Borehole telemetry apparatus

The invention relates to a telemetric device according to claim 1 and to a telemetric method according to claim 30.

Many attempts have already been made to ensure successful recording or Logging systems for or to develop in the execution of drilling as follows from the following US patents: US-PS 20 96 279 - concerning a system, be used according to the electrical conductor within the drill pipe; US-PS 38 25 078 - then a system is proposed using expandable wire grinding within the drill pipe; US-PS 23 54 887 - then a system is proposed according to which an inductive coupling of a coil or coils with a drill pipe near the drill bit is exploited, whereby the induced electrical potential at the earth's surface is measured, US-PS 27 87 759 and US-PS 34 88 629 - then proposed systems, according to which by pulsed restrictions on the Bohrschlickströmung or Drilling fluid flow pressure pulse signals are generated at the surface of the earth; US Pat. Nos. 3,186,222, 3,315,224, 3,408,561, 3,732,728, 3,737,845, 3,949,354 and 4,001,774 may be mentioned as further US patents.

Each of the proposals made by the aforementioned U.S. patents has had certain disadvantages with such sufficient consequence that commercial introduction of the subject proposals has been prevented. Thus, the difficulty and time associated with the large number of terminals and interconnections of the electrical conductors entails a significant disadvantage in systems such as those disclosed in US Pat. No. 2,096,279. Although an induced-electric-stress-utilizing system, as disclosed in US Pat. No. 2,354,887, may be considered as a system operable within a short distance, the signal-to-noise ratio of such a system prevents the system from suffering Use of this system for a practical reason in deep wells.

As the modern jet drilling system became common and large amounts of sludge or Silt occurred and high sludge or Sealing pressures were exerted, it was found that systems, as indicated in US-PS 27 87 759 were unreliable and too fast wear or Deterioration resulted. The introduction of a controlled restriction in the very high-efficiency mudstream has been unsatisfactory due to the demand for a large and powerful apparatus and mode of operation due to the rapid wear and the very high energy requirements.

The area at the bottom of a well is hostile during drilling. The drill bit and borehole opening vibrations may be on the order of 50g. The temperature is sometimes 204 ° C. The lower hole pressure may be above about 1054 at (15,000 psi). The drilling fluid flowing through the borehole edges and through the drill bits causes severe wear. With the drill bit assembly currently being used with improved bits, an uninterrupted drilling time of a particular drill bit on the order of 100 to 300 hours, or a sometimes even longer drilling time, can be achieved before it becomes necessary to replace the drill bit. Accordingly, a near the drill bit arranged, the state of the well formation and detecting a signal transmitting unit must be able to without care or Operation can be operated for long periods without an adjustment is required. This unit must be able to be operated with a permanent electrical supply voltage source. In addition, the signal transmission arrangement must be able to transmit a continuously exploitable signal or signals to the surface of the earth after each additional connection piece of the drill pipe is appropriately added to the drill string as the drilled hole reaches an increasing depth.

In general, systems with a pulsed stress of the silt for telemetric purposes are considered highly practical, since the drilling operation is the least disturbed or is interrupted. However, the reliability that has been achieved with such systems is currently unsatisfactory. The methods used so far, as have been mentioned in the above-mentioned US Pat. Nos. 2,787,759 and 3,488,629, use the introduction of a controlled or regulated restriction within the mud flow circuit. However, if the silt flow exceeds 600 gpm (corresponding to 2271 l / min) and the pump pressures exceed about 210 at (corresponding to 3000 psi), then control of this significant energy is accomplished by altering a restriction to generate However, telemetric signals complicated and requires a powerful deep-hole machinery.

US 37 42 443 and US 37 16 830 each specify a device or a method by means of which the signal-to-noise ratio of a signal as a measure of a drilling parameter is improved. From US 35 55 504 a filter for suppressing pressure wave noise of a Bohrparametersignals is known. The filter was taken into account in the drafting of claims 1 and 30 in the preamble.

The object of the present invention is to provide an effective telemetric apparatus or method for utilizing wells for telemetric purposes to transmit signals indicative of one or more downhole parameters to the surface of the earth. wherein effects of interfering Schlickimpulssignalen (noise) on or in the surface arrangement to be largely suppressed or eliminated.

This object is achieved with respect to the device by the features of claim 1 and in terms of the method by the features of claim 30.

Advantageous embodiments and developments can be found in the dependent claims.

In particular, preferred embodiments have the following advantages:

The energy required to produce a high pressure pulse on a tool that is close to the drill bit is significantly reduced by the special design of the circulation system.

For the generation of slip vibrations an existing, strong energy source is used.

In the generation of slip vibrations, an advantageous valve mechanism and a valve arrangement is used.

The actuation of the valve mechanism uses a suitable, independent, down hole electrical power supply source.

Further advantages and possible applications of the present invention will become apparent from the following description of embodiments of the invention in conjunction with the figures.

Fig. 1 shows schematically a conventional rotary drilling rig illustrating the use of an assembly according to the present invention.

Fig. 2 shows schematically the construction of a mud vacuum generator with a valve in the open position.

Fig. 2B schematically illustrates the silt-vacuum generator shown in Fig. 2A when the valve is in the closed position.

Fig. 3A shows schematically a physical embodiment of the mud vacuum generator of Figs. 2A and 2B along with instrument and probe areas within a drill string near the drill bit.

Figure 3B illustrates the mud vacuum generator shown in Figures 2A and 2B in proportional dimensions from a processing arrangement used in the actual manufacture of the assembly.

Fig. 3C is a diagram illustrating a radioactivity probe and its associated instrumentation.

Fig. 3D schematically shows a temperature sensor and the associated instrumentation.

Fig. 3E schematically shows a typical instrumentation for a control actuator of a valve of a mud vacuum generator.

Fig. 3F shows schematically the structure of a usable self-contained wellbore supply voltage source.

Fig. 3G shows schematically the construction of another type of usable, self-contained wellbore supply voltage source.

Fig. 4 shows schematically the structure of a typical above-ground installation according to a preferred embodiment of the invention, wherein the borehole parameter is determined by radioactivity.

Fig. 5 is a signal and pulse diagram in idealized form illustrating the waveform of certain signals and the timing relationships to aid in explaining a signal acquisition portion of the arrangement shown in Fig. 4;

Fig. 6 is a block diagram showing further details of a component of a signal extraction circuit shown in Fig. 4;

Fig. 7 illustrates in more detail a component of the signal acquisition circuit shown in Fig. 4.

Fig. 8 shows in a block diagram another embodiment of the aboveground plant.

Fig. 9 shows in a block diagram a still further arrangement of the aboveground plant.

Fig. 10 shows in a block diagram an alternative usable timing pulse generator.

11 shows in a block diagram a still further embodiment of an aboveground plant.

It is believed that prior to beginning the description of preferred embodiments of the invention, it should be understood that certain basic factors are explained.

In a borehole with a length or Depth of about 3000 m (corresponding to 10,000 feet) and a diameter of about 114 mm (corresponding to 4, 1/2 inches) is the mud or Mud volume within the pipe of the order of 18 925 l (equivalent to 5000 gallons). Assuming that the modulus of elasticity of the mass at compressed drilling mud is 400,000, the discharge of about 1.9 liters (corresponding to 0.5 gallons) of a liquid causes a pressure drop of about 2.8 at (corresponding to 40 psi) ( if it is assumed that the specified volume of 5000 gallons, corresponding to 18 925 l, is contained in a simple container). It can therefore be assumed that the discharge of silt near the bottom of such a drill pipe occurs at a rate of about 0.47 l / s (equivalent to 0.125 gallons / s) and a signal corresponding to 0.7 at / s (corresponding to 10 psi) / s) on the surface. The rate of change of pressure is referred to as index, in which case the index is equal to 10.

Three important experiments were carried out: 1. Measurements were taken in a test hole at a depth of about 540 m (equivalent to 1800 feet) and at mean differential pressures of about 70 at (corresponding to 1000 psi) over a valve at the bottom. Second Measurements were taken in an oil field well at a depth of approximately 2400 m (corresponding to 8000 feet) at low differential pressures of about 28 at (corresponding to 400 psi). Third Measurements were taken in a second oilfield well at a depth of about 1500 m (5000 feet) and high differential pressures (112 at (equivalent to 1600 psi)).

All three series of experiments have shown that the index of the pressure pulse recorded on the surface was much higher than calculated in the case that the valve was suddenly opened. The reasons are a) that highly compressed Bohrschlick can have a modulus of elasticity, which is slightly higher than 400,000 pounds per square inch (psi), corresponding to about 28,000 kg / cm², b) that a certain wave guiding action is present through the drill pipe, whereby the signal is caused spread much more favorably than would be the case in a large container of the same volume, and c) that the sudden opening of a valve at the bottom side of the bore causes a higher index than in the case of the large container, because of the elasticity of the overlying sludge or Schlick column.

In a typical borehole with a depth of about 4500 m (corresponding to 15,000 feet), the lower end of which is closed, a mark would appear at the top of the mud or Schlick column is placed, some 30 m (corresponding to some 110 feet) fall when a Schlickpumpendruck of about 210 at (equivalent to 3000 psi) is applied. This pressure is a relatively typical mud pump pressure in drill pipes. One can therefore regard the Schlick column as a column which is continually compressed by a few 30 m (corresponding to 100 feet) and which acts as a long spring in which a large amount of potential energy is stored. When a valve on the bottom of the drill pipe suddenly opens, this potential energy is released, resulting in the occurrence of a strong negative mud pressure pulse. Such a silt pressure pulse is much larger than would be the case if the silt would be incompressible.

In an experiment carried out within a borehole at a depth of about 1500 m (corresponding to 5000 feet), a small passage (with an area of ​​ca. 0.36 cm² (corresponding to 0.056 square inches) between the inside of the bore rim and the annulus according to a controlled sequence opened and closed. The pressure across the valve was about 112 at (corresponding to 1600 psi), and the discharge was calculated to be about 0.95 l / s (equivalent to 0.25 gallons / second). The volume of silt within the drill pipe was about 9463 liters (equivalent to 2500 gallons) and the silt was assumed to have a modulus of elasticity of 400,000. The pressure drop was calculated to be about 2.8 at / sec (corresponding to 40 psi / sec). (Here, too, it was assumed that the sludge or Schlick's column was a single container). In the tests, the pressure drop at the surface was measured at more than 7 at / sec (corresponding to 100 psi / sec) or even much higher than with the simple tank or Container calculation was expected. From this, the following conclusion was drawn: the presence of high pressures on the drill bit (values ​​of 70 at or even higher values ​​- corresponding to 1000 psi or correspondingly higher values) results in that high narrow signals can be formed on the surface by a very small bypass valve at the bottom near the drill bit is opened and closed. Valves with an opening of about 0.32 cm² (equivalent to 0.05 square inches) can produce strong signals from a depth of about 1500 meters (equivalent to 5000 feet). The decrease in signal height at depths between approx. 750 m (corresponding to 2500 feet) and 1500 m (corresponding to 5000 feet) was found to be very low. As a result, it is indicated that the signal attenuation is low.

The system according to the present invention has a number of significant advantages: the fast discharge at a rate of about 0.47 l / sec (corresponding to 0.125 gallons / sec) results in the generation of a "sharp" or "narrow" pulse, respectively; d. H. a pulse containing a high pressure change rate, d. H. has a high index (of for example 40). In addition, by the rapid opening of the bypass valve also reduces the wear for the following reasons or minimized. Clearly, when the by-pass valve is closed, there is no wear on the valve seat. When the valve is open (and the valve area is large compared to a subsequent restriction or following restrictions), then the valve will be exposed to the fluid occurring at low speed, and accordingly the wear will occur substantially in the following constriction or constrictions, which may be expandable and made of a totally non-erodible material, such as drilling carbide, can exist. Wear occurs in the by-pass valve only when it is involved in the process of opening or closing, i. H. then when the valve in question "overturns" and when the speed through the valve seat is then very high. Valve operation should therefore be handled as quickly as possible for opening and closing. There is no limit to the desired speed. The rate of discharge through the valve should also be high, but there is an upper limit above which a faster discharge or Removal does not bring benefits. The reason for this lies in the limit for a high-frequency transmission through the silt. Frequencies above about 100 Hz are heavily attenuated and are of little value in forming a fast surface impulse. In order to determine the maximum rate of discharge, it was necessary to perform experiments under full conditions, using real oil wells and large lengths of conventional wells. The experimental arrangements included a special large valve followed by an adjustable port.

Changing the size of the port can determine the flow rate in liters per second. It has been determined that flows in excess of about 1.14 liters per second (corresponding to 0.3 gallons per second) cause a small increase in the signal. The signals were then compared at a depth of about 1504 meters (corresponding to 5012 feet) using three different port sizes that were tested. These sizes correspond to a diameter of about 13 mm (corresponding to 0.509 inches), a diameter of about 11 mm (corresponding to 0.427 inches) and a diameter of about 6.8 mm (corresponding to 0.268 inches). It was found that at the diameter of 6.8 mm at the surface, a signal was generated which was nearly as strong as a signal generated at an opening diameter of about 13 mm.

Now, see FIG. 1 in which a typical drilling rig 10 is shown schematically, the a silt or Mud circulating pump 12, which is connected to a discharge pipe 14, a standpipe 16, a flexible high-pressure rotary hose 18, a pivot 20 and a drill string 22 which consists of the usual drill pipe and boring sleeves or Collars and a drill bit 26 of the jet type consists. A short distance above the drill bit 26 is within the drill sleeve 24 a negative mud pressure generating pulse generator 28, and further at the relevant point a sensing and instrument unit 30 is provided.

The negative mud pressure generating pulse generator 28 has a specific structure. It generates a series of programmed pulses, each of which involves a brief reduction in mud pressure. In one embodiment, this is accomplished by means including a valve which momentarily opens a passageway between the inside and outside of the drill sleeve 24. This means that the valve in question controls a passage between the inside of the drill sleeve 24 and the annular space 29 formed by the outside of the drill sleeve and the borehole.

An aboveground system, indicated generally at 32, is connected to a pressure transducer 100, which in turn is connected to the standpipe 16. Alternatively, the transducer 100 could, if necessary, be mounted in the fixed part of the pivot 20.

In Fig. 2A and 2B, the negative mud pressure-originating pulse generator 28 is shown schematically to facilitate the explanation of its function and operation. The negative mud pressure pulse generator consists of a valve inlet chamber 42, a valve outlet chamber 44, and a compensation chamber 72. The valve inlet chamber 42 is hydraulically connected to the inside of the drill sleeve 24 via an inlet passage 38. The valve inlet chamber 42 is also hydraulically connected via a passage 48 to the valve outlet chamber 44. The hydraulic disturbance through the passage 48 is controlled by the cooperation of a valve 36 with its seat 37. The Ventilauslaßkammer 44 is hydraulically connected via an outlet passage 51 with the annular space 29. In the exhaust passage 51, first and second compensation holes 52, 53 are inserted. The chamber 40 between the openings 52 and 53 is hydraulically connected via a pipe 74 to the compensation chamber 72. The inlet chamber 42 is connected via a cylinder 49 with the compensating chamber 72, which is also to be considered as an equalizing chamber. The respective cylinder 49 has a compensating piston 50, which is connected via a shaft 46 to the valve 36. The valve 36 is also by means of a shaft 47 (see FIG. 3A and 3B) is connected to an actuator 54.

The function and operation of the negative mud pressure inducing pulse generator 28 will now be explained. In Fig. 2B it is shown that the valve 36 of the negative mud pressure inducing pulse generator 28 is in the "closed" state. In this case, this figure illustrates by the dashed part the presence of a "high" pressure, and the white part illustrates a "low" pressure. (The pressure levels, such as "high", "low" and "medium" are relative pressures, i. that is, it is the difference between the pressure at a given location and the annulus pressure, which is considered zero here; the actual or actual pressure would then be equal to these pressure levels plus the pitch pressure which may be 700 at (corresponding to 10,000 psi) or even higher.

The effective area of ​​the valve 36 is chosen to be slightly larger than the effective area of ​​the piston 50 on the shaft side. Accordingly, when the valve 36 is closed or nearly closed, the force acting on the stem 46 extends in the direction indicated by the arrow in Fig. 2B; this force can be equal to about 1000 (aa '), where a is the effective area of ​​the valve 36 and a'. mean the effective area of ​​the balance piston 50 on the shaft side.

In Fig. 2A, the valve 36 is shown in the open state, i. H. in the state allowing mud flow from the valve inlet chamber 42 to flow toward the valve outlet chamber 44 and through the outlet passage 51 toward the annulus 29. The first and second equalization ports 52 and 53 each cause a certain constriction with respect to the mud flow, thereby causing each a pressure drop. Accordingly, the pressure within the chamber 72 can be set to have any value between the maximum pressure within the chamber 44 and the minimum value from the outlet side of the outlet passage 51; this pressure corresponds to the pressure within the annular space 29.

As stated above, in Fig. 2A as in Fig. 2B, the dashed portion indicates the high pressure area, and the white portion at the outlet of the outlet passage 51 illustrates the low pressure area.

While the valve is in the open flow state, the mud experiences two flow limitations: the orifice 52 and the orifice 53. Accordingly, the pressure in the chamber 40 is between the high pressure, as illustrated by the dashed area, and the low pressure at the exit of the exhaust passage 51. This mean pressure is indicated by the dotted area in FIG. 2A illustrates. The respective mean pressure has its origin in the chamber 40 between the openings 52 and 53; it is passed by the pipe 74 to the compensation chamber 72. Accordingly, the pressure in this balance chamber 72 can be adjusted to any reasonable value between the high pressure in the valve outlet chamber 44 and the low pressure on the outlet side of the outlet passage 51. The proportioning of the sizes of the openings 52 and 53 accordingly controls the pressure in the compensation chamber 72 and accordingly the force exerted on the balance piston 50. If the opening 53 were the same size as the opening 52, then the pressure in the chamber 40 (and in the equalizing chamber 72) would be approximately midway between the pressure of the valve outlet chamber 44 and the pressure in the annulus 29. Since the size of the opening 53 is larger than that of the opening 52, the pressure in the balance chamber 72 will decrease relatively, and in consideration that the size of the opening 53 is made smaller than that of the opening 52, the pressure in the balance chamber 72 relatively increased. For example, if the opening 53 is made small compared to the opening 52, then the pressure in the balance chamber 72 will be high, and accordingly, the force applied to the piston head of the piston 50 will be high and try to close the valve 36. In contrast, when the opening 53 is large compared to the opening 52, the pressure in the chamber 72 will be low. Accordingly, this pressure will tend to allow the valve 36 to remain in the open state. It thus appears that the force exerted on the piston head of the piston 50 force can be set between wide limits. In this way, therefore, a device for adjusting the action of the valve 36 is available.

It is important to note that the force exerted by the valve 36 of FIG. 28 tried to close, and the force which the valve 36 shown in FIG. 2A tries to open, determined by first and second, independent parameters. This means that the force that tries to close the valve, is derived from the effective area differences of the valve 36 and the piston rod side of the balance piston 50. In contrast, the force which attempts to open the valve is derived from the relative sizes of the openings 52 and 53. By properly setting these parameters, the valve 36 can be adjusted to open or close by the application of a weak external mechanical force.

It is also important to note that the valve 36 has a "bistable" action, meaning that the valve switches from the open state to the closed state or vice versa in accordance with a bistable device. In other words, the first parameter of the independent parameter concerned is chosen such that when the valve is within the range between the nearly closed state and the fully closed state, a predominant force of a certain magnitude is exerted in the valve closing direction and is maintained. The second parameter of the independent parameters is chosen so that when the valve is within the range between the nearly open state and the fully open state, an effective force of a certain magnitude is exerted and maintained in the valve opening direction.

Thus, it will be appreciated that the negative mud pressure generating pulse generator 28 of the invention utilizes existing energy derived from the mud pressure in such a manner as to greatly reduce the amount of external energy required to produce the same Actuate valve 36 and also the valve 36 to give a bistable action or switching action.

Further explanation of the negative mud pressure generating pulse generator 28 will be described with reference to FIG. 3A and 3B, which will now be discussed. In Fig. FIG. 3A schematically illustrates a physical embodiment of the negative mud pressure generating pulse generator 28 with its associated downhole device as shown in the drilling rig of FIG. 1 should be appropriate. The reference numerals shown in FIG. 1, 2A and 2B have been used, corresponding parts in FIG. 3A. According to FIG. 3A, a subassembly 58 typically has an outer diameter of about 172 mm (corresponding to 6 3/4 inches) and a length of about 90 cm (corresponding to 3 feet). This sub-device 58 carries 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 generating pulse generator 28; it carries at its lower end part the instrumentation areas 62, 66 as well as a sensor area 64. The mud passes from the inside of the drill sleeve 24 around the housing 56 in the direction of the arrows. A filter 60 prevents sludge solids from entering the casing. The valve 36 is shown operated by an actuator 54. When the valve 36 is open, as shown in FIG. 2A, some sludge may enter the annulus 29 in a bypass flow. The curved arrows illustrate the direction of this by-pass mud. The pressure that presses the mud into the annulus 29 is the pressure on or over the rays of the chisel 26. When the valve 36 is closed, the by-pass to the annulus 29 is closed.

The freely movable piston 76 separates the chamber 72 from an oil-filled chamber 78. The actuator 54 is mounted within an oil-filled chamber 80. A balance passage 82 connects the chamber 78 to the chamber 80. In cooperation with the freely movable piston 76 and the passage 74 thus the chambers 72, 78 and 80 are maintained at substantially the same pressure as the chamber 40th The passage 82 is shown in FIG. 3A partially illustrated by dashed lines and in Fig. 3B is not shown at all, since it lies in a different plane than the illustrated sectional plane.

Designated at 68 is a standard drill sleeve and at 69 is designated a container sub-container. The area 66 has a diameter of approx. 60 mm (corresponding to 2 3/8 inches); it sits in a 4.5 foot (equivalent to 15 feet) standard sleeve with an outside diameter of about 172 mm (corresponding to 6 3/4 inches) and an inside diameter of about 83 mm (corresponding to 3 1/4 inches). The unit 30 is provided with special centering arms 70 which are fixed in the container sub-container 69. The centering arms 70 are designed to center the unit 30 while permitting free passage of the slurry.

In Fig. 3B, corresponding reference numerals are used as in FIG. 2A, 2B and 3A. In this case, in Fig. 3B illustrates the negative mud pressure generating pulse generator 28 in sufficient proportion and in such detail that one of ordinary skill in the art illustrates the actual construction of the particular pulse generator. It should be noted that in FIG. 3B, the actuator 54 is shown as including two electric lifting magnets arranged in opposing relationship. The winding 55 of the upper lifting magnet is arranged so that an upward force is exerted on its armature 57, while the winding 59 of the lower lifting magnet is arranged such that a force in the downward direction on the armature 61 of the relevant lifting magnet is exercised. The anchors 57 and 61 are loosely coupled to a mechanical hinge 63 which is fixed to the shaft 47 so as to achieve a "hammering" effect. This means that when energized, the winding of a solenoid, the armature of the respective solenoid moves a short distance before it receives the load of the shaft 47 with a hammer-like impact. This "hammering" effect has a beneficial effect on the opening and closing operations of the valve 36. Suitable solenoids for this application are those of size 6EC with medium lift and conical surface as manufactured by Ledex, Inc., Dayton, Ohio.

Coming back to explaining the negative mud pressure generating pulse generator 28, various other factors and features are now considered.

The openings 52 and 53 are formed to have smaller opening areas than the passage 48 so that the velocity of the mud flow across the sealing surfaces of the valve 36 and over its seat 37 is significantly reduced compared to the velocity of the mud flow through the openings 52 and 53. Accordingly, the wear concentrates on the openings 52, 53, which are made of a wear resistant material (such as boron carbide) and which are also easily interchangeable in the "field", as shown in FIG. 3B is illustrated. These small non-erodible openings 52, 53 make the negative mud pressure generating pulse generator 28 completely "fail safe," meaning that whatever happens during operation of the valve 36 (such as sticking in the open position), the amount of mud, which can flow through the openings 52, 53, has no significant adverse effects on drilling. Another advantage resulting from the fact that the apertures 52, 53 are easily interchangeable in the "field" is that the apertures in question can be calculated to be most suitable for changing weights and viscosities of the slurry.

Since the negative mud pressure generating pulse generator 28 is subjected to strong vibrational forces, the structure for stability of the valve 36 must be designed both in the open position and in the closed position. The required stability is achieved by the "hydraulic stop" or "bistable" action of the valve 36, which has been previously described.

The vertical acceleration associated with drilling is significantly greater in the upwardly-directed direction than in the downward-directional direction. When the teeth of the drill bit 26 hit a hard rock, the drill bit and sleeves 24 are pushed up, meaning that upward acceleration occurs. However, when the drill bit is raised and brought out of contact with the rock, there is little force other than acceleration due to gravity, thereby pushing down the drill bit and the drill sleeves. Accordingly, the upward acceleration may be several hundred g, while the downward acceleration is only of the order of 1 g. The valve 36 must therefore be designed so that in the closed state high upward acceleration values ​​try to keep the valve in question closed, which means that the valve seat is even better. The high downward acceleration values ​​(which, however, are assumed to be small) tend to open the valve. This is in the case of FIG. 3A and 3B show construction achieved.

Due to the performance of various tests and experiments, it has been found that a force of about 34 pounds, corresponding to about 15.42 kp, may be required to actuate the valve 36 when the first and second of the two independent parameters, such as as described above, are selected to provide a suitable "hydraulic stop" or "bistable" action to achieve adequate stability for the valve 36. With the addition of good technical safety factors, the required force became 70 to 100 pounds, corresponding to 31.75 to 45.36 kp. Applying a force of this magnitude over the required distance of valve travel for electromagnetically controlled solenoids of adequate size would require an electrical power of about 350 W, i. H. nearly 1/2 hp. With such a high power requirement, it appears at first sight that the energy needed for the number of actuations of the valve 36 required for successful operation is likely to be well beyond the capacity of any available self-contained downhole supply voltage source , However, this apparent energy problem is overcome when it is considered that the negative mud pressure generating pulse generator 28 according to the present invention produces a very fast action for the valve 36. This means that the valve 36 can be designed to open (or close) to the application of the required 350 watts for only about 20 milliseconds. The amount of energy required to open (or close) the valve is thus

There are modern high density batteries of reasonable size that can be accommodated within the space that exists within the sleeve 24 and that can readily deliver 2000 watt hour energy. Therefore, one can provide (even without recharge, as will be explained below) a sufficient battery of sufficient energy to operate the valve 36 about one million times.

Assuming that the valve is actuated once every four seconds, a single charge of the battery will continue to operate the valve for one month. There is a significant requirement for logging during the execution of a well that the wellbore assembly is capable of operating unattended (i.e. H. without battery recharge) over at least the time between "round trips", d. H. during the time that a single drill bit can drill without replacement. The best drill bits only last about 100 to 300 hours, which is why the 30-day value indicated above is more than sufficient.

The practical construction of the negative mud pressure inducing pulse generator 28 is a complex matter. Although careful calculations were made using the modern theory of hydrodynamics, in the last stages many parameters had to be determined by empirical methods. An essential reason for this is that the "viscosity" of the drilling mud or Bohrschlicks is thixotropic and that the dynamic behavior is quite different from the behavior of liquids with a classical or so-called Newtonian viscosity. Drilling mud "weight" (grams per cubic centimeter) and "viscosity" change over a wide range. The fact must be taken into account that the "weight" usually changes over a much smaller range than the "viscosity". The drilling mud usually contains not only colloidal particles in a suspension, but also larger sand bodies and other particles.

A series of experiments was performed to determine the minimum size of the discharge opening (which controls the rate of fluid drainage with which the fluid is delivered into the annulus). In this series of tests, smaller replaceable openings were provided following a large "servo" valve (25.4 mm diameter). At a depth of 2400 m (corresponding to 8000 feet) and 1500 m (corresponding to 5000 feet), the investigations were made by careful measurements that measured the size of the negative mud pressure pulse at the surface, as a function of the size of the discharge - or. Diverting. While this size was successively reduced, the height of the impulse on the surface appeared to be nearly independent of the size of the opening until a surprisingly small opening area of ​​ca. 0.32 cm² (equivalent to 0.05 square inches). At this time, a small decrease in the pulse height was observed. This feature was relatively unexpected; however, it was later understood after carefully considering the elasticity properties of the mud column and the stored potential energy in that column as discussed above. This finding led to the view that a small pulse generator for producing a negative mud pressure could produce useful signals at the surface. Thereafter, calculations were made and it was determined that the "servo" principle is not required for valve actuation. The "servo" valve solution was therefore dropped. Subsequently, the direct acting and very fast acting pulse generator was developed to produce a negative mud pressure; he has proved successful.

In a practical pulse generator 28 for producing a negative mud pressure, the following dimensions may be considered typical: port 52 - 12.7 mm internal diameter (0.50 inch equivalent); Opening 53 - inner diameter approx. 7.8 mm (equivalent to 0.306 inches); Stroke of the valve 36 - approx. 3.2 mm (corresponding to 0.125 inches); Diameter of the piston 50 - approx. 9.7 mm (corresponding to 0.383 inches); Diameter of the valve 36 on its seat - about 10.9 mm (equivalent to 0.430 inches); Angle of the seat 37 relative to the axis of valve movement - 60 °; Diameter of the opening on the seat 37 or passage 48 - approx. 9.5 mm (equivalent to 0.375 inches); Diameter of valve stem 46, 47 - approx. 4.7 mm (equivalent to 0.187 inches).

FIG. 3F schematically illustrates a battery of a specific type which is well suited for feeding the downhole device according to the invention.

Deep oil wells have variously high bottom hole temperatures between 149 ° C and 204 ° C (corresponding to 300-400 ° F) on. Many electric batteries can not be operated at this temperature. But there is one exception: the modern batteries with molten salt. These batteries work well at high temperatures of 400 ° C to 500 ° C or even higher temperatures; However, they do not work properly at lower temperatures, because at such temperatures, the electrolyte solidifies and stops conducting electrically. A lithium-aluminum-iron-sulfide-molten salt battery is manufactured by Eagle Pitcher Co., Joplin, Missouri. Other manufacturers also produce high energy molten salt batteries specifically intended for use in electric vehicles. These batteries are very suitable for operation at high temperature.

As shown in FIG. As shown in Fig. 3F, an arrangement is provided which effectively starts the battery before it is immersed in the hot area of ​​the oil well and keeps the battery charged in use. In Fig. 3F is labeled 155 the associated battery. With 156 heating elements are referred to, which are arranged or are designed that a small amount of heat is delivered to the battery 155. Designated 157 is a cladding having thermal insulation, for example, a material known as "superinsulating material" such as that available from Union Carbide Co., New York, or "Multifoil" from The Thermo Electron Co., Waltham, Mass., Is produced. Initially, an external voltage (from a voltage source, not shown) is delivered to terminal 158 (while the device is at the surface, prior to insertion into the bore). This voltage activates the heating elements 156 and the battery electrolyte melts. Further, the battery 155 is charged by the voltage applied to the terminal 158 before the device in question is introduced into the oil well. When the battery 155 has a temperature within its normal operating temperature range, the circuit to the heater 156 is opened by the thermostat switch 159. This switch is closed during such periods of time as the delivery of additional heat to the battery 155 is required. If a data recording or Logging occurs during drilling, the vibration of the tool causes the device 160 generates a charging current. The device 160 is described in detail elsewhere (see US-PS 39 70 877). Instead of the device described at the above-mentioned place, a small mud-fed turbine and an electric generator could be used to keep the battery charged since only a continuous charging power of about 1 W is required.

In Fig. 3G is schematically illustrated a battery of still another specific type. This battery can be used to feed the deep hole plant according to the present invention. This battery preferably uses lithium sulfur type cells such as those available from Power Conversion Inc., Mt. Vernon, New York. In addition, LeClanche-type cells or lead-acid cells may also be used for this battery. All such cells, when exposed to high temperatures (which are normally present in deep wells), develop high internal pressures such that the cells tend to explode. According to one aspect of the present invention, an arrangement (in FIG. 3G), which overcomes this problem. According to FIG. 3G, a plurality of individual cells 161 of the aforementioned type are provided in series between a ground terminal 162 and a positive terminal 163. Each cell is preferably provided with a conventional pressure relief cap or pressure relief valve 164. In accordance with the invention, the cells 161 are housed in a reservoir or reservoir 165 capable of withstanding pressures exceeding those pressures that could be developed by the electrolyte of the cells 161. Within the reservoir 165, a liquid 166 is provided which has the same or similar pressure-temperature characteristics as the electrolyte. This means that the liquid 166 will develop a 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 or lead-acid cell cell, the liquid 166 may be water because the container 165 is hermetically sealed and pressure resistant. The liquid 166 (in this example, water) will never boil - no matter how high the temperature is. Rather, in the space above the liquid 166, there is simply a vapor pressure high enough to equalize the vapor pressure generated by the hot liquid 166.

The same principle can be applied when the cells are of the lithium-sulfur type. The liquid 166 should be sulfur dioxide. The sulfur dioxide vapor produced by the cells 161 will always be in pressure balance with the reservoir 165, since the sulfur dioxide fluid in this supplemental reservoir 165 will always produce pressures equal to those pressures generated by the cells 161.

However, sulfur dioxide and water according to the examples given above are often not satisfactory, namely a) considering that sulfur dioxide is highly corrosive, and considering that water is an electrical conductor and can short the batteries. An alternative substance is di-chlorodifluoromethane, commonly referred to as freon, available from E. I. DuPont & Co, Wilmington, Delaware. Many types of freons have been developed with a virtually unlimited number of thermodynamic properties, i. H. with pressure-temperature ratios. Other substances can be readily determined, such as hydrocarbon vapors, propane or butane, or mixtures of vapors and gases. Suffice it to say that the battery cells 161 are enclosed in a container 165 and that a small amount of a substance having similar temperature-pressure relationships as the electrolyte in the battery cells 161 is introduced into this container. In Fig. Figures 3F and 3G illustrate only a small number of cells connected in series. In fact, a large number of cells are normally used. In the manufactured plant according to FIG. 3G, 17 power conversion co-lithium sulfur cells have been used.

Another significant feature of the present invention is that the amount of time that the valve 36 is kept "open" has no relation to the required energy requirement. The only energy required is the energy to be provided to actuate the valve 36 to the "open" position. The importance of this feature should be fully apparent from the following discussion.

It has been determined experimentally that the valve must be kept open for a period of about 1/2 to 1 second, to provide a strong signal from a depth of 3,000 to 6,000 m (corresponding to 10,000 to 20,000 feet) and that any electromechanical device (solenoid or other device) not only requires large amounts of energy during this period, but also overheats and burns under drilling conditions, probably due to the self-generated heat.

As stated above, two typical probes are provided as examples of the types that can be used in the operation of the present invention. In Fig. Figure 3C illustrates a natural gamma-ray sensor with its associated circuitry, which in this example is of the analog type. In Fig. 3D is illustrated a temperature sensor, which is for example of the digital type. Each of these sensors may be connected to the input terminal of the instrument panel shown in FIG. 3E is illustrated and will be discussed in more detail below.

According to FIG. 3C, a Geiger counter 168 is provided, which is provided with a conventional high voltage source + HV. Geiger counter 168 generates pulses; it is connected via a capacitor 169 to an amplifier 171 and generates at its output pulses corresponding to those pulses of the vulture counter 168. A reduction circuit 172, which makes a reduction by 1024, produces one output pulse for every 1024 Geiger counter pulses. The output of this divider circuit 172 is illustrated by pulses following one another in a time period of t1. The higher the gamma-ray intensity, the higher will be the frequency of the pulses at the output of the divider circuit 172, and the shorter will be the time t1.

In Fig. 3D is the case of the temperature sensor illustrated. The temperature is determined by means of a thermistor 173, i. H. by means of a semiconductor whose resistance varies with temperature (the semiconductor in question being provided with a suitable supply voltage source - not shown). It is assumed that the output signal of the thermistor 173 is a DC voltage proportional to the temperature. The amplifier 174 amplifies this DC voltage and effectively squeezes it to an analog-to-digital converter 175, which in turn generates a series of binary bytes in succession. Each byte is indicative of a number that is proportional to the detected temperature. The output signals of power amplifiers 185 and 186 are used to control the feeding of the windings of lifting magnets, which are to some extent coupled together with their rear sides (as will be described below), in order to actuate the valve 36. When the winding 55 is energized, the lifting magnet armature 57 (see FIG. 3B), thereby exerting an upward pressure on the shaft 47 under actuation of the valve 36, which thereby enters the "open" position. When the winding 59 is energized, the lifting magnet armature 61 is moved downwardly whereby the shaft 47 makes a downward movement and actuates the valve 36 to enter the "closed" position.

In the probes used in accordance with the present invention, the size of the downhole parameter is represented by electrical impulses. The sequence of pulses represents a code (a binary code or other code), and this code sequence characterizes the size of the parameter. In Fig. FIG. 3E illustrates how each single pulse of this code is processed to actuate the valve 36. According to FIG. 3E is designated 177 such a pulse that occurs during a short period of time, which is only a few microseconds. This pulse 177 is impressed on the circuitry contained in the block 178. This circuit block 178 includes a monostable flip-flop and suitable inverse rectifier circuits as known in the electronics art. The respective circuit 178 outputs on the occurrence of a single input pulse from two output signals, which are separated in time by t1. The first pulse normally coincides in time with the input pulse, and the second pulse occurs later by a period of t1, as illustrated by pulses 179 and 180. These electrical pulses 179, 180 are now in the blocks 181 and 182 imprinted circuits or fed. These two circuits are identical; these are so-called pulse extension circuits, which are known per se in the field of electronics. Each input pulse is extended so that output pulses 183 and 184 be delivered. These pulses will be Darlington power amplifiers 185 and 186 supplied (as they are from the company Lambda Mfg. Co, Melville, New York, and sold under the type designation PMD16K100).

In the practice of the electronic logic and power circuitry of FIG. 3E, which has been used in the preferred embodiment, the following values ​​have been chosen as constants: t1 = 500 ms and t2 = 20 ms. In operation, when a single pulse 177 is delivered via line 167, the Darlington amplifier 185 is turned on for a period of 20 ms and then turned off. Then, 500 ms later, the Darlington amplifier 186 is turned on for a period of 20 ms and then turned off. This opens the valve 36 for a period of 500 ms without requiring any energy during this period. Energy is needed only during the short 20 ms period required to actuate the valve 36 to the open or closed position. Incidentally, the numerical values ​​given above are for illustrative purposes only. Suffice it to say that by making the action of the valve 36 (a) very fast and (b) bistable, very high mud pressures and mud volumes can be carried by the valve actuation without the requirement of using large amounts of energy is. In addition, as described above, relatively low power batteries can operate the valve about one million times.

In a practical embodiment of this device, the weight of the entire valve mechanism 36 according to FIG. 2A or 3A including the lifting magnet armature 54, the shaft 46 and the piston 50 about 255 g (corresponding to 9 ounces). The valve 36 has been designed so that it is at a differential pressure of about 112 at 1600 psi and is proportioned to operate at optimum performance. This implies that the force required to open and close the valve 36 must exceed the force due to the vertical acceleration of the entire apparatus near the bit 26.

Assuming a vibration value of 60 g and the weight of approx. 255 g (corresponding to 9 ounces) is the maximum vertically directed force on the valve 36 due to the vibration of the tool 56 about 31 pounds or 15.42 kg (equivalent to 34 pounds). To be sure that the valve 36 is not inadvertently closed, the force holding the valve closed as shown in FIG. 2B and the valve holding open the valve shown in FIG. 2A exceed about 31 pounds (equivalent to 34 pounds). By suitable choice of the first and the second of the independent parameters, as described above, a compensation state is achieved. By balancing is meant here that the force required to open the valve 36 is equal to the force needed to close the valve.

The aboveground equipment used in accordance with the present invention, in terms of the methods and arrangements for eliminating spurious effects that may be present in the output of the pressure transducer 100, may take various forms, as will now be described.

FIG. 4 shows a typical above-ground installation according to a preferred embodiment of the invention. In this plant, the downhole parameter determined is the radioactivity of formations traversed by the well as drilling progresses. The corresponding part of the data logger located below the earth's surface has been previously described and illustrated in Figs. 2A, 2B and 3A to 3G.

According to FIG. 4 is by a connected to the standpipe 16 pressure transducer 100, the change or Variation of the mud pressure within the standpipe converted into a changing electrical voltage. This voltage is indicative of a mixture of two component signals: the usable information carrying signal and the interfering signal. The information carrying signal is a series of short, negative mud pressure pulses generated by the sudden opening and closing of the valve 36. The noise signal is in the form of relatively slow and periodic pressure changes generated by the strokes of the mud pump 12. These mud pump signals show the tendency to mask the information or hide, which is desired to achieve by exploiting the short negative mud pressure pulses.

One of the objects of the invention is to recover from the "contaminated signal generated by the transducer a" clean "signal which provides the desired information. This is achieved by means of a signal acquisition circuit 102, which is connected to the output terminal 101 of the pressure transducer 100. The signal acquisition circuit eliminates spurs and generates at its output terminal 108 a train of pulses from which the information concerning the borehole parameter can be readily obtained.

The signal extraction circuit 102 is controlled in a certain manner by a series of timing pulses obtained from a pulse generator 111 and output to control terminals 113, 114. The pulse generator 111 is mechanically driven by the mud pump 12 to produce a suitable number of timing pulses per pump revolution. For this purpose, a chain driven drive assembly 112 is provided.

The "clean" information-carrying signal received by the signal acquisition circuit 102 is in the form of pulses derived from the actuation of the valve 36 of the generator 28. The relevant information is given by the time intervals separating the pulses. A time-amplitude converter 115 connected to the output terminal 108 of the signal extraction circuit converts these pulses derived from the actuation of the valve 36 of the generator 28 into signals the size of which is indicative of the intervals therebetween. The converter 115 is a per se known electronic device; it may be constructed of components such as those manufactured by Burr-Brown, Tuscon, Arizona, USA. For further detailed description of time-to-amplitude converters, reference may be made to the document "Nuclear Instruments and Methods" 121 (1974), pages 547 to 566, North Holland Publishing Co., and more particularly to the article "Logic Design of High Precision Time to Pulse Height Converters "by M. Bertolaccini and S. Cova.

The signals picked up by the converter 115 are in turn supplied to the input terminal 109 of a reciprocating circuit 118. The reciprocaling circuit 118 (which may be manufactured, for example, by Analog Devices, Inc., Norwood, Mass.) Provides output voltages that are reciprocal values ​​of the input voltages. Accordingly, when an input voltage of the size M is supplied to the reciprocating circuit 118, an output voltage having a magnitude of 1 / M is obtained. These 1 / M size signals are in turn recorded on the registration strip of a recorder 120. The recording registration strip of the recording apparatus 120 is moved in correlation with the changing depth of the sensor unit 30 by a depth sensing device 121. The depth sensing device may be, for example, a modified or conformal arrangement as sold by The Geolograph Medeavis Company of Oklahoma City, Oklahoma, USA.

In order to more clearly illustrate the operational characteristics of the signal acquisition circuit 102, the behavior of the various signals involved in the operation of the circuit concerned is analyzed. These signals are shown schematically in simplified and idealized form as time-varying signals in FIG. 5 illustrated. Assume that: F (t) = S (t) + N (t) where S (t) is the useful information bearing signal formed by the mud pressure negative pulses P1, P2 and P3 which are aligned along the time axis t. (See Fig. 5 (Axis A)). The times of occurrence of these pulses, which correspond to the times of actuation of the valve 36 of the generator 28, with t1, t2 or t3. The time intervals separating these pulses are λ1 = t2-t1, λ2 = t3-t2 and λ3 = t4-t3. These periods are indicative of the intensity of the measured radiation. When these time intervals are large, the intensity is relatively weak and, conversely, the intensity is relatively strong when the respective time spans are short. The noise generated by the mud pump 12 is shown in FIG. 5 (Axis A) is illustrated by a periodic but not necessarily sinusoidal function N (t) having a period of T. The length of the period is related to the speed of the pump.

To facilitate the explanation, the relative scales in FIG. 5 distorted chosen. In practice, there may be 50 to 80 oscillations of N (t) between the time of occurrence of P1 and P2. Accordingly, λ1 and λ2 may change from 50T to 80T. In Fig. 5 (Axis A), however, only a few oscillations of N (t) between P1 and P2 are illustrated. Moreover, in practice, the negative mud pressure pulses P1, P2, P3 do not have a pure rectangular shape, as shown in FIG. 5 (Axis A) is illustrated. Moreover, the actual pulses are much narrower than any of those shown in FIG. 5 (Axis A) are illustrated. From the actual experience, the height of the pulse P1, P2 or P3 is about 0.1 to 0.01 of the maximum amplitude of the vibration N (t).

The axes AE are arranged one above the other in FIG. 5 such that the signals can be compared in their temporal relationships with one another. Using these representations, the instrumental steps involved in the operation of the signal extraction circuit 102 can now be selected. These are the following steps:

Step 1: The input signal F (t) is offset by a quantity T so that the following relation is obtained: (F (tT) = S (tT) + N (tT) (2) where S (tT) and N (tT The two signals are illustrated in Fig. 5 (axis B) The signal S (tT) is represented by the pulses P1^(A), P2^(A) and P3^(A) shown. These pulses are obtained by the corresponding pulses P1, P2 and P3 are offset by an amount of T according to figure (axis A). The signal N (tT) according to FIG. 5 (axis B) is represented as a signal which is in exact synchronism with N (t) according to FIG. 5 (axis A). This is due to the periodicity of the signal. Thus, N (tT) ≡ N (t) (3)

Step 2: The offset input function F (tT) is subtracted from the original input function F (t), giving the following relationship: M (t) = F (t) -F (tT) (4)

Taking into account the equations (1), (2) and (3), M (t) = S (t) -S (tT) (5)

Accordingly, the noise signal has been eliminated; it does not occur in M ​​(t). This can be seen from a consideration of Fig. 5 (axes A and B).

As shown in Fig. 5 (axis C), M (t) consists of pulses which occur in pairs. Each pulse pair contains a negative pulse and a positive pulse. These two pulses are separated from each other by a time interval of T. Accordingly, a pulse pair is shown consisting of a pulse P1^(B) and a pulse P1^(≙); this pulse pair is followed by a pulse pair consisting of a pulse P2^(B) and a pulse P2^(≙), This is followed by another pair of pulses, consisting of a pulse P3^(C) and a pulse P3^(≙), etc.

Step 3: The quantity M (t) is offset by a period of T such that M (tT) is obtained. Accordingly, the entire sequence of the pulses according to FIG. 5 (axis C) is shifted along the time axis by T so that it occurs in the position shown in FIG. 5 (axis D). The pulse arrangement of the pulses can be seen from FIG. 5 (axis D). Each pulse pair, like the pulses P1^(≙) and P1^(≙) comprehensive pulse pair, is with respect to the pulse pair comprising the pulses P1^(B) and P1^(≙) (as illustrated in Figure 5 (axis C)) offset by T. Correspondingly, the pulse pair with the pulses P2^(C) and P2^(≙) with respect to the pulses P2^(B) and P2^(≙) comprehensive pulse pair is offset by T, and so on.

Step 4: The offset pulses according to FIG. 5 (axis D) are compared with the pulses according to FIG. 5 (axis C). It should be noted that some of these pulses according to FIG. 5 (axis D) occur coincident in time with some pulses according to FIG. 5 (axis C). The timing of the coincident occurrence of such pulses are shown in Fig. 5 (axis E) as pulses P1^(D), P2^(D) and P3^(D) recorded. Accordingly, P1 coincides^(D) with P1^(≙) and P1^(C), furthermore, P2 coincides^(D) with P2^(≙) and P2^(C), and P3^(D) coincident with P3^(≙) and P3^(C),

The times at which the pulses P1^(D), P2^(D) and P3^(D) occur are t1 + T, t2 + T and t3 + T, respectively.

The pulses P1^(D), P2^(D) and P3^(D) corresponding to the pulses P 1, P 2 and P 3 illustrated in FIG. 5 (axis A). Accordingly, the pulses shown in Fig. 5 (axis E) also characterize this useful function, which is now S (tT) since it is only offset by T. It will be appreciated that the pulses G of Figure 5 (axis E) provide that information which is attempted to be obtained. The time span between P1^(D) and P2^(D) is λ1, and the time span between P2^(D) and P3^(D) is λ2, etc. The quantities λ1, λ2, etc. are indicative of the radiation measured by the gamma ray detector.

The foregoing steps will now be considered in terms of their relationship to the performance of the signal acquisition circuit 102 and, more particularly, those two component parts designated 105 and 107 in Fig. 4, respectively, which are shown schematically in Figs.

The component 105 receives at its input terminal 101 (which is the same terminal as the terminal of the signal acquisition circuit 102 shown in FIG. 4) the signal F (t) on. As shown in FIG. 6 represented, this signal is supplied via an amplifier 130 to the input terminal 131 of a delay network 132. The delay network causes a delay of the signal F (t) by T; it thus generates at its output terminal 134 the signal F (tT). This signal represents the sum of two component signals S (tT) and N (tT), which are shown in FIG. 5 (Axis B) are shown.

The signal F (tT) is supplied to the one input terminal 134 of a subtractor 135. The other input terminal 136 of the subtractor receives directly the signal F (t) which is supplied from the terminal 101 via a conductor 137. Accordingly, at the output terminal 106 of the subtractor 135, the difference signal M (t) = F (t) -F (tF) is obtained. This is illustrated in Fig. 5 (axis C).

The delay network 132 is provided with a control terminal 113 which receives a signal controlling the delay time T. It is important that the duration of the delay time T be equal to the duration of the period of the mud pressure oscillations generated by the mud pump 12.

The magnitude of the delay time T is controlled by the timing pulses derived from the pulse generator 111, which is also shown in FIG. 4 is shown. These pulses are supplied via the conductor 110 to the control terminal 113. It should be noted that the delay time T is equal to the period of the vibration of the mud pressure, which is generated in successive strokes of the mud pump 12. Accordingly, the frequency of these timing pulses must be controlled by the rotation of the pump.

Assuming that the pump performs N1 strokes per second, T is thus 1 / N1. The pulse generator 111 generates timing pulses having a relatively high frequency of N2, which is a multiple of N1. Accordingly, N2 = KN1, where K is a constant chosen to be 512. If the strokes of the pump were one per second, this would require that the signal generator generate 512 pulses per second. It will be appreciated that the pulse frequency of the mud pump 12 varies with time and, accordingly, N2 changes to insure that the delay time generated by the delay network 132 is always equal to a period of the mud pressure oscillations generated by the mud pump 12.

Delay network 132, controlled as described above, may be a so-called Reticon model SAD-1024 dual analog delay line, as sold by Reticon Corporation, Sunnyvale, California, USA.

The instrumental steps described above are steps 1 and 2 performed by the component 105 of the signal acquisition circuit 102. In this case, the input signal F (t) - which by its components in FIG. 5 (Axis A) is illustrated - transformed into an output signal M (t) which occurs as a series of pulse pairs and is shown in FIG. 5 (Axis C) is illustrated. Now continue with the description of further instrumental steps required to achieve the desired goals. These steps are performed by the component 107 of the signal extraction circuit 102.

Now, see FIG. 7 Referenced. The signal M (t) is now output via the conductor 140 to a delay network 141. This delay network is identical to the one shown in FIG. 6 illustrated delay network 132. It receives at its control terminal 114 the same control signal which has been supplied to the control terminal 113 of the delay network 105. Accordingly, the delay time caused by the delay network 141 is T, and the signal appearing at the output of the delay network 141 is M (tT), as shown in FIG. 5 (Axis D) is illustrated. This output signal is supplied via an amplifier 143 to an input terminal 145 of an AND gate 146. At the same time, the instantaneous signal M (t) is supplied via the conductor 147 and the amplifier 148 to the other input terminal 149 of the AND gate 146. These two input signals M (t) and M (tT), which are supplied to the AND gate 146, are shown in FIG. 5 (Axis A or Axis D) is illustrated. As stated above, some occur in FIG. 5 (Axis C) pulses coincident with pulses as shown in FIG. 5 (Axis D). Those pulses which coincide occur in the output signal of the AND gate 146. These pulses are shown in FIG. 5 (Axis E) as P1^(D), P2^(D) and P3^(D) designated. These coincident pulses are the output pulses of the component 107 and thus the signal extraction circuit 102.

Thus, it should be apparent that with the help of the component 107, the instrumental steps 3 and 4 are executed. In this case, the signal M (t), as shown in FIG. 5 (Axis C) is illustrated, in the in Fig. 5 (Axis E) illustrated signal S (tT) has been transformed. The last-mentioned signal provides the quantities λ1, λ2, λ3, etc. representing the information that was desired to be obtained. It should be remembered that the signal S (tT) is represented by a train of pulses, as shown in FIG. 5 (Axis E) is shown. These pulses are applied to the time-amplitude converter 115, at whose output signals of different sizes, such as λ1, λ2, λ3, etc. to create. These signals characterize the time periods between the occurrence of the pulses. These signals, in turn, are sent to the reciprocating circuit 118 of FIG. 4 supplied and converted by this circuit into other reciprocal signals which the sizes 1 / λ1, 1 / λ2 or Own 1 / λ3. These reciprocal signals are detected by the recorder 120 of FIG. 4 recorded. It will be appreciated that the magnitudes 1 / λ1, 1 / λ2 and 1 / λ3 are indicative of the intensity of formation radioactivity determined by the sensing unit 30 at various depths of the borehole.

In the foregoing, a device device has been described with the aid of which linking steps are performed which lead from the function F (t) to a function S (tT). These steps have been carried out by displaying these functions in an analog (non-digital) form. Alternatively, if desired, the entire process may also be digitized as shown schematically by FIG. 8th is illustrated. According to FIG. 8th the output signal of the pressure transducer 100 is supplied to an analog-to-digital converter 103, whose output signal is supplied to a digital computer 104. The in Fig. 8th indicated operations are performed by the 122, 123, 124, 125 and 126 in the digital computer 104 designated elements. Timing signals are supplied from a pulse generator 111 or 140 to the digital computer 104 to control the delay times in accordance with the pump speed. The operations performed within the scope of FIG. 8th Rows indicated by a dashed line are sequential mathematical operations which can be detected in a flow chart. The output signal of the computer 104 is supplied to a digital-to-analog converter 127, whose output signal is fed to a recording device 120.

In Fig. 9 an arrangement is shown which in some respects corresponds to that shown in FIG. 4 similar arrangement is shown. However, the data to be obtained and recorded are the temperature at the locations of the sensor unit 30 according to FIG. 1. According to FIG. 9 These data, as supplied to the signal acquisition circuit 102, are present in digital form (see FIG. 3D). The signal extraction circuit 102 of FIG. 9 agrees with the in Fig. 4 signal recovery circuit, except that the time-amplitude converter 115 and the reciprocating circuit 118 shown in FIG. 4 are replaced by a digital-to-analog converter 141. The output signals of a suitable pulse generator are supplied to the control terminal 110 of the signal extraction circuit 102.

It is not always convenient to provide a mechanical connection to the mud pump 12, as shown by the chain drive transmission assembly 112 of FIG. 4 is illustrated. Rather, an alternately operating device for generating the pulses required for the signal extraction circuit may be desired. In Fig. 10 such an alternating device is shown. In a typical embodiment, the signal extraction circuit 102 of FIG. 4 supplied at its terminal 110 with pulses that occur at a pulse rate of 512 pulses per full pump stroke. It should be readily understood that this pulse rate must be exactly synchronized with the pump strokes. All in Fig. 5 indicated "times", such as T, t1, t2, etc., are not referred to as so-called "real time points"; Rather, they are directly related to the speed of the mud pump 12, which is why, strictly speaking, the times T, t1, t2, etc. not in seconds or minutes, that is, by time units, but rather by "gallons of mud." When it is said that at the terminal 110 of FIG. 4 512 pulses per mud pump stroke, it is meant that voltage pulses occur at the terminal 110 at a frequency equal to the 512th harmonic of the pump stroke frequency. In Fig. 10 is illustrated how this can be achieved without a mechanical connection to the pump shaft.

In Fig. 10 145 denotes a voltage-controlled oscillator which generates at its output 110 electrical pulses whose frequency is controlled by a DC voltage which is supplied to the input terminal 108 of the oscillator. With the component 150, a binary divider or a reduction circuit is referred to, which reduces the frequency of the pulses which are supplied to its input terminal 116. The reduction circuit generates output pulses at its output terminal 117. These output pulses have a frequency equal to 1/512 of the frequency of the input pulses. Denoted by component 119 is a phase comparator which compares two input signals (one input signal originates from the reduction circuit output terminal 117 and the other input signal originates from the output terminal 130 of a pressure transducer 100). The phase comparator provides at its output terminal 128 a voltage which is a zero volt DC voltage when the input signals at the two inputs 117 and 130 occur with exactly the same phase angle. The phase comparator outputs a positive voltage on the output side when the input signal at the input terminal 117 leads the input signal at the input terminal 130 in phase. The phase comparator, on the other hand, outputs a negative DC voltage on the output side when the input signal at the input terminal 117 lags the input signal at the input terminal 130 in phase. A battery 129 provides suitable voltage to the voltage controlled oscillator 145. The circuit 151 just described is known as a phase locked loop. The mode of operation is best explained by means of an example. Assuming once that the pump pulse frequency (pump stroke frequency) has a value of 1 Hz and that the voltage controlled oscillator outputs signals having a frequency of 512 Hz, the reduction circuit 150 outputs a signal on the output side whose frequency is exactly 1 Hz. The 1 Hz signal from the reduction circuit 150 and the 1 Hz signal from the pressure transducer 100 will then match each other in frequency and phase, and an output voltage of zero volts will appear at the output terminal 128 of the comparator. The voltage controlled oscillator 145, when properly biased by the battery 129, generates exactly 512 pulses per stroke.

It is now assumed that the speed of the mud pump 12 increases. The frequency of the signal appearing at the terminal 130 will then be slightly higher than 1 Hz, ie 1 + Δ1 Hz. The comparator 119 then outputs an output signal at the output terminal 128 which is no longer given by a DC voltage of zero volts, but, for example a voltage of + Δ2 V.

This small increase in voltage is applied to the voltage controlled oscillator 145 at terminal 108; it causes the frequency of the oscillator to be increased until the nominal pulse rate of 512 pulses per second has increased to a value f such that f / 512 = 1 + 1.

Thus, the frequency at the terminal 110 will always follow exactly the frequency of the mud pump 12 and always be a multiple of one 512th.

In the foregoing, two arrangements for obtaining timing pulses for the signal extraction circuit 102 have been described (the pulse generator 111 shown in FIG. 4 and the phase locked loop 151 shown in FIG. 10). A third arrangement that may be used to achieve such timing pulses is shown in FIG. 11 illustrated. This arrangement is based on the principle of auto-correlation. According to FIG. 11 At the input terminal 154 of a correlator 152, the output signal of the pressure transducer 110 is supplied. Further, the correlator takes on the function F (t), which includes the periodic signal N (t) and the function S (t), which can be considered as a random function. The output of the pressure transducer 100 is also supplied to the input terminal 101 of the signal extraction circuit 102. The correlator 152 is capable of generating at its output terminals the autocorrelation function of F (t) given by

The stroke indicates the averaging over a suitable period of time in the expression given above. The function Φff (τ) can be expressed as follows: Φ_ff(τ) = Φ_ss(τ) + Φ_nn(τ) where and and.

The function Φ_ss(τ) ranges from zero to any value of τ = τ 0; over τ & sub0; In addition, Φ holds_ff(τ) = Φ_nn(τ) (10)

Since Φ_nn(τ) is periodic, so is the function Φ_ff(τ) periodically; it has the period τ. This function, which is obtained at the output of the correlator 152, is in turn supplied to a pulse multiplying circuit 153 which generates a train of timing pulses similar to those provided by the pulse generator 111 of FIG. 4 be generated. These pulses are supplied to the input terminal 110 of the signal extraction circuit 102. The pulse multiplying circuit 153 multiplies the frequency of the input pulses by a phase control system similar to that shown in FIG. 10 represented system or by any other conventional device. The remaining elements in FIG. 11 are the same as in FIG. 4; an exception, of course, is the fact that the pulse generator 111 and its chain drive assembly 112 are omitted.

Commercially available autocorrelation-based apparatus are available to obtain a periodic signal from a composite signal containing a periodic signal and a random signal (see, for example, "Statistical Theory of Communications", by Y. W. Lee, John Wiley, New York, 1960, pages 288-190). The correlator 152 of FIG. 11 may be Model 3721A from Hewlett Packard Company of Palo Alto, California. The correlator 152 could also be any device of the types described in the following references: A. E. Hastings and J. E. Meade "A Device for Computing Correlation Function", Review of Scientific Instruments, Vol. 23, 1952, pages 347 to 349; F. E. Brooks, Jr. and H. W. Smith, "A Computer for Correlation Functions", Review of Scientific Instruments, Vol. 23, 1952, pages 121 to 126.

Although various embodiments of the invention have been described above, it should be understood that it is possible to deviate from the spirit of the invention to make a variety of changes and modifications. For example, probes for only two downhole parameters have been given. However, it should be appreciated that probes could be used for various other downhole parameters as well. In addition, it will be appreciated that probes can be used simultaneously for a variety of downhole parameters. In this case, conventional methods would be used (such as the time division method, the multiplex method or the like). to process the data that characterizes the multitude of parameters.

When drilling deviated or oblique holes, variously a turbine or "mud motor" is used, such as a so-called dynadrill, manufactured by Smith Industries, Inc. of Houston, Texas. In such a case, the drill string 31 shown in FIG. 1 not turned by the turntable on the surface. Rather, the rotational action to guide the bit 26 is derived from such a mud motor, which is typically contained just above the bit 26 in the drill string, comprising members 22, 24, 28 and 30 as shown in FIG. 1. When such a mud motor is used, there is a large pressure drop across the engine as the mud engine in question drains its power from the mud flow. This large pressure drop can be used to cause the pressure difference between the inside of the drill string and the annulus. In such a case, a "nozzle" type drill bit need not be used.

The presence of a pressure drop across the mud motor merely enhances the operation of the plant of the present invention as long as the pulse generator causing a negative mud pressure is located above the mud motor.

As used herein, the term "flow restrictor" applies to both a nozzle type bit and a mud motor, or both. The term "high pressure zone" refers to the drilling fluid pressure on the upstream side of the "flow restrictor", and the term "low pressure zone" refers to the drilling fluid pressure on the downstream side of the "flow restrictor".

It should be appreciated that in some cases a variety of mud pumps are used in a single rig and that these pumps are not necessarily operated synchronously.

For example, if three pumps are used, the periodic pressure curve of Fig. 5A would not in practice be a simple periodic function, as illustrated by N (t), but would be the sum of the three components, each of which is periodic Function is and moreover owns their own certain period.

By using three delay systems (as shown in FIG. 6), each synchronized with its own pump, the respective periodic component of the disturbing mud pulse pressure signal can be eliminated separately. By a suitable connection, a signal is then generated, from which the disturbing mud pump pressure signals are eliminated.

The invention thus provides improved systems, Devices and methods are provided for measuring downhole parameters in a well, which is drilled into the earth with the help of a device which is a drill string, a mud pump for circulating a drilling fluid and a flow restricting device, which is arranged near the bottom side of the drill string in such a way that a pressure drop is caused between the flow restrictor and a well annulus, surrounding the drill string. In accordance with one aspect of the invention, the improvements include the use of wellbore pulsing means to produce negative mud pressure pulses that are used to produce a wellbore pressure. Downhole parameter information to an aboveground facility to transfer. The improved wellbore pulseper utilizes a valve assembly that provides a by-pass to the flow restrictor in such a manner that effective pulses are effectively generated with minimal electrical energy overhead. In accordance with another aspect of the invention, an improved structure is provided which surrounds the impulse device and receives the associated downhole arrangement. In accordance with yet another aspect of the invention, improved methods are provided for deriving negative mud pressure pulse signals from spurious signals resulting from mud pressure fluctuations due to the operation of the mud pumping device. In yet another aspect of the invention, improved DC downhole voltage devices are provided.