U.S. patent application number 11/954919 was filed with the patent office on 2009-06-18 for grease injection system for riserless light well intervention.
Invention is credited to Olav Inderberg, John Johansen.
Application Number | 20090151956 11/954919 |
Document ID | / |
Family ID | 40751712 |
Filed Date | 2009-06-18 |
United States Patent
Application |
20090151956 |
Kind Code |
A1 |
Johansen; John ; et
al. |
June 18, 2009 |
GREASE INJECTION SYSTEM FOR RISERLESS LIGHT WELL INTERVENTION
Abstract
A subsea lubricator system is disclosed which includes a
lubricator tube adapted to be positioned subsea above a subsea
well, a pressure control head adapted to be positioned above the
lubricator tube, at least one pressure sensor adapted for sensing
at least one of a pressure in the subsea well or an ambient
seawater pressure proximate the pressure control head, and at least
one pump that is adapted to be positioned subsea to inject a
lubricant into the pressure control head at a pressure that is
greater than the sensed pressure. A method of operating a subsea
lubricator system positioned above a subsea well, the lubricator
system including a pressure control head, is also disclosed which
includes monitoring at least one of a pressure within the well and
an ambient seawater pressure proximate the lubricator system, and
injecting a lubricant into the pressure control head at a pressure
that is greater than the monitored pressure.
Inventors: |
Johansen; John; (Kongsberg,
NO) ; Inderberg; Olav; (Kongsberg, NO) |
Correspondence
Address: |
WILLIAMS, MORGAN & AMERSON
10333 RICHMOND, SUITE 1100
HOUSTON
TX
77042
US
|
Family ID: |
40751712 |
Appl. No.: |
11/954919 |
Filed: |
December 12, 2007 |
Current U.S.
Class: |
166/350 ;
166/250.15 |
Current CPC
Class: |
E21B 33/072 20130101;
E21B 33/076 20130101 |
Class at
Publication: |
166/350 ;
166/250.15 |
International
Class: |
E21B 7/12 20060101
E21B007/12 |
Claims
1. A method of operating a subsea lubricator system positioned
above a subsea well, said lubricator system comprising a pressure
control head, the method comprising: monitoring at least one of a
pressure within said well and an ambient seawater pressure
proximate said lubricator system; and injecting a lubricant into
said pressure control head at a pressure that is greater than said
monitored pressure.
2. The method of claim 1, wherein the method comprises monitoring
both of the pressure in the well and the ambient seawater pressure
and monitoring a pressure within the pressure control head.
3. The method of claim 2, wherein the step of injecting a lubricant
into the pressure control head is performed at a pressure that is a
set value greater than both of the monitored well pressure and the
monitored ambient seawater pressure.
4. The method of claim 2, wherein the step of injecting a lubricant
into the pressure control head is performed at a pressure that is a
set value greater than at least one of the monitored well pressure
and the monitored ambient seawater pressure.
5. The method of claim 1, further comprising actuating at least one
pump that is positioned subsea to inject said lubricant into said
pressure control head at said pressure that is a set value greater
than said monitored pressure.
6. The method of claim 1, wherein said lubricant is obtained from
an accumulator that is positioned subsea and contains said
lubricant.
7. The method of claim 1, wherein said lubricant is a petroleum
based lubricant.
8. The method of claim 1, wherein said lubricant is a
non-hydrocarbon containing lubricant.
9. The method of claim 1, wherein said lubricant is a
bio-degradable lubricant.
10. The method of claim 1, wherein said lubricant comprises fish
oil.
11. The method of claim 5, further comprising actuating at least
one additional pump that is positioned subsea to inject said
lubricant into said pressure control head at said pressure that is
a set value greater than said monitored pressure.
12. The method of claim 11, further comprising injecting said
lubricant into said pressure control assembly at two spaced apart
locations.
13. The method of claim 5, wherein actuating said at least one pump
comprises actuating said at least one pump using battery power.
14. The method of claim 5, wherein said at least one pump is
operatively coupled to a battery power source and a power cable
supplied from a surface vessel or platform, and wherein said at
least one pump may be actuated using electrical power supplied from
either said battery power source or from said power cable.
15. The method of claim 1, wherein injecting a lubricant into said
pressure control head comprises injecting a lubricant into said
pressure control head at a pressure that is at least 15 psi greater
than the monitored pressure.
16. A method of operating a subsea lubricator system positioned
above a subsea well, said lubricator system comprising a pressure
control head, the method comprising: monitoring at least one of a
pressure within said well and an ambient seawater pressure
proximate said lubricator system; injecting a lubricant into said
pressure control head at a pressure that is a set value greater
than said monitored pressure; and obtaining said lubricant from an
accumulator that is positioned subsea and contains said
lubricant.
17. The method of claim 16, wherein the method comprises monitoring
both of the pressure in the well and the ambient seawater pressure
and monitoring a pressure within the pressure control head.
18. The method of claim 17, wherein the step of injecting a
lubricant into the pressure control head is performed at a pressure
that is a set value greater than both of the monitored well
pressure and the monitored ambient seawater pressure.
19. The method of claim 16, further comprising actuating at least
one pump that is positioned subsea to inject said lubricant into
said pressure control head at said pressure that is a set value
greater than said monitored pressure.
20. The method of claim 16, wherein said lubricant is a
non-hydrocarbon containing lubricant.
21. The method of claim 16, wherein said lubricant is a
bio-degradable lubricant.
22. The method of claim 16, wherein said lubricant comprises fish
oil.
23. The method of claim 19, further comprising actuating at least
one additional pump that is positioned subsea to inject said
lubricant into said pressure control head at said pressure that is
a set value greater than said monitored pressure.
24. The method of claim 19, further comprising injecting said
lubricant into said pressure control assembly at two spaced apart
locations.
25. The method of claim 19, wherein actuating said at least one
pump comprises actuating said at least one pump using battery
power.
26. The method of claim 19, wherein said at least one pump is
operatively coupled to a battery power source and a power cable
supplied from a surface vessel or platform, and wherein said at
least one pump may be actuated using electrical power supplied from
either said battery power source or from said power cable.
27. The method of claim 16, wherein injecting a lubricant into said
pressure control head comprises injecting a lubricant into said
pressure control head at a pressure that is at least 15 psi greater
than the monitored pressure.
28. A subsea lubricator system, comprising: a lubricator tube
adapted to be positioned subsea above a subsea well; a pressure
control head adapted to be positioned above said lubricator tube;
at least one pressure sensor adapted for sensing at least one of a
pressure in said subsea well or an ambient seawater pressure
proximate said pressure control head; and at least one pump that is
adapted to be positioned subsea to inject a lubricant into said
pressure control head at a lubricant pressure that is greater than
said sensed pressure.
29. The system of claim 28, further comprising a lubricant
accumulator that is adapted to be positioned subsea and contain
said lubricant to be injected into said pressure control head.
30. The system of claim 28, wherein said lubricant pressure is
greater than said sensed pressure by a set value.
31. The system of claim 30, wherein said set value is at least 15
psi.
32. The system of claim 29, further comprising a lubricant return
line that extends between said pressure control head and a used
lubricant container.
33. The system of claim 28, further comprising a control system
that is adapted to be positioned subsea, said control system
adapted to receive said sensed pressure and actuate said at least
one pump in response to said sensed pressure.
34. The system of claim 33, wherein said control system controls
said at least one pump such that said lubricant pressure is greater
than said sensed pressure by a set value.
35. The system of claim 33, wherein said control system is adapted
to regulate a pressure of the lubricant injected into the pressure
control head.
36. The system of claim 28, wherein said system comprises at least
two pumps that are adapted to be positioned subsea, each of which
are adapted to inject liquid into said pressure control head.
37. The system of claim 36, wherein said first and second pumps are
adapted to inject said lubricant into said pressure control head at
spaced apart locations.
38. The system of claim 28, wherein said system further comprises a
battery that is adapted to be positioned subsea, said battery
adapted to supply electrical power to said at least one pump.
39. The system of claim 38, wherein said system further comprises
an umbilical from a surface vessel or platform that is adapted to
supply electrical power to said at least one pump.
40. The system of claim 28, wherein said system comprises at least
one pressure sensor for sensing a pressure within said subsea well,
at least one pressure sensor for sensing a pressure of said ambient
seawater, and at least one pressure sensor for sensing a pressure
within the pressure control head.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The invention relates to a method for controlling grease
injection to a subsea intervention system and an apparatus
comprising a housing containing a control unit and a pump for
grease.
[0003] 2. Description of the Related Art
[0004] When performing intervention in a hydrocarbon well, it is
necessary to isolate the well from the environment. Intervention is
often carried out using wireline techniques (braided wire,
composite cable or slickline). To contain the pressure in the well
during operations and avoid hydrocarbons escaping to the
environment, intervention operations involve the use of a stuffing
box which is part of a pressure control head (PCH). The PCH
provides a dynamic seal between the cable and the wellbore
enclosures to maintain pressure control and prevent wellbore fluids
from leaking into the environment. However, because of its braided
(wire rope like) exterior, the cable has a bumpy, crevice-filled
surface which is difficult for the PCH to seal around as the cable
passes through the PCH as it travels into and out of the well.
[0005] FIG. 1 is a schematic drawing showing a prior art subsea
lubricator system 100 attached to a subsea well 105. The subsea
well 1055 extends into a subterranean formation and has a Christmas
tree 106 attached to the wellhead and a flowline/umbilical 107
extending to a process facility. The subsea lubricator stack 100
includes a pressure control unit (BOP) 111, a lubricator (pipe) 112
and the pressure control head (PCH) 113.
[0006] The lubricator system 100 further comprises a control system
(IWOCS) 115 with a separate workover umbilical 117 extending to the
surface. The control system 115 controls the system 100. In prior
art operations, grease is pumped down the line 117 and further
through line 123 to the PCH 113 to maintain a seal between the
braided wire or cable 109 and the seawater environment.
[0007] Current practice is to inject grease into the PCH body 113
at a higher pressure than that of the well. In addition, grease has
to be replenished at some rate to replace grease lost to the
surface of the braided cable 109 as it passes through the ends of
PCH 113 (going into or out of the well). The grease injection rate
is controlled by periodic visual monitoring of the sealing ends of
the PCH 113 for leakage and monitoring the grease injection
pressure.
[0008] This operation gets complicated when performing this
practice subsea on a subsea well. This involves the use of a subsea
riserless light well intervention (RLWI) stack. For RLWI, the PCH
113 is now remote and difficult to monitor; making it difficult to
determine when and how much grease needs to be injected.
Furthermore, as the stack is run in deeper water, the length of the
grease supply line feeding the PCH 113 grows longer, making it
increasingly difficult to pump viscous grease down to the PCH 113
at a reasonable surface pressure or pump rate. The long grease
lines and viscous grease becomes more problematic as deeper colder
environments are encountered. To do that requires pumping grease at
some empirical rate monitored visually. In subsea situations, the
pumping pressure is exacerbated by the length of the grease line
going down to the subsea PCH 113 and the rate is often a pure
guess, often resulting in sending too much grease down to
conservatively compensate for the unknown conditions.
[0009] Current practice for subsea grease injection requires the
surface deployment of grease lines as shown in U.S. Pat. No.
4,821,799, which is hereby incorporated by reference in its
entirety. That patent discloses the use of an accumulator to enable
a better control of injection pressures.
[0010] There is also a more subtle problem associated with grease
injection to a subsea PCH 113, namely, water ingress. Normally, the
PCH 113 is lowered to the lubricator tube 112 together with the
tool. However, in some operations, the PCH 113 is run independently
after the wireline tools, cable, etc. are landed in the RLWI
stack's lubricator tube 112. As the PCH assembly is lowered down to
the sea floor, the braided cable 109 passes through the PCH 113. If
grease is not supplied at a sufficient pressure and rate to offset
the increase in ambient seawater pressure, and the loss of grease
to the cable 109 passing by, seawater could weep past the seal ends
of the PCH 113 into the main cavity of the PCH 113 and/or the tube
112. If this occurs, there is an increased risk that the water will
help to form a hydrate plug inside the PCH 113 (later exposed to
wellbore pressure and fluids) and prevent the cable 109 from freely
moving through the PCH 113.
[0011] The present invention is directed to methods and devices
solving, or at least reducing the effects of, some or all of the
aforementioned problems.
SUMMARY OF THE INVENTION
[0012] The following presents a simplified summary of the invention
in order to provide a basic understanding of some aspects of the
invention. This summary is not an exhaustive overview of the
invention. It is not intended to identify key or critical elements
of the invention or to delineate the scope of the invention. Its
sole purpose is to present some concepts in a simplified form as a
prelude to the more detailed description that is discussed
later.
[0013] The present subject matter is generally directed to a method
and a device for controlling grease injection to a subsea
intervention system, where there is provided an at site pressure
compensated system for providing the grease at a pressure higher
than the outside pressure, this being either the well pressure, the
pressure of the water around the subsea system, outside pressure,
or both of these pressures.
[0014] According to one aspect, the present subject matter may be
employed in an intervention workover control system (IWOCS) that is
all electric or electro-hydraulic that may comprise a processor
with the capability to handle information, for example, to record
outside ambient seawater pressure, pressure inside the PCH and
below the PCH (inside the well). As mentioned above, the purpose of
the grease and PCH is to create a dynamic seal that generates a
slightly higher (grease) pressure inside the PCH than the pressure
of the environment above the PCH or the pressure in the well
below.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] The invention may be understood by reference to the
following description taken in conjunction with the accompanying
drawings, in which like reference numerals identify like elements,
and in which:
[0016] FIG. 1 is a schematic depiction of an illustrative prior art
subsea lubricator system;
[0017] FIG. 2 shows a sketch of an intervention system on a subsea
well;
[0018] FIG. 3 is a diagram showing the grease injection module in
IWOCS mode; and
[0019] FIG. 4 is a diagram showing the grease injection module in
autonomous mode.
[0020] While the invention is susceptible to various modifications
and alternative forms, specific embodiments thereof have been shown
by way of example in the drawings and are herein described in
detail. It should be understood, however, that the description
herein of specific embodiments is not intended to limit the
invention to the particular forms disclosed, but on the contrary,
the intention is to cover all modifications, equivalents, and
alternatives falling within the spirit and scope of the invention
as defined by the appended claims.
DETAILED DESCRIPTION OF THE INVENTION
[0021] Illustrative embodiments of the present subject matter are
described below. In the interest of clarity, not all features of an
actual implementation are described in this specification. It will
of course be appreciated that in the development of any such actual
embodiment, numerous implementation-specific decisions must be made
to achieve the developers' specific goals, such as compliance with
system-related and business-related constraints, which will vary
from one implementation to another. Moreover, it will be
appreciated that such a development effort might be complex and
time-consuming, but would nevertheless be a routine undertaking for
those of ordinary skill in the art having the benefit of this
disclosure.
[0022] The present subject matter will now be described with
reference to the attached figures. The words and phrases used
herein should be understood and interpreted to have a meaning
consistent with the understanding of those words and phrases by
those skilled in the relevant art. No special definition of a term
or phrase, i.e., a definition that is different from the ordinary
and customary meaning as understood by those skilled in the art, is
intended to be implied by consistent usage of the term or phrase
herein. To the extent that a term or phrase is intended to have a
special meaning, i.e., a meaning other than that understood by
skilled artisans, such a special definition will be expressly set
forth in the specification in a definitional manner that directly
and unequivocally provides the special definition for the term or
phrase.
[0023] FIG. 2 is a schematic drawing showing a subsea lubricator
system 10 described herein attached to a subsea well 5. The subsea
well 5 extends into a subterranean formation and has a Christmas
tree 6 attached to the wellhead and a flowline/umbilical 7
extending to a process facility. The subsea lubricator stack 10
includes a pressure control unit (BOP) 11, a lubricator (pipe) 12
and the pressure control head (PCH) 13.
[0024] The lubricator system 10 further comprises a control system
(IWOCS) 15 that controls the system 10. Electrical power is
supplied to the control system by electrical power line 17. In one
illustrative embodiment, a grease injection module 21 is attached
to the PCH 13. An electric cable 23 connects the grease injection
module 21 with the control system 15. With the grease injection
module 21 attached to the PCH 13, it can be raised and lowered
together with the PCH 13 and operate in an autonomous mode. In
another embodiment, the grease injection module 21 is not attached
to the PCH 13, but rather is made as a part of the control system
15. In that case, an additional fluid line 25 (shown as a dashed
line) is employed to supply grease or lubricant to the PCH 13. In
some embodiments, a single line from the control system 15 to the
grease injection module 21 may contain both electrical and fluid
lines.
[0025] The subject matter disclosed herein proposes the elimination
of a grease line (like the grease line 117 shown in FIG. 1) to or
from the surface to supply lubricant to the PCH 13. In one
embodiment, as shown in FIG. 3, lubricant may be supplied to the
PCH 13 by use of a depth compensated accumulator 31 filled with a
lubricant or grease. The grease injection module 21 comprises an
accumulator 31 for grease operatively connected via line 33 to a
pump 35. The outlet grease line 37 from the pump 35 is connected to
the PCH 13. The pump 35 is controlled by an electric motor 36. A
first power supply cable 32 connects the control system 15 with the
electric motor 36 for the pump 35. The grease line 37 has a one way
valve 43, a shut-off valve 44 and a pressure and temperature sensor
45.
[0026] In the embodiment shown in FIG. 3, there is also provided a
second pump 38 with associated motor 39, having a separate power
supply cable 34. A second grease line 41 connects the pump 38 with
the PCH 13. As above, the second grease line 41 includes a one way
valve 46, a shut-off valve 47 and a pressure and temperature
transmitter 48. The second pump 38 may be added to provide for
redundancy in the system, in case of failure of the first pump 35.
Providing dual pumps 35, 38 also makes it possible to generate
higher grease pumping rates in case of emergency, with both pumps
operating together. They may also be used for the rare times when
the cable 9 is travelling very quickly through the PCH 13 and may
require more grease than one electric motor/pump can supply.
[0027] As an alternative, grease may be wiped from the cable 9 as
it passes out of the PCH 13 and returned to a container in the
grease injector module 21. For example, as shown in FIG. 3, a
return grease line 52 that is in fluid communication with a
canister 54 may be provided. In this way, very little, if any,
grease will be released to the environment.
[0028] In addition, an ROV attachment 22 may be added to provide a
means to periodically replenish the grease in the accumulator 31
for long duration jobs.
[0029] In operation, the control system 15 closely monitors the
pressure of the environment outside of the PCH 13, the pressure
inside the PCH 13 and/or the pressure in the well 5. Periodically,
the control system 15 actuates one or both (depending upon the
situation) of the grease pumps 35, 38 to pump grease into the PCH
13. The grease pressure is closely monitored and the pump(s) 35
and/or 38 are regulated to generate a very small pressure
differential between the PCH 13 and the well 10, e.g., a
differential of approximately 15 psi. Stated another way, the
grease is injected at a pressure that is a set or established value
above at least one of the monitored pressures.
[0030] The close in-situ monitoring of the various pressures by the
control system 15 minimizes the amount of grease or lubricant
needed because the differential pressure can be kept to a minimum
value, e.g., a 15 psi differential pressure. A lower differential
pressure or set value may also be employed. This is a significant
benefit as compared to prior art systems where operators merely
guessed as to the volume of grease needed, and the associated
difficulties trying to pump the grease down a grease line. Keeping
the differential pressure or set value to a minimum also lessens
the amount of grease that works itself past the seal elements (not
shown) in the PCH 13 into the well and/or the environment. By
employing two pumps 35 and 38, the grease may be injected into the
PCH 13 in two locations (again opening one or two lines to
compensate for situations of high cable speed, rapid loss of
grease, etc.). There also may be a third grease injection line 51
in a location below the PCH 13 for better control of the
differential pressure between the PCH 13 and the well, if
necessary.
[0031] In the embodiment shown in FIG. 4, the grease injection
module 21 is equipped with its own separate control unit 60
configured as an autonomous version of the control system 15. The
autonomous control unit 60 comprises a processor and data storage
(not shown) and is preferably powered by a battery 62. Thus, the
electric control can be separated from the main control system 15,
while retaining the monitoring and injection control features for
grease injection into the PCH 13. This embodiment simplifies the
packaging of the PCH 13 assembly by eliminating the need for the
subsea electrical connection 23 (FIG. 2) after the PCH 13 is
lowered separately and latched to the rest of the intervention
(RLWI) stack. However, this autonomous feature adds two new
capabilities. First, as the PCH 13 assembly is lowered to the sea
floor, it independently monitors the increase in ambient seawater
pressure and can adjust by injecting grease into the PCH 13 at just
a slightly higher than ambient pressure differential, e.g., a 15
psi differential, to keep seawater from entering the cavity in the
PCH 13, thereby avoiding the hydrate plugging issues. The control
unit 60 is battery powered to maintain its autonomy. Second, in the
event that the surface vessel needs to depart and/or the cable is
cut somewhere outside of the PCH 13 and the control system 15 is
disconnected, the grease injection pressure containment feature of
the PCH 13 is maintained even though the rest of the control system
15 is shut down, for as long as battery power is present.
[0032] Another issue is the grease itself. Current practice is to
use some form of viscous petroleum based grease that has a certain
amount of stickiness to adhere to the surface of the seals (not
shown) in the PCH 13 and the rough exterior of the cable 9,
creating a pseudo smooth surface on the braided cable. However,
this creates its own "leakage to the environment" as the grease
laden cable 9 emerges out the top of the PCH 13 during wireline
retrieval. In addition, the ambient seawater environment may be as
low as 4.degree. C. (39.degree. F.), which may lead to an increase
in the grease's viscosity or lead to a hardening condition. To
alleviate this condition, it is contemplated to replace petroleum
grease with a bio-degradable, non-hydrocarbon lubricant, such as a
fish oil based lubricant, e.g., cod liver oil, so as to
significantly lower the viscosity of the lubricant and eliminate
hydrocarbon discharge to the environment.
[0033] The benefit of the present invention is that its
architecture is substantially depth insensitive, eliminating the
pressure flow rate problems associated with pumping viscous grease
longer distances (at higher surface pump pressures) and eliminates
waste by using environmentally friendly lubricants that are
injected at much lower differential pressures because the injection
process is monitored. It also eliminates a line going into the
water which is beneficial for better line management; critical for
deepwater (>500 m.about.1500 ft.) operations.
[0034] The particular embodiments disclosed above are illustrative
only, as the invention may be modified and practiced in different
but equivalent manners apparent to those skilled in the art having
the benefit of the teachings herein. For example, the process steps
set forth above may be performed in a different order. Furthermore,
no limitations are intended to the details of construction or
design herein shown, other than as described in the claims below.
It is therefore evident that the particular embodiments disclosed
above may be altered or modified and all such variations are
considered within the scope and spirit of the invention.
Accordingly, the protection sought herein is as set forth in the
claims below.
* * * * *