In this paper, the historical review for the drilling troubles encountered in the Nahr Umr (N.Umr) shale formation and the rock mechanics approach to improve the wellbore stability are described. An integrated approach is adopted for this study including the historical review for the actual drilling practices implemented to date, the studies of geomechanics, rock mechanics and chemistry for the N. Umr shale formation.

The historical review is performed based on the actual drilling data from year 1991 to March 2004.

The geomechanics model is determined with the data from the N. Umr shale formation and adjacent reservoirs. Logging data and collected formation sample data i.e. cores, cuttings are utilized to measure the properties of the formation. Numerical models considering the anisotropy and poroelastic nature of the shale lead the quantification of the failure mechanism.

Laboratory testings are conducted to analyze the basic chemical properties of the shale, and the interaction between the shale and mud. A newly produced testing apparatus is applied to determine the shear strength change of the shale under saturated condition with mud. Scanning Electron Microscope is utilized to ensure the failure mechanism and evaluate the validity of the shale inhibitors.

In this paper, the outline of the approaches is shown with some details of the testing and analysis methods.

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