Wireless Telemetry for Transmitting
Pressure and Temperature Data on a Drillstem Test, Kent Holder, Dick
Heine, David Copeland, SPE 35241, March 1996.
ABSTRACT
Wireless Telemetry for
Transmitting Pressure and Temperature Data on a Drillstem Test
An openhole drillstem test (DST) simulates
producing conditions to help operators determine if a formation may be
commercially productive during the drilling phase of the well. A DST
isolates a formation with packers, and a tester valve opens to expose the
formation to lower hydrostatic, which causes the formation to produce. After
a predetermined flow period, a downhole shut-in valve closes to start a
buildup period. The sequence of flow and closed-in periods is repeated as
required.
Testing can provide information such as
effective permeability, skin damage, formation pressure, flow rate, fluid
type, and radius of investigation. Effective permeability, skin damage, and
formation pressure calculations are possible only if the buildup period is
long enough to reach Horner data. The duration of close-in periods is
generally based on rule of thumb, bubble-hose response, or field experience.
Surveys of current DST reports indicate that 30% of formations tested were
not shut in long enough for Horner data to be obtained. The best method to
determine the length of flow and shut-in periods is to monitor the pressures
real-time at the surface. Wireline surface readout is available but is
costly and poses risks, since the wireline is in the well.
Once the pressure data were
acquired, we performed conventional semilog and log-log analysis, and we
simulated test profiles to verify the analyses of the test data. Both
surface and downhole pressure data were compared for consistency, and both
types of data were analyzed in exactly the same fashion. The results of
these analyses were essentially identical. This approach gave consistent
estimates of reservoir pressure, permeability, skin factor, and fracture
half-length for both of our case histories.