Method for measuring pressure in an underground formation

1. A method for measuring pressure in an underground formation containing a fluid, comprising:

establishing fluid communication between a first test chamber arranged in a drilling well and the underground formation, via a flowline;

moving a piston in the first test chamber so as to suction fluid into the first test chamber;

ensuring fluid isolation of the first test chamber relative to the flowline;

maintaining fluid isolation of the first test chamber;

measuring the pressure in the flowline at a point in the flowline isolated from the first test chamber during the maintaining of the fluid isolation of the first test chamber; and

repeating the preceding steps with the first test chamber or another test chamber.

2. The method according to claim 1 , wherein the fluid isolation of the test chamber is done by closing at least one valve between the flowline and the test chamber, and establishing the fluid communication between the test chamber and the underground formation by opening said valve.

3. A method for determining the permeability of the underground formation or determining the mobility of the fluid of the underground formation, comprising a pressure measurement according to the method of claim 1 , and calculating the permeability of the underground formation or the mobility of the fluid of the underground formation from the result of the pressure measurement.

4. The method according to claim 1 , which is implemented using a downhole well tool arranged in the drilling well.

5. The method according to claim 4 , wherein the downhole well tool includes a plurality of test chambers, the method including a preliminary step for choosing a test chamber.

6. The method according to claim 5 , wherein each test chamber is associated with a particular flow rate range, the method including the preliminary steps of:

choosing an appropriate flow rate;

choosing a test chamber whereof the flow rate range comprises the appropriate flow rate;

and wherein the fluid is suctioned in the test chamber at the selected fluid rate.

7. The method according to claim 6 , wherein the choice of the flow rate is made in a flow rate range comprised between a minimum flow rate and a maximum flow rate, the ratio of the maximum flow rate to the minimum flow rate being greater than or equal to 10.

8. A device for measuring pressure in an underground formation containing a fluid, comprising:

at least one test chamber provided with a piston;

a flowline in fluid communication with the at least one test chamber;

a pressure sensor in the flowline;

a probe adapted to establish a fluid communication between the underground formation and the flowline;

the piston configured to move in the at least one test chamber so as to suction fluid into the at least one test chamber; and

at least one closing system configured to repeatedly

establish fluid communication between the at least one test chamber arranged in a drilling well and the underground formation, via the flowline;

ensure fluid isolation of the at least one test chamber relative to the flowline;

maintain fluid isolation of the at least one test chamber;

the pressure sensor being located in the flowline at a point in the flowline isolated from the at least one test chamber during the maintaining of the fluid isolation of the at least one test chamber.

9. The device according to claim 8 , further comprising a plurality of test chambers, wherein each test chamber of the plurality of test chambers comprises a piston.

10. The device according to claim 9 , wherein the at least one closing system includes a single valve adapted to fluidly isolate the plurality of test chambers from the flowline.

11. The device according to claim 9 , wherein the at least one closing system includes a plurality of valves, each valve being adapted to fluidly isolate one of the plurality of test chambers from the flowline.

12. The device according to claim 9 , wherein at least two of the plurality of test chambers have different volumes.

13. The device according to claim 9 , wherein each piston for each test chamber is respectively controlled by an electric motor connected to a worm screw having a screw pitch, wherein the screw pitch differs from one test chamber to the next.

14. A downhole well tool adapted to perform measurements in an underground formation containing a fluid, the downhole well tool including a cable adapted to be inserted into a drilling well and a measuring device for measuring pressure in the underground formation, the measuring device provided with the cable and comprising:

at least one test chamber provided with a piston;

a flowline in fluid communication with the at least one test chamber;

a pressure sensor in the flowline;

a probe adapted to establish a fluid communication between the underground formation and the flowline;

at least one closing system adapted to repeatedly fluidly isolate the at least one test chamber from the flowline; wherein the pressure sensor is configured to measure pressure in the flowline:

after each isolation of the at least one test chamber from the flowline;

while maintaining fluid isolation of the at least one test chamber relative to the flowline; and

at a point in the flowline isolated from the at least one test chamber.

15. The downhole well tool according to claim 14 , wherein the measuring device comprises a plurality of test chambers, and each test chamber of the plurality of test chambers comprises a piston.

16. The downhole well tool according to claim 15 , wherein the at least one closing system includes a single valve adapted to fluidly isolate the plurality of test chambers from the flowline.

17. The downhole well tool according to claim 15 , wherein the at least one closing system includes a plurality of valves, each valve being adapted to fluidly isolate one of the plurality of test chambers from the flowline.

18. The downhole well tool according to claim 15 , wherein at least two of the plurality of test chambers have different volumes.

19. The downhole well tool according to claim 15 , wherein each piston for each test chamber is respectively controlled by an electric motor connected to a worm screw having a screw pitch, wherein the screw pitch differs from one test chamber to the next.

20. A method for measuring pressure in an underground formation containing a fluid, the method employing the device of claim 8 or 14 , the method comprising the following consecutive steps:

establishing fluid communication between at least one test chamber arranged in a drilling well and the underground formation, via a flowline;

moving the piston in the at least one test chamber to suction fluid into the at least one test chamber;

ensuring fluid isolation of the at least one test chamber relative to the flowline;

measuring the pressure in the flowline while maintaining fluid isolation of the at least one test chamber relative to the flowline, wherein the measuring occurs at a point in the flowline isolated from the at least one test chamber; and

repeating the preceding steps.