With the development of China’s oil and gas exploration and development to complex oil and gas fields, the drilling efficiency and safety of complex formations with large hardness and strong abrasiveness have become increasingly significant. Optimizing drilling parameters is an effective means to increase the rate of penetration (ROP) and improve drilling efficiency. However, traditional drilling parameter optimization methods with only a single objective of increasing the ROP lack consideration of the drill string’s drag which may also be increased when drilling parameters change. When drilling a horizontal well, increased drag can reduce drilling efficiency. Aiming at this problem, this paper uses the logging data of the oil field as the data source, establishes an intelligent ROP prediction model through the random forest algorithm, and calculates the string drag using the “hard-string” model. Finally, the nondominant sorting genetic algorithm-II (NSGA-II), which is a domination-based multiobjective optimization algorithm, is used to optimize the drilling parameters to increase the ROP and reduce the drag at the same time. The optimized drilling parameters guide the drilling operations. We used the proposed method to optimize the parameters during the drilling of a new horizontal well. The results show that the ROP of the horizontal section of the new well increases by 10.3%, and the drag reduces by 4.5% on average compared with the adjacent well.

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The galvanic corrosion of oil and gas production string is related to wellbore integrity and production safety. In order to study the galvanic corrosion of an oil and gas well tubing assembly and maintain production safety, this paper studied the galvanic corrosion behavior between 13Cr alloy steel tubing and the downhole tools of 9Cr and P110 in formate annular fluid via experimental and numerical simulation methods. The chemical composition, HTHP corrosion tests and electrochemical measurement of the three materials were investigated to analyze the corrosion mechanism and electrochemical parameters. Then, a full-sized 3D galvanic corrosion model of 13Cr tubing and a 9Cr/P110 joint combination was established using COMSOL Multiphysics software based on the electrochemical test results. The mechanism and current variation law of the galvanic corrosion of different tubing materials are discussed and analyzed in the paper. The results revealed that the corrosion rates obtained based on the electrochemical test are as follows: P110 (0.072 mm/y) > 9Cr (0.033 mm/y) > 13Cr (0.0022 mm/y). The current densities of a combination of 13Cr tubing with a 9Cr joint and 13Cr tubing with a P110 joint vary dramatically: the current density of the 13Cr tubing–P110 joint reach 1.6 × 10−4 A/cm2, higher than the current density of the combination of 13Cr tubing and a 9Cr joint. The results of a 3D FEM analysis show that the 13Cr tube demonstrates obvious galvanic corrosion with 9Cr and P110 joints, which is consistent with the analysis results of the polarization curve. This study therefore explains the galvanic corrosion mechanism of different tubing materials and provides guidance for the safe use of tubing in the productive process.