Method and apparatus for controlling pressure and detecting well control problems during drilling of an offshore well using a gas-lifted riser

• US 6,668,943 B1
• Filed: 05/31/2000
• Issued: 12/30/2003
• Est. Priority Date: 06/03/1999
• Status: Expired due to Fees

• Current Assignee: Exxonmobil Upstream Research Company (Exxon Mobil Corporation)
• Original Assignee: Exxonmobil Upstream Research Company (Exxon Mobil Corporation)
• Inventors: Van Acker, Torney M., Ehrhardt, Mark E., Maus, L. Donald
• Primary Examiner(s): Shackelford, Heather
• Assistant Examiner(s): KRECK, JOHN J
• Application Number:
  US09/584,526
• Time in Patent Office: 1,308 Days
• Field of Search: 175/5, 175/7, 175/25, 175/38, 175/48, 175/212, 175/218
• US Class Current: 175/5
• CPC Class Codes: E21B 21/001 specially adapted for underwater drilling dual gradient drilling E21B21/082
• 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 21/085 Underbalanced techniques, i.e. where borehole fluid pressure is below formation pressure

Abstract

A method and apparatus for controlling the riser base pressure and detecting well control problems, such as kicks or lost circulation, during drilling of an offshore well using a gas-lifted riser. The pressure control apparatus preferably includes two separate control elements, one to adjust the pressure at the surface (p_rs) and the mass flow rate out of the top of the riser ({dot over (m)}_o) to compensate for changes in riser base pressure (p_rb) and the other to adjust either or both of the boost mud flow rate (q_b) and lift gas flow rate (q_g) to maintain a constant or nearly constant mass flow rate entering the base of the riser ({dot over (m)}_i). According to the method of the present invention, the well return flow rate (q_w) is preferably determined by directly measuring various other parameters and then computing q_w from the measured parameters. The computed value of q_w may be compared to the drill string flow rate (q_c) to detect well control problems, such as kicks or lost circulation.

Claims

1. A method for controlling the pressure at the base of a gas-lifted riser during drilling of an offshore well, said method comprising the steps of:

determining the riser base pressure (p_rb); and

using a throttling device located at or near the top of said riser to adjust the mass flow rate out of the top of said riser ({dot over (m)}_o) and the riser surface pressure (p_rs) to compensate for changes In the riser base pressure (p_rb).

2. A method for controlling the pressure at the base of a gas-lifted riser during drilling of an offshore well, said method comprising the steps of:

determining the mass flow rate into the base of said riser ({dot over (m)}_i); and

adjusting one or both of the boost mud flow rate (q_b) and the lift gas flow rate (q_g) to substantially minimize variations in the mass flow rate into the base of said riser ({dot over (m)}_i).

3. The method of claim 2, wherein the step of determining the mass flow rate into the base of said riser ({dot over (m)}_i) further comprises the steps of:

determining boost mud density (ρ

_b), boost mud flow rate (q_b) lift gas density (ρ

_g), lift gas flow rate (q_g), well return density (ρ

_w) and well return flow rate (q_w); and

calculating the mass flow rate into the base of said riser ({dot over (m)}_i), where

4. The method of claim 3, wherein the step of determining the well return flow rate (q_w) further comprises the steps of:

determining lift gas absolute temperature (T_g), riser mix density (ρ

_mix),

and riser mix absolute temperature (T_mix); and

calculating the well return flow rate (q_w), where

5. The method of claim 3, wherein said method further comprises the steps of:

determining the drill string flow rate (q_c), and

comparing the drill string flow rate (q_c) to the well return flow rate (q_w) to detect well control problems such as kicks or lost circulation.

6. A method for controlling the pressure at the base of a gas-lifted riser during drilling of an offshore well, said method comprising the steps of:

determining riser base pressure (p_rb) and the mass flow rate into the base of said riser ({dot over (m)}_i);

using a throttling device located at or near the top of said riser to adjust the mass flow rate out of the top of said riser ({dot over (m)}_o) and the riser surface pressure (p_rs) to compensate for changes in the riser base pressure (p_rb); and

adjusting one or both of the boost mud flow rate (q_b) and the lift gas flow rate (q_g) to substantially minimize variations in the mass flow rate into the base of said riser ({dot over (m)}_i).

7. The method of claim 6, wherein the step al determining the mass flow rate into the base of said riser ({dot over (m)}_i) further comprises the steps of:

determining boost mud density (ρ

_b), boost mud flow rate (q_b), lift gas density (ρ

_g), lift gas flow rate (q_g), well return density (ρ

_w), and well return flow rate (q_w); and

calculating the mass flow rate into the base of said riser ({dot over (m)}_i), where

8. The method of claim 7, wherein the step of determining the well return flow rate (q_w) further comprises the steps of:

determining lift gas absolute temperature (T_g), riser mix density (ρ

_mix), and riser mix absolute temperature (T_mix); and

calculating the well return flow rate (q_w), where

9. The method of claim 7, wherein said method further comprises the steps of:

determining the drill string flow rate (q_c); and

comparing the drill string flow rate (q_c) to the well return flow rate (q_w) to detect well control problems such as kicks or lost circulation.

10. A method for controlling the pressure at the base of a gas-lifted riser during drilling of an offshore well, said method comprising the steps of:

determining boost mud density (ρ

_b), boost mud flow rate (q_b), lift gas density (ρ

_g), lift gas absolute temperature (T_g), lift gas flow rate (q_g), riser mix density (ρ

_mix), riser mix absolute temperature (T_mix), well return density (ρ

_w) and riser base pressure (p_rb);

calculating the well return flow rate (q_w), where

11. The method of claim 10, wherein said method further comprises the steps of:

determining the drill string flow rate (q_c); and

comparing the drill string flow rate (q_c) to the well return flow rate (q_w) to detect well control problems such as kicks or lost circulation.

12. A method for controlling the pressure at the base of a gas-lifted riser during drilling of an offshore well, said method comprising the steps of:

a) determining a setpoint value for riser mix density (ρ

_mix);

b) determining the actual value of riser mix density (ρ

_mix);

c) adjusting one or both of the boost mud flow rate (q_b) and the lift gas flow rate (q_g), to substantially minimize the difference between said setpoint value and said actual value;

d) determining well return flow rate (q_w) and drill string flow rate (q_c);

e) comparing the drill string flow rate (q_c) to the well return flow rate (q_w) to detect well control problems such as kicks or lost circulation;

f) determining boost mud density (ρ

_b), boost mud flow rate (q_b), lift gas density (ρ

_g), lift gas flow rate (q_g), lift gas absolute temperature (T_g), well return density (ρ

_w), riser mix density (ρ

_mix), and riser mix absolute temperature (T_mix); and

g) calculating the well return flow rate (q_w), where

13. Apparatus for controlling the pressure at the base of a gas-lifted riser during drilling of an offshore well, said apparatus comprising:

means for determining the mass flow rate into the base of said riser ({dot over (m)}_i); and

means for adjusting one or both of the boost mud flow rate (q_b) and the lift gas flow rate (q_g) to substantially minimize variations in the mass flow rate into the base of said riser ({dot over (m)}_i).

14. The apparatus of claim 13, wherein said means for determining the mass flow rate into the base of said riser ({dot over (m)}_i) comprises:

means for determining boost mud density (ρ

_b), boost mud, flow rate (q_b), lift gas density (ρ

_g), lift gas flow rate (q_g), well return density (ρ

_w) and well return flow rate (q_w); and

means for calculating the mass flow rate into the base of said riser ({dot over (m)}_i),

where

15. The apparatus of claim 14, wherein said means for determining well return density (ρ

_w) comprises a differential pressure transducer adapted to measure the pressure differential between two vertically spaced-apart points in the lower end of said riser.

16. The apparatus of claim 14, wherein said means for determining the well return flow rate (q_w) comprises:

means for determining lift gas absolute temperature (T_g), riser mix density (ρ

_mix), and riser mix absolute temperature (T_mix); and

means for calculating the well return flow rate (q_w), where

17. The apparatus of claim 14, said apparatus further comprising:

means for determining the drill string flow rate (q_c); and

means for comparing the drill string flow rate (q_c) to the well return flow rate (q_w) to detect well control problems such as kicks or lost circulation.

18. The apparatus of claim 13, wherein said means for adjusting one or both of the boost mud flow rate (q_b) and the lift gas flow rate (q_g) comprise surface-controlled flow control valves installed in the lift gas injection line and the boost mud line.

19. Apparatus for controlling the pressure at the base of a gas-lifted riser during drilling of an offshore well, said apparatus comprising:

means for determining riser base pressure (p_rb) and the mass flow rate into the base of said riser ({dot over (m)}_i);

a throttling device for adjusting the mass flow rate out of the top of said riser ({dot over (m)}_o) and the riser surface pressure (p_rs) to compensate for changes in the riser base pressure (p_rb), said throttling device being located at or near the top of said riser; and

means for adjusting one or both of the boost mud flow rate (q_b) and the lift gas flow rate (q_g) to substantially minimize variations in the mass flow rate into the base of said riser ({dot over (m)}_i).

20. The apparatus of claim 19, wherein said means for determining the mass flow rate Into the base of said riser ({dot over (m)}_i) comprises:

means for determining boost mud density (ρ

_b), boost mud flow rate (q_b), lift gas density (ρ

_g), lift gas flow rate (q_g), well return density (ρ

_w) and well return flow rate (q_g); and

means for calculating the mass flow rate into the base of said riser ({dot over (m)}_i),

where

21. The apparatus of claim 20, wherein said means for determining the well return flow rate (q_w) comprises:

means for determining lift gas absolute temperature (T_g), riser mix density (ρ

_mix), and riser mix absolute temperature (T_mix); and

means for calculating the well return flow rate (q_w), where

22. The apparatus of claim 21, said apparatus further comprising:

means for determining the drill string flow rate (q_c); and

means for comparing the drill string flow rate (q_c) to the well return flow rate (q_w) to detect well control problems such as kicks or lost circulation.

23. Apparatus for controlling the pressure at the base of a gas-lifted riser during drilling of an offshore well, said apparatus comprising:

means for determining boost mud density (ρ

_b) boost mud flow rate (q_b), lift gas density (ρ

_g), lift gas absolute temperature (T_g), lift gas flow rate (q_g), riser mix density (ρ

_mix), riser mix absolute temperature (T_mix), well return density (ρ

_w) and riser base pressure (p_rb);

means for calculating the well return flow rate (q_w), where

24. The apparatus of claim 23, said apparatus further comprising:

means for determining the drill string flow rate (q_c); and

means for comparing the drill string flow rate (q_c) to the well return flow rate (q_w) to detect well control problems such as kicks or lost circulation.

25. Apparatus for controlling the pressure at the base of a gas-lifted riser during drilling of an offshore well, said apparatus comprising:

means for determining the actual value of riser mix density (ρ

_mix);

means for adjusting one or both of the boost mud flow rate (q_b) and the lift gas flow rate (q_g) to substantially minimize differences between said actual value of riser mix density (ρ

_mix) and a predetermined setpoint value of riser mix density (ρ

_mix);

means for determining the drill string flow rate (q_c);

means for determining he well return flow rate (q_w), wherein said means for determining comprises means for determining boost mud density (ρ

_b), boost mud flow rate (q_b), lift gas density (ρ

_g), lift gas flow rate (q_g), lift gas absolute temperature (T_g), well return density (ρ

_w), riser mix density (ρ

_mix), and riser mix absolute temperature (T_mix);

means for calculating the well return flow rate (q_w), where