U.S. patent application number 10/065100 was filed with the patent office on 2004-03-18 for two stage downhole drilling fluid filter.
Invention is credited to Downton, Geoff, Menger, Christian, Phan, Henry.
Application Number | 20040050591 10/065100 |
Document ID | / |
Family ID | 28673464 |
Filed Date | 2004-03-18 |
United States Patent
Application |
20040050591 |
Kind Code |
A1 |
Downton, Geoff ; et
al. |
March 18, 2004 |
TWO STAGE DOWNHOLE DRILLING FLUID FILTER
Abstract
A two stage filter for drilling fluid using downhole tools
filters solid materials from the drilling fluid and has a first,
outer filter section and a second, inner filter section. A portion
of the drilling fluid flowing through the first section is received
by the second section, and passed on to the fluid using device of
the tool. A flow area of the first filter section is greater than a
flow area of the second filter section.
Inventors: |
Downton, Geoff;
(Minchinhampton, GB) ; Menger, Christian;
(Bristol, GB) ; Phan, Henry; (Richmond,
TX) |
Correspondence
Address: |
TIM CURINGTON
SCHLUMBERGER, BRUNEL WAY
STROUFWATER PARK, STONEHOUSE
GLOUCESTERSHIRE
GL10 3SX
GB
|
Family ID: |
28673464 |
Appl. No.: |
10/065100 |
Filed: |
September 17, 2002 |
Current U.S.
Class: |
175/312 ;
175/314 |
Current CPC
Class: |
E21B 21/002 20130101;
E21B 7/04 20130101 |
Class at
Publication: |
175/312 ;
175/314 |
International
Class: |
E21B 027/00; E21B
043/34 |
Claims
What is claimed is:
1. A downhole tool comprising a drilling fluid using device and a
two stage filter for filtering solid materials from the drilling
fluid, the two stage filter comprising a first, outer filter
section and a second, inner filter section, the drilling fluid
flowing from the first section to the second section, wherein a
flow area of the first filter section is greater than a flow area
of the second filter section.
2. The downhole tool of claim 1 wherein a majority of the drilling
fluid flowing through the second filter section is received from
the first filter section.
3. The downhole tool of claim 1 wherein the first filter section
has a first plurality of flow apertures and the second filter
section has a second plurality of flow apertures
4. The downhole tool of claim 3 wherein an average cross-section
area for the second plurality of apertures is greater than an
average cross-section area for the first plurality of
apertures.
5. The downhole tool of claim 4 wherein the average cross-section
area for the second plurality of apertures is more than 20% greater
than the average cross-section area for the first plurality of
apertures.
6. The downhole tool of claim 3 wherein the flow area of the first
filter section is at least two times greater than the flow area of
the second filter section.
7. The downhole tool of claim 3 wherein the ratio of an average
diameter of the second plurality of apertures to a thickness of a
shell of the second filter section is less than 2.
8. The downhole tool of claim 7 wherein the ratio of the average
diameter of the second plurality of apertures to the shell
thickness is about 0.72.
9. The downhole tool of claim 1 wherein a ratio of the flow area of
the second filter section to a total surface area of the second
filter section is less than about 0.15.
10. The downhole tool of claim 9 wherein the ratio of the flow area
of the second filter section to the total surface area of the
second filter section is in the range from about 0.02 to about
0.15.
11. The downhole tool of claim 10 wherein the ratio of the flow
area of the second filter section to the total surface area of the
second filter section is less than about 0.06.
12. A two stage filter for filtering solid materials from a
drilling fluid comprising a first, outer filter section and a
second, inner filter section, the drilling fluid flowing from the
first section to the second section, wherein a flow area of the
first filter section is greater than a flow area of the second
filter section.
13. The two stage filter of claim 12 wherein a majority of the
drilling fluid flowing through the second filter section is
received from the first filter section.
14. The two stage filter of claim 12 wherein the first filter
section has a first plurality of flow apertures and the second
filter section has a second plurality of flow apertures
15. The two stage filter of claim 14 wherein an average
cross-section area for the second plurality of apertures is greater
than an average cross-section area for the first plurality of
apertures.
16. The two stage filter of claim 15 wherein the average
cross-section area for the second plurality of apertures is more
than 20% greater than the average cross-section area for the first
plurality of apertures.
17. The two stage filter of claim 14 wherein the flow area of the
first filter section is at least two times greater than the flow
area of the second filter section.
18. The two stage filter of claim 14 wherein the ratio of an
average diameter of the second plurality of apertures to a
thickness of a shell of the second filter section is less than
2.
19. The two stage filter of claim 18 wherein the ratio of the
average diameter of the second plurality of apertures to the shell
thickness is about 0.72.
20. The two stage filter of claim 12 wherein a ratio of the flow
area of the second filter section to a total surface area of the
second filter section is less than about 0.15.
21. The two stage filter of claim 20 wherein the ratio of the flow
area of the second filter section to the total surface area of the
second filter section is in the range from about 0.02 to about
0.15.
22. The two stage filter of claim 21 wherein the ratio of the flow
area of the second filter section to the total surface area of the
second filter section is less than about 0.06.
23. A rotary steerable downhole tool comprising a two stage filter
for filtering solid materials from the drilling fluid, the two
stage filter comprising a first, outer filter section and a second,
inner filter section, the drilling fluid flowing from the first
section to the second section, wherein a flow area of the first
filter section is greater than a flow area of the second filter
section.
24. The rotary steerable downhole tool of claim 23 wherein a
majority of the drilling fluid flowing through the second filter
section is received from the first filter section.
25. The rotary steerable downhole tool of claim 23 wherein the
first filter section has a first plurality of flow apertures and
the second filter section has a second plurality of flow
apertures
26. The rotary steerable downhole tool of claim 25 wherein an
average cross-section area for the second plurality of apertures is
greater than an average cross-section area for the first plurality
of apertures.
27. The rotary steerable downhole tool of claim 26 wherein the
average cross-section area for the second plurality of apertures is
more than 20% greater than the average cross-section area for the
first plurality of apertures.
28. The rotary steerable downhole tool of claim 25 wherein the flow
area of the first filter section is at least two times greater than
the flow area of the second filter section.
29. The rotary steerable downhole tool of claim 25 wherein the
ratio of an average diameter of the second plurality of apertures
to a thickness of a shell of the second filter section is less than
2.
30. The rotary steerable downhole tool of claim 29 wherein the
ratio of the average diameter of the second plurality of apertures
to the shell thickness is about 0.72.
31. The rotary steerable downhole tool of claim 23 wherein a ratio
of the flow area of the second filter section to a total surface
area of the second filter section is less than about 0.15.
32. The rotary steerable downhole tool of claim 31 wherein the
ratio of the flow area of the second filter section to the total
surface area of the second filter section is in the range from
about 0.02 to about 0.15.
33. The rotary steerable downhole tool of claim 32 wherein the
ratio of the flow area of the second filter section to the total
surface area of the second filter section is less than about 0.06.
Description
BACKGROUND OF INVENTION
[0001] 1. Field of the Invention
[0002] This invention relates to downhole tools useful for forming
boreholes into the earth. Specifically, a two stage downhole
drilling fluid filter for these downhole tools is disclosed that is
resistant to clogging by lost circulation material and
detritus.
[0003] 2. Description of the Related Art
[0004] When drilling boreholes into the earth, a liquid drilling
fluid, now well known simply as "mud" or "drilling mud", is often
used to flush the cuttings from the bottom of the well bore to the
surface. Originally, the mud was used only for flushing out the
cuttings. It was not long however, before the drilling industry
realized that the drilling mud, often supplied at high pressures
and high flow rates, could be used to power other devices in the
drill string that support the drilling operation, including
telemetry pressure pulses, power, and primary well control.
[0005] However, at times during drilling, a portion of the drilling
fluid may flow into the formation being drilled. This is considered
a serious situation, and oftentimes special additives called lost
circulation materials (LCM) are added to the mud to slow or stop
this undesired diversion of the mud. LCM is designed to plug the
types of gaps in the rock formations that tend to open when
circulation is lost. Unfortunately, these gaps are very similar to
the clearances and passageways in the drilling mud powered tools.
Consequently, the designers of these tools place limits on how much
and what types of LCM can be used with their tools.
[0006] Another problem with the use of these drilling fluid using
downhole tools is that, at times, other undesirable materials that
damage the tools find their way into drilling mud. Items such as
plastic wrapping and bagging material and other contaminants
introduced by the field personnel can contaminate the drilling mud
and block the fluid passages in the mud powered tools as badly as
LCM.
[0007] It is now commonplace to have numerous tools in the drilling
string which use the drilling mud to supply power for their
operation. Such tools include drill bits, drilling motors, drilling
turbines, rotary directional drilling devices, mud driven electric
generators, hole opening devices, measuring while drilling tools,
downhole communication devices, and many others.
[0008] In many of these tools, the mud powered systems are designed
to tolerate these particles by allowing very high volume flow
through the system and by providing large restrictions (chokes)
when it is necessary to provide a pressure differential.
[0009] In other tools, particularly rotary drilling tools, single
stage filter elements have been used. The total filter area in
these tools is sized in a manner to provide sufficient flow through
the filter if the filter gets partially obstructed and blocked by
particles. Unfortunately, these filters can collapse under the
differential pressure once a sufficiently high number of holes are
blocked.
[0010] In addition, these filters tend to exhibit uneven wear.
After long use, single stage filters tend to wear preferentially at
the inlet end. Typically only the first 10% to 50% of the
"upstream" end of the filter wears out, leaving the majority on the
surface unworn. In some cases this uneven wear forces the entire
fluid using tool to be rebuilt when only a portion of the filter
erodes away.
[0011] Newer types of rotary drilling tools may have drilling fluid
powered actuators that have relatively small passageways leading
from rotary vales and have fluid chokes to create working pressure
differentials in the drilling fluid, as described in U.S. Pat. Nos.
5,265,682; 5,553,678; 5,803,185; 6,089,332; 5,695,015; 5,685,379;
5,706,905; 5,553,679; 5,673,763; 5,520,255; 5,603,385; 5,582,259;
5,778,992; 5,971,085 all herein incorporated by reference. In these
tools, larger particulates present in the drilling fluid in form of
drill cuttings or drilling fluid additives can block the choke
holes in the actuation system or cause damage to or jamming of the
rotary valve. In particular, high levels of lost circulation
material added under certain operating conditions can adversely
affect the actuation system.
[0012] Therefore, some form of filtering is required in these
tools, as these particulates must be filtered from the drilling
fluid diverted from the main fluid flow for the hydraulic actuation
system. The filter also needs to be kept clean during operation to
ensure functionality of the actuators and prevent collapse of the
filter element due to a build-up in differential pressure when
filter holes get blocked.
[0013] Unfortunately, the hereinbefore-described limitations of the
single stage filter have affected the performance of these devices.
For example, due to space and structural constraints, the prior art
filters had relatively small holes for fluid flow. The small hole
size limits space availability in the tool and requires the filter
element to be a main structural component in the tool.
Additionally, the filter hole size and shape was limited to prevent
early blockage of the filter element. These constraints became
particularly limiting when attempts were made to scale these tools
down to smaller borehole diameters.
SUMMARY OF INVENTION
[0014] Disclosed is a two stage filter for a downhole tool for
filtering solid materials from the drilling fluid. The downhole
tool may be any of the type using the drilling fluid for
operations, but the two stage filter is particularly applicable to
rotary steerable type downhole tools. The two stage filter
comprises a first, outer filter section and a second, inner filter
section, the drilling fluid flowing from the first section to the
second section. The flow area of the first filter section is
greater than the flow area of the second filter section.
[0015] In this tool, a majority of the drilling fluid flowing
through the second filter section is received from the first filter
section. The two filter sections of the tool have holes or
apertures in them. The average cross-section area for the apertures
in the inner section may be greater than an average cross-section
area for the apertures in the outer section.
[0016] In this tool the average cross-section area for the second
plurality of apertures may be more than 20% greater than the
average cross-section area for the first plurality of apertures.
Also, the flow area of the first filter section of the tool may be
at least two times greater than the flow area of the second filter
section.
BRIEF DESCRIPTION OF DRAWINGS
[0017] FIG. 1 is a partial section view of a drilling system for
forming boreholes in the earth.
[0018] FIG. 2 is a perspective view of the outer filter section of
the two stage filter of the present invention.
[0019] FIG. 3 is a perspective view of the inner filter section of
the two stage filter of the present invention.
[0020] FIG. 4 is a perspective view of a rotary steerable tool,
wherein the two stage filter of the present invention may be
used.
[0021] FIG. 5 is a partial section view of the two stage filter of
the present invention assembled in the downhole tool of FIG. 4.
[0022] FIG. 6 is a partial section view of a section of the rotary
steerable tool of FIG. 4.
DETAILED DESCRIPTION
[0023] Referring now to FIG. 1, when drilling boreholes 10 into
earthen formations 12, it is common practice to use a bottom hole
assembly 14 as shown in FIG. 1. The bottom hole assembly (BHA) 14
is typically connected to the end of the tubular drill string 16,
may be rotatably driven by a drilling rig 18 from the surface. In
addition to providing motive force for rotating the drill string
16, the drilling rig 18 also supplies a drilling fluid 20 under
pressure and flow created by a surface mud pump (not shown),
through the tubular drill string 16 to the bottom hole assembly 14.
The drilling fluid 20 is typically laden with drilled abrasive
formation material, as it returns to a mud tank 24 and is then
repeatedly re-circulated through the borehole 10.
[0024] In the BHA 14, may be drilling fluid using downhole tools 26
including a drill bit 28. These fluid using downhole tools 26 may
be one or more of drilling motors, drilling turbines, rotary
directional drilling devices, mud driven electric generators, hole
opening devices, measuring while drilling tools, and downhole
communication devices.
[0025] Referring now to FIGS. 2 and 3, in order to provide a clean
supply of pressurized drilling fluid 20 to one of these fluid using
downhole tools 26, a two stage filter 30 is provided within the
tool 26. The two stage filter 30 is for filtering solid materials
from the drilling fluid 20 and has a first, outer filter section 32
and a second, inner filter section 34, the drilling fluid 20 enters
the first section 32 through a first set of apertures 38 to the
second section 34. A portion of this drilling fluid 20 then flows
through a second set of apertures 42 in the second section 34 for
supply to the portion of the tool 26 using the drilling fluid 20. A
flow area of the first filter section 32 is greater than a flow
area of the second filter section 34. Preferably, the flow area of
the first filter section 32 is at least two times greater than the
flow area of the second filter section 34.
[0026] The most common form for apertures 38, 42 is circular holes.
For convenience, in this specification these apertures 38, 42 will
hereinafter be shown, described and referred to as holes or
circular holes, but it should be understood that the term is not
intended to limit the invention only to apertures 38, 42 in the
form of circular holes, and that the areas and other
characteristics of these apertures 38, 42 for the two stage filter
30 of the present invention apply equally to apertures of any shape
and configuration.
[0027] The first filter section 32 has an outer filter gauze 36
with small filter holes 38 that prevent particulates larger than
the hole diameter from passing through. The outer filter gauze 36
has a smooth surface, a very large flow area, and is relatively
thin. The passageway of the drilling fluid 20 through the filter
holes 38 is thus short. Particles stuck in the filter holes 38 are
swept away by the main fluid flow, which is perpendicular to the
orientation of the filter holes 38. The filter is thus
self-cleaning.
[0028] After passing the first, outer filter section 32, the fluid
is in the small cavity (indicated by numeral 40 in FIG. 5) between
the outer filter gauze 36 and second, inner filter body section 34.
The average size (and consequently the average cross-section area)
of the filter holes 42 is greater than those of the first, outer
filter section 32. However, the total flow area of the second,
inner section 34 is much less than that of the first, outer filter
section 32. It is desirable that the average cross-section area for
the holes 42 of the second filter section 34 be at least 20% larger
than the average cross-section area of the holes 38 in the first,
outer filter section 32. Due to the difference in hole size (and
number of holes as will be described later), the drilling fluid 20
filtered through the first, outer filter section 32 strikes the
outside surface shell 44 of the second filter section 34 and is
reflected back, resulting in a diffuse flow field in the cavity 40
between the two filter elements. This also reduces or eliminates
the uneven wear experienced by prior art filters, at the inlet end
of the first filter section 32.
[0029] A portion of the drilling fluid 20 reaching the cavity 40
flows back through the first, outer filter section 32 and back into
the main flow stream. This aids the removal of particulates
blocking holes in the outer filter gauze 36 by the main fluid flow.
This outward flow also tends to carry away the larger particles
that manage to enter the cavity 40 through the first filter section
32. It is believed that the mass of these particles tends to make
them remain in the cavity 40 and therefore swept away, rather than
making the abrupt change in direction necessary to enter into the
holes 42 of the second, inner filter section 34. A portion of the
filtered drilling fluid 20 within the cavity 40 does however pass
through the second filter section 34 to be directed to the fluid
using device 26.
[0030] Referring now to FIGS. 4 and 6, in one embodiment, a rotary
steerable tool 50 consists of two major components, a control unit
52 and a bias unit 54. The maximum rated operating temperature for
the rotary steerable tool 50 is 125.degree. C. (257.degree. F.)
with a hydrostatic pressure rating of 20,000 psi (138 MPa). The
rotary steerable tool 50 operates at flow rates of 200 to 400
gpm.
[0031] The rotary steerable tool 50 provides hole direction control
by selectively providing hydraulic pressure in form of drilling
fluid 20 to hinged pads 56 mounted on the outer diameter of the
bias unit 54.
[0032] The bias unit 54 is linked to the control unit 52 via the
control shaft 56. This control shaft 56 carries the first portion
58 of a 3-way rotary valve, generally indicated by reference
numeral 60. The lower member 62 of the rotary valve 60, rotating
with the bias unit 54, has three ports 64 (only one is shown), each
leading to one of the three actuators 66 (only one is shown). As
each of the three ports 64 in the lower member 62 rotates into
alignment with the opening in the (non-rotating) first portion 58
of the rotary valve 60, the corresponding pad 68 is actuated moving
outwards, and applying a force between the borehole 10 and the bias
unit 54.
[0033] Approximately 4% of the drilling fluid flowing through the
rotary steerable tool 50 is diverted from the main flow and
utilized for the actuation of the pads. Because the valve,
passageways, and the ports are vulnerable to blockage by solids in
the drilling fluid 20, the drilling fluid 20 is passed through the
two-stage filter 30 prior to delivery to the valve. A differential
pressure of about 750 psi (5.2 MPa) is used between the inside of
the tool and the borehole for the pad actuation.
[0034] In the first, outer filter section 32 the thickness of the
shell is quite small compared to the diameter of the holes 38.
Furthermore, the holes 38 occupy a very high portion of the surface
area of the first filter section 32. The number of holes 38 and the
thinness of the shell make this first filter section 32 appear as a
gauze.
[0035] In the embodiment illustrated in FIG. 2, the first, outer
filter section 34 has a diameter of 53.5 mm, a shell thickness of
0.8 mm, and an active length of 65.0 mm. Therefore, the first
filter section 34 has a total active surface area of about 10,589
mm squared. The holes 38 have a 1.0 mm diameter and occupy 2,262 mm
squared of that surface. Therefore, the flow area of the first,
outer filter section 32 is 2,262 mm squared and the area density of
the holes is about 21% of the total area of the first filter
section 32.
[0036] The second, inner filter section 34 forms a main load
bearing component of the rotary steerable tool 50 and the shell 44
has a relatively thick wall.
[0037] In the second filter section 34, the thickness of the shell
44 is quite high compared to the average diameter 70 of the holes
42. It is believed that to have the above described self cleaning
effect, the average diameter 70 of the holes 42 in the second
filter section 34 should be less than double the thickness of the
shell 44. In other words, in the second, inner filter section 34 of
the present invention, the ratio of the average hole 42 diameter 70
to the thickness of the shell is less than 2. This is believed to
enhance the ability to eject particles from the flow stream back
into the void space 44 between the filter sections 32, 34.
[0038] In the preferred embodiment shown, this ratio is far less,
for the hole 42 diameter is 2.5 mm and the shell thickness is 3.5
mm, making the hole diameter to shell thickness ratio equal to
about 0.72. It should be understood, however, that this ratio would
be very dependent upon the diameter 72 of the second filter section
34. As the diameter 72 of the second filter section 34 decreases
with scaling of the tool to smaller borehole diameters, the ratio
of the average hole 42 diameter to the thickness of the shell 44
will necessarily increase, approaching the value of 2.
[0039] The average cross-section area for the holes 42 of the
second filter section is about 4.91 mm squared, and the average
cross-section area for the holes 38 of the first filter section is
about 0.79 mm squared. Therefore, in the preferred embodiment, the
average cross-section area for the holes 42 of the second filter
section is more than 6.25 greater than the average cross-section
area of the holes 38 in the first filter section.
[0040] Also in the preferred embodiment, the holes 42 of the
second, inner filter section 34 are grouped into a first region 74
and a second region 76. There is a relationship between the area of
the holes 42 in the region 74, 76 of the shell 44 of the second
filter section 34 to the total surface area of that region 74, 76
of the shell 44. This is necessary to make the drilling fluid 20
which is filtered through the first filter section 32 reflect back
after it hits the outside surface shell 44 of the second filter
section 34, as mentioned earlier. A relatively high portion of the
surface shell 44 needs to be free of holes 42 for the drilling
fluid 20 to be reflected in this manner. The resulting diffuse flow
field in the cavity 40 between the two filter elements 32, 34
carries away the ejected particles described above and has proven
to be remarkably self-cleaning. The result is that this two stage
filter system filters much more of the solids from the drilling
fluid 20 than the single stage filters of the prior art.
[0041] The second, inner filter section 34 has eleven rows of these
holes, making the total flow area of the second filter section 34
just 431 mm squared. The total flow area of the first, outer filter
section 32 is much greater 5.24 times greater to be exact in this
embodiment.
[0042] It has been found that the area density of the holes 42 in
regions 74, 76 of the shell 44 should be less than about 0.15 of
the total area of that region 74, 76 of the shell 44. This value is
much lower than what has been used previously, and it is necessary
to maintain a relatively high flow rate of the drilling mud through
the holes 42. The high flow rate helps prevent the particles which
do manage to get past the first, outer filter section 32 from
clogging the holes 42 for any length of time. In order to assure
the high flow rate through the holes 42, the total number of holes
42 in the shell 44 are limited. Accordingly, the holes are grouped
into multiple regions 74, 76 of the shell 44 as shown. Alternately,
the holes 42 may be grouped in other manners, or just evenly
dispersed across the whole surface of the shell 44. The limitation,
however, is that the area density of the holes 42 in each region
74, 76 of the shell 44 remain less than about 0.15.
[0043] In the embodiment illustrated in FIG. 3, the first region 74
of the second filter section 34 has two rows of eight by 2.5 mm
diameter holes 42 spaced over the 10.5 mm wide region 74. In the
preferred embodiment, therefore, the ratio of hole area to shell
area is less than about 0.06. Again this ratio is sensitive to the
overall diameter 72 of the shell 44 of the second filter section,
34 and therefore this ratio may vary from about 0.02 to 0.15
depending upon the exact design, while still providing the
described benefit.
[0044] Although the two stage filter arrangement of the present
invention has been described in relation to downhole rotary
steerable drilling tools, the filter arrangement has applications
in numerous other type of downhole fluid using devices. For
example, many devices use drilling fluid to create impulses in the
drilling fluid to communicate data from downhole to the surface.
The two-stage filter of the present invention fitted in these
devices would allow designs with higher signaling accuracy, but
were prone to clogging without the filter. It is also desirable to
use solenoids in downhole fluid using devices for control of fluid
flow. Past solenoid designs adapted to operate without filters had
very high power consumption due mainly to the anti-clogging design.
Much smaller, less powerful solenoids may now be used in tools
equipped with the two stage filter arrangement of the present
invention.
[0045] Whereas the present invention has been described in
particular relation to the drawings attached hereto, it should be
understood that other and further modifications apart from those
shown or suggested herein, may be made within the scope and spirit
of the present invention.
* * * * *