CA1150716A - 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 downhole 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 invention, improved methods are provided for extracting negative 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

~:~56~716 This is a divisional Application of Copending Canadian Application Serial No. 314,590 filed on October 27, 1978 by Serge A. Scherbatskoy.
This invention generally pertains to logging while drilling apparatus, systems and methods and more particularly pertains to systems, apparatus, and me*hods utilizing mud pulsations for telemetry to transmit signals representing one or more downhole parameters to the earth's surface.
Many efforts have been made to develop successful logging while dril-ling systems, as suggested by the following examples: Karcher, United States Patent No. 2,096,279 proposes a system utili~ing 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 coup-ling of acoilor coils with the drill pipe near the drill bit wlth measurement o:E 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 clrilling 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.
Each of the abovementioned proposals has had some drawback of suf-ficient ccnsequence to prevent its commercial acceptance. For example, the inconvenience and time involved for the large number of connections and dis-connections of electrical connectors is a significant drawback in systems such as proposed by Karcher. Though an induced electric potential system such as proposed 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.

: .
: ' ' -" ~

~15`~7~6 When modern jet bit drilling became commonplace and very large mud volumes and high mud pressures were employed, the systems as proposed by Arps, proved to be unreliable and subject to rapid deterioration. The introduction of a controlled restriction into the very powerful mud stream, of necessity, required large and powerful apparatus and operation was unsatisfactory because of rapid wear and very high energy requirements.
The environment is very hostile at the bottom of a well during dril-ling. Drill bit and drill collar vibrations may be in the order of 50 g. The temperature is frequently as much as 400F. The bottom hole pressure can be more than 15,000 psi. The drilling fluid flowing through the drill collars and drill bit is highly abrasive. With present drilling equipment including im-proved drill bits, the continued drilling time with a particular bit can be in the order of 100 - 300 hours and sometimes longer before it becomes necessary to change the drill bit. Accordingly, a downhole formation condition sensing and signal transmitting unit mounted near the drill bit must be capable of operating unattended for long periods of time without adjustment and with a con-tinuing source of electrical power. Also, the signal communication apparatus must be capable of transmitting a continuing usable signal or signals to the earth's surface after each additional joint of drill pipe is conventionally added to the drilling string as the drilled borehole is increased in depth.
In general, systems using mud pulsations for telemetry are considered the most practical since the drilling operation is least disturbed. To date, however, the reliability that has been achieved with such systems is not satis-factory. 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.
A general objective of the present invention is to provide a success-ful 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.
According to a first broad aspect of the present invention, there is provided a method of making measurements in a borehole while drilling by using a fluid circulation system and a fluid pump which generates within said system recurrent pressure variations, comprising the steps of measuring selected parameters at various depths in said borehole and generating in said system pressure changes indicative of the values of said parameters, comprising a first step of producing first signals representing a superposition of said pressure changes and said recurrent pressure variations and a second step util-izing the recurrence of said variations for cleriving rom said first signals resultant signals representing substantially said pressure changes.
According to another broad aspect of the present invention, there is provided a method of performing measurements in a drill hole concurrently wi~h the operations associated with the drilling of said hole wherein the measure-ments are carried out by sensing a selected parameter at an appropriate depth in said hole, comprising the steps of transmitting through a transmission chan-nel to the top of the drill hole a useful sensory effect indicative of the value of said parameter, producing a first function representing a superposition of said useful sensory effect and of an interfering sensory effect which is gener-ated in said channel and is associated with at least one of said operations, , .

1~5~7'16 producing an autocorrelation function, and combining said autocorrelation func-tion with said first function to obtain an indication of the value of said parameter.
According to a further broad aspect of the present invention, there is provided a method of performing measurements in a drill hole using a fluid circulation system and a pump means which forces fluid into said system and generates in said fluid recurrent pressure variations, comprising a first step of measuring a selected downhole parameter and generating in said fluid a se-quence of individual pressure pulses representing the value of said parameter, a second step of de*ecting said pulses, a third step of translating each indi-vidual detected pulse into a corresponding group of at least two component pul-ses having a characteristic distribution in time, thereby producing a sequence of groups of pulses representing the value of sai.d parameter, and a ourth step of selectively passing pulses having said characteristic distribution and de-riving from said selectively passed pulses a measure of the value of said parameter.
According to yet another broad aspect of the present invention, there is provided a method of performing measurements in a drill hole in the earth concurrently with the operations of drilling said hole, wherein the measure-ments are carried out by sensing a selected parameter in said drill hole and producing useful signals representing the value of said parame*er, comprising the steps of transmitting up through a transmission channel to the top of the drill hole said useful signals thereby obtaining within said channel at the top of the drill hole a superposition of said useful signals and of interfering signals which are associated with at least one of said drilling operations, pro-ducing at the top of said drill hole first data representing said superposition, expressing said first data into digital format, obtaining second data represen-.

~L5~371~

tative of said interfering signals in digital format, and digitally processing the information expressed by said first and second data to dete~nine thè value of said parameter.
According to still another broad aspect of ~he present invention, there is provided a system of performing measurements in a drill hole concurrently with at least some of the drilling operations comprising a drill string wherein said measurements are carried out by means of a measurement assembly comprising a sensor means disposed near the bottom of said string for generating useful signals representative of the magnitude of downhole parameters and for transmit-ting said signals from the bottom of said hole to the top of said hole, a first means provided at the top of said hole for producing first signals representing a superposition of said useful signals and of interfering signals associated with at least one of said drilling operations and a second means comprising an autocorrelator responsive to said first signa:ls for deriving an indication of said useful signals.
According to yet another broad aspect of the present invention, there is provided a system for performing measurenlen~s in a well being drilled in theearth using a hollow tubular drill string having a fluid passage therethrough, a periodically operated pump, a source of drilling fluid, means operatively con-necting said pump to said source of drilling fluid and to said hollow drill string whereby said pump forces drilling fluid through said passage, a sensing means in the lower portion of said string for sensing the value of a downhole parameter, a first means responsive to said sensing means for producing in said circulation system a succession of pressure pulses indicative of the value of said parameterJ a second means at the top of said well for producing a succes-sion of electrical primary pulses in which each single electrical primary pulse has a corresponding single pressure pulse, a third means of tr~nslating said 1~L5~716 succession of primary pulses into a succession of corresponding pairs of second-ary pulses, said secondary pulses in each pair being separated in time by a determined time interval, and a fourth means for obtaining from said succession of pairs of secondary pulses a quantity representing the value of said parameter.
According to one more aspect of the present invention, there is pro-vided a system for performing measurements in a drill hole concurrently with the operations of drilling said hole, in which the measurements are carried out by sensing selected parameters at various depths in said hole and transmitting through a transmission channel to the top of the drill hole useful signals representing values of said parameters, comprising a first means at the top of said drill hole for producing first signals representing a superposition of said useful signals and of interfering signals resulting from at least one of said drilling operationsJ a second means for expressing said first signal in digital format, a third means for expressing said interfering signals in digital format, and a digital processing means operated in conjunction with said first and said second means for obtaining values of said parameters.
According to a final aspect of the present invention, there is pro-vided a system of making measurements in a well being drilled in the earth us-ing a hollow tubular drill string having a fluid passage therethrough, a re-currently operated pump system, a source of drilling fluid, means operatively connecting said pump system to said source of drilling fluid and to said hollow drill string to form a fluid circulation system whereby drilling fluid is forced ~ :
by said pump system through said drill string passage and produces recurrent pressure variations in the fluid circulation system, a sensing means in the lower portion of said string for sensing the value of a downhole parameter, a means responsive to said sensing means for producing in said fluid circulation system pressure changes representing the value of said parameter, comprising a . .
~ ~ ' ~5~716 drilling fluid pressure sensitive transducer near the top of said string for producing first signals representing a superposition of said pressure chànges and said recurrent pressure variations and clectronic means connected to said transducer and operated in a definite relationship to the recurrence in the operation of said pump system for deriving from the output of said pressure transducer second signals in which the effect of said periodic pressure varia-tions is selectively attenuated.
The invention, as well as that of Copending Application Serial No.
314,590 will now be described in greater detail with reference to the accompany-ing drawings, in which:
Figure 1 is a schematic illustration of a conventional rotary drilling rig showing apparatus of the present invention incorporated therein;
Figure 2A is a schematic illustration of a negative mud pressure pulse generator with its valve in the open position;
Figure 2B is a schematic illustration of the negative mud pressure pulse generator of Figure 2A, with its valve in the closed position;
Figure 3A is a schematic illustration of a physical embodiment of the negative mud pressure pulse generator of Figures 2A and 2B, together with in-strumentation and sensor sections in place in a drill string near the drill bit;
Figure 3B is a drawing of the negative mud pressure pulse generator of Figures 2A and 2B taken in proportional dimensions from an engineering as-sembly draNing used in actual manufacture of the device;
Figure 3C is a schematic diagram of a radioactivity type sensor and associated instrumentation;
Figure~r3D is a schematic diagram of a temperature type sensor and associated instrumentation;
Figure 3E is a schematic diagram of typical instrumentation for con-1~5~7~

trolling actualion of the valve of the negative mud pressure pulse generator;
Figure 3F is a schematic illustration of one type of self-contàined downhole power source that may be utilized;
Figure 3G is a schematic illustration of another type of self-contained downhole power source that may be utilized;
Figure 4 is a schematic illustration showing typical aboveground equipment in accordance with a preferred embodiment of the invention, wherein the downhole parameter being sensed is radioactivity;
Figure 5 is a graphic illustration, in idealized form, showing cer-tain wave forms and pulses and time relationships to aid in explanation of the signal extractor portion 102 of Figure 4;
Figure 6 is a schematic block diagram showing component lOS of the signal extractor 102 of Figure 4 in further detail;
Fig~re 7 is a schematic block diagram showing component 107 of the signal extractor 102 of Figure 4 in further detail;
Figure 8 is a schematic block diagram showing another form of above-ground equipment that may be utilized;
Figure 9 is a schematic block diagram showing still another form of aboveground equipment that may be utilized;
Figure 10 is a schematic block diagram showing an alternate timing pulse generator that may be utilized;
Figure 11 is a schematic block diagram showing still another form of aboveground equipment that may be utilized.
Before proceeding with description of preferred embodiments of the invention, it is believed that understanding 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 ' ' : , :

~L5~716 pipe is of the order of 5,0Q0 gallons. Assuming that the bulk elastic modulus for compressed drilling mud is 4QQ,QQQ, then discharging .5 gallons of fluid will cause a pressure drop of 4Q psi, ~if we consider the 5,QQ0 gallons as be-ing 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 dp index and in this case the dp index is equal to lQ.
Three important experiments were performed;
1. Measurements were made in a test well at 1,8QQ' and moderate dif-ferential 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 differential pressures ~1,600 psi).
All three series of experiments inclicated that the dp index of the pressure pulse received at the surface when t:he valve is suddenly opened was substantially higher than calculated. The reasons for this are:
~a~ highly co~pressed drilling mud may have an elastic modulus somewhat higher than 400,000;
~b) there is some wave guide action by the drill pipe that causes the signal to travel much more favorably than it would in a large tank of the same volume; and ~c) the sudden opening of a valve at the bottom of the well causes a higher dtP index than in the case of 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 _ 9 _ ~ .

~5~7~6 drop some 110 feet when 3,000 psi mud pump pressure is applied ~3,000 psi is arather typical mud pump pressure in deep wells). One can, thereforel consider the mud column as being continually compressed by some 100 feet and acting as a long spring in which a large amount of potential energy is stored. When a valve at the bottom of the drill pipe is suddenly opened, this potential energy is re-leased, causing a large negative mud pressure pulse; such mud pressure pulse being substantially larger than would be the case if the mud were incompres-sible.
In the experiments conducted at 5,000' in a drilling well, a small passageway ~.056 in.2 area) between the inside of the drill collar and the an-nulus, was opened and shut in accordance with a controlled sequence. The pres-sure 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. (again using the assumption that mud column was a simple tank). In the tests the pressure drop at the surace was measured to be over 100 psi/sec. or considerably more than would be expected from the simple tank calculation. The following conclusion was reached: With high pressures existing across the drill bit ~1,000 psi or more), large sharp signals can be developed at the surface by opening and clos-ing a very small bypass valve at the sub-surface near the drill bit. Valves having an opening of .05 in.2 can produce large signals from a 5,000' depth and the reduction in signal magnitude from depths between 2,500' and 5,000' have been found to be very small; thus, indicating that the signal attenuation is small.
The system of the present invention has a number of important advan-tages: The rapid discharge at a rate of as little as 0.125 gallons/sec will :

~L15~71 6 generate a "sharp" pulse, that is a pulse containing a high rate of change of pressure, i.e., a high dPt index ~e.g. 40). Furthermore, the rapid opening of the bypass valve will also minimize wear for the following reasons: When the bypass valve is closed, there obviously is no wear on the valve seat. When the valve is open (and the valve area is large compared to a restriction or restric-tions following it), the valve will be exposed to low velocity fluid and~ con-sequently, the wear will be mostly in the following restriction 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 as fast as pos-sible for opening and closing and there is no limit to the desirable speed.
The rate of discharge through the valve should also be fast but there is an upper limit beyond which faster discharge does not benefit. The reason for this is the limit to high frequency transmission through the mud. FTequencies higher than about 100 Hz are strongly attenuated and are of little value in building up a fast pulse at the surface. To determine the maximum 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 experiment-al arrangements comprised a special large valve followed by an adjustable ori-fice.
Changing the orifice size can determine 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 dif:Eerent orifice sizes were tested, .509" diameter, .427" diameter and .268" diameter. It was determined that the .268" diameter orifice generated a signal at the surface nearly as intense as the one gene~ated 1~S~6 by the .509" diameter orifice.
Referring now to Figure 1, there is schematically illustrated a typical drilling rig 10 including a mud circulating pump 12 connected to a dis-charge pipe 14, a standpipe 16, a high pressure flexible rotary hose 189 a swivel 20 and a drilling string 22, comprising the usual drill pipe and drill 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 in-side and the outside of the drill collar 24, i.e., the valve controls a passage-way between the inside of the drill collar 24 and the annulus 29 formed by the outside 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. Alter-natively, the transducer 100 could be connected into the stationary portion of swivel 20, if desired.
Figures 2A and 2B show the negative mud pressure pulse generator 28 in diagramatic form to facilitate explanation of its function and manner of operation. The negative mud pressure pulse generator comprises a valve inlet chamber 42, a valve outlet chamber 44, and a compensator 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 hydraulically connected via a passageway 48 to the valve outlet chamber 44. Hydraulic flow through passageway 48 is controlled by the cooperation of a valve 36 with its 7~6 seat 37. The valve outlet chamber 44 is hydraulically connected via an outlet passageway 51 to the annulus 29. Interposed in the outlet passageway Sl are irst and second compensator orifices 52, 53. The chamber 40 between the ori-fices 52, 53 is hydraulically connected via a conduit 74 to the compensator 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 of a shaft 46. The valve 36 is also connected, by means of a shaft 47 ~see Figures 3A and 3B) to an actuator device 54.
The function and operation of the negative mud pressure pulse genera-tor 28 will now be explained. Figure 2B shows the valve 36 of the negative mud pressure pulse generator 28 in the "closed" condition. In this figure, the striated part indicates "high" pressure and the blank part indicates "low"
pressure. ~Pressure magnitudes, such as "high1', "low" and "intermediate" are relative pressures, i.e., the difference bett~een the pressure at a given loca-tlon and the annulus pressure which is here considered to be zero; the actual or real pressure would be equal to these magnitudes plus the hydrostatic head, which may be lO,000 psi or higher.) The effective area of the valve 36 is made somewhat larger than the efEective 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 direc-tion shown by the arrow in Figure 2B and may be equal to about l,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.
Figure 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 29. The first and second compensator orifices 52 and 53 each provide a predetermined restriction to the mud flow and each causes 1~5~7~6 a pressure drop. Consequently, the pressure inside the chamber 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 in-side the annulus 29.
As is pointed out above, in Figure 2A, as in Figure 2B, the striated part indicates "high" pressure and the blank part at the exit of outlet passage-way 51 is "low" pressure. During the valve "open" flow condition, the mud encounters two restrictions to flow: orifice 52 and orifice 53, as. a conse-quence 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: are.a in Figure 2A. This "intermediate" pressure is originated in the chamber 40 between orifices 52 and 53 and communicates via conduit 74 to the compensator chamber 72. The pressure in this compensator chamber 72 can, con-sequently, 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. The proportioning of the sizes of the orifices 52 and 53, therefore, con-trols the pressure in compensator 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 chamber 44 and the annulus 29. As the si~e 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. For 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 will be high and tend to close the valve 36.

_ 14 -ilS~ ~7~16 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 SO can be adjusted between wide limits, thus providing a means for adjus*ing the action of the valve 36.
It is important to note that the force tending to close the valve 36 in Figure 2B, and the force tending to open the valve 36 in Figure 2A, are de-termined by first and second independent par~meters, i.e., the force tending to close the valve is derived from the effective area differences of the valve 36 and the rod side 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 adjusting 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" ac-tion, 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 magnitude in the valve "close"
direction is applied and maintained; and the second said independent parameter is chosen 50 that when the valve is within the region of nearly open to fully open, a predominant force of predetermined magnitude in the valve "open" direc-tion is applied and maintained.
Thus, it is apparent that the negative mud pressure pulse generator 28 of the present invention utilizes existing energy derived from the mud pres-sure in such a manner so as to greatly reduce the amount of external energy re-quired to operate the valve 36 and, in addition~ to impart to the valve 36 a "bi-stable" or "toggle" action.

~ ., 1~5~7 iL6 Further discussion of the negative mud pressure pulse generator 28 will be facilitated by reference to Figures 3A and 3B, which will now be de-scribed. Figure 3A illustrates in schematic form a physical embodiment of the negative mud pressure pulse generator 28 and associated downhole equipment as it would be installed in the drilling apparatus of Figure 1. The reference numerals that are applied in Figures 1, 2A and 2B refer to corresponding parts when applied to Figure 3A. In Figure 3A, 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 ~not shown). The inner housing 56 contains the negative 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 the housing 56 in the direction of the arrows.
A filter 60 prevents mud solids from entering the housing. The valve 36 is shown to be operated by an actuating device 54. When the valve 36 is open, as shown in Figure 2A, some mud is bypassed into the annulus 29. The bent arrows show the direction of this bypassed mud. The pressure that forces the mud into the annulus 29 is the pressure across the jets of bit 26. When ~alve 36 is closed, the bypass to the annulus 29 is closed.
The floating piston 76 separates chamber 72 from an oil filled chamber 78. Actuating device 54 is mounted within an oil filled chamber 80. An equal~
i~ing passageway 82, connects chamber 78 with chamber 80. Thus, in coopera-tion with floating piston 76 and passageway 74, the chambers 72, 78 and 80 are maintained at essentially the same pressure as the chamber 40. Passageway 82 is partially shown in dashed lines in Figure 3A and is not shown in Figure 3B
since it is located in a different plane from the cross section shown.
Numeral 68 represents a standard drill collar and numeral 63 a box-box sub. Section 66 is 2 3/8" in diameter and fits into a standard 15' 6 3/4"

O.D. - 3 1/4" I.D. drill collar. The unit 30 is provided with special central-izer arms 70 which fit snugly into box-box sub 69. The centralizer arms 70 are designed to centralize the unit 30 while allowing free passage of mud.
Figure 3B bears the corresponding reference numerals of Figures 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 con-struction. It may be noted that in Figure 3B the actuating device 54 comprises a pair of electrical solenoids arranged in opposition. The winding 55 of the upper solenoid is disposed to exert a force in the upward direction on its arma-ture 57, while the winding 59 of the lower solenoid is disposed 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 pi.cking up the load of shaft 47 with a hammer like impact. This "hammer" action has a beneficial effect upon the opening and closing operations of the valve 36. Suitable solenoids for this application are the Size 6EC, medium stroke, conical face, type manufactured by Ledex, Inc., of Dayton, Ohio.
Reverting now to discussion of the negative mud pressure pulse gen-erator 28, there are several further factors and features that should be con-sidered.
The orifices 52, 53 are made to have smaller opening areas than that of the passageway 48, so that the velocity of mud flow over the sealing surfaces of valve 36 and its seat 37 is significantly reduced when compared to the velo-city of mud flow through the orifices 52, 53; thus, concentrating wear on the orifices 52, 53, which are made of wear resistant material ~such as boron car-bide) and which are also made readily replaceable in the "field", as indicated :
.

, in Figure 3B. These small non-erodable orifices 52, 53 make the negative mud pressure pulse generator 28 completely "fail safe", i.e., no matter what 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 previsus-ly 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 en-counter a hard rock, the drill bit and drill collars 24 are forced upwards, i.e., accel~ratedin the upward direction; but once the drill bit is raised upward and out of contact with the rock, there is little force other than the acceleration due to gravity that forces the drill bit and drill collars downwardly. Conse-quently, the acceleration upward can be several hundred g's but the acceleration down~ard is only of the order of lg. 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 Figures 3A and 3B.
I determined, by conducting various tests and experiments, that a force of approximately 34 pounds would be required to actuate the valve 36 when the first and second independent parameters hereinbefore described had been 711~

chosen to provide appropriate "hydraulic detent" OT "bi-stable" action to achieve adequate stabili~y 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, with elec-tromagne~ic drive solenoids of reasonable size, would require about 350 watts of electric power; i.e., nearly 1/2 horsepower. With such a large power require-ment 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 consider-ed that the negative mud pressure pulse generator 28 of the present invention provides a very rapid action -for the valve 36; i.e., the valve 36 can be made to open ~or to close) with the application of the required 350 watts for only about 20 milliseconds. The amount of energy required to open ~or close) the valve is, therefore, looo 60 . 60 ~ 002 watt hours There are available modern high density batteries of reasonable size and capable of being included in ~he space provided within the drill collar 24 and which can easily provide 2,000 watt hours of energy. Therefore (even without recharging~
as is described later herein) a reasonable battery can provide enough energy to operate the valve 36 about one million times. Assuming that the valve is ope-rated 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 log-ging while drilling that the downhole apparatus be capable of operation un-attended ~i.e., without battery recharge) for at least the length of time between "round trips", i.e., the time that a single bit can drill without re-placement, the best bits last only about 100 - 300 hours and, therefore, the ., 19 ' ~5~7 ~

30 day figure above is more than adequate.
The practical design of 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 of the para-meters had to be determined by empirical methods. An important reason for this is because the "viscosity" of drilling mud is thixotropic and the dynamic be-havior is quite different from that of liquids having classical or so called Newtonian viscosity. Drilling mud "weight" (grams per cc) and "viscosity" vary over wide ranges and consideration must be given to the fact that "weight" usu-ally 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 an-nulus). In this set up, a large "servo" valve ~1" diameter) was followed by smaller replaceable orifices. In 8,000' and 5,000' well depth experiments care-ful measurements were made of the magnitude of the negative mud pressure pulse at the surface as a function of the size of the discharge orifice. As this size was successively reduced, the magnitude of the pulse at the surface seemed al-most independent of the size of the orifice until the surprisingly small .05 in. orifice area was reached, at which time a slight reduction in pulse magni-tude was observed. This phenomenon was quite unexpected, but was later under-stood after careful consideration of the elastic properties of the mud column and the stored potential energy therein as was hereinabove explained. This discovery produced the realization that a small negative mud pressure pulse generator could produce useful signals at the surface. Calculations were there-after made and it was determined that the "servo" principle for the valve actu-~56~7~L6 ation was not necessary and the "servo" valve approach was abandoned. The di-rect~ very fast acting, negative mud pressure pulse generator of this invention was thereupon designed and has proved to be successful.
In a negative mud pressure pulse generator 28 of practical design the following dimensions may be considered as typical; orifice 52, 0.500" in diam-eter; orifice 53, 0.306" in diameter; stroke of valve 36, 0.125"; diameter of piston 50, 0.383"; diameter of valve 36 at its seating surface, 0.430"; angle of seat 37 relative to axis of valve movement, 60; diameter of opening at seat 37 or passageway 48, 0.375"; diameter of valve shaft 46, 47, 0.187".
In Figure 3F there is schematically illustrated a special type of 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 exception; the modern molten salt: batteries. They operate well at high temperatures of 400 - 500C or even higrher but will not operate properly at lower temperatures principally because the electrolyte solidifies and ceases to conduct electrically. A lithium 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 ba~teries are very well adapted for high tem-perature operation.
As illustrated in Figure 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 Figure 3F, reference numeral 155 designates the battery proper; reference numeral 156 designates heating elements that are arranged to provide a small amount of heating to the '' ,';::
- i ~L~5~7~6 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., Walthem, Mass. Initially an external voltage ~not shown) is applied to the terminal 158 ~while the instrument is at the surface and be-fore immersion into the well~. This voltage activates the heating elements 156 and the battery electrolyte melts. Furthermore, the battery 155 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 clos-es 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 Pat-ent 3,970,877, Russell, et al. Instead of the Russell, et àl, 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 re-quired.
In Figure 3G there is schematically shown another special type of battery that may be used to power the downhole equipment of the present inven-tion. This battery preferably uses cells of the Lithium Sulphur type, such as are manufactured by Power Conversion Inc., of Mt. Vernon, New York. It may also use LeClanche type cells or Lead Acid type cells. All 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 invention, there is provided an arrangement ~il-lustrated by Figure 3G) by which this prbblem is overcome. In Figure 3G, a plurality of individual cells 1~1 such as one of the above mentioned types are Trademark ~:

~lS~'716 connected in series between a ground terminal 162 and a positive terminal 1630 Each cell preferably is provided a conventional pressure release cap or vent 164. In accordance 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 reservoir 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 tG 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 or Lead Acid type cell, the liquid 166 can be water since the container 165 is hermetic and pressure resistant, the liquid 166 ~in this ex-ampleJ water) will never boil - no matter how high the temperature. It will simply build up vapor pressure in the space above the liquid 166 high enough to be an equilibrium 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 Dioxide. The Sulphur Dioxide vapor generated by the cells 161 will always be in pressure equilibrium with the container 165 because the Sulphur Dioxide liquid in this auxilliary contain-er 165 will always generate pressures equal to those generated by the cells 161.
~ Sulphur Dioxide and water, given as examples above, are often unsatis-factory ~a) because Sulphur Dioxide is highly corrosive and because water is an electric conductor and can short out the batteries. An alternative substance is dichlorodifluoromethane, popularly called Freon and manufactured by E.I.
DuPont and Co., Wilmington, Delaware. Many types of Freons have been developed with almost an unlimited number of thermodynamic properties, i.e., pressure-temperature relations. Other substances can readily be found, such as hydro-carbon vapors, propane or butane or mixtures of vapors and gases. S~ffice it ~1~S~16 to say, that I enclose the battery cells 161 in a container 165 and place in this container a small quantity of a substance having similar pressure-tempera-ture relations to ~hat of the electrolyte in the battery cells 161. In Figures 3F and 3G, I show only a small number of cells connected in series. In actuali-ty, a larger number is normally employed. In the manufactured instrument of Figure 3C, I employ 17 Power Conversion Co. Lithium Sulphur cells.
Another important feature of the present invention i5 that the length of time the valve 36 is maintained "open" has no relation to the amount of energy required. The only energy required is that expended to actuate the valve 36 to the "open" position. The importance of this feature is fully appreciated from the following consideration:
It has been determined by experiment that in order to provide a strong signal from a depth of 10,000 to 20,000, the valve must remain "open"
for about 1/2 to one second and any electromechanical ~solenoid or other) device operating for this length of time would not only require large amounts of energy but would overheat and under well 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 in-venti~n. Figure 3C illustrates a natural gamma ray sensor and its associated circuitry which in this example is of the analog type. Figure 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 Figure 3E which will be hereinafter described.
With reference to Figure 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 ~lS~i6 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.
Figure 3D illustrates the case of the temperature sensor. The tem-perature 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 thermistor 173 is a DC voltage proportioned to temperature. The amplifier 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 pro-portional to the sensed temperature. The ou1:puts of the power amplifiers 185, 186 are utilized to control energization of 1:he 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 Figure 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 of the downhole parameter is represented by electric pulses. The sequence of the puls-es represents a code (binary or other) and this sequence represents the magni-tude of the parameter. Figure 3E illustrates how each single pulse of this code is processad to operate the valve 36. In Figure 3E, numeral 177 represents one such pulse which is narrow in time; being only a few microseconds long.
This pulse 177 is impressed upon the circuitry contained in block 178. This 7i6 block 178 contains a so called "one shot" univibrator and suitable inverting rectifying circuits well known in the electronics art and provides (in rèsponse to the single input pulse) two output pulses separated in time by tl (the first pulse is normally time coincident with 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 respectively applied to the "Darlington" power amplifiers 185 and 186 ~as manufactured by Lambda Mfg. Co. of Melville, New York, and sold under the type PMD16K100).
rn the practical design of the electronic logic and power circuitry of Figure 3E that I use in this preferred embodiment, I have chosen as constants tl = 500 milliseconds and t2 = 20 milliseconcls. In operation, when a single pulse 177 is impressed on lead 167, the Darlington 185 is turned on for 20 milli-seconds and then turned off. Then 500 milliseconds later the Darlington 186 is turned on for 20 milliseconds and then turned off. Thus, the valve 36 is opened for 500 milliseconds without requiring any energy during this period. Energy is required only during the short 20 millisecond periods that are required to actu-ate the valve 36 to the "open" or to the "close" position. The figures given above are for illustrative purposes Gnly. Suffice it to say that by making the action of the valve 36: ~a~ very fast and ~b) bi-stable; very high pressures and volumes of mud can be valved without the necessity of employing large amounts of energy and as hereinabove described, relatively small energy batteries can operate the valve about one million times.
In a typical embodiment of ~his apparatus, the weight of the entire `: ' .. .

~L~5~716 valve mechanism 36 of Figures 2A or 3A, including the solenoid armature 54, shaft 46 and piston 50 is approximately 9 ounces. The valve 36 has been designed to operate at a differential pressure of 1,600 psi and proportioned to operate at optimum performance, including the consequence that the force 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, maxi-mum 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 valve closed in Figure 2B and the force keeping the valve open in Figure 2A must both exceed about 34 pounds. By suitable choice of the first and second independent parameters hereinabove described, a "balanced" con-dition is achieved. By "balanced" is meant that the force required to open the valve 36 is equal to the force required to c]ose it.
Above ground equipment utilized with the present invention, particular-ly as to methods and apparatus for eliminating interferring effects that are present in the output of pressure transducer lO0, can take various forms, as will now be described.
Figure 4 shows typical above ground equipment in accordance with a preferred embodiment of the invention, wherein the do~nhole parameter being sensed is the radioactivity of formations traversed~b~ the bore while drilling is in progress. The corresponding portion of the logging equipment which is below the earth's surface has been previously described and sho~m in Figures 2A, 2B, and 3A-G.
Referring now to Figure 4, pressure transducer lO0 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 :,;

. .: :

115q)~16 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 inter-ferring signal is in the form of relatively slow and periodic pressure varia-tions 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 utiliz-ing the short negative mud pressure pulses.
One of th0 objectives of this invention is to recover, from the "con-taminated" signal produced by the transducer, a "clean" signal which gives the desired information. 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 information regarding the downhole parameter can be readily obtained.
The signal extractor 102 is contro]led in a predetermined 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 the mud pump 12 to produce an appropriate number of timing pulses per revolu-tion of the pump. A chain drive transmissio~ assembly 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 actuatio~ of the valve 36 of generator 28 into signals having magnitudes representing the inter-vals therebetween. The convertor 115 is a well known electronic device and can ~. ' ' ':
~:

be made up of components mc~lufactured by the Burr-Brown company of Tuscon, Arizona, U.S.A. Por further detailed description of time-to-amplitude conver-tors see: hl. Bertolaccini and S. Cova, "Logic Desi~n of High Precision Time to Pulse Height Convertors", Nuclear Instruments and Methods 121 ~1974), pp.
547 - 566, North Holland Publishing Co., The signals derived from 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 i`nput voltages. Thus, if a voltage of magnitude M is applied to reciprocation circuit 118, an output voltage having magnitude l/M is obtained. These signals having magnitudes l/M
are in turn recorded on the chart of a recorder 120. The recoTd chart of record-er 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 modi-fication or adaptation of equipment such as marketed by The Geolograph Medeavis Company of Oklahoma City, Oklahoma, U.S.A.
In order to show more clearly the operating features 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 Figure 5. Let F(t) = S(t) + N(t) (1) where S(t) is the useful information carrying signal formed by the negative mud pressure pulses Pl, P2, and P3 aligned along the time axis t. [See Figure 5 (axis A)] The times of arrival of these pulses, which correspond to the times of actuation of the valve 36 of generator 28, are tl, t2 and t3, respectively.
The time intervals which separate these pulses are ~1 = t2 ~ tl, ~2 = t3 ~ t2 = t4 - t3, etc. are indicative of the intensity of the radiation measured.
If these time intervals are large~ the intensity is relatively weak and con-versely, if they are small, the intensity is relatively strong. The interfering signal produced by the mud pump 12 is represented in Figure 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.
To facilitate explanation, the relative scales in Figure 5 have been distorted. In actual practice, there may be 50 to 80 oscillations of N(t) between the time of arrival of Pl and P2. Thus, ~1 and ~2 may vary from 50T to 80T. However, in Figure 5 ~axis A) only a few oscillations of N(t) between Pl and P2 have been shown. Furthermore, in actual practice the negative mud pres-sure pulses Pl, P2, P3 do not have clean rectangular forms as in Figure 5 (axis A). Moreover, the actual pulses are much smaller than those which have been shown in Figure 5 ~axis A). In actual experience, the magnitude of Pl, P2 or P3 is about 0.1 to 0.01 of the maximum amp~itude of the pulsations N(t).
Axes A - E in Figure 5 are positioned one below the other so that one can compare the signals in their time relationships one to another. Using 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 I
We displace the input F(t) by an amount T, to obtain F~t - T) = S~t - T) ~ N(t - T) ~2) where S(t - T) and N(t - T) are, respectively, the displaced useful signal and displaced interfering signal. Both signals are shown in Figure 5 ~axis B). The signal S~t - T) is represented by pulses pl~a), p~a) and P3~a) which have been obtained by displacing by an amount T the corresponding pulses Pl, P2 and P3 in Figure 5 (axis A). The signal N(t - T) in Figure 5 (axis B) is shown to be in exact synchronism with N(t) in Figure 5 (axis A). This is due to the periodicity of the signal. Thus~

115~716 N(t - T) N(t) (3) 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) (5) Thus, the interfering signal has been eliminated and does not appear in M(t).
This can also be seen from inspection of Figure 5 (axes A and B).
As shown in Figure 5 (axis C), M(t) consists of impulses which occur in pairs. Each pair contains a negative and a positive pulse separated one from another by a time interval T. Thus, we observe a pair consisting R pl(b) and pl(b) which is followed by a succeeding pair consisting of P2(b) and P2(b) , then by another pair consisting of p3(c) and p3~c) and so on.
Step 3 We displace M(t) by a time T so as to obtain Mlt - T). Thus, the entire sequence of pulses in Figure 5 ~axis C) is shifted along the time axis by T so as to appear as shown in Figure 5 ~axis D). The arrangement of pulses as in pairs has been preserved in Figure 5 ~axis D). However, each pair such as pl(c) and pl(c) is displaced with respect to the pair pl(b) and pl(b) ~shown in Figure 5 (axis C)] by T. Similarly, 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 Figure 5 (axis D) with those in Figure 5 (axis C). We note that some of these in Figure 5 (axis D) are in time coincidence with some of the pulses in Figure 5 (axis C). The instances at which coincidence occurs are recorded in Figure 5 (axis E) as pulses Pl~ ), ~L~5~7:~

P2(d) and p3(d) Thus, Pl( ) coincides with Pl(b) and Pl~C) p~d) coincides with P2(b) and P2(C) P3( ) coincides with p3(b) and p3(c) The times at which the pulses pl(d), p2(d) and p3(d) occur are tl + T, t2 ~ T
t3 T.
The pulses pl(d), p2(d) and p3(d) correspond to the pulses Pl, P2 and P3 shown in Figure 5 (axis A). ~onsequently, the pulses in Figure 5 ~axis E) also represent this useful function which now is S(t - T) since it has only been displaced by T. It is evident that the pulses in Figure 5 (axis E) provide the information which we are seeking to obtain. The time interval between pl(d) and P2~d) is ~1~ and the time interval between P2td) and p3~d) is ~2, etc.. The quantities 1~ 2~ etc. are indicative of the radiation measured by the gamma ray detec~or.
The above steps will now be conside~ed as they relate to the perfor-mance of the signal extractor 102 and more particularly to that of its two com-ponent parts designated in Figure 4 as 105 ancl 107 and shown schematically in Figures 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 Figure 4~ the signal F(t). As shown in Figure 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, producing at its output terminal 134 the signal F(t - T). This signal is a sum of two component signals S(t - T) and N(t - T) which are shown in Figure 5 (axis ~) ~
The signal F(t - T) is applied to one input terminal 134 of a sub-tractor 135. The other input terminal 136 of the subtractor receives directly 1~LS~ 6 the signal F~t), which is transmitted from terminal 101 by means of conductor 137. Thus, at the output terminal 106 of the subtractor 135 we obtain the dif-ference signal M~t) = F~t) - F(t - T). This is shown in Figure 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 oscillations produced by the mud pump 12.
The amount of the delay T is controlled by the timing impulses derived from pulse generator 111 shown also in Figure 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 of 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 the rate of pulsation of the mud pump 12 varies with time and, accordingly, N2 will vary so as to insure that the delay 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, ma~ be a Reticon Model SAD-1024 Dual Analog Delay Line as marketed by Reticon Corpora-tion, Sunnyvale, California, U.S.A.
The instrumental steps herebefore described are the steps 1 and 2 per-formed by the component 105 of the signal extractor 102. We have transformed 5~71~;

the input signal F~t) [represented by its components in Figure 5 ~axis A)] into an output signal M(t) which appears as a succession of pairs of pulses and is shown in Figure 5 ~axis C). We will now proceed to describe further instrumental steps which are required in order to accomplish the desired objectives. These are performed by the component 107 of the signal extractor 102.
We refer now to Figure 7. The signal M~t) is now applied through conductor 140 to a delay network 141~ This delay network is identical to that designated as 132 in Figure 6. It receives, at its control terminal 114l the same control signal which was applied to the control terminal 113 of the delay .lO 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 Figure 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 149 of the AND gate 146. These two input signals M~t) and M~t - T) which are applied to the AND gate 146 are shown in Figure 5 (axes A and D), respectively. We have previously observed that some impulses shown in Figure 5 ~axis C) occur in coincidence with impulses in Figure 5 ~axis D). Those impulses that occur in coincidence appear in the output of the AND gate 146. They are designated in Figure 5 ~axis E) as Pl~d), P2~d) and p3~d). These coincldent pulses are the output of pulses of the co~ponent 107, and consequently af the signal extractor 102.
It is thus apparent that by means of the component 107, we have per-formed the instrumental steps 3 and 4. We have transformed the signal M~t) shown in Figure 5 ~axis C) in~o the signal S~t - T) shown in Figure 5 ~axis E).
The latter provides the quantities ~lJ ~2~ ~3~ etc., which represent the infor-mation it was desired to obtain. It should be recalled that the signal S~t - T) . ~

; , ':

3L1~i~716 is represented by a succession of pulses as shown in Figure 5 (axis E).~ These pulses are transmitted to the time-to-amplitude convertor 115 to produce at thè
output of the time-to-amplitude convertor 115 signals of various magnitude such as ~ 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 Figure 4 into other reciprocal signals having magnitudes 1/~ 2, 1/~3, respectively. These reciprocal signals arerecorded by recorder 120 of Figure 4. It is apparent that the quantities 1/~ 2 and 1/~3 represent the intensity of radioactivity of formations sensed by the sensor unit 30 at various depths in the borehole.
We have described above an instrumental means for performing logical steps leading from the unction F~t~ to a function S~t - T). These steps have been performed by representing these functions in an analog ~non-digital) form.
Alternatively, if desired, the entire process can be digitalized, as shown diagrammatically by Figure 8. In Figure 8, the output of the pressure transducer 100 is fed to an analog-to-digital convertor 103, the output of which is fed to a digital computer 104. The operations indicated in Figure 8 are performed by the elements designated 122, 123, 124, 125 and 126 in the digital 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 Figure 8 are performed mathematically in a sequence which may be flow chartedO The output of the com-puter 104 is fed to a digital-to-analog convertor 127, the output of which is fed to the recorder 120.
In Figure 9, there is shown an arrangement similar in some respects to that of Figure 4, but ~Iherein the data to be obtained and recorded .is the tem-perature at the location of sensor unit 30 of Figure 1. In Figure 9, these data~

:. :
' as presented to the signal extractor 102 are in digital form (see Figure 3D).
The signal extractor 102 of Figure 9 is identical to that of Figure 4, but the time-to-amplitude convertor 115 and the reciprocation circuit 118 of Figure 4 are replaced by a digital-to-analog convertor 141.- The ~utput signals of an appropriate pulse generator will be applied to the control terminal 110 of the signal extractor 102.
It is not always convenient to provide a mechanical connection to the mud pump 12, a~ shown by the chain drive transmission assembly 112 in Figure 4, and an alternate means for generating the pulses required for the signal extrac-tor may be desirable. Figure 10 illustrates such an alternate means. In atypical example, the signal extractor 102 of Figure 4 is provided at its ter-minal 110 with pulses at a rate of 512 pulses per full pump stroke. It must be clearly understood that this rate must be rigorously synchronized with the pump strokes. All the "times" shown as T, tlJ t2, etc. in Figure 5 are not so-called "real time", but are directly related to the speed of the mud pump 12 and rigorously, T, tl, t2, etc. should be expressed, not ;n seconds or m;nutes of "t;me" but ;n "gallons of mud". ~hen it said that at terminal 110 of Figure 4, there are 512 pulses per mud pump stroke, it is meant that at terminal 110 there are present voltage pulses hav;ng a frequency equal to the 512th harmonic of the pump stroke frequ~ncy. Figure 10 shows how this can be accomplished without mechanical connection to the pump shaft.
In Figure 10, component 145 is a VCO or "voltage controlled oscillator"
which at its output 110 produces electric pulses the frequency of which is con-trolled 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 frequency of the input pulses. Component _ 36 -~L5~7:~

119 is a phase comparator that compares two inputs ~one from scaler output ter-minal 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 input at 130 in phase. A battery 129 is provided to properly bias the VCO 14S. The circuit 151, just described, is known as "phase locked loop". The operation is best explained by an example: Asswme that the pwmp pulse frequency ~pwnp stroke frequency) is 1 H~ and the VCO is generat-ing 512 Hz. The output of the scaler 150 will then generate exactly l Hz. The 1 Hz from the scaler 150 and the 1 Hz from the pressure transducer 100 will then be exactly matched in frequency and phase and the output of the comparator at terminal 128 will be zero volts, and the VC0 :L45, when properly biased by battery 129, wlll generate exactly 512 pulses per stroke.
Asswme now that the mud pwnp 12 speeds up. The frequency at terminal 130 will than be somewhat greater than 1 Hz - i.e., 1 ~ ~lHz. The comparator 119 will then provide an output at terminal 1:28 which will no longer be zero volts DC, but for ex~mple, ~ a2v, this small voltage increment will be applied to the VCO 145 at terminal 108 and increase its frequency until the nominal 512 pulses per second is increased to a value f such that f/512 = 1 ~ al.
Thus, the frequency at terminal 110 will alt~ays accurately follow the frequency of the mud pwmp 12 and will always be its 512th multiple.
Two arrangements for obtaining timing pulses for the signal extractor 102 have been hereinabove described (pulse generator lll of Figure 4 and the "phase locked loop" circuit 151 of Figure 10). A third arrangement that may be used for obtaining such timing pulses is illustrated by Figure 11 and is based on "auto-correlation". In Figure 11, the input terminal 154 of a correlator 152 -: ~

56~716 is supplied by the output of the pressure transducer 100, and receives the func-tion F(t) which contains the periodic signal N~t) and the function S(t) which may be considered a random function. The output of the pressure transducer 100 is also applied to the input terminal 101 of the signal extractor 102. The cor-relator 152 is adapted to produce across its output terminals the autocorrelation function of F(t) which is ~ff(T) = [S(t) + N(t)] ~S(t ~ T) + N(t ~ 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 ~ff~ ) ~55(T) ~ ~n~(T) (7) wllere ~55(T) = S(t)S(t ~ T) (8) and ~nn~T) = N(t)N(t ~ T) (9) The function ~55~T) reaches zero at some value of T = To and beyond To, we have ~ff(T) = ~nn(T) ~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 produces a succession of timing pulses similar to those produced by the pulse generator 111 in Figure 4 and which are applied to input terminal 110 of the signal extractor 102. The pulse multiplier 153 multiplies the frequency of the input pulses by a phase locked loop system similar to that of Figure 10 or by any other conventional means. The remaining elements in Figure 11 are the same as those in Figure 4, except, of course, that the pulse generator 111 and its chain drive transmission ~L~5~716 assembly 112 are eliminated.
There are commercially available instrumental means based on auto~
correlation ~or recovering a periodic signal from a mixture of a periodic and a random signal ~see, for example, Statistical Theory of Communications, by Y.W.
Lee, John Wiley, New York, N.Y., 1960, pp. 288 - 290). The correllator 152 of Figure 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 i4 the following references: A.E. Hastings and J.E. Meade "A Device for Comput-ing Correlation Functions", Review of Scientific Instruments, Vol. 23, 1952, pp. 347 - 349; and F.E. Brooks, Jr. and H.Wo Smith, "A Computer for Correlation Functions", Review of Sciontific Instruments, Vol. 23, 1952, pp. 121 - 126.
While I have shown 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 from the spirit thereof.
I have disclosed herein, as example!;, sensors for only two downhole parameters, it is, however, to be understood that sensors for various other down-hole 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 ~such as time sharing, multiplex-ing, or the like) to handle the data representing tlle plurality of parameters.
When deviated or inclined wells are drilled, a turbine 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 Figure 1~ is not rotated by the rotary table at the surface. The rotating action to turn the bit 26 is derived from such a mud motor, which usually is located immediately above the bit 26 in the drill string comprising elements, 22, 24, 28, 30, of Figure 1.
When such a mud motor is employed, a large pressure drop occurs across it ' 11S~ 16 ~since the mud motor derives its power from the mud flow). This large pressure drop can be utilized to supply the pressure difference between the inside"of the drill string and the annulus and, in such case, a "jet" type bit need not be employed.
The presence of the pressure drop across the mud motor merely enhances the operation of my invention so long as the negative mud pressure pulse genera-tor is located above the mud motor.
The term "flow restriction means", for purposes herein, applies to either a jet type bit, or a mud motor, or both. The term "high pressure zone"
` 10 applies to the drilling fluid pressure on the upstream side of the "flow restric-tion means" and the term "low pressure zone" applies to the drilling fluid pres-sure on the downstream side of the "flow restriction means".
It is recognized that, in some instances~ a plurality of mud pumps are employed on a single drilling rig and these pumps are not necessarily operated in synchronism.
In an example of three pumps, the periodic pressure curve of Figure 5A
would, in the practical case, not be a simple periodic function as shown by N~t) but would be the sum of three components, each component being periodic and hav-ing l*S own distinct period.
By the employement of three delay systems, as shown in Figure 6, each synchronized with its own pump, each periodic component of the interfering mud ` pulse pressure signal can be separately nullified. Suitable interconnection will :
then produce a signal from which the interfering mud 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 to be in-terpreted in a limiting sense.

Claims (29)

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

1. A method of making measurements in a borehole while drilling by using a fluid circulation system and a fluid pump at the earth's surface for circula-ting the fluid, which pump generates within said system interfering recurrent pressure variations, and using the steps of determining one or more selected parameters at various depths in said borehole and generating downhole in said system information carrying pressure changes indicative of the values of said parameters, said method comprising a first step of producing first signals representing a superposition of said information carrying pressure changes and said interfering recurrent pressure variations and a second step of utili-zing the time intervals representing the recurrence of said interfering vari-ations for deriving from said first signals resultant signals representing substantially said information carrying pressure changes.

2. The method of claim 1 in which said second step comprises producing second signals which represent the behaviour of said superposition at time intervals which are different from the time intervals at which said first signals are produced.

3. The method of claim 1 in which said recurrent variations are periodic variations and the recurrence of said variations is the periodicity of said variations.

4. The method of claim 3 in which said second step comprises producing second signals representing said periodic pressure variations and combining said first signals with said second signals for deriving said resultant signals.

5. The method of claim 3 in which said second step consists in displacing said first signals by an amount representing the period of said variations thereby producing displaced signals, and combining said first and said dis-placed signals for deriving said resultant signals.

6. The method of claim 5 in which displacing signifies delaying and dis-placed signifies delayed.

7. The method of claim 5 in which combining said signals means subtracting one of said signals from the other of said signals.

8. The method of claim 1 in which said step of generating pressure changes includes the step of diverting a portion of the fluid from said circulation system through a valve, and opening the valve to permit fluid flow therethrough and closing the valve to prevent fluid flow therethrough.

9. The method of claim 8 in which said steps of opening and closing the valve includes actuating the valve by relatively short electrical energizations.

10. A signal extracting apparatus for use in making measurements in a well being drilled in the earth using a hollow tubular drill string having a fluid passage therethrough, a recurrently operated pump system, a source of drilling fluid, means operatively connecting said pump system to said source of drilling fluid and to said hollow drill string to form a fluid circulation system whereby drilling fluid is forced by said pump system through said passage and produces recurrent pressure variations in the fluid circulation system, a sensing means in the lower portion of said string for sensing the value of a downhole parameter, a means responsive to said sensing means for producing in said circulation system pressure changes representing the value of said para-meter, the signal extracting apparatus comprising a drilling fluid pressure sensitive transducer near the top of said string for producing first signals representing a superposition of said pressure changes and said recurrent pressure variations and electronic means connected to said transducer and operable in a predetermined relationship to the recurrence of said pressure variations for deriving from the output of said pressure transducer second signals in which the effect of said recurrent pressure variations is selec-tively attenuated.

11. The apparatus of claim 10 in which said recurrently operated pump system is adapted to operate-periodically whereby said recurrent-pressure variations are periodic pressure variations.

12. The apparatus of claim 11 in which said electronic means is adapted to operate in a predetermined relationship to the time interval representing the periodicity of said pump system.

13. The apparatus of claim 11 in which said electronic means comprises a means for producing signals representing the periodicity of said pump system and a means responsive to said periodicity representing signals and to said first signals for producing said second signals.

14. The apparatus of claim 11 in which said electronic means comprises a means for producing signals representing said periodic pressure variations and a means for combining said periodic variations representing signals with said first signals for producing said second signals.

15. The apparatus of claim 11 in which said electronic means comprises a means for displacing said first signals with respect to time by an amount representing a period of said periodic pressure variations to thereby produce displaced signals, and a means for subtracting said first signals from said displaced signals to thereby produce said second signals.

16. The apparatus of claim 11 in which said electronic means comprises means for delaying said first signals with respect to time by an amount re-presenting a period of said periodic pressure variations to thereby produce delayed signals, and a means for subtracting said first signals from said delayed signals to thereby produce said second signals.

17. A method of extracting signals while performing measurements in a drill hole in which a drilling fluid column is employed concurrently with the operations associated with the drilling of said hole wherein the measurements are carried out by sensing a selected parameter at an appropriate depth in said hole, and by transmitting through the drilling fluid column to the top of the drill hole a useful sensory effect indicative of the value of said parameter, said method comprising producing a first function representing a superposition of said useful sensory effect and of an interfering sensory effect which is generated in said channel and is associated with at least one of said operations, producing an autocorrelation function, and combining said autocorrelation function with said first function to obtain an indication of the value of said parameter.

18. The method of claim 17 in which said step of producing an autocorrela-tion function includes the step of producing an autocorrelation of said first function.

19. The method of claim 17 in which said step of producing an autocor-relation function includes the step of producing an autocorrelation of a function representing said interfering sensory effect.

20. The method of claim 17 comprising an additional step of deriving from the autocorrelation of said first function an autocorrelation of a function representing said interfering sensory effect and in which said step of com-bining said autocorrelation function includes combining an autocorrelation of said function representing the interfering sensory effect with said first function to obtain an indication of the value of said parameter.

21, A signal extracting apparatus for use in performing measurements in a drill hole concurrently with at least some of the drilling operations, the drilling operations including a drill string wherein said measurements are carried out by means of a measurement assembly including a sensor means dis-posed near the bottom of said string for generating useful signals represen-tative of the magnitude of downhole parameters and for transmitting said signals from the bottom of said hole to the top of said hole through the drilling fluid column, the signal extracting apparatus comprising a means at the top of said hole for producing first signals representing a superposition of said useful signals and of interfering signals associated with at least one of said drilling operations and a means comprising an autocorrelator responsive to said first signals for deriving an indication of said useful signals.

22. The apparatus of claim 21 in which said autocorrelator is adapted to generate an autocorrelation function of said first signals.

23. The apparatus of claim 21 in which said autocorrelator is adapted to generate an autocorrelation function of said interfering signals.

24. A signal extracting apparatus for use in performing measurements in a drill hole, in which a drilling fluid column is employed concurrently with the operations of drilling said hole, in which the measurements are carried out by sensing selected parameters at various depths in said hole and trans-mitting through the drilling fluid column to the top of the drill hole useful signals representing values of said parameters, the signal extracting apparatus comprising a means at the top of said drill hole for producing first signals representing a superposition of said useful signals and of interfering signals resulting from at least one of said drilling operations, a first means for expressing said first signals in digital format, a second means for expressing said interfering signals in digital format, and a digital and electronic processing means operated in conjunction with said first and said second means for obtaining values of said parameters.

25. The apparatus of claim 24 in which said useful and said interfering signals are expressed by corresponding pressure changes in said drilling fluid column.

26. A method of extracting signals while performing measurements in a drill hole in the earth, in which a drilling fluid column is employed concurrently with the operations of drilling said hole, wherein the measurements are carried out by sensing a selected parameter in said drill hole, by producing useful signals representing the value of said parameter by transmitting up through the drilling fluid column to the top of the drill hole said useful signals thereby obtaining within said channel at the top of the drill hole a superposition of said useful signals and of interfering signals which are associated with at least one of said drilling operations, said method compri-sing producing at the top of said drill hole first data representing said superposition, expressing said first data into digital format, obtaining second data representative of said interfering signals in digital format, and digitally processing the information expressed by said first and second data to determine the value of said parameter.

27. The method of claim 26 in which said useful signals and said inter-fering signals are represented by pressure variations in said drilling fluid column.

28. A signal extracting apparatus for use in performing measurements in a drill hole, in which a drilling fluid column is employed concurrently with the operations of drilling said hole, in which the measurements are carried out by sensing one or more selected parameters at one or more depths in said hole and transmitting through the drilling fluid column to the top of the drill hole useful signals representing values of said parameters, the signal extracting apparatus comprising a means at the top of said drill hole for producing first signals representing a superposition of said useful signals and by interfering signals resulting from at least one of said drilling operations, and electronic processing means for deriving from the signal producing means at the top of the hole values of said parameters.

29. A method of extracting signals while performing measurements in a drill hole in the earth, in which a drilling fluid circulating system is em-ployed concurrently with the operations of drilling said hole, wherein the measurements are carried out by sensing a selected parameter in said drill hole, by producing useful signals representing the value of said parameter by trans-mitting up through the drilling fluid circulation system to the top of the drill hole said useful signals thereby obtaining within said fluid circulation system at the top of the drill hole a superposition of said useful signals and of interfering signals which are associated with at least one of said drilling operations, said method com-prising producing at the top of said drill hole first data representing said superposition, obtaining second data representative of said interfering signals and processing the information expressed by said first and second data to determine the value of said parameter.