Downhole liquid pressure seismic source and bit positioning system

A method of and apparatus for determining the precise position of the drill bit on the bottom of a long drill string in a deep borehole in the earth, during a drilling operation. The method comprises placing a plurality of geophones in a three-dimensional array near the surface of the earth, above the expected position of the drill bit in the earth, causing at least a low energy seismic source to be initiated near the drill bit in the earth, repeating the source a number of times, and determining at the surface of the earth the times of initiation of each of the seismic waves. Responsive to the known times of initiation, stacking each of the repeated geophone signals from each of the geophones, for each of the repetitions of the source, whereby each of the stacked signals will be in-phase with those that resulted from earlier and later repetitions of the source. Several embodiments of an improved downhole seismic source are described, and an improved type of three-dimensional array.

BACKGROUND OF THE INVENTION 
This invention is in the field of elastic wave generation and detection in 
the earth. More particularly, it is concerned with determining the 
position in the earth of the drilling bit during a drilling operation in a 
deep borehole. 
In the prior art, various means have been devised for determining the 
position of the borehole in north-south and east-west coordinates, at 
selected depths during a drilling operation. This has been done by using 
survey instruments specially designed for introduction through the drill 
pipe, which by their internal mechanisms make a record of the slope of the 
borehole at each of a plurality of selected depths, as well as a measure, 
in relation to the magnetic compass, of the azimuth of the slope of the 
borehole. 
The disadvantage of this particular system is that it requires a stopping 
of the drilling process so that the drill stem can be broken and the 
survey instrument inserted on a wire line into the drill pipe. Since the 
cost of operation of the drill rig runs into many hundreds or thousands of 
dollars a day, time lost from the drilling operation makes these 
measurements extremely costly. 
More recently several patents have been issued which involve a seismic 
method of measurement involving the use of a seismic source at or near the 
bit and detecting the first arrivals of the seismic waves at a plurality 
of geophones, positioned in a two-dimensional array around the borehole, 
and determining the position of the source by measurement of travel times 
of the seismic waves to each of the geophones. 
These methods hold some promise, except that they involve the need for a 
high-energy seismic source at the bit, to provide a useful signal from the 
geophones. It is extremely difficult to provide large-energy seismic waves 
without interrupting the drilling process. 
SUMMARY OF THE INVENTION 
It is a primary object of this invention to provide a simple and 
inexpensive means for independent determination, at any selected time, of 
a measurement indicative of the position of the bit, and the bottom of the 
borehole during a drilling operation. 
It is a further object of this invention to provide a method of determining 
the position of the bottom of the borehole without interrupting the 
drilling operation. 
It is a still further object of this invention to provide a continuing 
operation, whereby the position of the bit can be determined at a 
plurality of selected depths, spaced a selected number of feet apart in 
depth, whereby a continuous log of the bit position, with time, is 
obtained. 
It is a still further object of this invention to provide an apparatus and 
method for generating a low energy seismic signal at a point near the 
bottom of a deep borehole, to provide a seismic signal which is a direct 
function of the vertical position of the drill pipe in the hole. 
Still more particularly the object is to provide a drill string, including 
a spline near the bottom thereof, in the borehole, and to provide means 
responsive to the separation of the two parts of the spline to create the 
seismic signal. Thus, by keeping the bottom half of the spline firmly on 
the bottom of the hole by means of drill collars, apparatus can be 
initiated by lifting the upper part of the drill stem a matter of a few 
inches and then lowering it again. 
These and other objects are realized and the limitations of the prior art 
are overcome in this invention by generating at least a low energy seismic 
wave at the bottom of the borehole, at selected intervals of time. 
These weak seismic signals are detected at each of a plurality of geophones 
near the surface of the earth, positioned in at least a two-dimensional, 
and preferably a three-dimensional array, around the anticipated position 
of the bit. The geophone signals are digitized and temporarily stored, and 
then stacked for a great number of repetitions. Because of the weak 
seismic source and the high level of seismic noise, the signal-to-noise 
ratio (S/N R) will be very poor, and it is anticipated that a great many 
repetitions and stacking will be required to obtain a useful signal. 
The key to the detection problem lies in the method of summing, or 
stacking, successive received signals, in synchronism with the previously 
received signals. This method is often used in conventional seismic 
prospecting, where repetitions of 10 to 12 times, or so, are common. Such 
repetitions provide a signal-to-noise improvement proportional to the 
square root of the number of repetitions. Thus improvements in S/N R of 3 
or 4 to 1 can be obtained in normal operations. The repetitions must be 
done with the source substantially stationary, and all stacked signals 
travelling by identical paths. 
The cost in time and money of having great numbers of repetitions must be 
weighed in terms of the value of the S/N R improvement. This limits the 
number of repetitions usually carried out in surface seismic prospecting. 
However, in this application to bit location, time is no problem, since the 
rate of progress of the bit is relatively slow. Thus, an hour or more can 
be devoted to providing a very precise position indication. If the time of 
travel of the signal from the bit to the surface is of the order of 2-3 
seconds, or more, in one respect the rate of repetition cannot profitably 
be less than say 5 to 6 seconds, which permits about 700 repetitions per 
hour. However, since only a short length of trace is required, 
encompassing a short time, say 100 to 250 milliseconds, repetition rates 
of 1 second could be used if the signal initiation mechanism will support 
it. This would permit 3600 repetitions per hour. 
Depending on the hardness of the rock, the rate of penetration of the bit 
may be from 1 foot per hour, to possibly 25-50 ft. per hour; and if 
several hours are required to obtain sufficient repetitions to overcome 
the noise, then the position of the bit has been altered during the 
stacking process, and the successive seismic waves will not all travel by 
the same path. This introduces additional travel times in the later 
signals. If stacking is timed by the time of initiation of the seismic 
waves, then the received signals of later repetitions will be out-of-phase 
with the signals from earlier repetitions. Thus the stacking will not be 
sharp and the precision of position determination will be poor. 
One of the principal improvements in this method involves, among a number 
of factors, the measurement of the incremental downward movement of the 
drill pipe. This is determined from a "starting", or "first" time, such as 
when a new length of drill pipe is inserted into the drill string. 
The stacking is done with a conventional seismic stacker or summer, such as 
an analog magnetic drum, or a digital disc, or by CCD delay lines, etc. 
The time of initiation is controlled at the surface, responsive to the 
summer, and successive repetitions of the seismic signal are started 
earlier, by a time interval which is a function of the downward movement 
of the drill pipe. This function can be proportional to the incremental 
movement, or to some trigonometric function of this movement, taking 
account of the instantaneous direction of the bottom of the hole 
determined from earlier measurements. For the most precise measurements, 
the additional travel times can be calculated for each of the paths to 
each of the geophones to ensure synchronous stacking even though the 
successive paths may be different. 
By this system of stacking, the stacking or integration time can be very 
large, up to several hours, thus providing signal-to-noise ratio 
improvements of 30, 40, or 50 to 1, or more. 
It will be clear that this large number of repetitions can only be done if 
they do not interfere with the drilling, which would be the case for a 
number of the methods to be discussed. The method does not strictly 
require that the seismic source be initiated by signal from the surface 
provided only that a signal up the pipe or by conductor can be received at 
the surface to control the timing of the stacking. 
Analysis of the stacked signals would provide a determination of the 
position of the bottom of the borehole coincident with the position of the 
bit at the "starting time". Stacking could be continued even while the 
pipe is not turning, and the bit is off bottom, such as when "washing" the 
hole", and so on, providing only that the source could be initiated. 
In other words, since the drilling operation is naturally slow, and since 
the receiving apparatus can be run, more or less, continuously without 
interrupting drilling, very long integration times are possible. Thus very 
weak seismic signals can be detected, providing only that the stacking can 
be synchronized with the times of initiation of the signals, from the 
ever-changing position of the source, by a knowledge of the continuing 
movement of the source. 
In view of the high multiplicity of repetitions, I prefer to make use of 
the capability of recovering true signal amplitude of noisy signal 
information, by digitizing the received signals plus noise to 1 bit, for 
simplicity of processing, and then using a great many repetitions. 
Another improvement of this continuation-in-part application is the 
construction of and the method of operation of an improved seismic source 
that can be controlled from the surface. 
Still another improvement involves the use of a three-dimensional array of 
geophones or sensors at the surface, for improvement in signal/noise 
ratio. 
The general method of generating the seismic waves is to provide a valve 
system containing at least two parts which is installed in the drill stem 
in ways which are well-known in the industry. In one method, one of the 
two parts of the valve is lifted with respect to the second part by means 
of a tension member, or steel cable, inside of the drill pipe reaching to 
the surface, where it is lifted a selected short distance by means such as 
a hydraulic cylinder, for example. 
Another method is to provide a spline section in the drill stem near the 
bottom thereof, and attach one part of the valve means to the upper part 
of the drill stem above the spline and the second part of the valve to the 
lower part of the drill stem below the spline. Thus by lifting the pipe a 
matter of a few inches at the surface of the earth, the valve can be 
operated and the precise time of operation can be determined. 
In another embodiment the valve has two parts which rotate with respect to 
each other. One part is attached to and rotates with the drill stem, and 
the other part is in the form of an outer sleeve which is rotatable with 
respect to the drill stem and has means to prevent its rotation while in 
the hole. Thus, characteristic signals can be generated either by lifting 
the pipe or lifting the valve with a tension member, or rotating one part 
of the valve with respect to the other part, or by any combination of 
these methods. 
With respect to the geophone receivers, it is part of this invention to 
utilize, for at least one receiver, at the surface a vertical array of 
sensors which are positioned in a shallow borehole drilled from the 
surface down to a selected depth. The separate sensors are spaced at 
selected intervals down this borehole, and are independently connected 
through amplifiers to the recording apparatus. Means are provided for 
determining the differential time delay between the passage of a seismic 
wave generated in the borehole below the bottom sensor, as it sequentially 
passes each of the sensors. As the seismic wave passes upwardly and is 
intercepted by each of the succeeding sensors, the time delays can be 
determined. The received signals generated by each of the separate sensors 
can then be stacked, by time shifting so that each of the received signals 
are in phase with each other. This type of operation provides very good 
protection against noise in the earth which is travelling horizontally and 
provides improved signal-to-noise ratio for signals which are travelling 
substantially vertically.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring now to the drawings, and in particular to FIG. 1, there is shown 
one embodiment of the invention. This involves a valve system which is 
inserted into the drill string and which, of course, can be installed in a 
short sub, so that it can be quickly inserted into or removed from the 
drill string, as is well known in the art. 
The drill stem and valve is indicated generally by the numeral 10 and 
involves the upper portion of the drill string or drill stem, indicated 
generally by the numeral 12, which extends from the surface down through 
the point of assembly of the valve. The lower or continuing portion of the 
drill string, indicated generally by the numeral 14 includes one or more 
drill collars if used, and a bit, not shown but well known in the art. 
For convenience, the drill string is shown to include a spline, indicated 
schematically by the numeral 24, which is a well-known construction of 
drilling equipment, known in the industry. There are two groups of 
longitudinal fingers which are interrelated with each other. One group is 
attached to the drill string above the spline, that is, to the part 12, 
and another set of fingers which is part of the lower drill string 
indicated by the numeral 14. A vertical sliding motion of the upper drill 
stem is possible by means of the spline, while still providing torque to 
the bit and to the lower part of the drill stem. 
Normally drilling mud would be flowing down inside of the drill stem 12 and 
14 in accordance with the arrow 37 and down through the openings in the 
bit and up around the outside of the drill stem in the annulus between the 
drill stem and walls of the borehole, previously cut by the bit. 
The purpose of the valve, which will now be described, is to provide a 
means, operable at the surface, for closing off the flow of mud through 
the drill stem, so that it will not flow through the bit. When this 
happens due to the inertia of the long, moving column of mud or water, the 
water tends to compress and build up pressure at the point of closure, in 
a phenomena well known as "water hammer". The compression causes a high 
internal pressure, such that when the valve is again opened after a short 
interval of time, the compressed water will expand extremely rapidly, and 
eject water through the valve and down through the openings in the bit. 
This sudden on-rush of water or mud will cause a compressional elastic 
wave in the earth, which will then travel upwardly to the seismic 
detectors at the surface. 
Shown in FIG. 1 is a central cylindrical rod of metal, indicated generally 
by the numeral 16, which is adapted to slide freely, axially, in an 
opening 28 inside the upper part of the lower drill stem 14. This part is 
labeled numeral 18. The inner valve, or first part of the valve 16, has an 
axial opening 40 at the top which joins a plurality of radial openings 42, 
which extend outwardly to the inner surface 28 of the part 18. 
At a certain position there are one or more openings 44 through the wall of 
the part 18, so that when the inner valve 30 is positioned at the level 
indicated in the drawing, there will be communication between the space 
inside of the drill string 12, so that mud or water flowing down the drill 
string can go through the central opening 40 from the top 34 of the inner 
valve 30, down through the radial openings 42, and through the openings 44 
in the wall of the part 18. The mud will then flow downwardly through the 
annular space 45, in accordance with arrow 33, through radial openings 48 
and 46, and through the central passage 49 and out through the bottom end 
32 of the inner valve, and down through the lower drill stem 14 to the 
bit, in accordance with arrow 37. 
Consider that the inner valve 30 has moved downwardly, from the position 
shown, where the top 34 is at level I, to a second position where the 
radial openings 42 are completely below the openings 44, and top 34 is at 
level II. It is clear that the passage from the upper drill stem through 
the valve is closed off, since the openings 42 are positioned against the 
solid wall of the part 18. Therefore, the flow of drilling mud through the 
valve will be cut off and a corresponding "water hammer" pressure will 
build up in the drill stem above the valve. 
Consider now that the inner valve 16 is lowered further so that the top 
edge 34 is at level III and is below the opening 44 in the part 18. It is 
clear then that the drilling mud will be able to flow from above the valve 
over the top edge 34 and out through the openings 44 into the annular 
passage 45, back through the openings 48, the radial passages 46, and 
longitudinal passage 49. Thus, the flow of mud is suddenly and explosively 
reinitiated. This reinitiation will generate the seismic pulse as the 
expanding water rushes out through the openings in the bit. 
The inner valve 16 is now in its lower portion, where the bottom edge 32 
can be abutted on the shoulder 38, for example. There is still free 
passage of mud through the valve and through the bit. Following the same 
procedure, except by lifting the inner valve 16, will go through the same 
procedure of closing off the passage for a first selected time until the 
water hammer pressure builds up to a selected value, and lifting still 
further, until the passages 42 and 44 are in alignment, where there will 
be an opening provided for explosively exhausting liquid from above the 
valve out through the bit. 
It is clear therefore that by judicious movement of the inner valve 16 
downward a few inches and upward a few inches, the valve can generate a 
seismic impulse of some magnitude. 
The drawing shows a bale 35 on the top of the inner valve, which is 
supported by a cable 29, which passes upwardly through the inside of the 
drill stem 12 to the surface. There it can pass outwardly through a 
stuffing gland so that the valve core 30 can be lifted and lowered by 
corresponding lifting and lowering of the steel cable 28. This type of 
construction is illustrated in U.S. Pat. No. 2,370,818 in the name of 
Daniel Silverman, issued Mar. 6, 1945. 
However, if the drill stem has a spline 24 as previously described, then 
the bale 35 of the inner valve 30 can be attached, by means shown 
schematically by dashed lines 41, so that it is securely fastened to the 
inner wall 21 of the upper drill stem 12. In this case, the valve motion, 
that is, the motion of the inner valve 30 with respect to part 18 and the 
lower part of the spline 14, can be operated by lifting and lowering the 
top of the drill stem. Thus, the exact time of the operation can be 
determined by the times of lifting and lowering the pipe. 
In this regard, reference is made to the U.S. Pat. No. 3,817,345 in the 
name of John R. Bailey issued June 18, 1974, wherein a complete working 
system was provided for determining the time of operation of a source at 
the bottom of a drill stem knowing the instant at which the drill pipe was 
released at the surface, and knowing the length of pipe and the travel 
time of an elastic wave in the pipe. 
What has been described is a valve system which can be operated by steel 
cable from the surface, or by use of a spline, and lifting the drill stem 
at the surface by a short distance of the order of inches. Thus, the flow 
of drilling mud through the drill stem to the bit can be stopped for a 
selected interval of time, until the water hammer pressure builds up to a 
selected value. It can then be opened to release that pressure of the 
compressed water, to create a seismic signal by reinitiating the flow of 
drilling mud through the bit. 
Referring now to FIG. 2, there is a second embodiment, of a similar type of 
valve, in which a spline 58 is provided between an upper drill stem 
indicated generally by the numeral 52, which has fingers 60, which 
interleave with corresponding fingers 58, which are attached to the lower 
drill stem 54, which supports a bit down below. There is a seal 55 between 
the two parts of the spline, with the upper drill stem passing down into 
the lower drill stem through the opening 78, and supporting therein a 
sliding valve element 56. 
This central valve 56 is forced downwardly by a helical spring 63, so that 
it abuts the shoulder 68 and as the upper drill stem 52 is lifted, the 
inner valve 56 is lifted off the seat 69. This provides an opening from 
the inside 64 of the upper drill stem 52 down through the central opening 
72 of the inner valve, and out through radial openings 74, and out through 
the opening 76 in the lower drill stem 54. Thus, when the upper drill stem 
52 is lifted, there is a free passage for drilling mud through the 
openings 64, 72, 74, and 76. As the upper drill stem 52 is lowered, the 
central valve 56 will seat 70 against the valve seat 69, closing off the 
flow of mud through the drill bit. Then, after a selected interval, the 
drill stem is raised again to open the valve at the point 69. 
If the high pressure in the inside 64 of the upper drill stem 52 is high 
enough, it may hold the central valve 56 tightly closed against the 
shoulder 69. In this case, the upper drill stem 52 can be lifted in a 
jarring fashion, and shoulder 68 can be brought into conjunction, which 
will provide sufficient momentary upward force to lift the central valve 
56, and open the passage so that an explosive expansion of liquid can flow 
down through 76 and through the bit. 
So far, the two embodiments described in terms of FIGS. 1 and 2 have shown 
valve systems which can be operated either by cable, or by lifting the 
drill stem and the use of a spline, to momentarily close and then reopen 
the passage through the drill stem for the mud flow down through the bit. 
Of course, as in FIG. 1, the inner valve 56 of FIG. 2 can be operated by a 
cable, etc. 
Referring now to FIG. 3, there is shown a third embodiment of the invention 
which involves a rotary type of valve. The drill stem does not require a 
spline, and the valving is such that at one position of rotation the 
passage for drilling mud through the drill stem and the bit is closed off 
and at another position, the flow of drilling mud is reopened, but through 
the wall of the drill stem to the annulus surrounding the drill stem, 
rather than through the bit. The opening through the bit is then 
subsequently reopened, to get back to the starting point. Thus there are 
three separate positions of the valve--one position in which the valve is 
closed completely; a second position in which the valve is open to a 
passage of mud through the drill bit; and a third position where the valve 
is opened to passage of mud through the wall of the drill stem and out to 
the annulus. 
The situation where this highly compressed "water hammer" is available, and 
can be released directly from the inside of the drill stem, through the 
wall of the drill stem, to the annular space, should provide a greater 
seismic effect than when, as in FIGS. 1 and 2, the compressed liquid is 
released down through the narrow passages of the drill bit, where the 
effect of the release of compression is reduced due to further restriction 
of the flow to the small passageways. 
In the prior art there is an instance of a device for creating a seismic 
impulse in the region of the bit by alternately opening and closing a 
passage through the wall of the drill stem, while the drilling mud is 
flowing down through the bit. This is shown in U.S. Pat. No. 4,040,003, 
entitled "Downhole Seismic Source", issued Aug. 2, 1977. In FIGS. 5, 6 of 
this patent the openings through the bit are always open, and there is no 
way that the water hammer effect can be developed. Here, all that the 
opening through the wall would do, would be to bypass the restriction 
through the bit, and the resulting pressure drop through the restrictions 
in the drill bit. 
There is no mechanism shown for that device, where there are three valve 
positions; namely, where there is: A flow through the drill bit, a 
complete closure of all flow, and then the sudden opening of a flow 
through the wall of the drill stem. In other words, in the mechanism of 
FIG. 3, there is a complete shutoff of all flow, and therefore, there is a 
resultant high value of compression and "water hammer" pressure, which is 
absent from FIGS. 5 and 6 of U.S. Pat. No. 4,040,003. 
In FIG. 3 the drill stem is indicated generally by the numeral 100, and 
includes an upper portion 108 that continues upwardly to the surface, and 
has a center line 118. There is a complete transverse bulkhead closure 110 
across the inner space of the drill stem. The drill stem continues 
downwardly with the pipe 112 down to the bit. There is an outer sleeve 
indicated generally by numeral 104 which surrounds the enlarged portion 
117 of the drill stem. This has a relieved annular volume 132. Thus, 
liquid can flow downward through the drill stem in accordance with arrow 
120, then pass out through at least one radial opening 114 into the space 
132, which is completely around the sleeve 104, and then back in through 
an opening 116 in the drill stem in accordance with arrow 122, and then 
down through the drill stem 123 to the bit. Now, consider that the sleeve 
124 is held in position, and the drill pipe 108, 112 is at the position of 
the opening 114 indicated at level I. The drill pipe is lifted until this 
opening 114 is above the space 132, and is dead-ended against the inner 
wall of the sleeve, at the position II. In that case, all flow of liquid 
is cut off from the space above the bulkhead 110. Therefore, "water 
hammer" will build up in the drill stem. If the pipe 108 is dropped back 
to position I, the valve will open through the drill stem and the drill 
bit. In other words, this valve in FIG. 3, when lifted from position I to 
position II, creates a shutoff. When it is lowered through the same depth, 
the valve is opened again. This sort of action is similar to that of FIGS. 
1 and 2. 
In position III, that is, when the opening 114 is opposite the opening 130 
in the sleeve 124, the situation looks like the cross-section in FIG. 5. 
Here the outer sleeve 124 remains stationary, and the drill stem, 
indicated by the cross-section of the ring or tube 117, rotates in the 
direction of the arrow 134. In this position, drilling mud from inside of 
the upper drill stem, above the bulkhead 110, flows in accordance with 
arrow 136 into the space 132, and down in accordance with arrow 122, into 
the drill stem again. 
However, when this opening 114 turns another half-turn and approaches the 
position of the line 137, the opening 114 is closed by the inner wall of 
the sleeve and during the time the pipe turns between the direction 137 
and 138, there is a buildup of water hammer pressure in the upper drill 
stem. As the opening 114 becomes opposite the opening 130 in the sleeve, 
there is now a sudden rush of expanding water, explosively flowing out of 
the opening 130 into the annulus to provide the seimic impulse. Thus, in 
each revolution, the valve sequentially assumes three positions; namely, 
its present position in FIG. 5 where the arrow 136 shows flow out through 
the opening 114 into the annular space 132 and down through the bit; the 
other position between 137 and 138 where the inner space of the drill stem 
is completely closed off by the wall of the sleeve; and then the third 
position during a short interval when this internal pressure is relieved, 
through the opening 130 in the sleeve. 
Thus, the seismic impulse can be generated once each revolution, going 
through the three separate sequential positions, with the mud flowing 
through to the bit, the mud stopped, and the pressurized mud released to 
the annulus, then the opening through the sleeve is closed and the opening 
through the bit is opened, and the process repeats. By choice of width of 
the shoulder 141 the opening through the sleeve 130 can be closed before 
passage is opened through the bit. Or by making this shoulder narrow, the 
outlet through the bit can be opened before the opening 130 is closed. 
Shown in FIG. 3 is a fourth position indicated by level IV where the 
opening 114 is again closed off, and an upper fifth position at level V, 
where the opening is again opened to the annulus. Thus by building the 
sleeve without the opening 130, then a procedure could be carried out 
whereby with the sleeve and the drill stem in such a relative position 
indicated by numeral I, the internal volume of the drill stem is open to 
the bit. Between the positions I and IV, the opening 114 will be closed 
off by a wall, so that there would be a buildup of water hammer pressure, 
and then as the opening 114 got to level V, there would be a release of 
that pressure through the opening 128 out into the annulus. 
Thus, by translation alone, it is possible to have a three-position valve, 
and to go sequentially from one to the other. In one case (lifting the 
pipe), the buildup pressure would be released to the annulus, and on the 
down travel of the pipe (or up travel of the sleeve), the second operation 
of water hammer pressure would be relieved through the drill bit. 
Thus, by any selected combinations of rotation of the sleeve 124, or 
non-rotation of the sleeve and translation of the sleeve, relative to the 
drill stem, a variety of types of sequential closings and openings can be 
provided, for generating seismic waves in the earth. 
The position at level V is shown as cross-section, plane 4--4 in FIG. 4. 
Here a plurality of openings 114 are shown which open into one or another 
of the enlarged openings 128 in the sleeve. There is always at least one 
or more openings 114 open to the annulus. Thus, a simple matter of 
relatively lifting one of the two parts, sleeve or stem, can open the 
interior of the stem to the annulus. This is a different situation than 
that shown in FIG. 5 where the rotation of the two parts of the valve 
provides a sequence of three positions of the valve. 
FIG. 6 shows an extension of FIG. 3 in which a spline 142 is provided in 
the drill stem so that the upper drill stem is 144, the lower drill stem 
is 100, and the sleeve is held, by such a means as a bow spring 154, to 
prevent it from rotating. If use were made of the features of FIG. 5, the 
bow spring would be required so there would be relative rotation between 
the sleeve 104 and the pipe 100. On the other hand, if the vertical 
relative motion situation of FIG. 4 is desired, then the bow spring would 
not be required, and the vertical motion of the sleeve 104 with respect to 
the drill pipe 100 would be to move it downward by the projecting fingers 
143 operating on the top surface 145 of the sleeve. This forces the sleeve 
down against the pressure of the spring 150, which is locked between a 
shoulder 152 and the sleeve, with a sliding ring 148 in between. Thus, if 
a combination of sliding and rotating is required, that is also possible 
by using the bow spring 154, the spline 142, and lifting and lowering the 
upper drill stem 144. 
Referring now to FIGS. 7 and 8, there is another feature of this invention 
in which the geophones that are positioned near the surface of the earth 
are generally positioned at the surface of the earth. If the seismic 
signal is a strong one, then that is perfectly adequate. However, there is 
a great amount of noise in the region of the surface geophones. This is 
due to the pumps that are operating on the drill rig. Also, the pipe is 
rotating and rubbing all along its length down the borehole. Thus there 
will be a lot of seismic noise picked up in the surface geophones which 
travels more or less horizontally from the drill rig to the geophones. 
I have found that there is great advantage in a situation of that sort, 
instead of providing one or a closely spaced group of several geophones at 
the surface, of drilling a shallow borehole 168 from the surface 161 down 
to a selected depth 167 in the earth 160, and positioning it at a selected 
radius 166 from the principal drilling borehole 162. This radius 166 would 
be the normal position of one of the geophones. In this shallow borehole 
168 I would put a series array of sensors 170A, 170B, 170C, 170D, 170E, 
170F, etc. These would be placed at selected spacings, and each of them 
would be connected through cable 172 to a multi-channel amplifier 174. The 
signal on 176 from the amplifiers would go to a recorder, as has been 
discussed in my co-pending application, Ser. No. 792,565. 
In the deep borehole 162, there is the drill stem 163, with drill collars 
164 and bit 165, which may be many thousands of feet deep. The seismic 
waves from the source which is near the bottom of the borehole will travel 
substantially vertically to reach the sensors 170. 
In FIG. 8 is a schematic drawing of what a seismic record would look like 
if these six sensors 170 were recorded on separate traces 180A, 180B, . . 
. 180F. 
If the vertical line 182 represents the time T0 at which the source is 
started, then there would be a time of vertical travel from the bottom of 
the borehole 162 until the wave front reached the lowermost sensor 170A. 
At that time, T1 there would be a wavelet 184A representing the time of 
arrival of the first energy from that seismic source at sensor 170A. A 
little time later represented by the time T2, wavelet 184B would represent 
the arrival of the seismic wave at the second sensor 170B, and so on. The 
wave would arrive at the top sensor 170F, at time T 6, and would look like 
the wavelet 184N. 
The differential time intervals between T1 and T2 would be a function of 
the vertical spacing between the detectors 170A and 170B, and the velocity 
of propagation of sound in the earth, in the vicinity of those two 
sensors. If there was horizontal noise reaching this vertical array of 
sensors, they would all be received at the same time T1 and the 
corresponding wavelets would line up along line 184. 
If it is vertically travelling energy reaching the sensors 170, their 
signals 180 would be aligned on a sloping dashed line 186, the slope of 
which is a function of the velocity of propagation, and the dimensions. 
Having this information, the separate signals 184A, 184B, etc. can be 
stacked or added together by introducing time shifts equal to the 
differential times between T1 and T2, for example, and T1 and T3, so that 
all of the signals 180 would be added together in the stacking, and an 
improved signal-to-noise ratio would be derived which would be less 
sensitive to horizontally travelling energy, which would not represent the 
signal of interest but would represent noise. Thus, by utilizing the 
vertical arrays in shallow boreholes as indicated in FIGS. 7 and 8, the 
signal-to-noise ratio of the detected signals 180 from the weak seismic 
sources can be improved, and the noise against which the interpretation 
must be made can be reduced. 
If the method of operation of the valve involves the use of an internal 
cable, some such mechanism as that illustrated in U.S. Pat. No. 2,370,818 
can be used, or the equivalent. 
If the method of operation of the valve is to lift the drill stem, then a 
method of operation can be employed in which a rotating arm or cam or a 
hydraulic cylinder is used to press transversely on the deadline of the 
hoisting cable from the crown block. Depending on the number of passes of 
the cable through the crown block, a lengthening of this cable by a foot 
or so will cause a lifting of the drill stem by several inches. 
The preferred operation is to initiate the source at selected intervals 
different from, and larger than, the period of rotation of the drill stem, 
and stacking a plurality of repetitive detected signals. 
Conversely, it is possible to repeat the source at successively increasing 
or decreasing time intervals, or in a random time pattern, or other 
selected time pattern, and then to correlate the received signal with a 
facsimile of the selected time pattern. 
It is possible also to operate as in FIG. 5 with a first selected number of 
repetitions synchronous with the period of rotation, to provide a group 
signal pattern, and then to repeat this group pattern at variable 
selectively longer time intervals, in a selected time pattern, and so on. 
Of course, the valve as described in FIG. 1 can be operated by a motor 
means at the valve, rather than by the cable 28. The motor system is 
suggested in FIG. 7 of my co-pending application, Ser. No. 792,565. It can 
be operated by means of conductor carried down inside of the drill stem, 
such as, for example, shown by U.S. Pat. No. 2,370,818. 
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.