Compared with land wells, the production environment and reservoir depth of offshore oil and gas wells are more complex and shallower. Further, HPHT production fluid there will produce strong temperature and pressure disturbance that affects the wellbore, which easily generates wellbore safety problems, such as wellhead growth and leakage caused by the incompatible deformation of casing and cement sheath. Therefore, obtaining an accurate wellbore temperature and pressure field is the key to implementing a wellbore safety assessment. Based on the gas–liquid two-phase separated method, this paper established an improved calculation model of wellbore temperature and pressure field for offshore HPHT wells. This model also takes into account the heat transfer environment characteristics of “formation-seawater-air” and the influence of well structure. Compared with the measured data of the case well, the error of temperature and pressure calculation results of the improved model are only 0.87% and 2.46%. Further, its calculation accuracy is greatly improved compared to that of the traditional gas–liquid homogeneous flow calculation model. Based on this model, the influencing factors of wellbore temperature and pressure in offshore gas wells are analyzed. The results show that forced convection heat exchange between seawater–air and wellbore is stronger than that between wellbore and formation. Reducing the gas–liquid ratio of the product can effectively reduce wellbore temperature and increase wellbore pressure. The gas production has a significant impact on the wellbore temperature. When the gas production rises from 10 × 104⋅m3/d to 60 × 104⋅m3/d, the wellhead temperature rises from 63 °C to 99 °C. However, due to the mutual influence of friction pressure drop and hydrostatic pressure drop, wellbore pressure increases first and then decreases with the increase in gas production. The improved model can provide a more accurate estimate of the time to reach the rated wellhead temperature. Meanwhile, this model displays accurate theoretical support for the rational formulation of the production plan after the well opening, so as to avoid excessive restrictions on the initial production rate.

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An electric drive downhole tubing cutting tool is the key equipment for tubing cutting in pressurized gas well workover operation. Cutting force control in radial feed movement of the cutting blade is the key to ensuring the successful cutting of tubing. In this article, the relationship model between cutting blade feed speed and cutting force is established by Matlab. Based on the mathematical model of cutting head rotation and blade feed movement, combined with the relationship between blade feed and cutting force obtained from cutting experiments. To keep the cutting force of the blade constant in the cutting process. Genetic algorithm was used to optimize the fuzzy proportional–integral–derivative control, and the automatic control scheme of the electric drive downhole tubing cutting tool was constructed. Based on Matlab/Simulink, the cutting force control simulation of the tubing cutting process is carried out. The performance of fuzzy proportional–integral–derivative control optimized by the genetic algorithm is compared with that of other standard controllers. The results show that the response speed and stability of the fuzzy proportional–integral–derivative control system are better than other algorithms. The steady-state error of the controller in the steady-cutting stage is < 5% based on the ground-cutting experiment of tubing, which meets the actual engineering needs and verifies the reliability and accuracy of the control system.

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