MPACT OF SHALE HYDRATION ON ITS MECHANICAL PROPERTY AND BOREHOLE WALL STABILITY

On the basis of optimization of antisloughing drilling fluids in Hutubi area of Xinjiang oil field, the relation between shale mechanical property and borehole wall stability and hydration caused by drilling fluid is further investigated. The result of test and calculation showed that the hydrated shale has a reduced compression strength and poor adhesive power, resulting in a significant impact on the safety window of drilling fluid density. For instance, in well Hu 002, the sloughing pressure of hydrated shale corresponded to an increase of 0.23g/cm3 in drilling fluid density and the fracture pressure corresponded to a decrease of 0.15g/cm3 in drilling fluid density. Under similar test condition, hydration of shale depends on the type of drilling fluid. In 3 type of anti——sloughing drilling fluid used in the test, the KCI amphoteric polysulfonate drilling fluid exhibits the best shale inhibiting effect.