CA1124228A - Systems, apparatus and methods for measuring while drilling - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

Improved systems, apparatus and methods for measuring downhole parameters in a well being drilled in the earth with apparatus comprising a drill string, a mud pump for circulating drilling fluid, and flow restriction means located near the bottom of the string so as to cause a pressure drop between the restriction means and the borehole annulus that surrounds the drill string. In accordance with one aspect of the invention, the improvements involve down-hole pulser means for generating negative mud pressure pulses which are utilized to transmit information concerning downhole parameters to above ground equipment. The improved downhole pulser means utilizes valve means to bypass the restriction means in a manner that results in the efficient generation of effective pulses with minimum expenditure of electric energy. In accordance with another aspect of the invention, improved structure is provided for housing the pulser means and for accommodating associated downhole apparatus. In accordance with another aspect of the in-vention, improved methods are provided for extracting nega-tive mud pressure pulse signals from interfering signals resulting from mud pressure variations due to the mud pump means. In accordance with a further aspect of the invention, improved direct current downhole power supplies are provided.

Description

~42~Z8 FIELD OF THE INVENTION
This invention generally pertains to logging while drilling apparatus, systems and methods and more particularly pertains to systems, apparatus, and methods utilizing mud pulsations for telemetry to transmit signals representing one or more downhole parameters to the earth's surface.
BACKGROUND OF THE INVENTION
Many efforts have been made to develop successful logging while drilling systems, as suggested by the following examples: Karcher, United States Patent No. 2,096,279 proposes a system utilizing electrical conductors inside the drill pipe. Heilhecker, United States Patent No. 3,825,078 proposes a system utilizing extendable loops of wire inside the drill pipe.
Silverman, United States Patent No. 2,354,887 proposes a system utilizing inductive coupling of a coil or coils with the drill pipe near the drill bit with measurement of the induced electrical potential at the earth's ~- surface. Arps, United States Patent No. 2,787,759 and Claycomb, United States Patent No. 3,488,629 propose systems in which pulsed restrictions to the drilling mud flow produce pressure pulse signals at the earth's surface.
Other related United States Patents are Nos. 3,186,222, 3,315,224, 3,408,561, 3,732,728, 3,737,845, 3,949,354 and 4,001,774.

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l~.Z~228 Each of the abovementioned proposals has had some drawback of sufficient consequence to prevent its commercial - acceptance. For example, the inconvenience and time in-volved for the large number of connections and disconnections of electrical connectors is a significant drawback in systems such as proposed by Karcher. Though an induced electric potential system such as propo~ed by Silverman may be considered operable for a short distance, the signal to noise ratio of such a system prohibits its use as a practical matter in deep wells.
When modern jet bit drilling became commonplace and very large mud volumes and high mud pressuxes were employed, the systems as proposed by Arps, proved to be unreliable and subject to rapid deterioration. The intro-duction of a controlled restriction into the very powerfulmud stream, of necessity, required large and powerful apparatus and operation was unsatisfactory because of ~apid wear and very high energy requirements.
The environment is ~ery hostile at the bottom of a well during drilling. Drill bit and drill collar vibrations may be in the order of 50 g. The temperature is frequently as much as 400 F. The bottom hole pressure can be more than 15,000 psi. The drilling ~luid ~lowing through the drill collars and drill bit is highly abrasive. With present drilling equipment including imp~oved drill bits, the con-tinued drilling time with a particular bit can be in the order of lO0 - 300 hours and sometimes longer before it becomes necessary to change the drill bit. Accordingly, a downhole formation condition sensing and signal txansmitting ~.Z~228 unit mounted near the drill bit must be capable of operating unattended for long periods of time without adjustment and with a continuing source of elect~ical power. Also, the signal communication apparatus must be capable of trans-mitting a continuing usable signal or signals to the earth'ssurface after each additional joint of drill pipe is conven~
tionally added to the drilling string as the drilled bore-hole is increased in depth.
In general, systems using mud pulsations for telemetry are considered the most practical since the drill-ing operation is least disturbed. To date, however, the reliability that has been achieved with such systems is not satisfactory. The previous methods such as those of Arps and Claycomb, utilize the insertion of a controlled restriction into the mud flow circuit. ~owever, when the mud flow surpasses 600 gpm and pump pressures pass 3000 psi, controlling this large energy by varying a restriction to produce telemetry signals is complicated and requires powerful downhole machinery.
~ general objective of the present invention is to pro~ide a successful logging while drilling system of the type utilizing mud pulsations for telemetry to transmit signals representing one or more downhole parameters to the earth's surface.
More specifically, it is an objective of the invention to provide such a system wherein the amount of energy that is required to generate a strong pressure pulse at a tool near the drill bit is significantly reduced.
Another objecti~e o~ the invention is the utili-zation of an existing large source of energy for the pro-duction of the mud pulsations.

According to one broad aspect of the invention, thereis provided for use in a system for conducting drilling oper-ations employing a string of drill pipe extending from the earth's surface having a drilling means such as a drill bit, hydraulic drill motor, or the like at the lower end, a pump by which drilling fluid is forced downwardly through the drill string interior and drilling means to flow back to the surface through the well annulus, the drilling means imposing a restric-tion to the drilling fluid flow forming a high pressure zone in the interior of the drill string and low pressure zone in the well annulus, a telemetering system comprising, a drilling fluid bypass above the drilling means providing fluid communi-cation between the interior of the drill string and the well annulus, the bypass being defined in part by a valve seat, a valve stem moveable to and away from said valve seat forming a valve to close and open said bypass, a means for detecting the magnitude of a downhole parameter and for producing an electrical signal representing said magnitude, and electro-magnetic solenoid means responsive to said electrical signal to rapidly operate said valve to generate pressure pulses in the drilling fluid, and means at the earth's surface to detect such pressure pulses and to provide a measure of the magnitude of said parameter.
According to another broad aspect of the invention, there is provided for use in a system for conducting drilling operations employing a string of drill pipe extending from the earth's surface having a drilling means such as a drill bit, hydraulic drill motor, or the like at the lower end, a pump by which drilling fluid is forced downwardly through the drill string interior and dri.lling means to flow back to the surface through the well annulus, the drilling means imposing a restric-tion to the drilling fluid flow forming high pressure zone in ~-6-4;~2~3 the interior of the drill string and low pressure zone in the well annulus, a telemetering system comprising, a drilling fluid bypass above the drilling means providing fluid communi-cation between the interior of the drill string and the well annulus, the bypass having an electrically energizable valve therein capable of rapid operation to open or close said bypass, a means for detecting the magnitude of a downhole parameter and for producing an electrical signal representing said magni-tude, an electrical energy source, means responsive to said signal for supplying a relatively large amount of electrical power to initiate opening said valve, and substantially less power when the valve is open or closed, to generate pressure pulses in the drilling fluid, and means at the earth's surface to detect such pressure pulses, and to provide a measure of the magnitude of said parameter.
According to a further broad aspect of the invention, there is provided for use in a system for conducting drilling operations employing a string of drill pipe extending from the earth's surface having a drilling means such as a drill bit, hydraulic drill motor, or the like at the lower end, a pump by which drilling fluid is forced downwardly through the drill string interior and drilling means to flow back to the surface through the well annulus, the drilling means imposing a restric-tion to the drilling fluid flow forming a high pressure zone in the interior of the drill string and low pressure zone in the well annulus, a telemetering system comprising, a drilling fluid bypass above the drilling means providing fluid communication between the interior of the drill string and the well annulus, the bypass being defined in part by a valve seat, a valve stem moveabl~ to and away from said valve seat forming a valve cap-able of rapid operation to close or open said bypass, a means for detecting the magnitude of a downhole parameter and for ~ 6a-~.Z~2;~3 producing an electrical signal representing said magnitude, a cylinder in communication with the bypass having a compensating piston therein connected to said valve stem so that fluid pres-sure exerts a first hydraulic force on the compensating piston in the direction corresponding to the opening of the valve and fluid pressure exerts a second hydraulic force on the valve stem in the direction corresponding to the closing of the valve, the net hydraulic force on the valve stem being proportional to the difference between said first force and said second force, and means responsive to said electrical signal to rapidly move said valve stem to generate pressure pulses in the drilling fluid, and means at the earth's surface to detect such pressure pulses and to provide a measure of the magnitude of said para- -meter.
The invention will now be described in greater detail with reference to the accompanying drawings.

-6b-~L~.2~ZZ~3 BRIEF DESCRIPTION OF THE DRAWINGS
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Fig. 1 is a schematic illustration of a conventional rotary drilling rig showing apparatus of the present invention incorporated therein.
Fig. 2A is a schematic illustration of a negative mud pressure pulse generator with its valve in the open position.
Fig. 2B is a schematic illustration of the negative mud pressure pulse generator of Fig. 2A, with its valve in the closed position.
Fig. 3~ is a schematic illustration of a physical embodiment of the negative mud pressure pulse generator of Figs. 2A and 2B, together with instrumentation and sensor sections in place in a drill string near the drill bit.
Fig. 3B is a drawing of the negative mud pressure pulse generator of Figs. 2A and 2B taken in proportional di-mensions from an engineering assembly drawing used in actual manufacture of the device.
Fig. 3C is a schematic diagram of a radioactivity -20 type sensor and associated instrumentation.
Fig. 3D is a schematic diagram of a temperature type sensor and associated instrumentation.
Fig. 3E is a schematic diagram of typical instru-mentation for controlling actuation of the valve of the negative mud pressure pulse generator.
Fig. 3F is a schematic illustration of one type of self-contained downhole power source that may be utilized.
Fig. 3G is a schematic illustration of another type of self-contained downhole power source that may be utilized.

~.24228 Fig. 4 is a schematic illustration showing typical aboveground equipment in accordance with a preferred embodi-ment of the invention, wherein the downhole parameter being sensed is radioactivity.
Fig. 5 is a graphic illustration, in idealized form, showing certain wave forms and pulses and time relationships to aid in explanation of the signal extractor portion 102 of Fig. 4.
Fig. 6 is a schematic block diagram showing component 105 of the signal extractor 102 of Fig. 4 in further detail.
Fig. 7 is a schematic block diagram showing component 107 of the signal extractor 102 of Fig. 4 in further detail.
Fig. 8 is a schematic block diagram showing another form of aboveground equipment that may be utilized.
Fig. ~ is a schematic block diagram showing still another form of aboveground equipment that may be utilized.
~ig. 10 is a schematic block diagram showing an alter-nate timing pulse generator that may be utilized.
Fig. ll is a schematic block diagram showing still another form of aboveground equipment that may be utilized.

iL~.24228 DETAILED DESCRIPTION OF INVENTION

Before proceeding with description of preEerred embodiments of the invention, it is believed that understand-ing will be enhanced by discussion of some basic factors.
In a 10,000' length of 4 1/2" drill pipe, the mud volume inside the pipe is of the order of 5,000 gallons.
Assuming that the bulk elastic modulus for compressed drill-ing mud is 400,000, then discharging .5 gallons of fluid will cause a pressure drop of 40 psi, (if we consider the 5,000 gallons as being in a simple tank). It can be assumed, therefore, that discharging mud near the bottom of such drill pipe at the rate of 0.125 gallons/sec. will cause a signal of 10 psi/sec. at the surface. We shall refer to the rate of change of pressure as the ~ index and in this case the ~ index is equal to 10.
Three important experiments were performed;
1. Measurements were made in a test well at 1,800' and moderate differential pressures of 1,000 psi across a valve at the bottom.

2. Measurements were made in an oil field drilling well at 8,000' and low differential pressures of 400 psi.

3. Measurements were made in a second oil field drilling well at 5,000' and high dif-ferential pressures (1,600 psi~.
All three series of experiments indicated that the ~ index of the pressure pulse received at the surface when the valve is suddenly opened was substantially higher than calculated. The reasons for this are: (a) highly com-pressed drilling mud may have an ~.2 ~2 Z ~

elastic modulus somewhat higher than 400,00Q; (b) there is some wave guide acti~n by the d~ill pipe that causes the signal to travel much more ~avorably tha~ it would in a large tank of the same volu~le; and (c~ the sudden opening of a valve at the bott~m o~ the well causes a h~ghe~
index than in the case o~ the large tank because of the elasticity of the mud column above it.
In a typical 15,000 foot drill string (with the bottom end closed off), if a marker were placed at the top of the mud column, this marker would drop some 110 feet when 3,000 psi mud pump pressure is applied (3,0QO ~si is a rather typical mud pump pressure in deep wells~. One can, therefore, consider the mud column as being continually compressed by some 100 feet and acting ~s a long spring in which a large amount of potential energy is sto~ed. When a valve at the bottom of the drill pipe is suddenly opened, this potential energy is released, causing a large negative mud pressure pulse; such mud pressure pulse being substan-tially larger than would be the case if the mud were incom-pressible.
In the experiments conducted at 5,00Q' in a drillingwell, a small passageway (.056 in.2 area2 between the inside of the drill collar and the annulus, was opened and shut in accordance with a controlled sequence. The pressure across the valve was 1,600 psi and the discharge was calculated to be approximately .25 gallons/sec. The volume of mud inside the drill pipe was approximately 2,500 gallons and assuming an elastic modulus for the mud of 400,000', the pressure drop was calculated to be 40 psi/sec.

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(again using the as~umption that mud column was a simple tank). In the tests the pressure drop ~t the surface was measured to be over 100 psi/sec. or considerably more than would be expected from the simple tank calculation. The following conclusion was ~eached: With high pressures exist-ing across the drill bit (1,000 psi or more2, large sharp signals can be developed at the surface by opening and closing a very small b~pass valve at the sub-surface near the drill bit. Valves having an opening of .05 in.2 can produce large signal~ from a 5,QQQ' depth and the reduction in signal magnitude from depths between 2,50a' and 5,0Q0' have been found to be very small; thus, indicating that the signal attenuation is small.
The system of the present inventi~n has a number of important advantages: The rapid discha~ge ~t a rate of , as little as 0.125 gallons/sec will generate a "sharp"
pulse, that is a pulse containing a high rate of change of pressure, i.e., a high ~ index (e.g. 40). ~urthermore, the rapid opening of the bypass valve will also minimi~e wear for the following reasons: When the bypass valve is closed, there obviously is no wear on the valve seat. ~hen the valve is open (and the valve area is large co~pared to a restriction or restrictions followin~ it~, the valve will be exposed to low velocity fluid and, consequently, the we~r will be mostly in the following restrictiDn or restrictions which can be made expendable and of very non-errodable material such as boron carbide. Wear occurs in the bypass valve only when it is in the process of opening or closing, i.e., is "cracked" and the velocity through the valve seat is then very high. The valve operation should, therefore, be ~.2~228 as fast as possible for openin~ and closing and there is no limit to the desirable speed. The rate of discharge through the valve should ~lso be ~ast but there is an upper limit beyond which f~ster discharge does not benefit.
The reason for this is the limit to high frequency trans-mission through the mud. ~requencies higher than about 100 Hz are strongly attenuated and are of little value in build-ing up a fast pulse at the surface. To determine the maxi-mum useful rate of discharge, it was necessary to set up experiments on a full scale using real drilling oil wells and long lengths of conventional drill pipe. The experimental arrangements comprised a special large ~al~e followed by an adjustable orifice.
Changing the orifice size can deter~ine the flow rate in gallons per second. It was determined that flows larger than about .3 gallons per second produced little improvement in the signal. In comparing the signals from a depth of 5,012 feet, three different orifice sizes were tested, .509" diameter, .427" diameter and .268" diameter.
It was determined that the .2~8" diameter orifice generated a signal at the surface nearly as intense as the one gene-rated by the .509" diameter orifice.

~L~.2~228 Referring now to Fig. 1, there is schematically illus-trated a typical drilling rig 10 including a mud circulating pump 12 connected to a discharge pipe 14, a standpipe 16, a high pressure flexible rotary hose 18, a swivel 20 and a drilling string 22, comprising the usual drill pipe and d~ill collars, and a jet type bit 26. A short distance above the bit 26, and mounted within drill collar 24, is a negative mud pressure pulse generator 28 and a sensing and instrumentation unit 30.
The negative mud pressure pulse generator 28 is of a special design. It generates a series of programmed pulses and, each pulse consists of a short momentary reduction in mud pressure. In one embodiment, this is accomplished by means including a valve that momentarily opens a passageway between the inside and the outside o~ the drill collar 24, i.e., the valve controls a passageway between the inside of the drill collar 24 and the annulus 29 formed by the ~utside of the drill collar and the well bore.
Aboveground equipment, generally designated as 32, is connected to a pressure transducer 100, which in turn is connected to standpipe 16. Alternatively, the transducer lO0 could be connected into the stationary portion of swivel 20, if desired.
Figs. 2A and 2B show the negative mud pressure pulse generator 28 in diagramatic form to facilitate ex-planation of its function and manner of operation. The negative mud pressure pulse generator comprises a valve ~ .2~22~3 inlet chamber 42, a valve outlet chamber 44, and a compen-sator chamber 72. The valve inlet chamber 42 is hydraulically connected via an inlet passageway 38 to the inside of the drill collar 24. The valve inlet chamber 42 is also hy-draulically connected via a passageway 48 to the valve outletchamber 44. Hydraulic flow through passageway 48 is con-trolled by the cooperation of a valve 36 with its seat 37.
The valve outlet chamber 44 is hydraulically connected via an outlet passageway 51 to the annulus 29. Interposed in the outlet passageway 51 are first and second compensator orifices 52, 53. The chamber 40 between the orifices 52, 53 is hydraulically connected via a conduit 74 to the com-pensator chamber 72. The inlet chamber 42 communicates with compensator chamber 72 via a cylinder 49, which receives a compensating piston 50 that is connected to the valve 36 by means o~ a shaft 46. The valve 36 is also connected, by means of a shaft 47 (see Figs. 3A and 3B) to an actuator device 54.
The function and operation of the negative mud pressure pulse generator 28 will now be explained. Fig.
2B shows the valve 36 of the ne~ative mud pressure pulse generator 28 in the "closed" condition. In this figure, the striated part indicates "high" pressure and the blank part indîcates "low" pressure. (Pressure magnitudes, such as "high", "low" and "intermediate" are relative pressures, i.e., the ~ erence between the pressure at a given location and the annulus pressure which is here considered to be zero;
the actual or real pressure would be equal to these magni~
tudes plus the hydrostatic head, which may be 10,000 psi or higher.) ~z~zz~

The effective area of the valve 36 is made some-what larger than the effective area of the piston 50 on the shaft side and, consequently, when the valve 36 is closed or nearly closed, the force on the shaft 46 is in the direction shown by the arrow in Fig. 2B and may be equal to about 1,000 X (a - a') where a is the effective area of the valve 36 and a' is the effective area of the compensating piston 50 on the shaft side.
Fig. 2A shows the valve 36 in the "open" condition, i.e., permitting mud flow from valve inlet chamber 42 to valve outlet chamber 44 and via outlet passageway 51 to the annulus 2~. The first and second compensator orifices 52 and 53 each provide a predetermined restriction to the mud flow and each causes a pressure drop. Consequently, the pressure inside the cha~ber 72 can be made to have any value between the maximum pressure inside chamber 44 and the minimum value at the exit of outlet passageway 51 which corresponds to the pressure inside the annulus 29.
As is pointed out above, in ~ig. 2~, as in Fig. 2B, the striated part indicates "high" pressure and the blank part at the exit of outlet passageway 51 is "low" pressure. During the valve "open" flow condition, the mud encounters two restrictions to flbw: orifice 52 and orifice 53, as a consequence of which, the pressure in the chamber 40 is intermediate between the "high" pressure indicated by the striated section and the "low" pressure at the exit of outlet passageway 51.
This "intermediate" pressure is indicated by the stippled area in Fig. 2A. This "intermediate" pressure is originated in the chamber 40 b`etween orifices 52 and 53 and communicates via conduit 74 to the compensator chamber 72. The pressure in this compensator chamber 72 can, consequently, be adjusted to any reasonable value between the "high" pressure in valve outlet chamber 44 and the "low" pressure at the exit of outlet passageway 51. Ihe proportioning of the sizes of the orifices 52 and 53, therefore, controls the pressure in compen-sator chamber 72 and, consequently, the force on compensator piston 50. If the orifice 53 were the same size as orifice 52, then the pressure in chamber 40 (and compensator chamber 72) would be about midway between that of valve outlet cham~er 44 and the annulus 29. As the size of orifice 53 is made larger than that of orifice 52, the pressure in compensator chamber 72 will be relatively decreased, and as the size of orifice 53 is made smaller than that of orifice 52, the pressure in compensator chamber 72 will be relatively increased. ~or example, if orifice 53 is made small compared to orifice 52, the pressure in compensator chamber 72 will be high and, therefore, the force on the head of piston 50 wil] be high and tend to close the valve 36. On the other hand, if orifice 53 is large compared to orifice 52, the pressure in chamber 72 will be low, thus, tending to allow the valve 36 to remain open. It is seen, therefore, that the force on the head of piston 50 can be adjusted between wide limits, thus, providing a means for adjusting the action of the valve 36.
It is important to note that the force tending to close the valve 36 in Fig. 2B, and the force tending to open the valve 36 in Fig. 2A, are determined by first and second independent parameters, i.e., the force tending to close .

~24Z28 the valve is derived from the effective area differences of the valve 36 and the rod si~e of compensator piston 50;
whereas the force tending to open the valve is derived from the relative sizes of the orifices 52 and 53. By suitably ad~justing these parameters, the valve 36 can be made to open or close by the application of a small external mechanical force.
It is also important to note that the valve 36 has a "bi-stable" action, i.e., the valve is "flipped" or "toggled"
from the "open" to the "closed" position or vice versa. In other words, the first said independent parameter is chosen so that when the valve is within the region of nearly closed to fully closed, a predominant force of predetermined ma~nitude in the valve "close" direction is applied and maintained;
and the second said independent parameter is chosen so that when the valve is within the ~egion of nearly open to fully open, a predominant force of predetermined magnitude in the valve "open" direction is applied and maintained.
Thus, it is apparent that the negative mud pres-sure pulse generator 28 of the present invention utilizes existing energy derived from the mud pressure in such a manner so as to greatly reduce the amount of external energy required to operate the valve 36 and, in addition, to impart to the valve 36 a "bi-stable" or "tog~le" action.
Further discussion of the negative mud pressure pulse generator 28 will be facilitated by reference to Figs.
3A and 3B, which will now be described. Fig. 3~ illustrates in schematic form a physical embodiment of ~he negative mud $~.Z~Z28 pressure pulse generator 28 and associated downhole equip-ment as it would be installed in the drilling apparatus o~
Fig. 1. The reference numerals that are applied in Figs. 1, 2A and 2B refer to corresponding parts when applied to ~ig.
3A. In Fig. 3~, a sub 58, which is typically 6 3/4" O.D.
and 3' long, supports an inner housing 56 by means of arms, or perforated or slotted support members Cnot shown~. The inner housing 56 contains the negati~e mud pressure pulse generator 28 and carries at its lower end portion instrumentation sections 62, 66 and sensor section 64. The mud from inside the drill collar 24 passes around ~he housing 56 in the direction of the ar~ows. ~ filter 60 prevents mud solids from entering the housing. The valve 36 is shown to be operated by an actuating device 54. ~hen the valve 36 is open, as shown in Fig. 2~, some mud is bypassed into the annulus 2~. The bent arrows show the direction of this bypassed mud. The pressure that ~orces the mud into the annulus 29 is the pressure across the jets of bit 26. ~hen valve 36 is closed, the bypass to the annulus 29 is closed.
2Q The floating piston 76 separates chambe~ 72 from an oil filled chamber 78. Actuating device 54 is mounted within an oil ~illed chamber 80. ~n e~ualizing passageway 82, connects chamber 78 with chambex 80. Thus, in cooperation with floating piston 76 and passageway 74, the chambers 72, 78 and 80 are maintained at essentially the same p~essure as the chamber 40. Passageway 82 is partially shown in dashed lines in Fig. 3A and is not sho~n in Fig. 3B since it is located in adifferent plane from the cross section shown.

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~.24228 Numeral 68 ~ep~esents a standard drill collar and numeral 69 a box-box sub. Section 66 is 2 3/8" in diameter and fits into a standard 15' 6 3/4" ~.D. - 3 1/4" I.D. drill collar. The unit 30 is provided ~ith special centralize~
arms 70 which fit snu~ly into box-box sub 6q. The centralizer arms 70 are designed to centralize the unit 3Q while allow-ing free passage o ~ud.
Fig. 3B bears the corresponding reference numerals of Figs. 2A, 2B and 3A and shows the negative mud pressure pulse generator 28 in sufficient proportion and detail to illustrate to one skilled in the art its actual construc-tion. It may be noted that in ~ig. 3B the actuating device 54 comprises a pair of electrical solenoids arranged in opposition. The winding 55 of the upper solenoid is dis-posed to exert a force in the upward direction on its arma-ture 57, while the winding 59 of the lowex solenoid is dis-posed to exert a force in the downward direction on its armature 61. The armatures 57, 61 are loosely coupled to a mechanical linkage 63 that is fixed to the shaft 47 so that a "hammer" effect is achieved; i.e., when a solenoid winding is energized, its armature moves a short distance before picking up the load of shaft 47 ~ith a hammer like impact.
This "hamme~" action has a beneficial effect upon the opening and closing operations of the valve 36. Suitable solenoids for this application a~e the Size 6EC, medium stroke, conical face, type manufactured by Ledex, Inc., of Dayton, Ohio.
Reverting n~w to discussion of the negative mud pressure pulse generator 28, there are several further factors and features that should be considered.

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The orifices 52, 53 are made to have smaller opening areas than that of the passa~eway 48, so that the velocity of mud flow over the se~ling surfaces of valve 36 and its seat 37 is significantly reduced when compared to the velocity of mud flow through the orifices 52, 53; thus, concentrating ~ear on the orifices ~2, 53, which are made of wear resistant material (such as boron carbide~ and which are also made readily replaceable in the "field", as indicated in Fig. 3B. These small non-erodable orifices 52, 53 make the ne~ative mud pressure pulse ~enerator 28 completely "fail safe", i.e., no matter ~hat happens to the operation of valve 36 (such as being stuck in the open position~ the amount of mud that is allowed to flow through the orifices 52, 53 would have no significant adverse effects on the drilling. A further advantage of making the orifices 52, 53 readily replaceable in the "field" is that they can be charged to best suit varying weights and viscosities of mud.
Because the negative mud pressure pulse generator 28 is exposed to severe vibration forces, the design must provide for stability of the valve 36 in both its open or closed position. The requisite stability is provided by the "hydraulic detent" or "bi-stable" action of the valve 36 which was previously herein described.
The vertical acceleration encountered in drilling is more severe in the upward than in the downward direction.
When the teeth of drill bit 26 encounter a hard rock, the drill bit and drill collars 24 are fvrced upwards, i.e., accelerated in the upward direction; but once the drill bit is raised upward and out of contact with the rock, there is ~.2~228 little force other than the acceleration due to gravity tha~
forces the drill bit and drill collars downwardly. Conse-quently, the acceleration upward can be several hundred g's but the acceleration downward is only of the order of 1 g.
The valve 36, therefore, must be designed so that when in the closed position, high upwards acceleration tends to keep it closed, i.e., makes it seat better, and high downward acceleration (assumed to be small~ tends to open the valve.
This has been accomplished in the design, as can be seen from Figs. 3A and 3B.
I determined, by conducting various tests and ex-periments, that a force of appro~imately 34 pounds would be required to actuate the valve 36 when the first and second independent parameters hereinbefore described had been chosen to provide appropriate "hydraulic detent" or "bi-stable"
action to achieve adequate stability for the valve 36.
With good engineering safety factors added, the required force became 70-100 pounds. The application of force of this magnitude over the required distance of valve travel, 20 with electromagnetic drive solenoids of reasonable size, would require about 350 watts of electric power; i.e., nearly 1/2 horsepower. With such a large power requirement it would appear at first glance that the energy needed for the number of actuations of the valve 36 that would be necessary for successful operation would be far beyond the capacity of any available self-contained downhole power source.
This apparent energy problem is overcome, however, when it is considered that the negative mud pressure pulse generator 28 of the present invention provides a very rapid action for 30 the valve 36; i.e., the valve 36 can be made to open (or ~.2~28 to close) with the application of the required 350 watts for only about 20 milliseconds. The amount o~ energy required to open (or close) the valve is, therefore, 350 - 20 _ ~ .002 watt hours There are available modern high density batteries of reason-able size and capable of being included in the space pro-vided withln the drill collar 24 and which can easily pro-vide 2,000 watt hours of energy. Therefore (even without recharging, as is described later herein~ ~ reasonable battery can provide enough energy to operate the valve 36 about one million times. Assuming that the valve is operated once every four seconds, a single battery charge is able to operate the valve continuously for over one month. It is an important requirement in logging while drilling that the downhole apparatus be capable of operation unattended (i~e., without battery recharge~ for at lease the length of time - between "round trips", i.e., the time that a single bit can drill without replacement, the best bits last only about 100-300 hours and, therefore, the 30 day figure above is more than adequate.
The practical design o~ the negative mud pressure pulse generator 28 is a complex matter. In my experience, although careful calculations were made using much of modern hydrodynamic theory, in the final stages, many o~ the para-meters had to be determined by empirical methods. ~n impor-tant reason for this is because the "viscosity" of drilling mud is thixotropic and the dynamic behavior i$ quite dif-ferent from that of liquids having classical or so called ~.Z ~2 Z ~

Newtonian viscosity. Dxilling mud "weight" (grams per cc) and "viscosity" vary over wide ranges and consideration must be given to the fact that "weight" ùsually varies over a much smaller range than "viscosity". Drilling mud usually contains not only colloidal particles in sUspension but also larger grains of sand and other particles.
An experimental set up was designed to determine the minimum size of the discharge orifice (which controls the rate of fluid discharge into the annulus~. In this set up, a large "servo" valve ~1" diameter~ ~as followed by smaller replaceable orifices. In 8,0QQ' and 5,0~0' well depth ex-periments careful measurements were made of the magnitude of the negative mud pre~sure pul$e at the surface as a function of the size o the discharge orifice. ~s this size was successively reduced, the magnitude of the pulse at the surface seemed almost independent of the size o~ the orifice until the surprisingly small .05 in.2 orifice area was reached,at which time a slight reduction in pulse mag-nitude was observed. This phenomenon was quite unexpected, but was later understood after careful consi.deration of the elastic properties of the mud column and the stored poten-tial energy therein as was hereinabove explained. This discovery produced the realization that a s~all negative mud pressure pulse generatol- could produce useful si~nal$ at the surface. Calculations were thereafter made and it was determined that the "servo" principle for the valve actuation was not necessary and the "servo" valve approach ~as ~ban-doned. The direct, very fast acting, ne~ative mud pressure pulse generator of this invention was thereupon designed and has proved to be successful.

~.Z4~28 In a negative mud pressure pulse generator 28 of practical design the ~ollowing dimensions may be considered as typical: orifice 52, 0.500" in diameter; orifice 53, 0.306" in diameter; stroke of valve 36, 0.125"; diameter of piston 50, 0.383"; diamete~ of ~alve 36 at its seating surface, 0.430"; angle of seat 37 relative to axis of ~ralve movement, 60; diameter of openin~; at seat 37 or passage-way 48, 0.375"; diameter of valve shaft 46, 47, 0.187".
In Fig. 3~ there is schematically illustrated a special type o battery that is well adapted to powering the downhole equipment of the present invention.
Deep oil wells frequently have high bottom hole temperatures 300-400F and many electric batteries cannot operate at this temperature. There is, however, an ex-ception; the modern molten salt batteries. They operate well at high temperatures of 400-500C or even higher but will not operate properly at lower temperatures principally because the electrolyte solidifies and ceases to conduct electrically. A litl ium aluminum iron sulphide molten salt battery is manufactured by the Eagle Pitcher Co., Joplin Missouri. Other manufacturers also manufacture high energy molten salt batteries that are especially intended for electric vehicle use. These batteries are very well adapted for high temperature operation.
As illustrated in Fig. 3F, I provide an arrangement that will "start up" the battery before it is immersed into the hot environment of the oil well and will maintain it charged when in use. In Fig. 3F, reference numeral 155 designates the battery proper; reference numeral 156 designates ~!.Z4~28 heating elements that are arranged to provide a small amount of heating to the battery 155; and reference numeral 157 designates a jacket containing thermal insulation, as for example, a material known as "Super Insulation"*
manufactured by the Union Carbide Co., New York, N.Y. or "Multifoil"*, manufactured by The Thermo Electron Co., Waltham, ~lass. Initially an external voltage (not shown) is applied to the terminal 158 (while the instrument is at the surface and before immersion into the well). This voltage activates the heating elements 156 and the battery electrolyte melts.
Furthermore, the battery lS5 is charged by the voltage applied at 158 before the instrument is immersed in the oil well. When the battery 155 is in its normal operating temperature range, the circuit to the heating element 156 is opened by the thermostatic switch 159, which closes during periods when additional heat to the battery 155 is required. When logging while drilling, the vibration of the tool will cause the device 160 to generate a charging current. The device 160 is described in United States Patent 3,970,877, Russell, et al. Instead of the Russell, et al, device, a small mud flow powered turbine and electric generator could be used to maintain the battery charged, since only about 1 watt of continuous charging power is required.
In Figure 3G there is schematically shown another special type of battery that may be used to power the downhole equipment of the present invention. This battery preferably uses cells of the Lithium Sulphur type, such as are manufactured by Power Conversion Inc., of Mt. Vernon, New *Trade Mark -25-~Z42Z8 York. It may also use LeClanche type cells or Lead Acid type cells. ~11 such cells, if exposed to high temperatures (such as those normally encountered in deep earth boreholes) would develop high internal pressure, so that the cells would tend to explode. In one aspect of the present inven-tion, there is provided an arrangement (.illustrated by Fig.
3G) by which this problem is overcome. In Fig. 3~, a plurality of individual cells-161 such as one of the above mentioned types are connected in series between a ground terminal 162 and a positive terminal 163. Each cell preferably is provided a conventional pressu~e release cap or.vent 164. In acco~-dance with the invention, the cells 161 are placed in a container or reservoir 165 which is capable of withstanding pressures exceeding those that could be developed by the electrolyte of the cells 161. Within the ~eservoi~ 165 there is placed a liquid 166 having the same or similar pressure-temperature characteristics as the electrolyte, i.e., the liquid 166 will produce vapor.pressure (when exposed to elevated temperatures~ that is substantially equal to the vapor pressure of the electrolyte in the cells 161. In the simple case of the LeClanche type o~ Lead Acid type cell, the liquid 166 can be water since the container 165 is hermetic and pressure resistant, the liquid 166 cin - this example, water) will never boil - no matter how high 25 the temperature. It will simply build up vapor pressure in the space above the liquid 166 high enough to be in equili-brium with the vapor pressure generated by the hot liquid 166.
The same principle can be used when the cells are of the Lithium Sulphur type, the liquid 166 could be Sulphur -~l~.Z4ZZ8 Dioxide. The Sulphur Dioxide v~por generated by the cells 161 will always be in pressure equilibrium with the container 165 because the Sulphur-Dioxide liquid in this auxilliary container 165 will always generate pressures equal to those generated by the cells 161.
Sulphur Dioxide and water, given as examples above, are often unsatisactory ~a~ because Sulphur Dioxide is highly corrosive and because water ic an electric conductor and can short out the batteries. ~n alternative substance is dichlorodifluoromethane, popularly called F~eon and manu-facuted by E. I. DuPont and Cs., Wilmington, Delaware. ~any types of Freons ha~e been developed ~ith almost an unlimited number of thermodynamic properties, i.e., pressure-tempera-ture relations. Othe~ substances can readily be found, such as hydrocarbon vapors, propane or butane or mixtures of '- vapors and gases. $uffice it to say, that I enclose the battery cells 161 in a containe~ 165 and place in this container a small quantity of a substance having similar pressure-temperature ~elations to that of the electrolyte in the battery cells 161. In Figs. 3F and 3G, I show only a small number of cells connected in series. In actuality, a larger number is normally employed. In the manufactured instrument of Fig 3G, I employ 17 Power Conversion Co.
~ Lithium Sulphur cells.
Another important feature of the present invention is that the length of time the ~alve 36 is maintained "Dpen"
has no relation to the amount of energy required. The only energy required is that expended to actuate the valve 36 to the "open7' position. The importance of this feature is fully appreciated from the following consideration:

~.Z42;28 - It has been determined by experiment that in order to provide a strong signal from a depth vf 10,000 t~ 20,000, the valve must remain "open" ~or about 1/2 to one second and any electromechani.cal Csolenoid or other2 device operating for this length of time would not only requi~e la~ge amounts of energy but would o~erheat and under ~ell conditions probably burn up from its self generated heat.
As is hereinabove pointed out, two typical sensors are disclosed as examples of the types that can be employed in the operation of the present invention. F~g. 3C illus-trates a natural gamma ray sensor and its associated cir-cuitry which in this example is o the analog type. ~ig. 3D
illustrates a temperature sensor which in this example is of the digital type. Either one of these sensors can be connected to the input terminal of the instrumentation illustrated by ~ig. 3E which will be hereinafter described.
With reference to Fig. 3C, a geiger counter 168 is provided with the conventional high voltage supply ~HV. The geiger counter 168 generates pulses and is connected through a capacitor 169 to amplifier 171 which generates pulses at its output that correspond to those of the geiger counter 168. A scale of 1024 circuit 172 generates one output pulse for each 1024 geiger counter pulses and its output is shown as pulses having a separation tl. The higher the gamma ray intensity, the higher will be the frequency of the pulses at the output of the scale of 1024 circuit 172 and the smaller will be the time tl.
Fig. 3D illustrates the case of the temperature sensor. The temperature is sensed by a thermistor 173, i.e., a semiconductor that varies in resistance with temperature (it is provided with a suitable power supply, not shown~ and it is assumed that the output of the thermister 173 is a DC
voltage proportioned to temperature. The a~lplifier 174 amplifies this DC voltage and impresses it on an analog-to-digital convertor 175 which in turn generates a series of binary bytes, one after the other, each representative of a number proportional to the sensed temperature. The outputs of the power amplifiers 185, 186 are utilized to control energization of the windings of the "back-to-back" coupled solenoids (hereinabove described~ to actuate the valve 36.
When winding 55 is energized the solenoid armature 57 (see Fig. 3B) is moved upwardly, pushing upwardly on shaft 47 to actuate valve 36 to the "open" position. When winding 59 is energized, the solenoid armature 61 is moved downwardly, pulling downward on the shaft 47 to actuate the valve 36 to the "close" position.
In the sensors utilized in the present invention, the magnitude o~ the downhole parameter is represented by electric pulses. The sequence o~ the pulses represents a code (binary or other~ and this sequence represents the magnitude of the parameter. ~ig. 3E illustrates how each single pulse of this code is processed to operate the valve 36. In Fig. 3E, numeral l77 represents one such pulse which is narrow in time; being only a few microseconds long. This pulse 177 is impressed upDn the circuitry contained in block 178. This block 178 contains a so called "one shot"
univibra~or and suitable inverting rectifying circuits well known in the electronics art and provides cin response to _~9_ ~.;242'~8 the single input pulse) two output pulses separated in time by tl (the first pulse is normally time coincident ~ith the input pulse and the second appears later by an amount of time equal to tl~ as shown by pulses 179 and 180. These electric pulses 179, 180 are now impressed, respectively, upon the circuitry contained in blocks 181, 182. These two circuits are identical and are so called pulse lengthening circuits, also well known in the electronics art. Each input pulse is lengthened to provide output pulses 183 and 184. These pulses are re$pectively applied to the "Darlington"
power amplifiers 185 and 186 (as manufactured by Lambda Mfg.
Co. of Melville, New Y~rk, and sold under the type PMD16K100).
In the practical desIgn of the electronic logic and power circuitry of Fig. 3E that I use in this preferred em-bodiment, L have chosen as constants tl - 500 milliseconds and t2 = 20 milliseconds. In operation, when a single pulse 177 is impressed on lead 167, the Darlington 185 is turned on for 20 milliseconds and then turned off. Then 500 milli-seconds later the Darlington 186 is turned on ~or 20 milli-seconds and then tu~ned off. Thus, the valve 36 is openedfor 500 milliseconds without requiring any energy during this period. Energy is required only during the short 20 millisecond periods that are required to actu~te the valve ~ 36 to the "open" or to the "close" position. The figures given above are for illustrative purposes only. Suffice it to say that by making the action of the valve 36: (a~ ve~y fast and (b) bi-stable; very high pressures and volumes of mud can be valved wîthout the necessity of employing large amounts of energy and as hereinabove described, relatively ~.24Z28 small energy batteries can operate the valve about one million times.
In a typical embodiment of this apparatus, the weight of the entire valve mechanism 36 o ~gs. 2~ or 3A, including the solenoid a~matu~e 54, shaft 46 and piston 50 is approximately 9 ounces. The valve 36 has been designed to operate at a differential pressure o~ 1,600 psi and pro-portioned to operate at optimum perormance, including the consequence that the ~orce required to open and shut the valve 36 must exceed the force due to vertical acceleration of all the apparatus near the bit 26.
Assuming a vibration figure of 60 g and the weight of 9 ounces, maximum vertical force on valve 36 due to the vibration of the tool 56 will be about 34 pounds. To be certain that the valve 36 will not open accidentally, the force keeping the v~lve closed in Fig. 2B and the orce keeping the valve open in Fig. 2A must both exceed about 34 pounds. By suitable choice of the first and second indepen-dent parameters hereinabove described, a "balanced'' conditîon is achieved. By ''balanced'' is meant that the force required to open the valve 36 is equal to the force required to close it.
Above ~round equipment utilized with the present invention, particularly as to methods and apparatus for eliminating interferring efects that are present in the output of pressure transducer 100, can take various forms, as will now ~e described.

l~,.Z4ZZ8 Fig. 4 shows typical above ground equipment in accordance with a preferred embodinlent of the invention, wherein the downhole parameter being sensed is the radio-activity of formations traversed by the bore while drilling is in progress. The corresponding portion of the loggin~
equipment which is below the earth's surface has been pre-viously described and shown in Figs. 2A, 2B, and 3A-G.
Referring now to Fig. 4, pressure transducer 100 connected to the standpipe 16 converts the variation of mud pressure within the standpipe into a varying electrical voltage. This voltage represents a mixture of two component signals: the useful, information carrying signal and the interferring signal. The information carrying signal is a succession of short, negative mud pressure pulses produced by the sudden opening and closing of the valve 36. The interferring signal is in the form of relatively slow and '- periodic pressure ~ariations which are generated by the strokes of the mud pump 12. These mud pump signals tend to mask or obscure the information one desires to obtain by utilizing the short negative mud pressure pulses.
One of the objectives of this invention is to recover, from the "contaminated" signal produced by the transducer, a "clean" signal which gives the desired infor-mation. This is accomplished by means of a signal extractor 102 which is applied to the output terminal 101 of the pressure transducer 100. The signal extractor eliminates the interferring effects and produces across its output terminal 108 a succession of pulses from which the infor-mation regarding the downhole parameter can be readily obtained.

~.2~'28 ~ he signal extractor 102 is controlled in a pre-determined manner by a succession of timing pulses obtained from a pulse generator 111 and applied to the control terminals 113, 114. The pulse generator 111 is mechanically driven by S the mud pump 12 to produce an appropriate number of timing pulses per revoluti~n of the pump. A chain drive trans-mission assembl~ 112 is provided for this purpose.
The "clean'' information carrying signal obtained from the extractor 102 is in the form of pulses derived from the actuation of valve 36 of generator 28. The relevant information is provided by the time intervals separating the pulses. A time-to-amplitude convertor 115 connected to the signal extractor output terminal 108 converts these pulses derived from the actuation of the valve 36 of generator 28 into signals having magnitudes representing the intervals therebetween. The convertor 115 is a well known electronic device and can be made up of components manufactured by the Burr-Brown company of luscon, Arizona, U. S. A. For further detailed description of time-to-amplitude converters see:
M. Bertolaccini and S. Cova,'''I,og'ic Design of High Precision Time 'to'Pul'se' Hei'ght' C'o'n'ver't'e'~s", Nuclear Instruments and Methods 121 (1974), pp. 547-566, North Holland Publishing Co ., The signals derived fr~m the convertor 115 are in turn applied to the input terminal 109 of a reciprocation circuit 118. The reciprocation circuit 118 (as, for example, -manufactured by Analog Devices, Inc. of Norwood, Mass.) produces output voltages which are the reciprocals of the ' input voltages. Thus, if a voltage of magnitude M is applied to reciprocation circuit 118, an output voltage having ~.Z 42'~ ~
magnitude l/M is obtained. These signals having magnitudes l/M are in turn recorded on the chart of a recorder lZ0.
The record chart of recorder 120 is moved in correlation with changing depth of the sensor unit 30 by a depth sensing device 121. The depth sensing device may be, for example, a modification or adaptation of equipment such as marketed by The Geolograph Medeavis Company gf ~klahoma City, Oklahoma, U. S. A.
In order to show more clearly the operating fea-tures of the signal extractor 102, we will analyze the behavior of the various signals which are involved. They are shown schematically in a simplified and idealized form as they vary with time in ~ig. 5. Let F(t) = S(t) ~ N(t) (12 where S(t) is the useful information carryin~ signal formed by the negative mud pressure pulses Pl, P2, and P3 aligned along the time axis t. [See Fig. 5 (axis A)~ The times of arrival oE these pulses, which correspond to the ti~es of actuation of the valve 36 of generator 28, are tl, t2 and ~0 t3, respectively. The time intervals which separate these pulses are ~1 = t2 ~ tl~ A2 = t3 - t2. ~3 t4 - t3, etc-are indicative of the intensity of the radiation measured.
If these time intervals are large, the intensity is relatively weak and conversely, iE they are small, the intensity is relatively strong. The interfering signal produced by the mud pump 12 is represented in Fig. 5 (axis A) by a periodic but not necessarily sinusodal function N(t) having a period T. The length of the period is related to the speed of rotation of the pump.

~.Z4228 To facilitate explanation, ~he relative scales in Fig. 5 have been distorted. In actual practice, there may be 50 to 80 oscillations o~ N(t) between the time of ar~ival of Pl and P2. Thus, ~i and ~2 may vary from 50T t~ 80T.
~owever, in Fig. 5 (axis A~ only a few oscillations oF N(t) b^tw^en Pl and P~ ha~rre been shown. Furthermore, in actual practice the negative mud pressure pulses Pl, P2, P3 do not have clean rectangular forms as in Fig. 5 (axis A). More-over, thè actual pulses are much smaller than those which have been shown in Fig. 5 Caxis A). In actual experience, the magnitude of Pl, P2 or P3 is about 0.1 t~ O.ûl of the ma~imum a.mpl~tude of the pulsations N(t).
Axes A-E in Fi~. 5 are positinned one below the othPr so that one can compare the signals in thèir time relationship~s on~ to another. Usinsr these figures, we can now enumerate the instrumental steps which are involved in the operation of the signal extractor 102. These are as follows:
Step 1 We displace the input F(t~ by an amount T, to obtain 2Q F(t - T) = S(t - T) ~ N(t - T) (2) where S(t - T) and N(t - T) are, respectively, ~he displaced u.seful signal and displaced interfering signal. Both signals are shown in Fig. 5 (axis B). The signal S(t - T) is represented by pulses Pl(a), P2(a) and P3(a~ which have been obtained by displacing by an amount T the corresponding pulses Pl, P2 and P3 in Fig. 5 (axis ~). The signal N(t -T) in Fig. 5 (axis B) is shown to be in exact synchronism with N(t) in Fig. 5 ~axis A). This is due to the periodicity of the signal. Thus>
N(t - T) - N(t) (3) ~.Z4Z28 Step 2 We subtract the displaced input function F(t - T) from the original input function F(t) to obtain M(t) = F(t~ - F(t - T) (4) Taking into account (1~, (2) and (3), we obtain M(t~ = S(t) - S(t-T) (52 Thus, the inter:Eering signal has been eliminAted and does not appear in M(t~. This can also be seen from inspection of Fig. 5 (axes ~ and B).
As shown in Fig. 5 (axis C), M(t~ consists of impulses which occur in pairs. Each pair contains a nega-tive and a positive pulse separated one from another by a time interval T. Thus, we observe a pair consisting of Pl(b) and Pl(b) which is followed by a succeeding pair consisting of P2(b) and P2(b) , then by another pair con-sisting of p~c) and P3~ and so on.Step 3 We displace M(t) by a time T so as to obtain M(t -T). Thus, the entire sequence of pulses in Fig. 5 (axis C) is shi~ted along the time axis by T so as to appear as shown in Fig. 5 (axis D). The arrangement of pulses as in pairs has been preserved in Fig. 5 (axis D). However, each pair such as Pl(C) and Pll~ is displaced with respect to the pair Pl(b) and Pl~b~ ~shown in Fig. 5 (axis C)] by T.
Similarily, the pair P2~C) and P2(C) is displaced with respect to the pair p2(b)and P2(b) by T, and so on.
Step 4 We compare the displaced pulses in Fig. 5 (axis D) with those in Fig. 5 (axis C). We note that some of these in Fig. 5 (axis D) are in time coincidence with some of the pulses in Fig. 5 ~axis C). The instances at which coincidence occurs are recorded in Fig. 5 ~axis E) as pulses Pl(d), 36 ~~~~

~.Z~Z28 pz(d) and p3(d~. Thus, Pl(d) coincides with Pl(b) and Pl(C) P2(d) coincides with P2(b) and P2(C) p3(d~ coincides with P3~ and p3(c) The times at which the pulses pl(d~, P2(d) and p3(d) occur 1 ' 2 and t3 ~ T-The pulses Pl~d~, P2(d2 and p3(d) correspond to the pulses Pl, P2 and P3 shown in Fig. S Caxis A). Con-sequently, the pulses in Fig. 5 (axis E) also represent this useful f~mction which now is S(t-T) since it has only been displaced by T. It is evident that the pulses in Fig. 5 (axis E) provide the information which we are seeking to obtain. The time interval between Pl(d~ and P2(d~ is Al, and the time interval between P2(d) and p3(d) is ~2' etc..
The quantities ~1~ A2, etc. are indicative of the radiation measured by the gamma ray detector.
The above steps will now be considered as they relate to the performance of the signal extractor 102 and more particularly to that of its two component parts de-signated in Fig. 4 as 105 and 107 and shown schematically in Figs. 6 and 7, respectively.
The component 105 receives at its input terminal 101 (which is the same as that of the signal extractor 102 of Fig. 4) the signal F(t~. As shown in Fig. 6, this signal is transmitted through an amplifier 130 to the input terminal 131 of a delay network 132. The delay network delays F(t) by T, thus, pr~ducing at its output terminal 134 the signal F(t-T). This signal is a sum of two component slgnals S(t-T) and N(t-T) which are shown in Fig. 5 (axis B).

~L~.Z4228 The signal F(t-T) is applied to one input terminal 134 of a subtractor 135. The other input terminal 136 of the subtractor receives directly the signal F(t~, which is transmitted from termin~l 10l. by means oE conductor 137.
Thus, at the output terminal 106 of the subtractor 135 we obtain the difference signal M(t~ ~ F~t~ - F(t-T). This is shown in Fig. 5 (axis C).
The delay network 132 is provided with control terminal 113 which receives a signal controlling the delay T. It is important that the length of the delay T be the same as the period of mud pressure oscillati~ns produced by the mud pump 12.
The amount of the delay T is controlled by the timing impulses derived rom pulse generator 111 shown also in Fig. 4 and applied via conductor 110 to the control terminal 113. It is noted that the delay T is the same as the period of oscillation of mud pressure produced in the successive strokes of the mud pump 12. Consequently, the frequency of these timing pulses must be controlled by the rotation o~ the pump.
Assume that the pump produces Nl strokes per second. Thus, T = l/Nl. The pulse generator 111 produces timing pulses at a relatively high rate N2, which is a multiple of Nl. Thus, N2 ~ KNl, where K is a constant which has been chosen to be 512. Thus, if the strokes of the pump are one per second this would require the signal generator to produce 512 pulses per second. It is apparent that ~he rate of pulsation of the mud pump 12 varies with time and, accordingly, N2 will vary so as to insure that the delay ~.24ZZ8 produced by delay network 132 will always be equal to one period of the mud pressure oscillations produced by the mud pump 12.
The delay network 132 which is controlled, as described above, may be a ~eticon ~odel SAD-1024 Dual Analog Delay Line as marketed by Reticon Corporation, Sunnyvale, California, U. S. ~..
The instrumental steps hexebefore described are the steps 1 and 2 performed by the component 105 of the signal extractor 102. We ha~e transformed the input signal F(t) [represented by its components in Fig. 5 (axis A)] into an output signal M(t) which appears as a succession of pairs of pulses and is shown in Fig. 5 (axis C). We ~ill now proceed to describe further instrumental steps ~hich are required in order to accomplish the desired objectives.
These are performed by the component 107 of the signal extrac~or 102.
We refer now to Fig. 7. The signal ~(t2 is now applied through conductor 140 to a delay network 141. This delay network is identical to that designated as 132 in Fig.
6. It receives, at its control terminal 114, the same control signal which was applied to the control terminal 113 of the delay network 105. Consequently, the amount of delay produced by delay network 141 is T and the signal appearing at the output of 141 is M(t-T) as shown in ~ig. 5 ~axis D).
This output signal is transmitted through an amplifier 143 to one input terminal 145 of an AND gate 146. At the same time, the undelayed signal M~t) is applied through the conductor 147 and amplifier 148 to the other input terminal 3~ --~L~.Z4228 149 of the ~ND gate 146. These two input signals M(t) and M(t-T) which are applied to the ~ND gate 146 are shown in Fig. 5 (axes A and D), respectively. ~e have previously observed that some impulses shown in Fig. 5 (axis C) occur in coincidence with imp~llses in Fig. 5 (a~is D). Those impulses that occur in coincidence appear in the output of the ~ND gate 146. They are designated in Fig. 5 (axis E) as Pl(d), P2(d) and p3(d). These coincident pulses are the output of pulses of the component 107, and consequently of the signal extractor 102.
It is thus apparent that by means of the component 107, we have per~ormed the instrumental steps 3 and 4. We have transformed the signal M(t) shown in ~ig. 5 (a~is C) into the signal S(t-T) shown in Fig. 5 (axis E). The latter provides the quantities Al, A2, ~3, etc., which represent the information it was desired to obtain. It should be recalled that the sîgnal S(t-T) is represented by a succes-sion of pulses as shown in Fig. 5 (axis E). These pulses are transmitted to the time-to-amplitude convertor 115 to produce at the output of the time-to-amplitude convertor 115 signals of various magnitude such as Al, ~2~ ~3, etc., that represent time intervals between the arrival of pulses.
These signals are in turn fed to and transformed by the reciprocation circuit 118 of Fig. 4 into other reciprocal signals having magnitudes 1~ 2, l!A3, respectively. These reciprocal signals are recorded by recorder 120 of Fig. 4.
It is apparent that the quantities l!Al, l!A2 and l/A3 represent the intensity of radioactivity of formations sensed by the sensor unit 30 at various depths in the borehole.

-~0-~L~.Z4Z28 We have described above an instrumental means for performing lo~ical steps leading from the function F(t) to a function S(t-T). These steps ha~e been performed by re-presenting these f~mctions in an analog (non-digital) form.
Alternati~ely, i~ de~ired, the entire process can be digi-talized, as shown diagramatically by Fig. 8. In ~ig. 8, the output of the pressure transducer 100 is fed to an analog-to-digital con~ertor 103, the output of which is fed to a digital computer 104. The operations indicated in Fig. 8 are performed by the elements designated 122, 123, 124, 125 and 126 in the dig~tal computer 104. Timing signals from a pulse generator 111 or 140 are introduced to the digital computer 104 in order to control the delays in accordance with the pump speed. The operations indicated in the dotted rectangle of ~ig. 8 are performed mathematically in a sequence which may be flow charted. The output of the computer 104 is fed to a digital-to-analog convertor 127, the output of which is fed to the recorder 120.
In Fig. 9. there is shown an arrangement similar in some respects to that of Fig. 4, but wherein the data to be obtained and recorded are the temperature at the location of sensor unit 30 o~ Fig. 1. In Fig. 9, these data, as presented to the signal extractor 102 are in digital form (see Fig. 3D). The signal extractor 102 of Fig. ~ is identi-cal to that of Fig. ~, but the time-to-amplitude convertor 115 and the reciprocation circuit 118 of ~ig. 4 are replaced by a digital-to-analog convertor 141. The output signals o~
an appropriate pulse generator will be applied to the control terminal 110 of the signal extractor 102.

- It is not al~ays convenient to provide a mechanical connection to the mud pump 12, as shown by the chain drive transmission assembly 112 in Fig. 4, and an alternate means for generating the pulses required for the signal e~tractor may be desirable. Fig. 10 illustrates such an alternate means. In a typical example, the signal. extractor 102 of ~ig. 4 is provided ~t its terminal 110 with pulses at a rate of 512 pulses per full pump stroke. It must be clearly understood that this rate must be rigorously sychronized with the pump strokes. All the "times" sho~n as T, tl, t2, etc. in Fig. 5 are not so-called "real time", but are direct-ly related to the speed of the mud pump 12 and rigorously, T, tl, t2, etc. should be expressed, not in seconds or minutes of "time" but in "~allons of mud". When it said that at terminal 110 o~ Fig. 4, there are 512 pulses per mud pump stroke, it is meant that at ter~inal 110 there are present voltage pulses having a frequency equal to the 512th harmonic of the pump stroke frequency. Fig. 10 shows how this can be accomplished without mechanical connection to the pump shaft.
In ~ig. 10, component 145 is a VC0 or "voltage controlled oscillator" which at its output 110 produces electric pulses the frequency o~ which is controlled by the DC voltage applied at its input terminal 108. Component 150 is a binary divider or scaler that divides the frequency of the pulses impressed on its input terminal 116 and generates output pulses at its output terminal 117 having a frequency equal to l/512th of f~equency of the input pulses~ Compon-ent ll9 is a phase comparator that compares two inputs (one ~.242Z8 from scaler output terminal 117 and one from the output terminal 130 of pressure transducer 100~, and provides at its output terminal 128 a voltage which is zero volts DC
when the two inputs 117 and 130 are exactly equal in phase;
and provides a positive voltage when the input at 117 leads the input at 130 in phase; and a negative DC voltage when the input at 117 lags the inptlt at 130 in phase. A battery 129 is pro~ided to properly bias the VCO 145. The circuit 151, just described, is known as "phase locked loop". The operation is best explained by an example: Assume that the pump pulse frequency (pump stroke frequency~ is 1 Hz and the VCO is generating 512 Hz. The output of the scaler 150 will then generate exactly 1 Hz. The 1 Hz f~om the scaler 150 and the 1 Hz from the p~essure transducer 100 will then be exactly matclled in frequency and phase and the output of the comparator at terminal 128 will be zero volts, and the VCO 145, when properly biased by battery 129, will generate exactly 512 pulses per stroke.
~ssume now that the mud pump 12 speeds up. The frequency at ter~lnal 130 will than be somewhat greater than 1 ~z - i.e., 1 ~ alHz. The comparator 119 will then provide an output at terminal 128 ~hich will no longer be zero volts DC, but for example, ~ a2V, this small voltage increment will be applied to the VC0 145 at terminal 10-8 and increase its frequency until the nominal 512 pulses per second is increased to a value f such that f/512 - 1 + ~l Thus, the frequency at terminal 110 will always accurately follow the frequenc~ of the mud pump 12 and will always be its 512th multlple.

~.242Zi 3 - Two arrangements for obtaining ti~ing pulses for the signal extractor 102 have been hereinabove described (pulse generato~ 111 of Fig. 4 ~nd the "phase locked loop"
circuit 151 of Fi~. 10). ~ third arran~ement that may be used for ~btaining such timing pulses is illustrated by Fig. 11 and is based on ''auto-correlation". In Fi~. 11, the input terminal 154 of a correlator 152 is supplied by the output of the pxessure transducer 100, and receives the function F(t) which contains the periodic signal N(t) and the function S(t2 which may be considered a ~andom function.
The output of the pressure transducer 100 is also applied to the input terminal 101 o~ the signal extractor 102. The correlator 152 is adapted to produce ac~oss its output terminals the autocorrelation function o F(t) which is ~ff CT) = [S(t2 ~ N(t2 ] rS(t+T~ -~ N(tr~T) ] (6) Where the bar in the above expression indicates averaging over an appropriate period of time. The function ~ff (T) can be expressed as - ~ ,bSS (,T) ~ tl3nn(T~
where ~s5 (T) - S(t2S(t ~ ~ (8) and ~ nn(T) = N(t~-N(t--~ r) The function ~5s (T~ reaches zero at some value of T = TO
and beyond rO, we have ~ ff (T) a ~nn(') (10) Since ~nn(T) is periodic, the function ~ff (T~ iS also periodic and it has the period T. This function, which is obtained in the output of the correlator 152 is in turn applied to a pulse multiplier 153 which produce~s a succession ~L~.Z~28 of timing pulses similar to those produced by the pulse generator 111 in Fig. 4 and which are applied to input terminal 110 of the signal extractor 102. The pulse mult-iplier 153 multiplies the f~equency of the input pulses by a phase locked loop system simila~ to that of Fig. 10 or by any other conventional means. The remaining elements in Fig. 11 are the same as those in ~ig. 4, except, of course, that the pul'se generator 1'11 and its chain d~ive trans-mission assembly 112 are elim~nated.
There are commercially available instrumental means based on auto-correlation ~or recovering a periodic signal from a mixture o~ a perisdic and a random signal ~see, for example,' S'ta't'i's'tic`a'l'Th'e'ory' of Communications, by Y. W. Lee, John Wiley, New York, N. Y., 1960, pp. 288-290).
The correllator 152 of Fig. 11 may be Model 3721A manufactured by Hewlett Packard Company of Palo Alto, California. The correllator 152 could also be one of the types described in the following references: A. E. Hastings and J. E.
Meade "A Device for Computing Correlation ~unctions", Revie _of''S'c _n'ti'~'ic 'Ins'trumen'ts, Vol. 23, 1952, pp. 347-349;
and F. E. Brooks, Jr. and H. W. Smith, "A Compute~ for Correlation Functions",' ~evie of Scientific Instruments, Vol. 23, 1952, pp. 121-126.

~L~.;Z 42Z8 While I ha~e sho~n my invention in several forms, it will be obvious to those skilled in the art that it is not so limited, but is susceptible of various changes and modifications without departing ~rom the spirit thereof.
I have disclosed herein, as examples, sensors for only two downhole parameters, it is, however, to be under-stood that sensors for various other downhole parameters could be used as well. It is also to be understood that sensors for a plurality of downhole parameters may be used at the same time, in which case, conventional techniques would be employed (sucIi as time ~h~ring, multiplexing, or the like) to handle the data representing the plur~lity of parameterS-When deviated or inclined wells are drilled, aturbine or "mud motor" such as a Dynadrill, manufactured by Smith Industries, Inc., Houston, Texas, is frequently employed. In such case, the drill string 31 of Fig. 1, is not rotated by the rotary table at the surface. The rotating ~46-'~ Z ~2 Z 8 action to turn the bit 26 is der~ved from such a mud motor, which usually is located immedi~tely above the bit 26 in the drill string compri$ing elements 22, 24, 28, 30, of Fig.
1. When such a mud m~tor ls employed, a large pressure drop occurs across it (since the mud motor derives its power from the ~ud flo~. This large pressure drop can be utilized to supply the pressure difference between the inside of the drill strin~ and the annulus and, in such case, a "jet" type bit need not be employed.
The p~esence of the pressure drop across the ~nud motor merely enhances the operation of my invention so long as the negative mud pressure pulse generator is located above the mud motor.
The term ".~low restriction means", for purposes herein, applies to either a jet type bit, or a mud motor, or both. The term "high pressure zone" applies to the drilling fluid pressure on the upstream side of the "flow restriction means" and the term "low pressure zone" applies to the dr-illing fluid pressure on the downstream side of the "flow restriction means".
It is recognized that, in some instances, a plurality of mud pumps flre employed on a single drilling rig and these pumps are not necessarily operated in syn-chronism.
In an example of three pumps, the periodic pres-sure curve of Fig. 5A would, in the practical case, not be a simple periodic function as shown b~ N(t~ but would be the sum of three co~ponents, each component being periodic and having its own distinct period.

~.Z~2Z8 By the employement of three delay systems, as shown in Fig. 6, each synchronized with its own pump, each periodic component of the interfering mud pulse pressure signal can be separately nullified. Suitable interconnec-5. tion will then produce a signal ~rom which the interferingmud pump pressure signals are eliminated.
The foregoing disclosure and the showings made in the drawings are merely illustrative of the principles of this invention and are not ts be interpreted in a limiting sense.

Claims (37)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. For use in a system for conducting drilling operations employing a string of drill pipe extending from the earth's surface having a drilling means such as a drill bit, hydraulic drill motor, or the like at the lower end, a pump by which drilling fluid is forced downwardly through the drill string interior and drilling means to flow back to the surface through the well annulus, the drilling means imposing a restriction to the drilling fluid flow forming a high pressure zone in the interior of the drill string and low pressure zone in the well annulus, a telemetering system comprising, a drilling fluid bypass above the drilling means providing fluid communication between the interior of the drill string and the well annulus, the bypass being defined in part by a valve seat, a valve stem moveable to and away from said valve seat forming a valve to close and open said bypass, a means for detecting the magnitude of a downhole parameter and for producing an electrical signal representing said magnitude, and electromagnetic solenoid means responsive to said electrical signal to rapidly operate said valve to generate pressure pulses in the drilling fluid, and means at the earth's surface to detect such pressure pulses and to provide a measure of the magnitude of said parameter.

2. For use in a system for conducting drilling operations employing a string of drill pipe extending from the earth's surface having a drilling means such as a drill bit, hydraulic drill motor, or the like at the lower end, a pump by which drilling fluid is forced downwardly through the drill string interior and drilling means to flow back to the surface through the well annulus, the drilling means imposing a restriction to the drilling fluid flow forming high pressure zone in the interior of the drill string and low pressure zone in the well annulus, a telemetering system comprising, a drilling fluid bypass above the drilling means providing fluid communication between the interior of the drill string and the well annulus, the bypass having an electrically energizable valve therein capable of rapid operation to open or close said bypass, a means for detecting the magnitude of a downhole parameter and for producing an electrical signal representing said magnitude, an electrical energy source, means responsive to said signal for supplying a relatively large amount of electrical power to initiate opening said valve, and substantially less power when the valve is open or closed, to generate pressure pulses in the drilling fluid, and means at the earth's surface to detect such pressure pulses, and to provide a measure of the magnitude of said parameter.

3. For use in a system for conducting drilling operations employing a string of drill pipe extending from the earth's surface having a drilling means such as a drill hit, hydraulic drill motor, or the like at the lower end, a pump by which drilling fluid is forced downwardly through the drill string interior and drilling means to flow back to the surface through the well annulus, the drilling means imposing a restriction to the drilling fluid flow forming a high pressure zone in the interior of the drill string and low pressure zone in the well annulus, a telemetering system comprising, a drilling fluid by-pass above the drilling means providing fluid communication between the interior of the drill string and the well annulus, the bypass being defined in part by a valve seat, a valve stem moveable to and away from said valve seat forming a valve cap-able of rapid operation to close or open said bypass, a means for detecting the magnitude of a downhole parameter and for producing an electrical signal representing said magnitude, a cylinder in communication with the bypass having a compensating piston therein connected to said valve stem so that fluid pres-sure exerts a first hydraulic force on the compensating piston in the direction corresponding to the opening of the valve and fluid pressure exerts a second hydraulic force on the valve stem in the direction corresponding to the closing of the valve, the net hydraulic force on the valve stem being proportional to the difference between said first force and said second force, and means responsive to said electrical signal to rapidly move said valve stem to generate pressure pulses in the drilling fluid, and means at the earth's surface to detect such pressure pulses and to provide a measure of the magnitude of said para-meter.

4. A telemetering system according to claim 1, 2, or 3 wherein said electrical signal is in the form of a succession of electrical pulses.

5. A telemetering system according to claim 1, 2, or 3 wherein said electrical signal is in the form of a succes-sion of electrical pulses and in which said electrical pulses are accumulated in a pulse storage means which generates elec-trical signals representative of the accumulated pulses, said valve being responsive to said generated electrical signals.

6. A telemetering system according to claim 1, 2 or 3 wherein said electrical signal is in the form of a succession of electrical pulses and wherein each electrical pulse produces a first voltage change to open said valve and a second voltage change to close said valve.

7. The telemetering system according to claims 1, 2 or 3 wherein said electrical signal is in the form of a succession of electrical pulses which are arranged in a sequence having a time distribution representative of said magnitude.

8. The telemetering system of claim 1, 2 or 3 wherein said electrical signal is in the form of a succession of electrical pulses and in which said electrical pulses are arranged in a sequence having a time distribution representa-tive of said magnitude and wherein said means of detecting the magnitude of a parameter is a pulse producing gamma ray detector.

9. The telemetering system of claim 1, 2 or 3 wherein said electrical signal is in the form of a succession of electrical pulses and in which said electrical pulses are arranged in a sequence having a time distribution representa-tive of said magnitude and wherein said means of detecting the magnitude of a parameter is a pulse producing scintillation counter.

10. The telemetering system of claim 1, 2 or 3 wherein said electrical signal is in the form of a succession of electrical pulses and in which said electrical pulses are arranged in a sequence having a time distribution representa-tive of said magnitude and wherein said means of detecting the magnitude of a parameter is a geiger counter.

11. The telemetering system of claim 1, 2 or 3 wherein said electrical signal is in the form of a succession of electrical pulses which are arranged in a sequence having a time distribution representative of said magnitude and wherein said means at the earth's surface comprises a pressure transducer for converting said pressure pulses to corres-ponding electric current signals, converter means connected to receive said corresponding electric current signals, and circuit means connected to receive signals derived from the output of said converter means to produce third signals representing in analog form the magnitude of said parameter.

12. The telemetering system of claim 1 in which a portion of said bypass has a longitudinal axis which is parallel the drill string axis, such portion having said valve seat therein, and wherein said valve stem is moveable in a linear path coincident with the axis through said valve seat, and wherein said electromagnetic solenoid means provides a force in axial coincidence with said valve stem to actuate said valve.

13. A system according to claim 1, 2 or 3 including means providing valve actuating electric current signals responsive to said magnitude representing electrical signal and including means wherein said valve when maintained in the open or the closed position employs electric currents whose magnitudes are less than the electric current magnitudes initially applied to open or close the valve.

14. A telemetering system according to claim 1, 2 or 3 wherein there is provided means for applying electromagnetic solenoid actuation force to said valve to accomplish transition from the closed to the open condition in a time of less than 20 milliseconds.

15. A telemetering system according to claim 1, 2 or 3 in which the rate of flow of the drilling fluid through said bypass is at least .125 gallons per second when said valve is made to open in at most 20 milliseconds to thereby produce sharp pressure pulses in the drilling fluid.

16. A telemetering system according to claim 1, 2 or 3 in which the rate of increase of drilling fluid flow through said bypass when the valve is made to open is at least 6.24 gallons per second per second to thereby produce sharp pressure pulses in the drilling fluid.

17. A telemetering system according to claim 1, 2 or 3 wherein said valve has a closed condition and an open condition and including means of deriving valve actuating signals from said magnitude representing electrical signal and including means for maintaining said valve in at least one of said con-ditions in the absence of an actuating signal.

18. A telemetering system according to claim 1, 2 or 3 wherein said valve has a closed condition and an open condition and including means of deriving value actuating signals from said magnitude representing electrical signal and including means employing hydraulically derived forces for maintaining said valve in at least one of said conditions in the absence of an actuating signal.

19. A telemetering system according to claim 1, 2 or 3 wherein said valve, after being moved to an open condition is urged to a closed condition by force of drilling fluid flow through said bypass.

20. A telemetering system according to claim 1 wherein said valve stem is connected to a compensating piston having fluid communication with said bypass providing a differential pressure thereacross to generate a force in the direction opposite to the force generated by fluid pressure on the valve stem to thereby reduce the force necessary to open said valve.

21. A telemetering system according to claim 1 wherein said electromagnetic solenoid means is arranged to apply force to move said valve from the closed to the open condition.

22. A telemetering system according to claim 1 wherein said electromagnetic solenoid means is arranged to apply force to move said valve from the open to the closed condition.

23. A telemetering system according to claim 1 wherein said electromagnetic solenoid means is arranged to apply a force in a first direction to open said valve and to apply a force in a second direction to close said valve.

24. A telemetering system according to claim 1, 12 or 20 wherein with said electromagnetic solenoid means there is provided armature means that is loosely coupled by a mechanical linkage to said valve stem such that when said solenoid means is energized said armature means will move a short distance before picking up the valve stem load with a hammer-like impact.

25. A telemetering system according to claim 21, 22 or 23 wherein with said electromagnetic solenoid means there is provided armature means that is loosely coupled by a mechanical linkage to said valve stem such that when said solenoid means is energized said armature means will move a short distance before picking up the valve stem load with a hammer-like impact.

26. A telemetering system according to claim 23 wherein said electromagnetic solenoid means comprises two windings arranged so that when one said winding is energized it exerts a force in said first direction to open said valve and when the other winding is energized it exerts a force in said second direction to close said valve.

27. A telemetering system according to claim 1, 2 or 3 including means for detecting the magnitudes of a plurality of downhole parameters near the bottom of said string, and means for producing electrical signals representing the magnitude of each parameter, said valve being actuated in accordance with said signals.

28. A telemetering system according to claim 1, 2 or 3 including fluid filter means in said fluid bypass between said drill string interior and said valve.

29. A telemetering system according to claim 1 or 3 wherein said valve stem is above said valve seat, whereby upward acceleration of said drill string urges said valve towards the closed condition.

30. The telemetering system according to claim 1, 2 or 3 in which said pressure pulses are superimposed upon interfer-ing pressure variations associated with at least one of said drilling operations, and wherein said means at the earth's surface includes a first means comprising a transducer to detect said superposition of pressure pulses and pressure variations and to produce a first signal representing said superposition, a second means for producing a second signal representing only interfering pressure variations and a third means operated in conjunction with said second means for deriving from said first signal a resultant signal indicative of the magnitude of said downhole parameter.

31. The telemetering system according claim 1, 2 or 3 in which said pressure pulses are superimposed upon inter-fering pressure variations associated with at least one of said drilling operations, and wherein said means at the earth's surface includes a first means comprising a transducer to detect said superposition of pressure pulses and pressure variations and to produce a first signal representing said superposition, a second means for producing a second signal representing only interfering pressure variations and a third means for combining said first and second signals to obtain a resultant signal indicative of the magnitude of said downhole parameter.

32. The telemetering system according to claim 3 including means of subjecting the side of said compensating piston opposite said valve to the pressure of the fluid downstream of the valve.

33. A telemetering system according to claim 3 wherein said net hydraulic force urges the valve to the closed condi-tion when the valve is near fully closed.

34. A telemetering system according to claim 3 including orifice means disposed between said valve seat and said well annulus to produce when the valve is open, an intermediate pressure zone, and means to connect said intermediate pressure zone with the side of said compensating piston opposite said valve stem, with the effective area differences between said valve stem and said piston and the relative sizes of said orifice means being selected such that said valve stem can be actuated to the open or closed position by application of forces of reduced magnitudes.

35. A telemetering system according to claim 34 wherein said drilling fluid bypass is defined by a valve inlet chamber and a valve outlet chamber, the inlet chamber being in commu-nication with said drill string interior, said valve seat being between the inlet and outlet chambers, an outlet pas-sageway connecting the outlet chamber with said well annulus, and wherein said orifice means are in the outlet passageway providing said intermediate pressure zone.

36. A telemetering system according to claim 1 including means providing electromagnetic solenoid actuating current signals responsive to said magnitude representing electrical signals and including means wherein said valve stem when maintained in the open condition or the closed condition employs electric currents whose magnitudes are less than the electric current magnitudes initially applied to actuate said valve stem.

37. A telemetering system according to claim 2 in which substantially less power includes substantially no power.