Method and apparatus for in-situ borehole stress determination

摘要

A borehole technique for in-situ determination of principal stresses operating in a plane normal to the borehole includes using a downhole jack to independently initiate three spaced apart fractures in a subterranean formation, measuring the breakdown pressure required to initiate the fractures and then using the measured breakdown pressures in two-dimensional axial transformation equations to compute the maximum and minimum stresses that are active in the normal plane. The technique is useful while drilling the borehole by lowering a jack having three platens that can be independently activated to bear against the borehole wall along three radii which are offset from each other about the borehole axis. In use each platen is extended in turn to bear against the borehole wall until a fracture is initiated.