jet sub 20 and the valve sub 26 extend substantially vertically in the wellbore 10 when the stimulation fluid is pumped through the work string 16 it enters the interior of the jet sub 20 and discharges through the openings 22 into the wellbore 10 and against the formation 12 details of the jet sub 20 and the ball valve sub 26 are shown in fig2 and 3 the jet sub 20 is formed by a tubular housing 30 that includes a longitudinal flow passage 32 extending through the length of the housing the openings 22 extend through the wall of the casing in one plane and can extend perpendicular to the axis of the casing as shown in fig2 and or at an acute angle to the axis of the casing as shown in fig3 and or aligned with the axis not shown thus the stimulation fluid from the work string 16 enters the housing 30 passes through the passage 32 and is discharged from the openings 22 the stimulation fluid discharge pattern is in the form of a disc extending around the housing 30 as a result of the high pressure stimulation fluid from the interior of the housing 30 being forced out the relatively small openings 22 a jetting effect is achieved this is caused by the stimulation fluid being discharged at a relatively high differential pressure such as 3000 6000 psi which accelerates the stimulation fluid to a relatively high velocity such as 650 ft sec this high velocity stimulation fluid jetting into the wellbore 10 causes drastic reduction of the pressure surrounding the stimulation fluid.