CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority and benefit from U.S. Provisional Patent
Application No. 61/682,389, filed August 13, 2012, for "Antifouling removable
streamer second skin and process of mounting," the entire content of which is
incorporated in its entirety herein by reference.
BACKGROUND
TECHNICAL FIELD
[0002] Embodiments of the subject matter disclosed herein generally relate to
devices and methods for limiting and/or preventing deposits on a streamer used
underwater and, more particularly, to a removable second skin mounted on the
streamer.
DISCUSSION OF THE BACKGROUND
[0003] During the past years, offshore drilling has continually increased.
Given high costs and risks associated with offshore drilling, to avoid a dry well,
marine seismic surveys are used to generate a profile (image) of the geophysical
structure under the seafloor. While this profile does not provide an accurate location
for the oil and gas, it suggests, to those trained in the field, the presence or absence
of oil and/or gas.
[0004] During a seismic exploration, as illustrated in Figure 1, a vessel 10
towsseismic detectors 12 distributed along a cable 14.Cable 14 carryingseismic
detectors 12 is called a streamer 16. A streamer may be up to 10 km long and may
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be formed from plural sections of few hundreds of meters each. Vessel 10 may tow
plural streamers 16 at once. Towed streamer 12 may have a constant depth relative
to the ocean surface 18 throughout its length, or have a variable depth profile.
[0005] Vessel 10 also tows a seismic source 20 configured to generateseismic
waves, which penetrate the solid structure under the seafloor 22, and are at least
partially reflected by interfaces 24 or 26 between layers having different seismic
wave propagation speeds. Seismic detectors 12 detect the reflected waves. The
time delay between firing the seismic source and detecting a related reflection
provides information about the location (depth) of reflecting interfaces.
[0006] Seismic exploration campaigns may last long periods (e.g.,several
months). During these campaigns, the streamerspreferably remain in the water
(except, for example,in cases of extreme unfavorable weather
conditions)becauserecovering/deploying the streamersis expensive and tedious.
Thus, thestreamers are immersed in sea water for several consecutive months, at a
shallow depth (a few meters), and are generally dragged at low speed (less than or
equal to 5 knots). In these circumstances, the streamers' outer surfacesare subject
to fouling, particularly due to the proliferation of microorganisms or bio-fouling. One
of the most common types of microorganisms attaching to streamers is barnacles
which adhere permanently to a hard substrate either by growing their shells directly
onto the substrate of by means of a stalk.
[0007] In time, bio-fouling results in substantial disadvantages such as:
(1) generating hydrodynamic flow noise;
(2)amalgams or incrustations forming on the streamer's outer surfaces, which are
likely to disturb seismic measurements;
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(3)increasing drag onthe streamers and, consequently, increasingfuel consumption
to tow them;
(4) of a strong, unpleasant stench developing within a few dayswhen streamers
covered with bio-fouling are recovered and exposed to air;and
(5)streamer skin being pierced by certain types of bio-fouling, resulting in liquid
intake inside the streamer.
[0008] Several techniques have been applied conventionally to address the
bio-foulingproblem. For example, a cleaning devicewith rotary brushes and/or
blades may be temporarily or permanently attached on streamers to clean their outer
surfaces. The use of cleaning devices is impeded by the presence of protruding
elements (e.g., floaters, or trajectory correction devices known as birds) on the
streamers. Although cleaning devices continue tobe subject to research and
improvement, their practical value (reliability versus cost) remains questionable.
[0009] Another conventional technique used to address the bio-fouling
probleminvolves using antifouling paints(also used on boat hulls), for example, paints
including cuprous oxides. Such antifouling paints are used with caution,from an
environmental standpoint, to minimize sea water pollution. The safe use of
antifouling paints may also be problematic for the persons likely to be in contact with
antifouling paints during the manipulation of seismic streamers. Furthermore,
techniques for applying "antifouling" paint are hardly compatible with technical and
economical constraints linked to seismic streamers because painting them is a long
and costly operation due to their length. In addition, to allow the paint to dry (to
minimize seawater pollution), the painted seismic streamers have to be stored in a
manner that requires a considerable amount of space, which is not economically
viable onboard a vessel.
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[0010] Applying a coppercoating on streamer's skinas well as loading the
streamer's skinwith a biocide substancehavealso been considered. However, the
copper coating and the streamer's skinare not removable, so the streamers still have
to be cleaned in tedious and expensive ways. Additionally, the biocide substance
included in the streamer's skin during manufacturing does not last for the lifetime of
the streamer and cannot be replenished laterfor streamersin use.
[0011] Accordingly, it would be desirable to provide devices, systems and
methods addressing the bio-fouling problem related to streamers used in marine
seismic explorations, in an economically attractive manner and avoiding the aforedescribed
problems and drawbacks.
SUMMARY
[0012] A removable second skin with antifouling properties can be easily
mounted on and removed from streamers onboard a vessel. The second skin has
also the effect of reducing turbulences at discontinuity locations along the streamer.
[0013] According to one exemplary embodiment, there is a streamer made of
plural sections and usable underwater for marine seismic surveys. The streamer
includes a first skin configured to separate its inside thereof from surrounding water
when the streamer is submerged, seismic receivers housed inside the first skin, and
a removable second skin. The removable second skin is configured to surround the
first skin along at least one streamer section length. The removable second skin
includes a flexible material with antifouling properties .
[0014] According to another embodiment, there is a streamer usable
underwater for marine seismic surveys and has a flexible material with antifouling
properties wrapped around an outer surface thereof.
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[0015] According to another embodiment, there is a marine seismic survey
system including a streamer configured to be used underwater and made of plural
sections. The streamer has a first skin configured to separate its inside thereof from
surrounding water when the streamer is submerged, seismic receivers housed inside
the first skin, and a removable second skin. The removable second skin is
configured to surround the first skin along the streamer's entire length. The
removable second skin includes a flexible material charged with a biocide
substanceand a closure system configured to join sides of the flexible material.
[0016] According to another embodiment there is a method for preventing biofouling
deposits on a streamer's outer surface. The method includes mounting a
removable second skin made of a flexible material charged with a biocide substance
over an outer surface of the streamer. The method further includes deploying the
streamer in water and recording seismic survey data using seismic receivers inside
the streamer. The method then includes recovering the streamer from the water and
removing the removable second skin from the streamer.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] The accompanying drawings, which are incorporated in and constitute
a part of the specification, illustrate one or more embodiments and, together with the
description, explain these embodiments. In the drawings:
[0018] Figure 1 is a schematic diagram of a seismic survey system;
[0019] Figure 2 is a cross-section of a streamer according to an embodiment;
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[0020] Figures 3A, 3B and 3C is illustrate closure systems according to
various embodiments;
[0021] Figure 4 illustrates another closure system according to an
embodiment;
[0022] Figures 5A, 5B, 5C and 5D illustrate closure systems including preformed
shapes,and tools used to interlock and/or unlock the pre-formed shapes
according to various embodiments;
[0023] Figure 6 illustrates a seismic survey system including a streamer
according to an embodiment;
[0024] Figure 7 illustrates a process of mounting the removable skin on the
streamer according to an embodiment;
[0025] Figure 8 is a cross-section of a streamer according to another
embodiment;
[0026] Figure 9 illustrates a process of mounting the second removable skin
according to another embodiment;
[0027] Figure 10 is a flowchart illustrating steps performed by a method for
preventing bio-fouling deposits on an outer surface of a streamer according to an
embodiment; and
[0028] Figure 11A illustrates locations favorable to abundant barnacle growth
on a streamer unprotected by the removable skin, and Figure 11B illustrates the
effect of using the removable skin at these locations.
DETAILED DESCRIPTION
[0029] The following description of the exemplary embodiments refers to the
accompanying drawings. The same reference numbers in different drawings identify
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the same or similar elements. The following detailed description does not limit the
invention. Instead, the scope of the invention is defined by the appended claims. The
following embodiments are discussed, for simplicity, with regard to the terminology and
structure of a seismic survey system including at least one streamer. However, the
embodiments to be discussed next are not limited to these structures, but may be
applied to other structures that are subject to bio-fouling while immersed.
[0030] Reference throughout the specification to "one embodiment" or "an
embodiment" means that a particular feature, structure or characteristic described in
connection with an embodiment is included in at least one embodiment of the subject
matter disclosed. Thus, the appearance of the phrases "in one embodiment" or "in an
embodiment" in various places throughout the specification is not necessarily referring
to the same embodiment. Further, the particular features, structures or characteristics
may be combined in any suitable manner in one or more embodiments.
[0031] According to one embodiment illustrated in Figure 2, a streamer 100
(seen in cross-section) usable underwater for marine seismic surveyshas the following
structure: a first skin 110, seismic receivers 120 housed inside first skin 110, and a
removable second skin 130. First skin 110 is a strength member configured to
separate and protect the inside from surrounding water when the streamer is
submerged. First skin 110 may include multiple layers of different materials. Seismic
receivers 120 as well as electrical cables or other electrical components are typically
located in a central zone of the streamer. Inside first skin 110, a material lighter than
water (e.g., a foam) may fill a predetermined volume to make the streamer buoyancy
neutral.
[0032] Removable second skin 130 is configured to surround first skin 120 along
the length of at least one section(of hundreds of meters) of a streamer 100. The second
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skin may be applied on few adjacent or separate sections or on all the sections of a
streamer. Removable second skin 130 includes a flexible material 132 antifuling
propertiesand a closure system 134 configured to join sides of flexible material 132.
The antifouling properties may be due to the flexible material being charged with a
biocide substance or having an outer foul-releasing (i.e., anti-adhesive) surface due to
a super-hydrophobic nanocoating, silicon coating, fluoropolymer, etc.
[0033] Preferably, the flexible material is acoustically transparent to have no
negative impact on the seismic measurements performed by the seismic receivers
inside the streamer. Flexible material 132, which may have a thickness of less than 1
mm, has antifouling properties. The flexible material may be polyurethane, polyvinyl
chloride (PVC), polyamides, anti-abrasive textile, fluored polymers or any other
thermoplastic, etc.
[0034] In one embodiment, the antifouling properties are due to an anti-adhesive
coating including silicon or fluored polymers. In another embodiment, the antifouling
properties may be due tothe flexible material's hydrophobic surface or
superhydrophpbic using nanotechnologies coatings. In yet another embodiment,
antifouling properties are due to an antifouling paint pre-applied on the flexible material
before mounting the removable second skin on the streamer.
[0035] The closure system may be configured to connect overlapping surfaces
of the flexible material. For example, the closure system may include an adhesive
layer 135 applied inbetween the overlapping surfaces 136 and 137 as illustrated in
Figure 3A, pressure buttons 138as illustrated in Figure 3B,and/or Velcro-type
connectors 139 as illustrated in Figure 3C.
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[0036] In another embodiment, sides 141 and 142 of the flexible material 132
are welded with ultrasound or by temperature when the removable second skin is
mounted along the streamer as illustrated in Figure 4.
[0037] According to yet another embodiment, the closure system includes preformed
shapes located along the sides and configured to interlock when the removable
second skin is mounted along the streamer. For example, Figure 5A illustrates a male
part 151 and a female part 152 engaged with each other and separated using a tool
153. In another example, Figure 5B illustrates a first type of molded shapes 155 and
156 engaged with each other and then separated using tool 157. Yet in another
example, Figure 5C illustrates a second type of molded shapes 158 and 159 engaged
with each other and separated using a tool 160. In yet another embodiment, Figure 5D
illustrates a zipper type of closing system 161 and a tool 162 that may be used to
close/open this type of system.
[0038] Figure 6 illustrates a marine seismic survey system 200 including a
streamer 210 configured to be towed underwater, for example, by vessel 220.Streamer
210 may be any of the above-described embodiments.
[0039] The removable second skin according to the above-described
embodiments may be mounted on the streamer as the streamer is moved to be
deployed in the water. For example, as illustrated in Figure 7, a streamer winch 310
may be stored on a lower deck 320 of the vessel. While the streamer moves from the
winch toward the sea, it passes through a second skin mounting area on an upper deck
330 where a removable second skin on a second winch 340 is applied to surround the
"naked" (i.e., without the removable second skin) streamer 350 for at least one
section's length (about 200 m). In the second skin mounting area, a worker joins sides
of the flexible material either by welding or by interlocking the closing system using the
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appropriate tool. Thus, after passing through the second skin mounting area 355,
streamer 360 is protected by the second removable skin. In one embodiment,the
second skin may be made of thermoretractable plastic heated during the streamer's
deployment.
[0040] The above-described operation may be reversed when the streamer is
recovered from the water: streamer 360 protected by the second removable skin has
its closure system opened while passing through the second skin mounting area 355,
the removed second skin being rolled back on the second skin winch 340 while the
naked streamer 350 is stored on the streamer winch 310. However, depending on the
length of time the streamer was submerged and/or how long it will be until the streamer
is deployed again, operators may decide to maintain the second removable skin on the
streamer when the streamer is recovered (e.g., storing streamer 360 protected by the
second removable skin on streamer winch 310).
[0041] According to another embodiment illustrated in Figure 8, a streamer 400
usable underwater for marine seismic surveyshas a first skin 410 configured to
separate an inside thereof from surrounding water when the streamer is submerged,
seismic receivers 420 housed inside the first skin, and a removable second skin 430
configured to cover the first skin 410 along the streamer's entire length. The removable
second skin 430 includes a flexible material charged with any antifouling properties
wrapped around the first skin along the streamer.
[0042] Removable second skin 430 may be mounted on the streamer as it is
moved to be deployed in the water on the deck of a vessel. For example, as illustrated
in Figure 9, a streamer winch 440 may be stored on a lower deck 450 of a vessel.
While the streamer moves from the streamer winch 440 toward the sea, it passes
through a second skin mounting area 455 on an upper deck 460 where a packing
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machine 470wraps the second skinaround the "naked" (i.e., without the removable
second skin) streamer 480. Thus, after passing through the second skin mounting
area, streamer 490 is protected by the second removable skin.
[0043] The above-described operation may be reversed when the streamer is
recovered from the water: the second removable skin is unwrappedfrom streamer 490
passing through the second skin mounting area 455, the naked streamer 480 being
then stored on the streamer winch 440. As previously mentioned, depending on the
length of time the streamer was submerged and/or how long it would be until the
streamer is deployed again, operators may decide to maintain the second removable
skin on the streamer when the streamer is recovered (e.g., storing streamer 490
protected by the second removable skin on streamer winch 440).
[0044] Figure 10 is a flow diagram of a method 500 for preventing bio-fouling
deposits on an outer surface of a streamer according to an embodiment. Method 500
includes mounting a removable second skin made of a flexible material charged with a
biocidesubstanceor has foul release properties.over a first outer skin of the streamer, at
510. Method 500 further includes deploying the streamer in water, at 520, recording
seismic survey data using seismic receivers inside the streamer, at 530, and recovering
the streamer from the water, at 540. Finally, the method includes removing the
removable second skin at 550. In one embodiment, mounting 510 includes joining
sides of the flexible material via a closing system. In another embodiment, mounting
510 includes wrapping the flexible material around the streamer. Mounting 510 may
occur when the streamer is moved to be deployed in the water.
[0045] It has been observed that barnacles tend to attach and grow at
locations along the stream at which the profile has discontinuities, and, thus,
turbulences. For example, as illustrated in Figure 11A, barnacle 610 grows in
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abundance at locations at which width varies (a portion 620 having a larger diameter
than the adjacent portions of the streamer 630 and 640) such as bird collars and
weights. One advantage of using the removable second skin is that such
discontinuities are smoothed out, and local bio-fouling protection is provided due to
the surrounding material 650 loaded with a biocide substance.
[0046] Another advantage is that the second skin is separated from the
streamer with relatively little effort, and, in the same time, any fouling deposited
thereon is removed. Thus, the expense and effort to clean the streamer is avoided
by using the removable second skin to cover the streamer. On the other hand, the
removable second skin may be cleaned and recycled, being less cumbersome to do
so than cleaning the heavy and bulky (i.e., carrying seismic receivers) streamers.
[0047] Another advantage is that toxic substance such as antifouling paints
may be applied on the second removable skin and dried before it is brought onboard
the vessel, thereby avoiding the problem of safely and economically applying
antifouling paints onboard.
[0048] The disclosed exemplary embodiments provide a removable second
skin, a streamer with a removable second skin,and related methods for preventing
bio-fouling deposits on an outer surface of a streamer. It should be understood that
this description is not intended to limit the invention. On the contrary, the exemplary
embodiments are intended to cover alternatives, modifications and equivalents,
which are included in the spirit and scope of the invention as defined by the
appended claims. Further, in the detailed description of the exemplary
embodiments, numerous specific details are set forth in order to provide a
comprehensive understanding of the claimed invention. However, one skilled in the
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art would understand that various embodiments may be practiced without such
specific details.
[0049] Although the features and elements of the present exemplary
embodiments are described in the embodiments in particular combinations, each
feature or element can be used alone without the other features and elements of the
embodiments or in various combinations with or without other features and elements
disclosed herein.
[0050] This written description uses examples of the subject matter disclosed to
enable any person skilled in the art to practice the same, including making and using
any devices or systems and performing any incorporated methods. The patentable
scope of the subject matter is defined by the claims, and may include other examples
that occur to those skilled in the art. Such other examples are intended to be within the
scope of the claims.
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I/We claim:
1. A streamer (100) made of plural sections and usable underwater for
marine seismic surveys, the streamer comprising:
a first skin (110) configured to separate an inside thereof from surrounding
water when the streamer is submerged;
seismicreceivers (120) housed inside the first skin; and
aremovable second skin (130)configured to surround the first skin along at
least one streamer sectionlength, the removable second skin including a flexible
material (132) with antifouling properties.
2. The streamer of claim 1, wherein the flexible material has an antiadhesive
coating from a group including a super-hydrophobic nanocoating, a silicon
coating, and a fluored polymers coating.
3. The streamer of claim 1, wherein the flexible material is charged with a
biocide substance.
4. The streamer of claim 1, wherein the second skin further includes a
closure system configured to connect overlapping surfaces of the flexible material,
the closure system including at least one of:
an adhesive layer applied in-between the overlapping surfaces;
pressure buttons; and
velcro type of connectors.
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5. The streamer of claim 1, wherein sides of the flexible material are
welded with ultrasound or by temperature when the removable second skin is
mounted along the streamer.
6. The streamer of claim 1, wherein the second skin further includes a
closure system configured to join sides of the flexible material and having pre-formed
shapes located along the sides,the pre-formed shapes being configured to interlock
when the removable second skin is mounted along the streamer.
7. Astreamer(400) usable underwater for marine seismic surveys having
aflexible material(420) with antifouling properties wrapped around an outer surface
thereof.
8. A marine seismic survey system (200), comprising:
astreamer (210, 100) configured to be used underwater, made of plural
sections and having
a first skin (110) configured to separate an inside thereof from
surrounding water when the streamer is submerged;
seismicreceivers (120) housed inside the first skin; and
a removable second skin (130) configured to surround the first skin
along at least one streamer section length, the removable second skin
including a flexible material (132) with antifouling properties.
9. The marine seismic survey system of claim 11, wherein the flexible
material has an anti-adhesive coating from a group including a super-hydrophobic
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nanocoating, a silicon coating, and a fluored polymers or is covered with an
antifouling paint.
10. A method (500) for preventing bio-fouling deposits on an outer surface
of a streamer, the method comprising:
mounting(510) a removable second skin made of aflexible material with
antifouling properties over an outer surface of the streamer;
deploying(520) the streamer in water;
recording(530) seismic survey data using seismic receivers inside the
streamer;
recovering(540) the streamer from the water; and
removing(550) the removable second skin from the streamer.