep wells during production, with onset timing closely correlated to water cut. High-water-cut wells exhibit 20 ℃ higher wellhead temperatures than low-water-cut wells. (2) Buckling extent progressively increases over time. Under BZ19–6 well parameters, buckling spans >2500 m, with locations matching field records, while thermal elongation reaches 3.1 m. (3) Raising packer positions reduces constrained tubing length but elevates buckling position. Thermally, this approach cannot fundamentally prevent buckling. (4) Conventional solutions (e.g., thickened 88.9mm or 73.02mm tubing) enhance buckling resistance but amplify thermal stresses. Thus, wall-thickness increase is ineffective against temperature-induced buckling. This study provides theoretical foundations and optimization strategies for tubing design in Bohai and analogous HTHP deep wells.