Abstract: Oil and gas wells that are ultra-deep and have ultra-high temperature and pressure pose significant challenges on wellhead equipment,well control and other operational and safety aspects.Since the drilling of such wells may involve a high probability of gas kicks during drilling and the potential for a catastrophic blowout,it is necessary to review the technical challenges posed in well control and to highlight relevant countermeasures.In addition to specifying a definition for wells with ultra-depth,ultra-high temperature and pressure,this paper reviews conditions of typical wells in the global settings.In addition,the paper provides a study on key challenges of such wells in formation pressure prediction,casing program optimization,overflow monitoring and bottom-hole pressure determination.Further,the paper highlights technical solutions for necessary well-control facilities,the enhancement of casing strength,and the early monitoring of overflows.In addition,an innovative well-killing technique involving dynamic variable parameters was proposed that incorporates specific features in well control for such wells.According to the design,well-kill operations can be performed by using killing fluids with various densities.Further,the flow rates of killing fluids can be adjusted in accordance with specific requirements.In this way,killing fluids with different densities can be used at different intervals to effectively reduce casing pressures and to dramatically enhance success rates for killing operations in one-operation.Relevant research results may provide necessary technical references in the development of key well control techniques and the deployment of necessary facilities in well control operations in ultra-deep wells with ultra-high pressures and temperatures.