New method for evaluating borehole stability in brittle shale

In the present,the typical experience can’t solve all the problems of borehole instability.Especially in brittle shale formation,there are not optical methods to solve in the lab.So setting up methods for brittle shale is very urgent.To solve the borehole instability in brittle shale because of micro-fractures,this paper set up a new evaluation method of hard brittle shale——the simulation and sealing about micro-fracture.The method could simulate little fracture from 1 μm to 50 μm,and the experiments of seal have been done.The relationship among velocity,peripheral pressure and fracture width was studied.Sealing efficiency of the silicate drilling fluid was reached to 90%.The result of experiments indicates that the method is possible,and has some guidance for improving the sealing capacity of drilling fluids.