To evaluate the fatigue reliability of different types of drill pipes during an offshore short-radius sidetracking process, the fatigue life and limit of G105, S135, and V150 steel and a new titanium alloy drill pipe were studied in air, high-temperature conditions, drilling fluid, and drilling fluid containing H₂S. First, the chemical composition, microstructure, and tensile properties of four kinds of drill pipe materials were tested. Secondly, the fitting effects of different S-N models were evaluated and identified, a fatigue test of four kinds of drill pipe under different environments (air, high temperature, drilling fluid, and H₂S drilling fluid) was carried out, and the S-N curves and fatigue limits of different drill pipes under different environments were obtained. Finally, the fatigue sensitivity of drill pipes to different factors was studied, and the potential corrosion fatigue mechanism was explained. The research results show that the fatigue life of a drill pipe in a non-corrosive environment (air and high temperature) is mainly related to steel grade, and the fatigue life of a titanium alloy drill pipe is better than that of a steel drill pipe in a corrosive environment. The dense passivation film on the surface of a titanium alloy drill pipe is an important reason for its better corrosion fatigue life than that of a steel drill pipe. This study provides important data support for selecting drill pipes in offshore short-radius sidetracking.

In this paper, based on electro-hydraulic composite intelligent well-completion technology, a new type of downhole multi-parameter real-time monitoring system design scheme is established. Firstly, a multi-parameter real-time monitoring system with a special structure is designed; secondly, its reliability is analysed by applying the method of numerical simulation; finally, in order to verify the reliability of the simulation results, a principle prototype is developed, and indoor experimental tests of fluid flow are carried out. The experimental results show that the flow rate is directly proportional to the differential pressure, and when the flow rate is certain, the higher the water content, the higher the differential pressure. The indoor experimental flow rate of 400~1000 m³/d is measured with high accuracy, and the error range is within 5%. Numerical simulation and experimental results with a high degree of fit, a flow rate of 400–1000 m³/d, the two error range within 10%, the integrated flow coefficient of the experimental value is stable between 0.75–0.815, the simulation value is stable between 0.80–0.86. The mutual verification of the two shows that the flow monitoring design meets the requirements and provides a reference basis for the structural design of the intelligent, well-completion multi-parameter real-time monitoring system.

Driven by the extreme high temperatures (≥150 °C) and high salinities of deep wellbore environments, the corrosion failure of drill strings in water-based drilling fluids (WBDFs) is becoming increasingly severe. This study systematically investigates the corrosion behaviors and underlying mechanisms of N80 steel in simulated WBDFs under varying temperatures (80–180 °C), inorganic salts (NaCl, CaCl₂, KCl), dissolved oxygen (DO) levels, and hydrodynamic conditions, utilizing weight-loss tests, SEM, and XRD. Results reveal that the corrosion kinetics are synergistically governed by temperature and salt concentration, exhibiting a non-linear “increase-then-decrease” trend with a peak at 120–150 °C. The aggressiveness of the inorganic salts ranks as NaCl > CaCl₂ > KCl. Specifically, highly penetrative free Cl⁻ in the ultra-high-concentration NaCl system induces severe interconnected localized pitting. Conversely, high-concentration Ca²⁺ in weakly alkaline environments couples with carbonate to form a protective inorganic scale, serving as a physical barrier. Although the “salting-out effect” of high-concentration salts effectively reduces the DO level, the synergy between residual oxygen and active Cl⁻ in dynamic flow fields still triggers highly concealed deep under-deposit pitting. At the extreme high temperature of 180 °C, background salt ions dictate the competitive interfacial film formation: the NaCl system undergoes oxygen depolarization to generate a porous Fe₃O₄ layer, whereas K/Ca-containing systems promote CO₃²⁻ adsorption, forming a dense and thermodynamically stable FeCO₃ film. This study elucidates the fundamental mechanisms of uncontrolled pitting induced by extreme HTHP environments, providing vital theoretical guidance for the anti-corrosion design of deep-well drilling engineering.