Research On Wellbore Stability Technique In Fangzheng Area

Wellbore stability is one of the most important considerations in any drilling operations. An unstable wellbore would mean that drilling performance is impeded through lost time. In severe cases, it would mean a wellbore collapse and total loss of a well. All this means extra costs and money-time losses. So it is important to research wellbore instability.The average drilling wellbore enlargement rate of 10.89% in Fangzheng area, and wellbore instability restricted the drilling speed severely. So we need to actively carry out wellbore stability technique studies to increase drilling speed in FangZheng Area. For the problem of Fangzheng area wellbore stability,this article first based on the shale mineral constituents and chemical properties of the collapsed layer of Fang-6 well. The results indicate that those physicochemical characteristics have little influence on borehole stability. Second, using the fracture survey of Fang-4 well, this article found the formation stresses calculation mode,and draw the formation stresses profiles change with the well depth in Fangzheng area deep formation. Finally, this article analyzed three formation pressure prediction methods and discovered that formation pore pressure can be predicted exactly with sound wave time difference method; formation caving pressure can be predicted exactly with the Huangrongzun mode; formation bursting pressure can be predicted exactly with the Mohr-coulomb mode. On this basis, this article established the calculation modes of formation pore pressure, formation caving pressure and formation bursting pressure.Using the conventional drillhole survey of Fang-6 well, this article draw the three formation pressure profiles,determined the secure drilling fluid density 's window in Fangzheng area,and offered pledge for deeply prospecting and exploitation in Fangzheng area.