Cased hole drill stem tests (DST) are conducted after the well has been cased and the formation of interest is behind casing. The casing is perforated by wireline perforating guns or with tubing conveyed perforating (TCP) guns connected to the bottom of the DST string to open the casing to the formation. The DST tool assembly is run at the bottom of the temporary production tubing or drill pipe (work string) and used for downhole well testing (inflow testing) and stimulation (injection).
Maximum well control is achieved with redundant valves controlling flow and multiple circulation points. The tool assembly is custom designed for each operation with adequate expansion joints (slip joints) installed to compensate for thermal and hydraulic expansion/contraction of the work string. Down hole pressure/temperature gauges record data throughout the tool string. The gauge data recorded below the closed downhole valve closest to the formation sandface is used for pressure transient analysis (PTA). Isolating the formation with pressure recorded below the downhole valve drastically reduces the amount of time required to collect the necessary data due to the elimination of dead volume (wellbore storage effect) in the workstring.
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