Method for measuring formation properties with a formation tester
A method is disclosed for estimating a formation pressure using a formation tester disposed in a wellbore penetrating a formation, said method comprising: (a) establishing fluid communication between a pretest chamber in the downhole tool and the formation via a flowline, the flowline having an initial pressure therein; (b) moving a pretest piston in a controlled manner in the pretest chamber to reduce the initial pressure to a drawdown pressure during a drawdown phase; (c) terminating movement of the piston to permit the drawdown pressure to adjust to a stabilized pressure during a build-up phase and measuring simultaneously in relation to time, pressure P(t) and temperature T(t) in the pretest chamber; (d) extracting an index i(t) dependent of the pressure P(t) and the temperature T(t) informing on the build-up phase; (e) analyzing index i(t) and repeating steps (b)-(d) or going to step (f); (f) determining the formation pressure based on a final stabilized pressure in the flowline. And more generally a method could be used for estimating type of a build up pressure phase, the build up pressure phase being done after a drawdown pressure phase, said both drawdown and build up phases being done to determine formation pressure using a formation tester disposed in a wellbore penetrating a permeable formation, said permeable formation being able to create a formation flow, said method being characterized by using an index to determine the contribution of formation flow on the pressure build up phase.
1. A method for estimating type of a build up pressure phase, the build up pressure phase being done after a drawdown pressure phase, said both drawdown and build up phases being done to determine formation pressure using a formation tester disposed in a wellbore penetrating a permeable formation, said permeable formation being able to create a formation flow, said method further comprising the step of using an index to directly inform at the beginning of the build up phase for estimating said type contributing to the build-up pressure phase.
2. The method of claim 1 , wherein said index is a function dependent of the effects of thermodynamic equilibrium in the formation tester and the effects of formation flow into the formation tester.
3. The method of claim 1 , wherein said index is a function dependent of the effects of temperature variation in the formation tester and the effects of formation flow into the formation tester.
4. The method of claim 1 , wherein said index i(t) is equal to:
Δ
T
Δ
P
·
δ
2
(
log
(
Δ
P
)
)
δ
t
2
,
where ΔT is the temperature variation, ΔP is the pressure variation and t the time.
5. A method for estimating a formation pressure using a formation tester disposed in a wellbore penetrating a formation, comprising:
(a) establishing fluid communication between a pretest chamber in the downhole tool and the formation via a flowline, the flowline having an initial pressure therein;
(b) moving a pretest piston in a controlled manner in the pretest chamber to reduce the initial pressure to a drawdown pressure during a drawdown phase;
(c) terminating movement of the piston to permit the drawdown pressure to adjust to a stabilized pressure during a build-up phase and measuring simultaneously in relation to time, pressure P(t) and temperature T(t) in the pretest chamber;
(d) extracting an index i(t) dependent of the pressure P(t) and the temperature T(t) informing on the build-up phase;
(e) analyzing index i(t) and repeating steps (b)-(d) or going to step (f);
(f) determining the formation pressure based on a final stabilized pressure in the flowline.
6. The method of claim 5 , wherein the pretest piston is moved such that a predetermined change in volume in the flowline occurs.
7. The method of claim 5 , wherein the movement of the pretest piston is controlled by controlling one of reduction of pressure in the flowline, rate of pressure change in the flowline, incremental volume change the pretest chamber and combinations thereof.
8. The method of claim 5 further comprising the step of setting the formation tester.
9. The method of claim 5 , wherein said index i(t) is a function dependent of the effects of thermodynamic equilibrium in the formation tester and the effects of formation flow into the formation tester.
10. The method of claim 5 , wherein said index i(t) is a function dependent of the effects of temperature variation in the formation tester and the effects of formation flow into the formation tester.
11. The method of claim 5 , wherein said index i(t) is equal to:
Δ
T
Δ
P
·
δ
2
(
log
(
Δ
P
)
)
δ
t
2
,
where ΔT is the temperature variation, ΔP is the pressure variation and t the time.
12. The method of claim 5 , wherein the pretest piston is moved at a fixed rate.
13. The method of claim 6 , wherein the pretest piston is moved such that a predetermined change in volume in the flowline occurs.
14. A method for estimating type of a build up pressure phase, the build up pressure phase being done after a drawdown pressure phase, said both drawdown and build up phases being done to determine formation pressure using a formation tester disposed in a wellbore penetrating a permeable formation, said permeable formation being able to create a formation flow, said method further comprising the step of using an index to determine the contribution of formation flow on the pressure build up phase, wherein said index i(t) is equal to:
Δ
T
Δ
P
·
δ
2
(
log
(
Δ
P
)
)
δ
t
2
,
where ΔT is the temperature variation, ΔP is the pressure variation and t the time.