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The low cost,safe and efficient disposal of gas field produced water has become the main factor restricting the stable production of natural gas in China. It is of great significance to solve the problem of treatment and disposal of gas field produced water to ensure national energy security. Therefore,based on a brief review of the current situation of water production in major gas fields in four major onshore petroliferous basins in China, the key challenges faced by the treatment and disposal of produced water from gas fields in China were analyzed, and countermeasures and suggestions for the treatment and disposal of gas field produced water were proposed. The research results show that most of the gas fields distributed in the Ordos Basin, Tarim Basin, Sichuan Basin and Qaidam Basin in China are facing the situation of simultaneous production of gas and water and the sharp increase of water production. Under the strategic goal of “double carbon”, key challenges include the increasing amount of water on the produced surface of gas fields, the lack of national level reinjection management systems and standards, the high cost of meeting surface discharge standards and limited application areas, and the early stage of comprehensive resource utilization. It is necessary to strengthen the research on the overall water control of gas reservoirs, improve the reinjection management and technical standard system of gas field produced water at the national level, promote the low-cost comprehensive resource utilization of gas field produced water, and expand the new path of gas field produced water disposal. The conclusions indicate that the gas reservoirs in China are diverse, and the geological, geomorphological, hydrological and climatic conditions are complex and changeable. It is necessary to promote the reinjection disposal, surface discharge and comprehensive utilization of produced water from gas fields according to local conditions, so as to support the realization of the strategic objectives of “stabilizing oil and increasing gas” and “double carbon” in China.

Friction torque disturbance affects the tracking performance of electromechanical actuator servo system, bringing position and speed tracking errors, and even may leading to instability of the servo system. Aiming at the problem of poor tracking performance of electromechanical actuator servo system under friction torque disturbance, a FOANN friction compensation algorithm is proposed to estimate and compensate the friction torque. Firstly, base on LuGre friction model, a electromechanical actuator model is established, and the unmeasured state variable in the LuGre model is estimated by radial basis function neural network. Secondly, a FOANN controller is designed, and the stability of corresponding closed-loop system is proved by Lyapunov stability theory. Finally, through simulation and experimental platform, the dynamic performance of FOANN is compared with those of traditional PD and MRAC. The simulation and experimental results show that, with the proposed FOANN friction torque compensation algorithm, the tracking errors of both position and velocity of electromechanical actuator servo system are greatly reduced. FOANN algorithm can effectively estimate and compensate friction torque, reduce the impact of friction disturbance and enhance the dynamic performance of the servo system.

The CO2-water-rock interaction is the core issue of CO2 geological sequestration. The injection of CO2 disrupts the chemical balance of rock-formation water， and the changes in the chemical properties of formation water， primary mineral dissolution， and secondary mineral precipitation will lead to changes in the physical properties of reservoir and caprock， such as porosity， wettability， and mechanical properties and thus directly affect the CO2 injection capacity， sequestration efficiency， and sequestration security and stability. Based on the mechanism of CO2-water-rock interaction， this paper systematically expounds on the research progress of the effects of CO2-water-rock interaction on porosity， permeability， wettability， and mechanical properties of formation rocks. The results show that the change in rock porosity and permeability caused by CO2-water-rock interaction is closely related to its initial porosity and permeability characteristics and mineral composition， and the change of rock porosity and permeability characteristics directly affects the injection capacity and sequestration potential of the reservoir and the sealing capacity of the caprock. The change in wettability is related to the initial hydrophilic and oil-philic characteristics. The CO2-water-rock interaction usually weakens the water wettability of the hydrophilic rocks and enhances that of the oil-philic rocks， thus affecting the microscopic distribution and seepage characteristics of the multiphase fluids in the pores of the rocks. Due to the dissolution of cement and the formation of dissolution holes， the CO2-water-rock interaction will cause rock damage， and the mechanical parameters such as compressive strength， tensile strength， and elastic modulus will decrease. To a certain extent， the security of sequestration is affected. Under the setting of carbon neutrality， the CO2-water-rock interaction and rock physical property response under the scenarios of micro-nano-scale pore， deep microbial mediation， impure CO2 or industrial tail gas injection， and full sequestration cycle still need to be further studied.