Method and apparatus for shallow water seismic operations

A seismic receiver array device for shallow water and near-shore operations which is comprised of an elongated low-profile, flexible casing having a plurality of geophones and hydrophones spaced along its length, and the geophones and hydrophones are electrically connected to a transmitter for transmitting the seismic impulses into a master receiver. Spikes are extended downwardly at spaced intervals along the length of the casing and a setting tool is provided to releasably anchor the spikes into the earth below a body of water.

This invention relates to geophysical prospecting apparatus; and more 
particularly relates to a novel and improved method and apparatus for 
conducting near-shore seismic operations and particularly in shallow water 
areas. 
BACKGROUND AND FIELD OF INVENTION 
In conducting seismic operations in shallow water or near-shore areas, 
there is a need for a receiver array device which is capable of accurately 
sensing or responding to seismic vibrations without being unduly affected 
by water current noise and other noises common to shallow water conditions 
and tidal zones. In the past, emphasis has been placed upon the use of one 
or more hydrophones which generally have exhibited poor signal-to-noise 
ratios to the extent that in severe operating conditions, operations must 
be suspended for long periods. Geophones have not been used extensively in 
shallow water areas, since a firm anchor must be established in solid 
contact with the earth beneath the water in order to accurately sense 
seismic vibrations. Because of the difficulty of anchoring and setting 
geophones in place, they have not been used in shallow water seismic 
operations. Furthermore, in the past, there has been no system which 
integrated the hydrophone and geophone receivers in the same or common 
unit or body. 
It is therefore desirable to provide for a single seismic receiver array 
device which can be deployed in near-shore and/or onshore areas and 
effectively advanced over wide areas to sense seismic impulses and 
transmit same to a transmitter with maximum efficiency and optimum 
signal-to-noise ratios. In this connection, the device should either be 
capable of operating while suspended in water or anchored to the earth or 
floor beneath the water, but in either mode be stable against undue 
shifting or twisting in the current and present in any of receivers which 
are deployed in a spatial configuration so as to produce an optimum 
signal-to-noise ratio whether through the utilization of a series of 
hydrophones or geophones or a combination of both. Further, it is 
important that the device be readily transportable to different locations 
and therefore should be of compact but durable construction as well as 
being modular to permit several receiver array devices to be 
interconnected to produce optimum sensitivity under different conditions 
of use. 
SUMMARY OF INVENTION 
It is therefore an object of the present invention to provide for a novel 
and improved method and apparatus for carrying out seismic operations and 
which is specifically adaptable for use in near-shore shallow water 
seismic exploration activities and particularly in harsh current and surf 
zone environments. 
It is another object of the present invention to provide for a novel and 
improved seismic receiver array device which is of compact, rugged 
construction and can either be operated by suspending in the water or by 
setting in the earth beneath the water and/or on land; and to this end a 
novel and improved setting tool is provided for use in combination with 
the receiver array device to firmly anchor it in a desired underwater 
location. 
A further object of the present invention is to provide for a novel and 
improved seismic receiver array device for near-shore seismic operations 
which is readily transportable to different intended locations and which 
is capable of employing a series of hydrophones, geophones or a 
combination of same in carrying out seismic operations and to transmit 
seismic signals to a recording device. 
A still further object of the present invention is to provide for a 
low-profile, compact seismic receiver array device which is of flexible 
but durable construction and can be readily utilized under harsh current 
conditions and surf zone environments as well as a wide range of water 
depths. 
An additional object of the present invention is to provide for a novel and 
improved method and apparatus for carrying out near-shore, shallow water 
seismic operations in which the device is easy to transport and use under 
variable conditions of use; and further wherein a streamlined flexible 
casing is employed as a housing for a series of hydrophones and geophones 
thereby providing a multiplicity of receivers in a single device so that 
efficient noise attenuation can be achieved. 
In accordance with the present invention, a preferred form of seismic 
receiver array device for shallow water, near-shore operations is 
comprised of an elongated flexible casing having a plurality of geophones 
along with hydrophones in pairs spaced along its length, neutrally or 
slightly negative buoyant support means forming a part of the casing, and 
downwardly extending earth-penetrating geophone spikes spaced along the 
length of the casing for overcoming the buoyancy of the casing and 
anchoring the geophones into the earth beneath the water where applicable. 
The geophones are electrically connected to a transmitter for directing 
the seismic impulses or vibrations sensed into the master receiver. 
A plurality of hydrophones along with geophones in pairs are disposed at 
spaced intervals along the length of the casing and similarly connected to 
a transmitter for transmission or recording of seismic impulses sensed 
when the device is immersed in water of more than 2 meter depth. When the 
device is anchored to the bottom by the geophone spikes, both geophones 
and hydrophones transmit seismic signals. However, where the device is 
suspended in water due to excessive water depth or other conditions, only 
the hydrophones are operative. Similarly, on land or in very shallow water 
conditions less than 2 meters in depth, only the geophones will be 
operative to transmit a signal. In order to facilitate anchoring of the 
earth-penetrating members, a setting tool includes a rigid convex foot 
engageable with the casing and upwardly extending telescoping or threaded 
members to force the cover and engaged casing downwardly until the 
earth-penetrating members become firmly anchored. The degree of buoyancy 
of the receiver array is preferably controlled by a fluid or gel-like 
substance disposed in the casing, and the casing itself has an upwardly 
convex cross-section, a flexible underside with a fluid or gel-like 
substance filling the interior of the casing in surrounding relation to an 
array of hydrophone and geophone receivers. In certain applications, 
stability may be afforded through the utilization of extension wings at 
opposite ends of the casing and which extend in lateral directions beyond 
the opposite side portions. 
A major feature of the proposed seismic system is to provide a receiver 
array device which is sufficiently flexible in operation to operate in a 
wide range of near-shore, shallow water environments and conditions. It is 
specifically designed to overcome some of the noise problems which inhibit 
operations within tidal and excessive current areas. The unique 
integration of geophones and hydrophones into a single receiving device 
provides maximum flexibility and efficiency of operations and promotes 
enhancement of the signal-to-noise ratios in harsh environments of 
near-shore transition zones.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring in detail to the drawings, a preferred form of seismic receiver 
array device 10 is illustrated in FIGS. 1 to 4 and is broadly comprised of 
a low-profile, upwardly convex elongated casing 12 have a hollow central 
body portion 14, a laterally extending underside in the form of a flexible 
heavy plastic sole 15 and upper arch-like cross-sectional supports 16 
which curve downwardly and merges with the casing sole 15 to terminate in 
opposite side edges 17 at opposite lateral outer edges of the sole 15. The 
cross-sectional supports 16 maintain the convex upward profile of the 
casing and secures the geophones 20 rigidly in place in the casing. The 
supports are only present at longitudinally spaced intervals where the 
geophones 20 are placed along the casing. The casing 12 forms with the 
sole 15 a sealed enclosure for fluid or a gel-like substance 18 and which 
substance is of a consistency or density to lend buoyance if necessary to 
the entire casing unit. A plurality of geophones 20 are disposed at 
longitudinally spaced intervals within the body 14, and held by the 
supports 16 at spaced intervals along the casing wall 12 and sole 15. 
Hydrophones 19 are disposed at longitudinally spaced intervals but are 
staggered with respect to the geophones 20 along the casing and are 
surrounded by the fluid or gel which fills the body cavity 14. 
In order to facilitate direct connection of the casing sole 15 to the 
earth, a plurality of earth penetrating members in the forms of spikes 24 
extend downwardly from the geophone casing through the bottom of the 
casing sole 15 and are permanently affixed thereto. The spikes 24 are of 
elongated rigid construction and may be of any desired length and 
construction to firmly anchor the casing and geophones to the earth at the 
bottom of the body of water where applicable. Typically, such spikes would 
have a slightly fluted profile which promotes ease of insertion into the 
earth but anchors the casing securely in the harsh operating environments 
or soft bottom conditions. Extraction is accomplished by exerting a 
pulling force on the tether lead or cable 30 to the casing. Electrical 
cables 28 extend from the geophones 20, and electrically conductive cables 
29 extend from the hydrophones 19, the cables 28 and 29 extending through 
an umbilical cord or cable 30 into a conventional transmitter T having an 
antenna A for sending data to recording instruments, not shown. One 
suitable form of transmitter is that illustrated and described in U.S. 
Pat. No. 4,704,584 in which a portable seismic telemetry buoy has a dual 
channel sensor input and is capable of being connected to the geophone and 
hydrophone cables 28 and 29. 
It should be noted that the cables 28 and 29 have opposite connector ends 
31 and 32, respectively, for connection to an additional casing 10 so that 
one or more casings may be arranged in end-to-end relation to provide 
additional sets of geophones 20 and hydrophones 19. Additional hydrophone 
or geophone receivers will result in better noise attenuation and thus 
better signal-to-noise ratios. Moreover, certain types of noise (long 
wavelengths) require longer receiver arrays to attenuate their affects. 
Accordingly, additional receivers are connected in series so that the 
signals from the receivers are summed and fed into the same transmitter. 
Another form of receiver array unit 10' is illustrated in FIG. 4 in which 
like parts are correspondingly enumerated to that of FIGS. 1 and 2. In 
this form, while the basic casing construction is identical to that of 
FIG. 1, extension wings 26 and 27 are provided at opposite ends of the 
casing for added stability. The base or casing sole 15 and upper casing 
wall 16 are of uniform cross-sectional configuration throughout the length 
of the unit 10', except across the extension wings 26 and 27 which are of 
relatively thin cross-section compared to that of the central 
cross-section of the casing. In a manner corresponding to that described 
with reference to FIGS. 1 to 3, the cables 28 and 29 include connector 
ends 31 and 32 for addition of one or more casings 10' in series. 
The preferred and modified forms of seismic device 10 and 10' are primarily 
intended for use in shallow waters so that, notwithstanding their slight 
buoyancy, they can be anchored into the earth or solid floor beneath the 
body of water. To this end, as shown in FIG. 5, a setting tool 40 is 
provided for forcing the spikes 24 into the earth and includes an inner 
cap 42 of generally concavo-convex configuration which generally conforms 
to the cross-sectional shape of the upper curved surface portion of the 
casing and terminates in lower edges 43. An inner pole 44 extends upwardly 
from the inner cap and is rigidly connected to the cap 42. In turn, an 
outer cap or cover 46 is superimposed on the inner cap 42 and terminates 
in lower outside edges 47 which extend downwardly a limited distance 
beyond the lower edges 43 of the cap 42. A hollow pole 48 is rigidly fixed 
to the outer cap 46 and extends upwardly from the cap 46 and is slidable 
down over inner pole 44. Claws or fingers 50 are pivotally connected to 
the lower edges 47 of the outer cover and are biased toward one another by 
spring members 52 to normally retain the cap 46 snugly against the inner 
cap 42 with the fingers 50 engaging the underside of the base 15. 
The setting tool is assembled as described in connected relation to the 
casing. By pressing the setting tool 40, and specifically the outer pole 
48 downwardly, the spikes 24 will penetrate the earth with sufficient 
clearance for the fingers 52 to pivot outwardly. Once the spikes are set, 
the outer pole 48 is drawn upwardly relative to the inner pole 44 causing 
the fingers 52 to diverge away from the casing sole 15 into a nearly 
vertical disposition so as to disengage the fingers 52 and the setting 
tool 40 then can be drawn upwardly with the inner pole until it is clear 
of the receiving array device 10. The concept is that the inner pole is 
the controlling member. The outer sleeve member only serves to manipulate 
the fingers 52. 
It will be evident that a single setting tool with a cap 42 length of 1' to 
2' can be employed and which is positioned above the first spike and 
successively advanced to anchor each successive spike along the receiving 
array device 10. In the alternative, a single setting tool assembly with a 
much longer cap 42 length (possibly 1 to 2 meters) with a series of claws 
or fingers at spaced longitudinal intervals along the outer edges 47 can 
be utilized and operated synchronously to anchor the spikes into the earth 
followed by removal of the assembly. 
Accordingly, it is to be understood that while a preferred form of 
invention has been set forth and described herein, various modifications 
and changes may be made without departing from the spirit and scope 
thereof as defined by the appended claims.