MWD or LWD is used on all directional wells. Two, doughnutshaped devices made of a rubberlike substance called packers are attached to it. The drillstem is lowered until one packer is just below and the other packer is just above the zone to be tested. The packers are then expanded to seal off that zone from the rest of the well. Figure 7-3 Drillstem Test Even though the well is still filled to the top with drilling mud, there is no pressure on the zone being tested because of the packers.
Any fluids can flow out of the zone and into the well.
A valve is opened in the drillstem and the fluids from that zone flow into the drillstem. Oil usually will not flow all the way up the drillstem to the surface. The valve in the drillstem is closed and the height of the oil in the drillstem is measured. Fluid pressures are also continuously recorded during the drillstem test.