Changes

  | part    = Critical elements of the petroleum system

  | part    = Critical elements of the petroleum system

  | chapter = Formation fluid pressure and its application

  | chapter = Formation fluid pressure and its application

  | frompg  = 5-1

  | frompg  = 5-30

  | topg    = 5-64

  | topg    = 5-32

  | author  = Edward A. Beaumont, Forrest Fiedler

  | author  = Edward A. Beaumont, Forrest Fiedler

  | link    = http://archives.datapages.com/data/specpubs/beaumont/ch05/ch05.htm

  | link    = http://archives.datapages.com/data/specpubs/beaumont/ch05/ch05.htm

==A DST plot==

==A DST plot==

[[file:formation-fluid-pressure-and-its-application_fig5-14.png|thumb|{{figure number|2}}DST plot showing the various pressures recorded during the different DST periods.]]

[[file:formation-fluid-pressure-and-its-application_fig5-14.png|300px|thumb|{{figure number|2}}DST plot showing the various pressures recorded during the different DST periods.]]

During a DST, pressure is continuously recorded against time. The record begins as the DST tool is lowered down the borehole and ends when the tool returns to the surface. [[:file:formation-fluid-pressure-and-its-application_fig5-14.png|Figure 2]] is a DST plot, showing the various pressures recorded during the different DST periods.

During a DST, pressure is continuously recorded against time. The record begins as the DST tool is lowered down the borehole and ends when the tool returns to the surface. [[:file:formation-fluid-pressure-and-its-application_fig5-14.png|Figure 2]] is a DST plot, showing the various pressures recorded during the different DST periods.

==Extrapolating true pressures==

==Extrapolating true pressures==

[[file:formation-fluid-pressure-and-its-application_fig5-15.png|thumb|{{figure number|3}}Example of how pressure is extrapolated from ISIP and FSIP on a Horner plot (pressure vs. psuedo or Horner time, or (T + ΔT)/ΔT. Copyright: Dahlberg;<ref name=ch05r5 /> courtesy Springer-Verlag.]]

[[file:formation-fluid-pressure-and-its-application_fig5-15.png|300px|thumb|{{figure number|3}}Example of how pressure is extrapolated from ISIP and FSIP on a Horner plot (pressure vs. psuedo or Horner time, or (T + ΔT)/ΔT. Copyright: Dahlberg;<ref name=ch05r5 /> courtesy Springer-Verlag.]]

DST pressures may not be reliable because the tool is not shut in long enough for pressure to stabilize at final reservoir pressure. A graphical procedure devised by Horner<ref name=ch05r10>Horner, D., R., 1951, Pressure build-up in wells: Proceedings of the Third World Petroleum Congress, The Hague, Section II, p. 503–521.</ref> infers the true reservoir pressure by extrapolating the shut-in periods to infinity.

DST pressures may not be reliable because the tool is not shut in long enough for pressure to stabilize at final reservoir pressure. A graphical procedure devised by Horner<ref name=ch05r10>Horner, D. R., 1951, Pressure build-up in wells: Proceedings of the Third World Petroleum Congress, The Hague, Section II, p. 503–521.</ref> infers the true reservoir pressure by extrapolating the shut-in periods to infinity.

[[:file:formation-fluid-pressure-and-its-application_fig5-15.png|Figure 3]] is an example showing how pressure is extrapolated from ISIP and FSIP on a Horner plot (pressure vs. psuedo or Horner time, or (T + ΔT)/ΔT

[[:file:formation-fluid-pressure-and-its-application_fig5-15.png|Figure 3]] is an example showing how pressure is extrapolated from ISIP and FSIP on a Horner plot (pressure vs. psuedo or Horner time, or (T + ΔT)/ΔT

==DST pressures from scout tickets==

==DST pressures from scout tickets==

Scout tickets are a common source of fluid pressure data. They list the duration of various episodes, the pressures measured during the episode, and the amount and types of fluids recovered. How reliable are scout ticket data and which pressure should one use for formation fluid pressure? As an example, Dahlberg<ref name=ch05r5>Dahlberg, E., C., 1994, Applied Hydrodynamics in Petroleum Exploration, 2nd ed.: New York, Springer-Verlag, 295 p. Excellent subsurface fluid pressure reference. Covers hydrodynamic and static fluids.</ref> studies 27 DSTs for formation pressure reliability. He extrapolates the reported pressures to true formation pressure using a Horner plot and finds that pressures must be increased an average of 10 psi.

[[Scout ticket]]s are a common source of fluid pressure data. They list the duration of various episodes, the pressures measured during the episode, and the amount and types of fluids recovered. How reliable are scout ticket data and which pressure should one use for formation fluid pressure? As an example, Dahlberg<ref name=ch05r5>Dahlberg, E., C., 1994, Applied Hydrodynamics in Petroleum Exploration, 2nd ed.: New York, Springer-Verlag, 295 p. Excellent subsurface fluid pressure reference. Covers hydrodynamic and static fluids.</ref> studies 27 DSTs for formation pressure reliability. He extrapolates the reported pressures to true formation pressure using a Horner plot and finds that pressures must be increased an average of 10 psi.

During a DST, two pressures measure the fluid pressure of the formation being tested: the ISIP and the FSIP. The higher is usually closest to true formation fluid pressure. In many cases, it is the ISIP.

During a DST, two pressures measure the fluid pressure of the formation being tested: the ISIP and the FSIP. The higher is usually closest to true formation fluid pressure. In many cases, it is the ISIP.

[[Category:Critical elements of the petroleum system]]  

[[Category:Critical elements of the petroleum system]]  

[[Category:Formation fluid pressure and its application]]

[[Category:Formation fluid pressure and its application]]