Wellbore annular pressure control system and method using gas lift in drilling fluid return line

Patent metadata

Field	Value
Publication number	US-9376875-B2
Application number	US-201314396577-A
Country	US
Kind code	B2
Filing date	Apr 29, 2013
Priority date	Apr 27, 2012
Publication date	Jun 28, 2016
Grant date	Jun 28, 2016

Abstract

A system and method include pumping drilling fluid through a drill string extended into a wellbore extending below the bottom of a body of water, out the bottom of the drill string and into the wellbore annulus. Fluid is discharged from the annulus into a riser and a discharge conduit. The riser is disposed above the top of the wellbore and extends to the water surface. The discharge conduit couples to the riser and includes a controllable fluid choke. A fluid return line is coupled to an outlet of the choke and extends to the water surface. Gas under pressure is pumped into the return line at a selected depth below the water surface. The controllable fluid choke may be operated to maintain a selected drilling fluid level in the riser, the selected fluid level being a selected distance below the water surface.

First claim

What is claimed is:

1. A system comprising:
a drill string extending into a wellbore below a bottom of a body of water;
a primary pump for selectively pumping a drilling fluid through the drill string and into an annular space created between the drill string and the wellbore;
a riser extending from a top of the wellbore to a platform on a surface of the body of water;
a fluid discharge conduit in fluid communication with the riser;
a controllable orifice choke coupled to the discharge conduit;
a fluid return line extending from the choke to the platform;
a source of compressed gas coupled to the fluid return line at a selected depth below the surface of the body of water;
a separator coupled to the fluid return line;
a flow meter coupled to a gas discharge end of the separator; and
a controller configured to receive an input signal from the flow meter and configured to compare a flow rate of gas measured by the flow meter to a flow rate of gas pumped into the fluid return line.

2. The system of claim 1 , further comprising a pressure sensor disposed at a selected depth in the wellbore or the riser.

3. The system of claim 2 , wherein the controller is configured to accept an input signal from the pressure sensor and configured to generate an output signal to operate the choke, wherein the choke is operated to maintain a selected hydrostatic pressure in the riser at a selected distance below the surface of the body of water.

4. The system of claim 3 , further comprising at least one fluid flow meter for measuring a flow of fluid into the wellbore or out of the wellbore, and wherein the controller accepts an input signal from the at least one fluid flow meter, the controller generating an output signal to operate the choke to maintain fluid pressure in the wellbore at a selected value.

5. The system of claim 1 , wherein the controllable orifice choke is disposed at a selected depth below the surface of the body of water.

6. The system of claim 1 , further comprising a pressure sensor coupled to the fluid return line.

7. The system of claim 1 , wherein the fluid return line extending from the choke to the platform includes a vertical portion disposed below the surface of the body of water.

8. The system of claim 1 , further comprising a check valve coupled to the fluid return line between the controllable orifice choke and an inlet in the fluid return line coupled to the source of compressed gas.

9. The system of claim 1 , wherein the pressure sensor is coupled to the discharge conduit proximate the fluid choke.

10. A method comprising:
pumping drilling fluid through a drill string extended into a wellbore extending below a bottom of a body of water, out the bottom of the drill string, and into the wellbore annulus;
discharging fluid from the wellbore annulus and into a riser disposed above the top of the wellbore, the riser extending to the surface of the body of water,
discharging fluid from the riser through a fluid return line, the fluid return line extending from below the surface of the body of water to the surface of the body of water;
pumping gas under pressure into the return line at a selected depth below the surface of the body of water;
maintaining a selected hydrostatic pressure in the riser at a selected distance below the surface of the body of water;
separating the gas from a fluid returned by the return line proximate the surface of the body of water;
measuring a flow rate of the gas separated from the fluid returned by the return line; and
comparing the flow rate of the gas separated from the fluid returned by the return line to a flow rate of the gas pumped into the return line.

11. The method of claim 10 , further comprising measuring a pressure of fluid in the riser at a selected depth, and operating a controllable fluid choke disposed between the riser and the fluid return line based on the measuring to maintain the selected hydrostatic pressure in the riser at the selected distance below the surface of the body of water.

12. The method of claim 10 , further comprising adjusting the hydrostatic pressure in the riser by adjusting a flow rate of gas pumped into the return line.

13. A method comprising:
pumping drilling fluid through a drill string extended into a wellbore extending below the bottom of a body of water, out the bottom of the drill string, and into the wellbore annulus;
discharging fluid from the wellbore annulus into a riser disposed above the top of the wellbore and into a discharge conduit, the discharge conduit including a fluid choke and a fluid return line coupled to an outlet of the fluid choke and extending to the water surface;
pumping gas under pressure into the return line at a selected depth below the water surface;
controlling a rate at which the gas is pumped into the return line and operating a back pressure pump to apply back pressure to the discharge conduit to maintain a level of fluid in the riser at a selected distance below the surface of the body of water;
wherein a controller receives input signals from at least one of a pressure sensor in the discharge conduit, a first flow meter coupled to a liquid discharge end of a separator configured to separate the gas from the fluid in the return line, and a second flow meter coupled to a gas discharge end of the separator, and wherein the controller sends output signals to operate the fluid choke and the back pressure pump to maintain the level of fluid in the riser at the selected distance below the surface of the body of water.

14. The method of claim 13 , further comprising operating the fluid choke in response to a measured flow rate in the discharge conduit proximate the fluid choke.

15. The method of claim 13 , further comprising restricting fluid flow from the return line to the fluid choke.

16. The method of claim 13 , further comprising venting gas from the return line to atmosphere.

17. The method of claim 13 , wherein the controlling the rate at which the gas is pumped into the return line comprises comparing the rate at which the gas is pumped into the return line to a rate at which drilling fluid is pumped through the drill string.

Assignees

• Smith International

Inventors

• Reitsma Donald D
• Sehsah Ossama R
• Couturier Yawan

Classifications

• E21B47/12

  Means for transmitting measuring-signals or control signals from the well to the surface, or from the surface to the well, e.g. for logging while drilling · CPC title

• E21B21/08 Primary

  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 title

• E21B21/001

  specially adapted for underwater drilling (dual gradient drilling E21B21/082) · CPC title

• E21B21/103

  Down-hole by-pass valve arrangements, i.e. between the inside of the drill string and the annulus (valves specifically for maintaining circulation of drilling fluid while connecting or disconnecting tubular joints E21B21/019) · CPC title

• E21B21/06

  Arrangements for treating drilling fluids outside the borehole · CPC title