Analysis of the Causes and Countermeasures for Wellbore Instability in Cenozoic Erathem in Jiyang Depression

To solve the problem of borehole instability in Cenozoic Erathem in Jiyang Depression effectively,this paper has classified and analyzed the cases of borehole instability from the aspects of structural belts distribution,paleosedimentary environment,lithology features,fluid properties and so on,and figured out the geological conditions and factors that caused borehole instability.According to the system engineering theory,five kinds of drilling fluid techniques to eliminate borehole instability have been found out,based on various borehole instability situations.At the same time,in view of present situation of drilling fluids used in high temperature and high pressure formation,the sloughing control for hard brittle shale in deep wellbore under the condition of high geothermal gradient in Cenozoic formation has been discussed.A series of ideas have been proposed such as,solving the borehole instability of calcareous hard and brittle shale,high bentonite consumption at high-temperature,effective sealing,and rational control of drilling fluid properties.Practical application has shown that the technical contermeasures mentioned above are of great significance for solving the borehole instability in Cenozoic Erathem in Jiyang Depression.