Apparatus and method for retrieving formation fluid samples utilizing differential pressure measurements

• US 5,622,223 A
• Filed: 09/01/1995
• Issued: 04/22/1997
• Est. Priority Date: 09/01/1995
• Status: Expired due to Term

• Current Assignee: Paul S. Madan
• Original Assignee: Halliburton Company
• Inventors: Vasquez, Rafael B.
• Primary Examiner(s): Tsay, Frank
• Application Number:
  US08/522,851
• Time in Patent Office: 599 Days
• Field of Search: 166/100, 166/264, 166/250.02, 166/321, 166/374, 166/66.4, 166/72, 73/151, 73/155
• US Class Current: 166/264
• CPC Class Codes: E21B 49/10 using side-wall fluid samplers or testers

Abstract

This invention provides a closed-loop system for in situ testing of formation fluid conditions and for selectively collecting substantially mud filtrate free formation fluid samples at original formation conditions. The system contains an elongated member having a probe that is sealingly placed against the wellbore formation to withdraw formation fluids. A surface controlled pump controls the flow of a fluid from the formation into a flow line placed in the elongated member. A pressure sensor provides downhole hydrostatic pressure and differential pressure sensor provides difference in pressure across two fixed points across the flow line. A temperature sensor and resistivity device are utilized in a conventional manner to respectively provide downhole fluid temperature and the resistivity of the formation fluid. The system determines the density of the formation fluid in the flow line from the differential pressure and in response thereto controls the fluid flow into the flow line to selectively collect the formation fluid samples that are substantially free from any mud filtrates while maintaining the fluid pressure above the bubble point pressure of the fluid. This invention provides a method for retrieving and collecting formation fluids from a zone of interest in a wellbore at the original formation conditions.

Claims

1. A system for retrieving a formation fluid from a formation, comprising:

(a) a probe adapted for placement against the formation for receiving fluid from the formation;

(b) a pump for controlling flow of the fluid ("flow rate") from the probe into a flow line;

(c) a differential pressure sensor coupled across the flow line for providing a signal representative of the difference in pressure between two fixed points in the flow line; and

(d) control circuit coupled to the pump and the differential pressure sensor for controlling the pump to control the flow rate of the fluid as a function of the differential pressure so as to maintain the pressure in the flow line above a predetermined pressure.

2. The apparatus as specified in claim 1, wherein the control circuit contains a first circuit for processing the differential pressure signals and a second circuit for controlling the operation of the pump.

3. A system for retrieving a formation fluid from a formation, comprising:

(a) a probe adapted for placement against the formation for receiving the formation fluid;

(b) a pump for controlling rate of flow of the formation fluid ("formation fluid flow rate") from the probe into a flow line;

(c) a differential pressure sensor coupled across the flow line for providing a signal representative of the difference in pressure between two fixed points in the flow line;

(d) a valve coupled to the flow line for selectively directing the formation fluid discharge from the flow line into a chamber or the wellbore; and

(e) a control circuit coupled to the pump, valve and the differential pressure sensor, said control circuit controlling the formation fluid flow rate into the flow line as a function of the differential pressure so as to maintain pressure in the flow line above a predetermined pressure, said control circuit further controlling the valve to collect the formation fluid in the chamber.

4. The apparatus as specified in claim 3 further having a telemetry coupled to the control circuit for transmitting data to and from the control circuit.

5. The apparatus as specified in claim 4 further having a surface control unit coupled to the telemetry by a wireline, said surface control unit receiving data from the downhole control circuit corresponding to the differential pressure sensor signals and in response thereto transmitting command signals to the control circuit for controlling the operation of the pump.

6. The apparatus as specified in claim 5 wherein the surface control unit further transmits signals to the control circuit to control the operation of the valve.

7. A system for retrieving and collecting a formation fluid from a zone of interest in a wellbore, comprising:

(a) a probe adapted for placement against the zone of interest in the wellbore for receiving the formation fluid;

(b) a pump for controlling the flow rate of the formation fluid from the probe into a flow line;

(c) a differential pressure sensor coupled across the flow line for providing a signal representative of the difference in pressure between two fixed points in the flow line; and

(d) a control unit for determining density of the formation fluid from the differential pressure signals and in response thereto controlling the flow of the formation fluid so as to maintain the pressure in the flow line above the bubble point pressure of the fluid.

8. The apparatus as specified in claim 7, wherein the surface control unit contains a computer and a display.

9. A system for retrieving and collecting a formation fluid from a zone of interest in a wellbore, comprising:

(a) a probe adapted for placement against the zone of interest in the wellbore for receiving the formation fluid;

(b) a pump for controlling flow of the formation fluid ("formation fluid flow rate") from the probe into a flow line;

(c) a differential pressure sensor coupled across the flow line for providing a signal representative of the difference in pressure between two fixed points in the flow line;

(d) a control circuit coupled to the pump and the differential pressure sensor for processing the differential pressure signal and for controlling the operation of the pump in response to command signals; and

(e) a control unit, said control unit receiving the differential pressure signals, computing density of the fluid in the flow line and determining from the density when the fluid flowing in the flow line is substantially free of mud filtrates, said control unit further causing the flow rate to change as a function of the density in a manner which ensures that the pressure in the flow line remains above the bubble point of the fluid in the flow line.

10. A system for retrieving and collecting a formation fluid from a zone of interest in a wellbore, comprising:

(a) a downhole tool adapted to be conveyed in the wellbore having

(i) a probe adapted for placement against the zone of interest for receiving the formation fluid;

(ii) a pump for controlling flow of the formation fluid ("flow rate") from the probe into a flow line;

(iii) a differential pressure sensor coupled across the flow line for providing a signal representative of the difference in pressure between two fixed points in the flow line;

(iv) a control valve for controlling the flow rate of the formation fluid from the flow line into a chamber;

(v) a resistivity device for providing information about resistivity of the fluid flowing through the flow line; and

(b) a surface control unit for causing the flow rate to change as a function of the density in a manner which ensures that the pressure in the flow line remains above the bubble point of the fluid, said control unit further determining from the resistivity of the formation fluid when the fluid in the flow line is substantially free of mud filtrates and causing the control valve to discharge the fluid that is substantially free of mud filtrates into a chamber.

11. A formation testing and fluid collection apparatus, comprising:

(a) a probe adapted to be sealingly placed against a wellbore formation for receiving the fluid from the formation;

(b) a pump coupled to the probe for controlling the flow of the fluid from the probe into a flow line;

(c) a buffer line placed coupled across flow line between two points that are at least two feet apart;

(d) a pair of valves placed in the buffer line at least two feet apart, each said valve adapted to selectively cause the buffer line to be in fluid communication with the flow line and wellbore fluid;

(e) a differential pressure sensor placed in the buffer line for providing difference in the pressure between two selected points;

(f) a first circuit for determining the pressure gradient from the differential pressure signals;

(g) a second circuit for controlling the flow rate through the pump; and

(h) a control unit, said control unit receiving signals from the first circuit and in response thereto generating control signal for the second circuit for controlling the flow of the fluid through the pump in a manner that will ensure that any fluid flowing into the flow line remains below the bubble point of any liquid gas contained in the fluid.

12. The system as specified in claim 11 further having a duplex telemetry coupled between the control unit and the first and second circuits for providing data transmission between the control unit and the first and second circuits.

13. The system as specified in claim 11 wherein the control unit receives data from the first circuit corresponding to the differential pressure sensor signals and in response thereto transmits command signals to the second circuit for controlling the operation of the pump.

14. The apparatus as specified in claim 11 further having a pressure sensor for providing signals representative of the pressure of the fluid in the flow line.

15. The apparatus as specified in claim 11 further having a temperature sensor for providing signals representative of the temperature of the fluid in the flow line.

16. The apparatus as specified in claim 11 further having a resistivity device for providing signals for determining the resistivity of the formation fluid.

17. A method for retrieving a formation fluid from a zone of interest in a wellbore, said method comprising the steps of:

(a) withdrawing the formation fluid from the zone of interest into a flow line;

(b) determining the pressure differential between two fixed points across the flow line;

(c) determining the density of the fluid from the differential pressure; and

(d) controlling the flow of the fluid into the flow line based on the fluid density determination in a manner that ensures that the pressure in the flow line remains above the bubble point of the fluid.

18. A method for retrieving and collecting a formation fluid from a zone of interest in a wellbore, said method comprising the steps of:

(a) discharging the formation fluid from the zone of interest into a flow line;

(b) determining the pressure differential between two fixed points across the flow line;

(c) determining the density of the fluid from the differential pressure;

(d) controlling the flow of the fluid into the flow line based on the fluid density determination in a manner that ensures that the flow line pressure remains above the bubble point of the fluid; and

(e) collecting the fluid from the flow line in a chamber above the bubble point pressure.

19. A method for retrieving and collecting formation fluid that is substantially free of mud filtrates from a wellbore formation, said method comprising the steps of:

(a) discharging the formation fluid into a flow line having a pump at one end that is adapted to control the fluid flow rate into the flow line and a two-way valve that is adapted in a first position to discharge the fluid from the flow line into the well bore in a second position into a collection chamber;

(b) determining the pressure of the fluid flowing into the flow line and the differential pressure of the fluid in the flow line between two fixed points across the flow line;

(c) determining density of the fluid from the differential pressure;

(d) determining resistivity of the fluid flowing into the flow line;

(e) determining from the density and the pressure of the fluid in the flow line the bubble point of the fluid;

(f) determining from the resistivity when the fluid flowing through the flow line is substantially free of mud filtrates;

(g) controlling the flow rate through the flow line by controlling the pump so as to maintain the flow line pressure above the bubble point pressure;

collecting the fluid from the flow line in a chamber above the bubble point pressure; and

(h) collecting the fluid in the collection chamber when the fluid flowing through the flow line is substantially free of mud filtrates and the fluid pressure is above the bubble point pressure.

20. A method for determining bubble point pressure of a formation fluid in a wellbore, comprising the steps of:

(a) discharging the formation fluid from a zone of interest into a flow line;

(b) determining the pressure of the fluid in the flow line and pressure differential between two fixed points across the flow line;

(c) determining the density of the formation fluid from the differential pressure;

(d) changing the fluid flow rate into the flow line; and

(e) repeating steps (b)-(d) a desired number of times, recording the pressure in the flow line and the differential pressure corresponding to each flow rate and determining therefrom the bubble point pressure of the fluid.