1989 34 elements of rock mechanics 34 p 2 1 through p 2 22 found in economides m j and nolte k g editors 34 reservoir stimulation 34 second edition prentice hall which is incorporated herein by reference in accordance with the present invention the maximum and minimum principle horizontal stresses operating in a subterranean formation are determined by first ascertaining the maximum and minimum values for radial stresses required to initiate a fracture in the subterranean formation using the equations equ1 where s stress applied by the downhole jack psi i j k indexes for direction of stress relative to some specified direction or azimuth and the maximum value for radial stress caused by the downhole jack r 39 max is given by r 39 max a b and likewise r 39 min a b where the 34 r 34 refers to radial stress and a and b are defined above the computed maximum and minimum radial stresses r max and r min respectively are obtained by adding the borehole pressure bp to the maximum and minimum radial stress as follows the orientation of r max is given by the angle theta u03b8 in degrees which is drawn anticlockwise from the i direction equ2 finally the maximum and minimum principal stresses u03c3 max and u03c3 min operating the normal plane are computed using the maximum and minimum radial stresses in the following 34 kirsch 34 equations that relate radial and tangential stresses surrounding a borehole to the principal stresses operating in the normal plane the downhole jack of this invention is designed to be applicable to a wide variety of subterranean materials ranging from sandy compositions to hard rock.