 In addition to packers a downhole valve is used to open and close the formation to measure reservoir characteristics such as pressure and temperature which are charted on downhole recorders within the BHA.Below are two types of BHA DST, Cased Hole which can be applied after the well has been cased, and Open Hole which may be performed before casing.Performed after the well is cased, cased hole drill stem testing uses a retrievable production packer that is set above the zone of interest.