Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
F-2742 ~ 5~3~
FLOATATION APPARATUS FOR
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MARINE SEISMIC EXPLORATION
Marine seismic exploration for oil is -typically done wi-th
the aid of a marine vessel which tows a line of seismic pulse
sources. These sources generate acoustic pulses which penetrate
subsea formations and are reflected back to a line of acoustic pulse
detectors such as geophones. The line of pulse detectors may be
either placed on the ocean floor or may also be towed behind -the
marine vessel.
In a typical marine seismic survey, as many as two lines of
twenty seisrnic pulse sources and many miles of acoustic pulse
detectors are towed by a single vessel. The sources and detectors
are kept near the surface by floa-ts or buoys.
Although there are several problems associated with a line
of seismic pulse sources and detectors, such as deployment retrieval
and storage, one of the rnost significan-t problems lies in the towing
operation. These buoys can cause a significant amount of drag which
reduces the speed a-t which the vessel may opera-te and may reduce the
total number of seismic pulse sources and acoustic pulse detectors
that may be used.
The present invention pertains to marine towing systems and
more particularly to seismic pulse source towing systems comprising
a string of acoustic pulse sources which are towed near the surface
in a marine environment. A commercially available buoy is mounted
on an expanded V-shaped frame having a fixed rudder. Connection is
made at a predetermined angle between a leading edge of the frame
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and a towing cable. The frame angles the buoy in the water which
reduces towing resistance to allow faster towing speeds and permits
additional acoustic pulse sources wi-th their associated buoys.
This invention provides in combination:
a marine vessel having a tow line;
floatation means for maintaining the surface position of a
marine apparatus;
frame means attached to the floatation means for connecting
the floatation means to the tow line;
bracket means fixed to the frame means at an angle inclined
to the horizontal having a plurality of adjustment means for
altering the tow depth of the marine apparatus;
rudder means moveably mounted on the frame means for
controlling planar parallel placement of the floatation means with
respect to the towing vessel; and
stabilizer means mounted on the frame means for mainta.ining
the center line of the floatation means perpendicular to the marine
vessel.
This invention also provides a floatation apparatus to be
towed by a vessel tow line through a fluid environment by a marine
vessel comprising:
floatation means for maintaining the surface position of a
marine apparatus;
frame means attached to the floatation means for connecting
the floatation means -to the tow line;
bracket means fixed to the frame means at an angle inclined
to the horizontal having a plurality of adjustment means for
alteriny the tow depth of the marine apparatus;
rudder means moveably mounted on the frame means for
controlling planar parallel placement of the floatation means with
respect to the towing vessel; and
stabilizer means mounted on the frame means for maintaining
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the center line o~ the floatation means perpendicular to the marine
vessel.
This invention further provides a method for controlling
the depth o~ a near surface marine apparatus towed by a marine
vessel comprising the steps of:
providing a floatation member having a frame with a
plurality of slots arranged at an angle inclined to the horizontal
~or connection to a tow line;
connecting the floatation member to the tow line through
one of the slots to tow the marine apparatus at a first
predetermined depth; and
towing the marine apparatus at a second predetermined depth
by connecting the floatation member to the tow line through another
one of the slots.
In the drawings appended bo this specification:
FIG. 1 is a plan view of a marine seismic system
FIG. 2 is a side view o~ the system o~ FIG. 1 ;
FIG. 3 is a side view of the present invention; and
FIG. 4 is a front view of the apparatus of FIG. 3.
FIG. 1 illustrates a marine vessel 10 towing seismic
acoustic pulse source lines 12 and 14. Each line 12 and 14 includes
a plurality of buoys 16 and 18 respectively. FIG. 2 illustrates a
side view of the seismic exploration system of FIG. 1. Line 14 is
illustrated as having an acoustic pulse source 2n below each buoy
18. There may be more than one pulse source 20 below each buoy 18;
however, one buoy 18 is pre~erred for each pulse source 2û due to
the combined weight of line 14 and pulse source 20.
ln typical seismic exploration, as many as twenty acoustic
pulse sources 20 may be attached to each of lines 12 and 14. In
addition, marine vesse~ lD may tow one or more lines o~ acoustic
pulse detectors ~not shown) and the total number o~ buoys used to
keep both detectors and sources may be in the hundreds. This can
result in a great amount of dxag being exerted by the buoys. Thus,
marine vessel 10 must he operated at slower speeds or the number
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of acoustic pulse sources 20 and detectors (not shown) must bereduced.
Figure 3 illustrates a side view of a floatation system 22
having a buoy 18 rotatably mounted at the end points of its center
line 24 on frame 26 attachment points 28 and 30. Buoy 18 is mounted
on frame 26 by chain links which permit a small amount of rotation
about its center axis depicted by center line 24. Frame 26 is
attached to line 1~ by cable 32 which is fixed to adjustable bracket
34 at point A. Cable 32 may be attached to either point A, B, C, D
or E of bracket 34 and is illustrated as attached to point A for
descriptive purposes only.
Cable 32 is attached to line 14 at connector 36. Cable 38
is attached to seismic acoustic pulse source 20 at connector 40 and
to line 14 at connector 36. Buoy 18 and pulse source 20 are
illustrated as being attached to connector 36 on line 14 in the
preferred embodiment. ~owever, both are not required to be joined
at the same location but may be spatially separated along line 14.
Frame 26 comprises a generally V-shaped base 50 having
plate 52 bridging vertex 54 of arms 56 and 58 of base 50. Frame 26
may be constructed of any high strength rigid material; however,
aluminum tubing is preferred for base 50 and sheet alurninum is
preferred to plate 52. Aluminum provides high strength and low
weight while also providing durability and resistance to salt water
corrosion.
Plate 52 provides stabilization to prevent buoy 18 from
turning while being towed by marine vessel 10. Without stabilizing
plate 52, buoy 18 would have a propensity to turn so its broadside
is perpendicular to its line of travel through the water, increasing
its drag and decreasing the depth at which pulse source 20 is
towed. Plate 52 maintains center line 24 perpendicular to the stern
of marine vessel 10.
Attached to arm 56 is bracket 34 having a plurality of
connection points, A, B, C, D and E for connection of cable 32
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between frame 26 and line 14.
Bracket adjustments A~ B, C; D and E are provided dependingupon the depth at which acoustic pulse source 2û is to be towed.
When cable 32 is connected to adjustment A, pulse source 20 is towed
at its shallowest depth, approximately twenty feet below the
surface. When cable 32 is connected to adjustment E, pulse source
20 is towed at its deepest available depth, approximately 30 feet.
Additional adjustments B through D give incremental depths for
towing. Bracket 34 with adjustments A through D permit an operator
to control the amount of drag exerted by buoy 18 when it is towed
through the water. By controlling the drag, an angle ~ between
cable 32 and tow line 14, may be altered and the distance between
the water surface, the location of buoy 18 and tow line 14 may be
shortened or lengthened.
Rudder 60 is attached to arm 58 and generally extends the
length of arm 58 from the vertex 54 of base 50 to the end of arm
58. The rudder is rotatably mounted on arm 58 ~o oontrol the po~ition
of buoy 18 with respect to vessel 10. Buoy 18 travels on a line
parallel to the line of motion of vessel 10 in the same plane, sea
level, and the rudder controls the displacement of the line of
travel for buoy 18 with respect to the parallel line of travel for
vessel 10. Thus, rudder 60 controls the planar parallel placement
of buoy 18 with respect to marine vessel 10. Rudder 60 also
provides additional stabilization of float 18 when used in
combination with plate 52.
Attachment points 28 and 30 at the end points of arms 56
and 58 respectively permit buoy 18 to partially rotate about center
line 24. This allows buoy 18 to rotate slightly when subjected to
forces different from those experienced to plate 52.
FIG. ~ is a front plan view of floatation system 22
illustrating buoy 18 as having a generally circular shape narrowing
down to rounded point 28 where it is partially rotatably mounted on
arm 56 of base 50. Rudder 60 is partially hidden from view by base
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50 due to its narrower width than tubular base 50.
While the present invention has been described by way of a
preferred embodiment, it is to be understood that the description is
for example purposes only and the present invention should not be
limited thereto but only by the scope of the following claims.
