System for imparting compressional and shear waves into the earth

A seismic vibrator system for imparting compressional and shear wave vibrations into the earth has an earth contacting base with a vertical post. A tubular hub is slidably received on the post in a piston/cylinder relationship. Spaced apart horizontal top and bottom plates are secured to the hub. A mass is slidably supported between the plates. Pistons interconnect the hub and the mass. Hydraulic energy is used to reciprocate the mass vertically on the post and horizontally between the plates.

REFERENCE TO PENDING APPLICATIONS 
This application is not related to any pending applications. 
REFERENCE TO MICROFICHE APPENDIX 
This application is not referenced in any microfiche appendix. 
BACKGROUND OF THE INVENTION 
The present invention provides an improved system for generating in the 
earth's surface seismic signals that can be used in geophysical 
exploration. 
Geophysical exploration, or more precisely seismic exploration, involves 
the introduction of energy into the earth. Energy waves generated at the 
earth's surface travel through the earth and when an energy wave 
encounters a strata which has a different velocity or density a small 
portion of the energy wave is reflected back which can be detected at the 
earth's surface. The reflected signals can be analyzed to estimate the 
shape, composition, depth and size of various strata within the earth and 
this information is employed in predicting where oil, gas or other 
valuable minerals may be located. 
Seismic wave producing energy is induced into the earth surface for 
purposes of conducting seismic exploration in two basic formats, that is, 
compression waves (sometimes known as P-waves) and orthogonal shear waves 
(sometimes known as S1 and S2 type waves). Simply stated, compressional 
waves are typically generated by oscillating or vibrating weight along a 
vertical axis to the earth's surface whereas shear waves are typically 
generated by oscillating or vibrating weight along an axis that is 
inclined from the vertical. 
For background information relating to seismic signal generating systems, 
reference may be had to the following previously issued United States 
patents: 
______________________________________ 
U.S. Pat. No. 
INVENTOR TITLE 
______________________________________ 
5,666,328 Crowell et al 
Three Axis Seismic Vibrator 
5,694,375 Woodall Ultra-Broadband Hydrophone 
5,703,833 Allen One Step Inversion/Separation 
Scheme Using A Plurality Of 
Vibrator Sources 
5,710,720 Algrain et al 
Phase Lock Loop Based 
System and Method For 
Decomposing and Tracking 
Decomposed Frequency 
Components Of A Signal, With 
Application To Vibration 
Compensation System 
5,717,170 Anstey Swinging-Weight Vibrator For 
Seismic Exploration 
______________________________________ 
The United States patent references cited in U.S. Pat. No. 5,666,328 
contain additional background information relating to the subject of this 
disclosure. 
BRIEF SUMMARY OF THE INVENTION 
The invention disclosed herein relates to a system for imparting 
compressional and shear waves into the earth. Compressional waves are 
sometimes referred to as "P-waves" and shear waves are sometimes referred 
to as "orthogonal waves" or "S1 or S2 waves". The system includes an earth 
engaging baseplate that preferably has on its bottom surface an undulating 
shape to resist slipping so that thereby orthogonal vibrations can be more 
effectively transferred to the earth's surface. 
A post is uprightly supported from the baseplate. A tubular hub is slidably 
received on the post. A vertical and laterally translatable mass is 
supported to the hub. A translation system which, in the illustrated 
embodiment, is a hydraulic cylinder/piston apparatus, is employed that, 
when activated, imparts reciprocal vertical movement of the mass relative 
to the hub, which motion is transferred by the post to the baseplate for 
imparting compressional energy waves into the earth. 
A second translation assembly that, in the illustrated embodiment includes 
a cylinder/piston device, is employed to impart reciprocal lateral 
movement of the mass relative to the hub which results in orthogonal 
vibration transferred to the baseplate which is thereby transferred into 
the earth as seismic shear waves. 
In a preferred embodiment of the invention, spaced apart generally 
horizontal top and bottom plates are supported to the hub and thereby to 
the post. Slidably positioned between the top and bottom plates is a mass 
having an upper and a lower surface that slidably contacts horizontal 
surfaces of the top and bottom plates, the mass having an opening through 
it that receives the vertically extending post. Hydraulically actuated 
cylinder/piston devices are employed to impose reciprocal or vibrational 
motion of the mass sliding between the top and bottom plates. The top and 
bottom plates may be simultaneously moved downwardly on the post so that 
the bottom plate securely engages the baseplate so that reciprocal motion 
of the mass between the top and bottom plates is transferred directly to 
the baseplate. 
The disclosure includes, in an addition to the apparatus for imparting 
compressional and shear waves into the earth, a method by which the waves 
are imparted. The method includes the steps of positioning a baseplate in 
contact with the earth's surface, the baseplate having a vertical post 
extending uprightly therefrom. The second step of the method is supporting 
a mass on the baseplate. Thereafter the mass is selectably vertically 
vibrated to impart compressional wave energy to the baseplate and 
selectably laterally vibrated when it is desired to impart shear wave 
energy to the base. 
A better understanding of the invention will be obtained from the following 
description of the preferred embodiment, taken in conjunction with the 
attached drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring first to FIGS. 1 and 2, the basic components of the system for 
imparting compressional and shear waves into the earth are illustrated. A 
baseplate 10 has a bottom surface 12 configured to engage the earth's 
surface. The bottom surface 12 is preferably essentially planar when the 
machine is used for generating compressional waves, that is, where the 
vibrational energy is imposed along a vertical axis into the earth's 
surface. Shown in FIG. 1, but not in FIG. 4, is an adapter plate 14 that 
can be removably secured to the bottom surface 12 of baseplate 10, the 
adapter plate having an undulating lower surface 16 that is configured to 
substantially increase resistance against lateral displacement when placed 
against the earth's surface. Adapter plate 14 can be secured to baseplate 
10 such as by means of bolts or clamps (not shown). If the machine of this 
invention is to be used substantially exclusively for imparting shear wave 
energy into the earth's surface baseplate 10 can have an undulating bottom 
surface, such as surface 16 of the shear wave adapter plate. By the 
embodiment illustrated in FIG. 1 the adapter plate 14 may be used as 
required by the operator according to the specific type of seismic 
exploration being conducted and depending upon whether the emphasis is the 
creation of compressional and shear waves, it being understood that with 
adapter plate 14 attached, the machine can be employed to generate either 
shear or compressional waves. 
Axially affixed to baseplate 10 and extending vertically uprightly from it 
is a post 18. The lower end 20 (See FIG. 4) of post 18 is secured to 
baseplate 10. In the illustrated arrangement the end of post 18 is 
positioned in a recess 22 in a baseplate hub portion 24. By means of bolts 
26, post 18 is securely affixed to the baseplate or, more specifically, to 
baseplate hub 24. 
The upper end of post 18 is laterally supported by the upper end portion of 
stilt legs. In the illustrated embodiment there are four stilt legs 28A 
through 28D. FIG. 3 shows the four stilt legs in cross-section. Each of 
the legs has at its lower end a baseplate 30 that is secured to a mounting 
boss 32 attached to baseplate 10 (See FIGS. 1 and 4). In FIG. 1 the most 
forward stilt legs 28A and 28D (Seen in FIGS. 2 and 3) are not shown so as 
not to obscure other features of the vibrator. Stilt legs 28 are curved at 
their upper ends and the upper end portions oriented inwardly to a top 
manifold 34 to which an upper end portion of post 18 is attached. 
Reciprocally supported on post 18, as best seen in FIGS. 3 and 4, is a 
tubular hub 36. Also as shown in FIGS. 3 and 4 post 18 has, intermediate 
its upper and lower ends, a machined portion forming a piston 38. As seen 
in FIG. 4, piston 38 is formed by a machined surface having three 
circumferential grooves, each of which receives a sealing ring. An 
interior portion of hub 36 receives a tubular sleeve 40 that is held in 
place between upper and lower tubular adapters 42 and 44. The interior 
cylindrical surface of sleeve 40 functions as a cylinder that receives 
post piston portion 38. Internal passageways 46 and 48 are formed 
interiorly of the upper portion of post 18 communicating between the upper 
and lower ends of piston 38. By the application of relative hydraulic 
pressure between passageways 46 and 48, force can be imparted to move hub 
36 upwardly or downwardly on shaft 38. The tubular adapters 42 and 44 
function to provide circumferential bearing surfaces against the external 
cylindrical surface of the post to slidably guide the hub in its vertical 
up and down motion on the post. 
Affixed to the upper end of hub 36 is a top plate 50 and to the lower end 
of the hub a bottom plate 52. Top plate 50 has a lower, planar, horizontal 
surface 54 that is parallel to and spaced apart from a similar planar, 
horizontal surface 56 formed on bottom plate 52. Slidably positioned 
between the top and bottom plate surfaces 54 and 56 is a mass 58, the mass 
having a top planar surface 60 and a bottom parallel planar surface 62, 
the mass top surface 60 sliding on top plate surface 54 and the mass 
bottom surface 62 sliding on bottom plate top surface 56. 
Mass 58 is, in the illustrated embodiment, of circular external 
configuration and has integrally increased external diameter flange 
portions at the top and bottom as seen in FIGS. 1 and 4. Mass 58 further 
is defined by an opening 64 that receives post 18 and hub 36. Opening 64 
permits mass 58 to be moved laterally of the hub and the post in any 
direction and such a lateral movement is employed to impart orthogonal 
seismic wave generating energy to post 18 and more specifically, to 
baseplate 10. To assist in communicating lateral vibrational energy or 
shear wave energy to baseplate 10, bottom plate 52 has on its lower 
surface a circumferential downwardly extending lip portion 66 (FIGS. 1 and 
4) that, when the mass assembly is translated downwardly on post 18 meshes 
with and rests on a circumferential clamping member 68 at the upper 
surface of baseplate 10 or more specifically, to baseplate hub portion 24. 
When there is no hydraulic energy applied to either side of post piston 38 
the weight of the mass assembly causes the assembly to slide downwardly on 
post 18 until the bottom plate lip portion 66 engages clamping member 68 
to interlock the mass assembly to baseplate 10. This interlocking 
relationship can be increased by the application of hydraulic energy to 
impart high hydraulic pressure to the area within piston sleeve 40 above 
post piston portion 38 to force the mass assembly downwardly into 
increased locking engagement with baseplate 10. 
FIGS. 1 and 4 show the system in the relationship of components wherein it 
is being employed to generate compressional waves, that is, wherein the 
system is in condition for vibration of the mass assembly vertically with 
respect to the baseplate. When the assembly is in condition for imparting 
shear waves into the earth, the mass assembly is lowered to rest upon the 
baseplate and to interlock the lip portion 66 with clamping member 68. 
Mass 58 has four lateral openings therein, openings 70A and 70C being seen 
in FIG. 4 and openings 70B and 70D being seen in FIG. 3. The openings 70 
are in a common horizontal plane and are oriented 90.degree. to each 
other. Each of these openings receives a cylinder assembly 72 and each 
cylinder assembly receives a piston 74. The cylinder/piston assemblies 72, 
74 are employed to move mass 58 laterally with respect to hub 36. That is, 
as seen in FIG. 4, hydraulic energy can be reciprocally applied to the 
opposed cylinder assemblies 72A and 72C to cause pistons 74A and 74C to 
move mass 58 first to the right and then to the left. In addition, 
hydraulic pressure can be applied to fully withdraw pistons 74 away from 
engagement with hub 36. When cylinder assemblies 72A and 72C in 
combination with pistons 74A and 74C are employed to oscillate mass 58 
laterally with respect to hub 36, then pistons 74B and 74D are fully 
withdrawn so as not to interfere with the lateral oscillation of mass 58 
relative to the hub. In like manner, when pistons 74B and 74D (FIG. 3) are 
employed to laterally reciprocate the mass relative to the hub, then the 
pistons 74A and 74C (FIG. 4) are fully withdrawn from any contact with the 
hub. 
As seen in FIG. 4, mass 58 has on the interior surface of opening 64 upper 
and lower circumferential grooves which receive toroidal elastomeric 
bumpers 76 and 78. 
FIG. 3 illustrates passageways 80, 82, 84 and 86 formed within mass 58 to 
provide for the flow of hydraulic fluid by which the pistons are 
controlled. Servovalves 88 and 90 (FIG. 1) are employed to control the 
hydraulic system. Servovalve 88 is secured to the upper end of top 
manifold 34 while servovalve 90 is mounted to and moves with mass 58 for 
use in controlling the operation of the system, specifically for 
controlling the flow of hydraulic fluid to reciprocate the mass vertically 
or laterally. A displacement sensor assembly 92 provides an output signal 
employed to supply feedback for control of the machine. 
While element 58 is a "mass", in the compression wave mode the entire 
assembly which includes hub 36, top plate 50, bottom plate 52, mass 58, 
cylinder assemblies 72A through 72D and pistons 74A through 74D together 
constitutes an entire mass assembly that is moved sequentially vertically 
up and down on the post to impart compressional wave energy to baseplate 
10. When the system is employed in the shear wave mode the mass assembly 
is lowered to rest upon baseplate 10 by the engagement of the lip portion 
66 of bottom plate 52 with the clamp member 68 so that the shear wave 
energy is generated entirely by the lateral translation of mass 58 as 
supported between the top and bottom plates. It is important that mass 58 
reciprocate freely as supported between the top and bottom plates and for 
this purpose bearing surfaces 96 are provided. To further insure a low 
friction relationship between the mass and the plates, the bearing 
surfaces may be force lubricated and passageways are illustrated which can 
be employed for this purpose. 
The hydraulic circuitry of the system is not shown since it can vary in 
substantial detail and the means for reciprocally applying hydraulic 
energy to cause vibration of a mass is well known. Commercially available 
components can be used in the construction of hydraulic circuitry. 
Although not shown in the drawings the assembly requires a source of 
hydraulic pressure which can be a separate system employing a hydraulic 
pump with flexible hoses connecting source of hydraulic pressure to the 
system. 
When the system is to be used to impart compressional waves the first step 
is to lift the mass assembly out of engagement with baseplate 10 to an 
intermediate position as shown in FIGS. 1 and 4. Next, the hydraulic 
system is controlled to engage all pistons 74A through 74D so that they 
will restrain horizontal movement of mass 58 with the vertical movement of 
hub 36 on post 18. Then by the application of hydraulic energy through 
passageways 46 and 25M, the mass assembly vertically moved on post 18 
impart vibrational energy to baseplate 10. This vertical vibrational 
energy is coupled to the earth and generate compressional energy waves in 
the earth that function as seismic signals, reflection of such seismic 
signals being detectable by well known seismic exploration systems that 
include geophones and other instrumentation. The rate of vibration, that 
is, the signal cycles per second can be varied as controlled by the 
hydraulic energy applied to the device. 
When the device is used to generate shear waves the mass assembly is 
lowered to rest upon baseplate 10 and the hydraulic system is controlled 
to withdraw contact of one pair of opposed pistons with hub 36 while the 
other pair of opposed pistons is supplied reciprocally with hydraulic 
fluid pressure to cause the mass to oscillate laterally with respect to 
the hub. By alternately actuating one set of cylinder/pistons with the 
opposed set of cylinder/pistons the orientation of shear wave energy 
imparted into the earth can be varied by 90.degree. relationship, without 
moving or otherwise changing the machine and only by alternately 
controlling the way hydraulic fluid pressure is applied. Thus, the system 
can be used selectively to impart either compressional seismic signals or 
orthogonal, that is, shear wave seismic signals into the earth and the 
orientation of the shear wave signals can be selectively changed between 
90.degree. orientations without requiring the device to be moved. 
Since the mass assembly including the top and bottom plates 50 and 52 are 
all supported about the post 18 it is important that a means be provided 
to prevent the rotation of the cylindrical mass while the system is being 
used, particularly when used to generate shear wave energy. For this 
purpose an anti-rotational pin and bushing assembly 98 (FIGS. 1 and 4) is 
employed that functions to freely permit the vertical movement of the 
mass, including top plate 50, but which resists the rotation of the mass 
assembly about post 18. 
The claims and the specification describe the invention presented and the 
terms that are employed in the claims draw their meaning from the use of 
such terms in the specification. The same terms employed in the prior art 
may be broader in meaning than specifically employed herein. Whenever 
there is a question between the broader definition of such terms used in 
the prior art and the more specific use of the terms herein, the more 
specific meaning is meant. 
While the invention has been described with a certain degree of 
particularity, it is manifest that many changes may be made in the details 
of construction and the arrangement of components without departing from 
the spirit and scope of this disclosure. It is understood that the 
invention is not limited to the embodiments set forth herein for purposes 
of exemplification, but is to be limited only by the scope of the attached 
claim or claims, including the full range of equivalency to which each 
element thereof is entitled.