MUD LIFT DRILLING SYSTEM USING EJECTOR ASSEMBLY IN MUD RETURN LINE
A method is described for controlling pressure in a wellbore drilled below the bottom of a body of water wherein the wellbore has a fluid outlet in communication with a working fluid inlet of an ejector assembly to return drilling fluid to a drilling platform on the water surface. The method includes pumping drilling fluid into a drill string extending from the drilling platform into the wellbore and at least one of, (i) introducing fluid into a power fluid inlet of the ejector assembly at a rate selected to remove fluid from the wellbore fluid outlet at a selected rate and (ii) operating a controllable flow restriction in a flow path from the wellbore fluid outlet to the working fluid inlet of the ejector assembly, in order to maintain a selected wellbore pressure.
This disclosure is related to the field of controlled pressure drilling and “dual gradient” drilling. More particularly the disclosure relates to apparatus and methods for controlled pressure and/or dual gradient drilling that use ejector assemblies.
International Application Publication No. WO 2013/0177331 describes a managed pressure drilling system using a pump in a drilling fluid return line. The pump may be used to maintain a selected fluid level in a drilling riser disposed above a top of a subsea wellbore, wherein the riser extends from a subsea wellhead at the water bottom to a drilling platform above the water surface. By suitable operation of the pump, the fluid level may be maintained at a selected elevation at or below the water surface so that a pressure in the wellbore may be maintained at or below the hydrostatic pressure of the fluid column in the riser were it to extend from the bottom of the wellbore to the surface. In the case the fluid level elevation in the riser is maintained below the surface, the pressure elevation gradient of the fluid in the riser may be different than the fluid pressure elevation gradient of fluid (“mud”) pumped into a drill string used to drill the wellbore below the water bottom. In other implementations, a riser may be omitted, and drilling fluid being discharged from the wellbore may be returned to the surface by a separate return line having a pump therein.
The system shown in the '331 publication cited above is illustrative of “mud lift” drilling systems known in the art. Referring to
By coupling a subsea mud lift pump 20 to the liner 14 near the seabed (or to the wellhead when drilling, e.g., from a floating drilling platform), the returning drilling fluid can be pumped out of the annulus 30 and up to the drilling rig 1 to reduce the fluid pressure in the annulus 30. In some implementations, the annular volume above the wellbore may include a riser that may be partially or completely filled with drilling fluid and/or with a different riser fluid. The density of the riser fluid, if used, may be less than that of the drilling fluid. It is also possible to drill such wellbores without a riser by using a rotating control head or rotating diverter coupled to the top of the wellbore (i.e., the wellhead) to seal against the drill string 16.
The drilling fluid pressure existing at the level of the water bottom may be controlled from the drilling rig 1 by selecting the inlet pressure to the subsea mud lift pump 20. In riser-type drilling systems as shown in
H1 and H2 together make up the length of the riser section from the water bottom 8 and in some examples may extend upward to the deck 4 of the drilling rig 1. Filling the riser 12 at least in part with a riser fluid allows continuous flow quantity control of the fluid flowing into and out of the wellbore 15. Thus, it is relatively easy to detect a phenomenon, such as, for example, drilling fluid flowing out of the wellbore 15 into an exposed formation (“lost circulation”). It is furthermore possible to maintain a substantially constant drilling fluid pressure at the level of the water bottom when the drilling fluid density changes. Choosing a different inlet pressure to the subsea mud lift pump will cause the heights H1 and H2 to change according to the new selected subsea mud lift pump 20 inlet pressure. If so desired, the outlet 17 from the annulus 30 to the subsea mud lift pump 20 can be arranged at a level below the water bottom, by coupling a first pump pipe (not shown in
As explained above, using a riser to exert part of the hydrostatic pressure on the wellbore annulus is optional, and in other implementations the riser may be omitted. Such implementations may use a rotating control head or other rotatable sealing device (not shown) to seal the annular space above the top of the wellbore 15 while enabling rotation and axial motion of the drill string 16.
In
While the embodiment shown in
The volume of fluid flowing into and out of the tank 26 is typically monitored, making it possible to determine, e.g., whether drilling fluid is being lost into an exposed formation (i.e., one not sealed by the liner 14), or whether gas or liquid is flowing from an exposed formation and into the wellbore 15 and fluid circulation system.
As explained in the Background section herein, most lifting devices that perform the function of the subsea mud lift pump (20 shown in
In some embodiments, a drilling riser 14 may extend from a wellhead BOPE located on the bottom 8 of a body of water and may extend to a drilling platform 4 at the water surface as explained with reference to
In the present example embodiment, a pressure sensor C may be in pressure communication with the interior of the drilling riser 14 at a selected position. The pressure sensor C may be in signal communication with a pump controller (not shown separately) which may selectively operate the power fluid pump (26B in
In some embodiments, a booster line 14A may be included alongside the drilling riser 14 for injecting fluid when required, for example, such as when necessary to circulate out a fluid that may enter the wellbore 15 from a sub-bottom formation.
In other implementations, the riser 14 may be omitted, and drilling fluid being discharged from the wellbore 15 may be returned to the surface by a separate return line having an ejector assembly therein. Such return line may be hydraulically connected to the wellbore below the wellhead (BOPE in
An example ejector assembly D is shown in more detail in
Another embodiment shown in
A mud lift drilling system and method according to the present disclosure may provide the capability of controlling wellbore pressure without the need for a pump having moving parts disposed below the surface of a body of water. Embodiments of an ejector assembly according to the present disclosure may be replaceable by a wireline or slickline operation, or using a coiled tubing or semi-stiff spoolable intervention rod thus simplifying ejector assembly replacement if and when needed. A semi-stiff, spoolable intervention rod and deployments is available from Ziebel, AS, Stavanger, Norway under the registered trademark Z-LINE.
While the invention has been described with respect to a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that other embodiments can be devised which do not depart from the scope of the invention as disclosed herein. Accordingly, the scope of the invention should be limited only by the attached claims.
Claims
1. A method for controlling pressure in a wellbore drilled below the bottom of a body of water, the wellbore having a fluid outlet in fluid communication with a working fluid inlet of an ejector assembly to return drilling fluid to a drilling platform on the water surface, the method comprising:
- pumping drilling fluid into a drill string extending from the drilling platform into the wellbore; and
- at least one of, (i) introducing fluid into a power fluid inlet of the ejector assembly at a rate selected to remove fluid from the wellbore at a selected rate and (ii) operating a controllable flow restriction in a fluid path from the wellbore to the working fluid inlet of the ejector assembly, to maintain a selected wellbore pressure.
2. The method of claim 1 wherein the maintaining the selected wellbore pressure comprises maintaining a fluid level in a riser extending from a wellhead disposed on the bottom of the body of water to a drilling platform above the water surface.
3. The method of claim 1 further comprising removing the ejector assembly from a fluid return line extending from the drilling platform using at least one of a wireline, slickline, coiled tubing and a semi-stiff spoolable intervention rod extended into the fluid return line.
4. The method of claim 1 further comprising sealing an annular space between the drill string and an interior of a drilling riser extending from a wellhead proximate the bottom of the body of water to proximate the drilling platform.
5. A wellbore drilling system comprising:
- a drill string extending into the wellbore from a drilling platform at a surface of a body of water;
- a fluid pump coupled to an interior passage in the drill string;
- a fluid outlet connected to the wellbore, the fluid outlet in fluid communication with a working fluid inlet of an ejector assembly, an outlet of the ejector assembly in fluid communication with a fluid return line extending to the drilling platform;
- a pressure sensor in pressure communication with an interior of the wellbore; and
- means for pumping a power fluid into an inlet therefor in the ejector assembly, the means for pumping controllable in response to signals from the pressure sensor to enable maintaining a selected wellbore pressure.
6. The wellbore drilling system of claim 5 further comprising a variable flow restriction between the fluid outlet and the ejector assembly.
7. The wellbore drilling system of claim 5 further comprising a riser extending from the bottom of the body of water to the drilling platform and wherein the pressure sensor is in fluid communication with an interior of the riser.
8. The wellbore drilling system of claim 5 wherein the fluid return line is substantially vertical and the ejector assembly is disposed in the fluid return line such that the ejector assembly is removable from the fluid return line by at least one of a wireline, slickline, coiled tubing and a semi-stiff spoolable intervention rod extended into the fluid return line.
9. The wellbore drilling system of claim 5 further comprising a seal disposed in an annular space between the drill string and an interior of a drilling riser extending from a wellhead proximate a bottom of a body of water to proximate the drilling platform.
Type: Application
Filed: May 14, 2015
Publication Date: Mar 15, 2018
Inventors: Donald G. Reitsma (Kelowna), Iona M. Reitsma (Kelowna)
Application Number: 15/552,302