DETERMINATION OF FORMATION PRESSURE DURING A DRILLING OPERATION

• US 20090139321A1
• Filed: 11/30/2007
• Published: 06/04/2009
• Est. Priority Date: 11/30/2007
• Status: Active Grant

• Current Assignee: Schlumberger Technology Corporation (SLB)
• Original Assignee: Schlumberger Technology Corporation (SLB)
• Inventors: Flaum, Charles
• Granted Patent: US 7,765,862 B2
• Time in Patent Office: Days
• US Class Current: 73/152.510
• CPC Class Codes: E21B 21/08 Controlling or monitoring pressure or flow of drilling fluid, e.g. automatic filling of boreholes, automatic control of bottom pressure valve arrangements therefor E21B21/10
• CPC Class Codes: E21B 47/06 Measuring temperature or pressure
• CPC Class Codes: E21B 49/005 Testing the nature of borehole walls or the formation by using drilling mud or cutting data

Abstract

A drilling operation wherein a borehole can be drilled through earth formations with a drill bit at the end of a drill string, using recirculating drilling mud that flows downward through the drill string, exits through the drill bit, and returns to the earth'"'"'s surface in the annulus between the drill string and the borehole wall, at least a portion of which has a mudcake thereon, and a surface pumping system for pumping the mud to recirculate. Determining true formation pressure, including the following steps: providing a measurement device, having a probe, on the drill string; controlling the mud flow rate to obtain a first measured borehole pressure and measuring, with the probe of the measurement device, as a corresponding first probe pressure, the pressure in the formation adjacent the mudcake; controlling the mud flow rate to obtain a second measured borehole pressure and measuring, with the probe of the measurement device, as a corresponding second probe pressure, the pressure in the formation adjacent the mudcake; and deriving the true formation pressure from the first and second measured borehole pressures and the first and second probe pressures.

Claims

1. In a drilling operation wherein a borehole is being drilled through earth formations with a drill bit at the end of a drill string, using recirculating drilling mud that flows downward through the drill string, exits through the drill bit, and returns to the earth'"'"'s surface in the annulus between the drill string and the borehole wall, at least a portion of which has a mudcake thereon, and a surface pumping system for pumping the mud to recirculate;

a method for determining true formation pressure, comprising the steps of;

providing a measurement device, having a probe, on the drill string;

controlling the mud flow rate to obtain a first measured borehole pressure and measuring, with the probe of said measurement device, as a corresponding first probe pressure, the pressure in the formation adjacent the mudcake;

controlling the mud flow rate to obtain a second measured borehole pressure and measuring, with the probe of said measurement device, as a corresponding second probe pressure, the pressure in the formation adjacent the mudcake; and

deriving the true formation pressure from said first and second measured borehole pressures and said first and second probe pressures.

2. The method as defined by claim 1, wherein said step of providing a measurement device on the drill string comprises providing said measurement device near the drill bit.

3. The method as defined by claim 1, wherein said step of controlling the flow rate to obtain a second measured borehole pressure and measuring, with the probe of said measurement device, as a corresponding second probe pressure, the pressure in the formation adjacent the mudcake, includes controlling the flow rate to be different than the flow rate used to obtain said first measured borehole pressure.

4. The method as defined by claim 1, wherein said steps of controlling the mud flow rate are implemented from the earth'"'"'s surface.

5. The method as defined by claim 1, wherein said steps of controlling the mud flow rate are implemented, under control of a processor, from the earth'"'"'s surface.

6. The method as defined by claim 3, wherein said steps of controlling the mud flow rate are implemented, under control of a processor, from the earth'"'"'s surface.

7. The method as defined by claim 1, wherein said controlling and measuring steps are performed while the probe on said drill string is not rotating.

8. The method as defined by claim 5, wherein said controlling and measuring steps are performed while the probe on said drill string is not rotating.

9. The method as defined by claim 1, wherein said first and second measured borehole pressures are P_bh1 and P_bh2, respectively, and wherein said first and second probe pressures are P_pr1 and P_pr2, and wherein said deriving step comprises deriving said true formation pressure as

P_f=(Ratio*P_bh2−

V_bh1)/(Ratio−

1)

where

Ratio=(P_bh1−

P_pr1)/(P_bh2−

P_pr2).

10. The method as defined by claim 1, further comprising repeating the method at a number of different depth levels in the borehole, to obtain true formation pressure at said number of different depth levels.

11. The method as defined by claim 5, further comprising repeating the method at a number of different depth levels in the borehole, to obtain true formation pressure at said number of different depth levels.

12. The method as defined by claim 1, further comprising repeating the method at a number of different depth levels in the borehole, to obtain true formation pressure at said number of different depth levels, and producing from said number of obtained true formation pressures, a log of true formation pressure as a function of depth level.

13. The method as defined by claim 5, further comprising repeating the method at a number of different depth levels in the borehole, to obtain true formation pressure at said number of different depth levels, and producing from said number of obtained true formation pressures, a log of true formation pressure as a function of depth level.

14. In a drilling operation wherein a borehole is being drilled through earth formations with a drill bit at the end of a drill string, using recirculating drilling mud that flows downward through the drill string, exits through the drill bit, and returns to the earth'"'"'s surface in the annulus between the drill string and the borehole wall, at least a portion of which has a mudcake thereon, and a surface pumping system for pumping the mud to recirculate;

a method for determining true formation pressure, comprising the steps of;

providing a measurement device, having a probe, on the drill string;

controlling the mud flow rate to obtain a first measured borehole pressure and measuring, with the probe of said measurement device, as a corresponding first probe pressure, the pressure in the formation adjacent the mudcake;

controlling the mud flow rate to obtain a second measured borehole pressure and measuring, with the probe of said measurement device, as a corresponding second probe pressure, the pressure in the formation adjacent the mudcake;

controlling the mud flow rate to obtain a third measured borehole pressure, with the probe of said measurement device, as a corresponding third probe pressure, the pressure in the formation adjacent the mudcake; and

deriving the true formation pressure from said first, second, and third measured borehole pressures and said first, second, and third probe pressures.

15. The method as defined by claim 14, wherein said step of providing a measurement device on the drill string comprises providing said measurement device near the drill bit.

16. The method as defined by claim 14, wherein said steps of controlling the mud flow rate are implemented, under control of a processor, from the earth'"'"'s surface.

17. The method as defined by claim 14, wherein said controlling and measuring steps are performed while the probe on said drill string is not rotating.

18. The method as defined by claim 14, further comprising repeating the method at a number of different depth levels in the borehole, to obtain true formation pressure at said number of different depth levels.

19. The method as defined by claim 14, further comprising repeating the method at a number of different depth levels in the borehole, to obtain true formation pressure at said number of different depth levels, and producing from said number of obtained true formation pressures, a log of true formation pressure as a function of depth level.

20. A method for determining true formation pressure while drilling in a subterranean environment from using recirculation fluid that flows through a drill string and a void between the drill string and a formation being drilled, the method comprising the steps of:

providing a measurement device, having a probe, on the drill string;

providing a drill bit on a lower end of the drill string such that said measurement device is approximate the drill bit;

controlling a mud flow rate with a controlling means to obtain a first measured borehole pressure and measuring, with the probe of said measurement device, as a corresponding first probe pressure, the pressure in the formation adjacent a mudcake located approximate the void;

controlling the mud flow rate to obtain a second measured borehole pressure and measuring, with the probe of said measurement device, as a corresponding second probe pressure, the pressure in the formation adjacent said mudcake; and

deriving the true formation pressure from said first and second measured borehole pressures and said first and second probe pressures, wherein the derived true formation pressure is communicated to a bottom hole assembly.

21. The method as defined by claim 20, further comprising repeating the method at a number of different depth levels in the drilled formation, to obtain true formation pressure at said number of different depth levels.

22. The method as defined by claim 20, further comprising repeating the method at a number of different depth levels in the drilled formation, to obtain true formation pressure at said number of different depth levels, and producing from said number of obtained true formation pressures, a log of true formation pressure as a function of depth level.