Clamped Detector

Abstract

A composite detector particularly useful in seismic exploration is disclosed, with means to clamp the detector in a borehole so that a vertical traverse can be made. The tool includes the features of a moveable clamping system, a dual hydraulic system to protect delicate components from the pressure of the borehole fluid, a fail-safe interposed between the final hydraulic system and the clamping pistons, and a jettisonable weight to facilitate downward motion of the tool into the borehole. This invention pertains to the field of geophysical exploration, particularly seismic exploration. More in particular, the invention comprises a detector apparatus adapted to be placed into a hole by means of a cable as opposed to drill pipe, and clamped and unclamped onto and off of the wall of the hole remotely from the surface. In conventional seismic exploration, a shot hole is drilled and explosives placed therein. A relatively large array of surface detectors are placed in predetermined patterns and at predetermined distances from the shot hole, the shot is fired and the reflected waves through the earth from the shot are recorded by the detectors. The problems in conventional seismology solved by the invention include the invention's ability to make a vertical traverse of the detectors, and the invention's ability to position the detectors below the weathered layer. As is known, the weathered layer is the uppermost part of the crust of the earth which, because it is subject to the weather, man, and other disruptive forces, is not homogeneous in its ability to pass seismic vibrations, and thus detracts from the quality of such vibrations received at the detectors from deeper layers in the earth. The present invention is one of a family of related inventions all pertaining to improvement of the seismic method. The related inventions, all co-pending with the present invention and all assigned to the same assignee, are: "Precision Seismology" by Paul C. Wuenschel Ser. No. 227,985, filed Feb. 22, 1972, "Reproducible Shot Hole" by Paul C. Wuenschel, Ser. No. 82,907, filed Oct. 22, 1970, now U. S. Pat. No. 3,693,717 issued Sept. 26, 1972. "Device for Providing Slack in a Borehole Instrumentation Cable" by Carl A. Gustavson, Emmett B. Shutes and Paul C. Wuenschel, Ser. No. 256,780, filed May 25, 1972. The invention entitled "Precision Seismology" identified above is an overall method of using the present invention as well as the other inventions in a single integrated seismic exploration system. The present and the other inventions, however, do have utility other than use in that particular system. With regard to the present invention, aside from the seismic area, utility could be found in the fields of micro-earthquake recording, recording rock bursts in mining and tunneling operations, determination of fracture orientation in oil well hydrofracturing operations, and generally in any application where it is desired to measure a vector seismic field in a frequency range up to several hundred hertz. The invention comprises a two-part assembly including a lower detector unit connected by a multiple cable to an upper utilities unit which supplies power to and receives electrical signals and preamplifies said signals from the lower detector unit. This multiple cable is so configured that there is provided as limp a connection as possible between the two units, whereby the possibility of disruptive vibrations being transmitted from the upper to the lower unit is substantially eliminated. Both units, in the jargon of the art, are of "torpedo" configuration, i.e., thin and elongated for ease of use in relatively small diameter and relatively long boreholes. The lower instrument unit includes an array of three mutually perpendicular detectors so that vibrations in all directions are detected and can be conventionally recorded for further analysis by skilled seismologists. Another feature is the incorporation within the lower unit of a means to measure the degree of coupling in three mutually perpendicular directions of the lower unit to the borehole wall. The detector unit also includes, as an optical feature, a hydrophone so that the tube wave, i.e., an acoustic signal in the detector borehole liquid, if liquid is present, may be separately determined for use in correcting the seismic signals. The hole will be filled with some suitable fluid, such as drilling mud, air, or water. When air only is in the borehole, the hydrophone feature is not used. The clamping means include several improved features. Two pistons in the detector unit are provided, one closely adjacent to each of the ends of the unit. This arrangement, having each piston as close as possible to its associated end of the unit, assures the maximum strength couple for clamping the lower unit to the borehole wall. The arrangement assures that the couple will be around the center of mass of the lower unit. Further, by having the pistons near the ends of the lower unit, any possible torque action due to a tensile force in the multiple cable interconnecting the two units is minimized, along with the harmful effects such a torque action could have on the orientation of the detector unit. The two pistons are hydraulically connected by an open conduit to thereby operate in differential mode so that any irregularities in the borehole wall will be easily accommodated to assure a firm clamp between the detector unit and the borehole. In the upper utilities unit there are provided a fluid pressure tight instrument space or bay and other bays open to the borehole environment. There is also provided two essentially separate hydraulic systems. The reasons for and advantages of the above two structures intermesh for various reasons and to achieve various advantages. The prime mover is a reversible electric motor, which was chosen because of the relative ease of transmitting electric energy down a fluid filled borehole via a cable. The rotational motion of the motor is converted to a linear motion which drives a first piston in the first hydraulic system. These three components, the motor, the converter, and the first piston, are located in fluid pressure tight bays so that they are protected against possible damage from the borehole fluid. The first hydraulic system also includes a second piston driven by the first piston and a by-pass valve. The second piston is located in the open space so that, by the use of suitable balancing means, it experiences a hydrostatic head from the borehole fluid to thereby cancel this pressure out vis-a-vis the ambient pressure on the remaining hydraulic components driven from the second cylinder which are of necessity exposed to the borehole environment. Thus, the need to overcome any difference in hydrostatic head or ambient pressure on this second cylinder is automatically eliminated. The shut-off valve or by-pass valve interconnecting the first and second cylinder in the first hydraulic system is preferably located in the fluid tight bay because it is used for an initial adjustment of proper fluid flow and it is preferred to protect it from possible fouling by the borehole fluid. The second hydraulic system consists of a single acting cylinder or pressure chamber which is mechanically directly driven from the second cylinder of the first system, and which supplies pressurized hydraulic fluid to the clamping pistons in the lower unit via the hydraulic line forming part of composite cable interconnecting the two units. Yet another feature of the invention, integrated into the second hydraulic system and yet having utility in other environments, is fail-safe means to assure that the lower unit will not become locked in the borehole and with its pistons extended in the event the electric motor should malfunction. The fail-safe basically comprises a closed chamber having a piston mounted therein, which piston is mounted on a hollow shaft. The opening in the hollow shaft normally forms part of the path for hydraulic fluid from the piston in the upper unit of the second hydraulic system to the clamping pistons in the lower unit. Means are provided to mount the weight of the lower unit on the fail-safe hollow shaft, and these mounting means include shear pins, or the like destructible means, whereby in the event of a stuck lower unit, the upper unit can be pulled, breaking the shear pins and causing a relative motion of the piston in the fail-safe chamber to thereby create a vacuum pressure on the fluid holding the clamping pistons extended. Thus, the pressure on the clamping piston is released, and the pistons are literally sucked back into their housings in the lower unit. This retracting motion can be aided by springs in the piston assemblies themselves biasing the pistons to the retracted position. The space in the fail-safe body into which the fail-safe shaft mounted piston must move for its emergency type use is vented to the fluid tight space in the upper utilities unit, thereby facilitating its motion. Another feature of the invention, operating in cooperation with the lower clamping piston of the lower detector unit is a jettisonable weight which facilitates movement of the invention exploration tool down a borehole. This part of the invention comprises an adapter mounted between the nose end of the lower detector unit and a suitable weight such as a length of drill pipe or weighted tubing threadedly or otherwise suitably mounted on the lower end of the adapter. The adapter has spring loaded means to clamp onto the detector unit, which spring loaded means are operated by the lower clamping piston to thereby disconnect the adapter with its attached weight from the lower unit when the invention is in place in the hole. The adapter and weight can be made of materials which are destructible by the drill bit if the borehole is to be deepened after seismic measurements have been made. The basic invention could be used for other than seismic methods, such as: acoustic P and S wave techniques, magnetic methods, borehole sample collection, and radioactive techniques. All of these would be enhanced by having the lower unit firmly clamped to a borehole wall at an exact depth. The above and other advantages of the invention will be pointed out or will become evident in the following detailed description and claims, and in the accompanying drawing also forming a part of the disclosure, in which: FIG. 1 is a perspective elevational view showing the invention mounted on a truck as it might be for field use; FIG. 2 is an overall schematic view of the borehole exploration tool of the invention; FIG. 3 is a detailed view of the lower detector unit; FIG. 4 is a detailed view of the optional hydrophone as mounted in the nose of the detector unit; FIGS. 5, 6 and 7 are sequential views showing the use of the jettisonable weight feature of the invention; FIG. 8 is a cross-sectional view on line 8--8 of FIG. 5; and FIGS. 9, 10, 11 and 12 are sequential detailed views of the upper unit starting with the upper end at the left hand side of FIG. 9 and ending with the lower end at the right hand side of FIG. 12. Referring now to FIG. 1, the invention borehole exploration tool, for which the shorter name of "clamped detector" has evolved, is indicated at 10 mounted on a truck 12 by means of a boom assembly 14. As shown, the clamped detector 10 is about to be lowered into a detector borehole which is cased at its upper end in the conventional manner as at 16. The parts 12, 14 and 16 do not form a material part of the present invention, and any other equivalent conventional means may be used. Clamped detector 10 comprises a lower detector and clamping portion or unit 18, an upper utilities portion or unit 20, a composite electrical, hydraulic and structural cable 22 interconnecting the two portions 18 and 20, and another multiple cable 24 connected to the upper end of the utilities portion 20. An advantage of the invention is that this composite cable 22 interconnecting the upper and lower units 18 and 20 is flexible, whereby the lower unit, during use, can be isolated from the upper unit, as will be set forth in greater detail below. Reference should be had from time to time to FIG. 2 which shall serve as a master guide or plan of the entire tool 10 as the detailed description of the two portions 18 and 20 proceeds below. Referring now to FIG. 3, the detector portion 18 is shown in detail. At its lower end portion 18 comprises a nosecone 26 which encloses a space in which the hydrophone 28 of FIG. 4, described below, may be mounted, if desired. The lower portion 18 is of generally elongated cylindrical shape, and thus the various diametrically disposed walls, chambers, bulkheads and the like will be of generally circular cross-section, as is evident. The bottom of the lower unit 18 is defined by a bulkhead 30 to which the hydrophone 28 may be mounted as shown in FIG. 4. Bulkhead 30, at its upper end, comprises a neck 32 by which connection and alignment is made to a lower piston housing 34. A similar housing 36 is provided at the upper end to house the upper piston. The two piston housings are very similar and functionally identical, and each houses a piston assembly 38 and 40 respectively, which piston assemblies will be described in detail below. Pistons 38 and 40 and their associated structure comprise the clamping piston means or piston assemblies carried by the lower unit. An "O" ring 42 provides a seal at the mating surfaces between bulkhead 30 and housing 34. As mentioned above, it will be understood that the housing members 34 and 36 are generally cylindrical with respect to the overall shape of the entire lower unit, and the hole formed therein for housing the piston assemblies 38 and 40 is generally diametrically disposed with respect to the general cylindrical shape of the lower unit 18. At the end of the cross opening in housing 34 opposite the head of the piston, there is provided a closure and utility supply member or block 44. Block 44 is sealed into the lower piston housing 34 by means of an "O" ring 46 and is secured therein by any suitable means such as the screws 48 passing through suitably formed clearance openings in the member 44 and cooperating with suitably threaded openings in the housing 34. In the successfully constructed embodiment six such screws were provided, only one being shown in the drawing for the sake of clarity. To one side of the main cross passageway for the piston, housing 34 is formed with an offset longitudinal opening 50 for passage of shielded wire conductors to pre-amps in the upper unit from the hydrophone 28. The next bulkhead 52 defines the lower end of the detector portion itself, the upper end of which is defined by a similar bulkhead 54. Thus, the detectors are housed in the lower unit 18 between the two bulkheads 52 and 54. The lower unit 18 between the bulkheads 52 and 54 comprises a single piece of metal, a body member 56 formed with suitable openings which are closed by suitable caps to receive and hold the various detectors and shakers and their associated cables, all to be described below. Means are provided to impart vibratory motion to the lower unit after it is clamped in a borehole to test the response of both the vertical and horizontal detectors. The following components are diagrammatically indicated in FIG. 2 and shown in detail in FIG. 3. Working upwardly from bottom to top, after hydrophone 28, a vertical detector 58 is held in position on the axis of the body 56 by means of an assembly of an adjustable nut 62 threadedly received on suitable threads formed in a central opening formed in bulkhead 52, and by a slotted spacer 64 which bears against the detector 58 proper. A taper fit is provided between nut 62 and spacer 64 to centralize the force applied to detector 58. The slots on the left side of spacer 64 provide clearance for the hydrophone leads, as does the clearance space below nut 62. The two holes in the bottom of nut 62 are for a spanner wrench which is used to secure the parts tightly together. A central opening is provided in spacer 64 to accommodate the threaded stud 66 forming part of the particular detector 58 which was used. The spacer 64 could be solid if a stud-less detector were used. Bulkhead 52 is held onto body 56 by means of a plurality of bolt means, such as cap screws 68, four such screws were provided in the successfully constructed embodiment, and a fluid and pressure tight seal is provided at this juncture by means of an "O" ring 70. Another "O" ring 72 seals the juncture between the bulkhead 52 and the lower piston housing 34. The next component moving upwardly is a first horizontal detector 74 which is located generally parallel to pistons 38 and 40 in a suitably formed opening 76 in the body 56, and which is held in place by a suitable detector access opening closure and sealing assembly 78. Depending upon the particular commercial detector used, different shaped and configuration structures 78 may be required. That is, depending upon the nature of the detector 74 and its requirements, different hold down means, cable access points, central access points, sealing means, and the like, may be required, all as will be clear to those skilled in the art. The closure assembly 78 is held in place by a plurality of screws, not shown, which pass through suitably formed openings in the edges of the cap 79 and mate with blind threaded holes in the adjacent portion of the body 56. Four such screws for each of the three caps in the side of the detector assembly 18 were provided in the successful embodiment. Suitable sealing means, such as the "O" rings shown in FIG. 3, are provided in order to firmly hold the detector in position and to assure fluid tight seal between the body 56 and cap 79, and between cap 79 and closure assembly 78. In a similar manner, in upward sequence, the body 56 carries a horizontal shaker 80, a second horizontal detector 82, and a vertical shaker 84. Access is had to the elements 80 and 82 by means of structure similar to parts 78 and 79, which structure is not shown for the sake of simplifying the drawing. The two horizontal detectors 74 and 82 are offset from each other by 90.degree. about the axis of the detector unit 18. This is done so that waves coming from any direction will be picked up by the array of the three mutually perpendicular detectors 58, 74 and 82. Access is had to the vertical shaker 84 axially with respect to the axis of the unit 18, and structure around bulkhead 54 identical to that at bulkhead 52 is provided and is indicated by the same reference numerals. In place of the nut 62 and associated part 64 a cable distributing disc 86 is provided at the upper end of the shaker 84 around which the various cables 88 from the other unit are guided. Shaker 84 is mounted within a sleeve 90 to hold the cables 88 away from the shaker. Further insulation is provided by means of an inner cup 92 fixed to a bottom plate 94 with means to guide electrical leads 96. The leads 96 are associated with a pair of piezeoelectric crystals 98 which are positioned between the bottom plate 94 and the shaker to measure the force produced by the vertical shaker. Similar measuring means for horizontal shaker 80 are provided but are not shown for simplicity of drawing. As is known to those skilled in the art, a detector can be made to function as a shaker by supplying harmonically varying current to drive it in the useful seismic frequency range, the so-called motor mode; rather than the conventional use wherein the detector responds to vibrations received by it by producing electrical energy proportional to thsoe vibrations. The purpose of the shakers and the transducers, of course, is to check the quality of the clamp of the lower unit to the borehole. The next component of the unit 18 is the upper piston housing 36 with its associated piston assembly 40. The pistons 40 and 38 themselves are identical, the housings being identical also except for slight differences in accommodating to certain passageways and mating parts. Each of the pistons 38 and 40 comprises a piston head or cap 100 which is secured as by threads to a piston shaft 102, which shaft 102 has its outer end slotted as at 103 and flanged as at 104. The slots 103 across the flanges 104 are provided for access of hydraulic fluid into and aroun the piston shaft 102 particularly when the shaft is in the fully retracted postion. The flange 104 cooperates with a cylinder liner 106. A composite multi-flange packing member 108 is provided at the upper end of the upper piston housing 36 and has "O" rings to seal against the shaft 102, as well as flanges to hold the liner 106 in place and to define the innermost position of the piston cap 100. At the lower end, a closure member 110, similar to closure block 44, is provided. A spring, not shown, may be provided between the underside of the cap 100 through the shaft 102 and terminating at a spring anchor, not shown, which may be held in place by means of a set screw 112. The screw 112 also provides access to the hydraulic fluid passageway in the piston system. The piston assemblies, as shown diagrammatically in FIG. 2, are placed in the lower unit as far apart as possible close to the ends of the unit. In assembling the lower unit, care should be taken and was taken in the successfully constructed embodiment to make the mass distribution of the entire lower unit symmetrical about its center of mass. So positioning the pistons and so assembling the lower unit avoids the possibility of generating a torque force in the lower unit about its center of mass. Another optional feature, not shown, is the provision of telescoping pistons in lieu of pistons 38 and 40 shown to accommodate larger diameter boreholes. Such a device could comprise nested tubes with suitable travel limiting stops, and is within the skill of expert instrument designers. Means are provided to hydraulically interconnect the two pistons 38 and 40 and to supply them with hydraulic fluid. To this end, the next segment of the lower unit 18 is a hydraulic fluid distribution block 114. Block 114 is held to housing 36 by means of four socket head cap screws, not shown. Block 114 is formed with a diametrically disposed fluid passageway 116, one end of which terminates at an external bleed hole cover screw 118 and the other end of which terminates in a chamber 120. Passageway 116 communicates with a similar passageway formed in a central manifold 122 located axially within the block 114. Sealing means 124 in the form of "O" rings assure a tight seal between passageway 116 and the distribution port in the manifold 122. A hydraulic line 126, forming part of composite cable 22, is joined to the upper end of manifold 122 by means of an assemblage of hydraulic nut and hose adaptor 128. A short length of tube 130 is fixed to closure member 110 and housing 36, extends into chamber 120, and carries suitable sealing means 131 to form a fluid tight push fit "O" seal with a suitably formed opening in block 114. The hydraulic fluid is delivered, by an open connection, to the lower piston 38 by means of a similar connector 132 which cooperates with a suitably formed opening at the opposite end of closure member 110. Connector 132, in turn, communicates with a tube 134 which terminates at closure member 44 at the beaded and flanged end of piston shaft 102 of the lower piston assembly 38. This structure provides several advantages and a great deal of versatility. The two piston and housing assemblies are connected together solely by the tube 134, and a quick disconnect means is provided by tube 130 and its sealing means 131. Thus, this clamping arrangement could be moved and utilized with systems other than the shakers and detectors described between the bulkheads 52 and 54. That is, if desired, other downhole equipment such as a borehole gravimeter or the like, could be fitted between the bulkheads 52 and 54 and clamped firmly to the borehole wall. The tube 134 is positioned in an open channel 135 formed in body member 56, thus further simplifying making such changes. The open connection between the inner ends of the pistons provides a differential type of operation which will yield a firm clamp within the travel range of the pistons regardless of irregularities in the diameter of the hole. That is, one piston could move only 10 percent and the other move 95 percent of their full travel, and the force will be equal. Another advantage of this portion of the invention is that a very compact piston assembly is provided, and thus they may be located near the ends of the unit 18 to thereby enhance the couple between the unit and the borehole wall. For still greater versatility, as mentioned above, it should be possible to make a nesting piston shaft 102 to thereby make a telescoping piston, whereby the reach of the piston would be increased and the invention could be used in larger diameter boreholes. The remaining upper end of unit 18 comprises the means to interconnect the mechanical, electrical and hydraulic portions from composite cable 22 into the associated portions of the detector unit 18. To that end, there is provided a sleeve member 136 mounted on suitably formed threads on the upper end of distribution block 114 and sealed thereto by means of an "0" ring 138. The lower end of sleeve 136 extends out to the outside surface of the unit 18 and is provided with a plurality of spanner wrench holes 140 used to assemble this upper end of the apparatus of the invention. A protective cap 142 provided with wash openings 144 is mounted on suitably formed threads on the outside of sleeve member 136. Wash openings 144 are provided to permit borehole fluid to escape from the upper end of the detector 18, it having been determined that it is simpler to provide fluid and pressure tight seals around the various parts of the unit 18 than to provide seals around the composite cable 22. Distribution block 114 comprises a cavity 146 formed therein in spaced relation to the upper end, which cavity communicates by means of passageways 148 with a space 150 and another passageway 152 in the housing 36. Thus, access is provided for the various electrical cables 88 to their terminals 154 at the upper end of the unit 18. The interconnection of the cables 88 with the terminals 154 is conventional and is omitted in order to not further complicate the drawing. At its upper end distribution block 114 is formed with suitable openings to receive conventional hardward 156 for making fluid pressure tight electrical connections between the conductors in the electrical cables 158 forming part of composite cable 22 with the terminals 154. Hydraulic line 126 is of the standard variety and terminates at a ferrule 160. A sleeve 162 interconnects block 114, ferrule 160 and a cable strain member anchor block assembly 164 by means of an internal snap ring 163. A pair of thin strong cables 166 having beaded ends terminate at the anchor assembly 164. The cables 166 are required to maintain a uniform distance between the upper and lower units 20 and 18, and also to carry the weight of the lower unit so that the electrical cables 158 and hydraulic cable 126 will not carry this load. The cables 166 were purchased, cut to length and fitted with the beaded ends as shown. They were supplied by American Chain and Cable Company, Inc, 2250 Noblestown Road, Pittsburgh, Pennsylvania, and are known as aircraft type cables. The anchor 164 is a dual ring assembly, one ring above and one below the ball ends on the cables 166, with suitable slots in the upper ring for cable clearance, and the entire assemblage held together by snap-ring 163. Screws, not shown, are provided to hold block 114 to housing 36, and block 54 to main housing 56. Referring now to FIG. 4, there is shown the hydrophone of the invention which may be mounted in the protective nosecone 26 as an optional feature. Hydrophone 28 is advantageously used to measure the so-called tube wave. Hydrophone 28 is built upon a body member 168 having a flange portion 170 which is mounted on a suitable boss formed in bulkhead 30 by means of a plurality of screws 172, and a free and extending downwardly thereof on which the remaining parts are mounted. Sealing means 174 are provided at the junction of flange 170 and bulkhead 30. A conventional fluid pressure tight electrical fitting 176, like item 156 in FIG. 3, is provided in a suitable opening in the bulkhead 30 to pass the electrical leads through the bulkhead and into the passageway 50 and on to composite cable 22. A sheath 178 is provided on the inside of the body member 168. Member 178 is made of plastic or other suitable dielectric material to prevent an accidental contact between the conductors passing through this region and the part 168. The operation of hydrophone 28 is based upon the special spherical transducer 180 which converts pressure on it into electrical energy proportional to the pressure to thereby measure the acoustic signal in the borehole fluid. In the successfully constructed embodiment, this transducer 180 was made of a ceramic material called Glennite, was obtained from Gulton Industries and measured 1 inch O.D., 1/16 inch wall, with a 1/4 inch opening. The transducer 180 requires for its operation that each side thereof, i.e., the inside surface and the outside surface, be connected to a separate electrical lead and the voltage difference across the thickness of the transducer is then proportional to the pressure being measured. To this end, therefore, a spring contact 182 is positioned on the tip end of an electrode pin 184 and is constrained between the inside of the transducer 180 and a snap ring 186 fixed to pin 184. The electrode 184 is mounted within a plastic holder 188 which has a shoulder 190. The shank portion of holder 188 after shoulder 190 is received in a suitably formed opening in transducer 180. The remaining portions of holder 188 outwardly beyond shoulder 190 are received in a plastic or otherwise non-conducting sealing gland 192. Gland 192 carries an "O" ring 194 to form a seal between itself and the transducer 180 and a second "O" ring 196 to form a seal between itself and the associated portion of body member 168. A second contact spring 198 is seated within a suitably formed notch on the side of electrode holder 188 in a confining pocket formed in the inside wall of gland 192 and has one end bearing against the outside surface of transducer 180, and its other end suitably bent to form the contact 200. Electrode 184 has a contact 185 at its inner end for cooperation in the conventional manner with the contacts on fitting 176. Since the parts 188 and 192 are made of non-conducting material, and the springs 182 and 198 are made metal, the inside and outside surfaces of the transducer 180 may be hooked into a suitable circuit via fitting 176 while being electrically insulated from each other by the structure shown and described above. Means are provided to securely hold the transducer 180 in place to subject it to the pressure of the fluid entering the nose of unit 18 via the openings in nosecone 26, while at the same time protecting it against any stray particles, debris, or the like which might be in the borehole fluid. To these ends, the outer end of the body member 168 is threaded to receive an open cage member 202 which has an abutment portion 204 in which is seated a non-conducting buffer block 206 which bears against the adjacent portion of transducer 180 to thereby press the transducer in place on gland 192 against sealing means 194, which in turn holds gland 192 against its sealing means 196. Fitted over the combination of cage 202 and the head end of part 168 is a protective boot 208 formed of a pliable, borehole fluid impervious, non-electrical conducting material such as neoprene rubber or certain plastics. The head end of the body 168 is formed with a plurality of concavities, notches or other indentations 210 whereby pressure on the outside of the boot will tend to lock the boot onto the body by forcing parts of the boot into the concavities. The front end of the boot is preferably opened and corked as at 212. Alternatively, strings or other tie means could be provided at the area of the concavities in the cork 212 and the indentations 210 in the body to more positively fasten the boot 208 to these parts. An important function of the boot 208 is to assure that the outside surface of the transducer 180 does not come into contact with any fluid in the borehole. Such a contact between fluid and transducer could form an electrical "ground loop," which in turn would cause undesirable pick-ups and erroneous data at the recording apparatus. The inside of the transducer 180 will usually be filled with air because the apparatus will have been assembled in that medium. The space inside the boot 208 is preferably filled with a light oil or the like fluid, put in via corked opening 212, to transmit pressure from the well fluid outside the boot to the transducer. A silicone fluid was used in the successfully constructed embodiment. The front end of nosecone 26 is formed as at 214 to receive the corked front end of the boot, and said nosecone is formed with a front opening 216 to permit the flow of well fluid therein and to provide drainage. In the successfully constructed embodiment cage member 202 was a four armed spider, and nosecone 26 was formed with six relatively large slots. Referring now to FIGS. 5, 6, 7 and 8, there is shown the jettisonable weight adapter 218 of the invention. This feature comes into play when lowering the invention into a borehole for use, and is used to increase the weight of the lower unit so that it will be heavier than the upper unit and will pull it and the cable down the hole. A bolt 222 is provided to assure a firm connection between the adapter 218 and the pipe or pipes or weighted plastic tubing 220 serving as the weight. Means are provided to securely hold the assembly 218, 220 onto the nose end of the lower unit 18, and to release the weight automatically when the unit 18 is at the desired location in the borehole. To this end, the upper part of the adapter 218 is formed with a pair of parallel elongated slots 224 in which are secured a pair of stiff flat springs 226 by means of anchor plates 228. In spaced relation to its upper end each spring 226 is fitted with a pair of screws 230 which mount a block 231, which blocks, in the FIG. 5 position, fit into notches 232 formed in bulkhead 30, see FIGS. 4 and 8. The outwardly extending portions of the springs 226 above the screws 230 are of such a length that they will be in the path of the cap 100 of the lower piston assembly 38 during its extending stroke. The operation of the jettisonable weight of FIGS. 5, 6, 7 and 8 should be manifest. The blocks 231 fit into the notches 232 to form a secure connection while the assemblage is lowered into a borehole, the weight attached to the lower end of the adapter helping significantly during this operation. Thereafter, normal operation of the piston 38 lifts the blocks 231 out of the slots causing the weight 220 and the adapter 218 to fall deeper into the hole. The adapter 218 and weight 220 can be expendable and simply left in the hole or made of materials destructible by a drill bit, or they can be retrieved with conventional borehole "fishing" methods and apparatus. Referring now to FIGS. 9, 10, 11 and 12, and to FIG. 1, the upper unit or utilities portion 20 is shown in detail. The uppermost end of the upper unit 20 comprises the means 236 to form the interconnection between the cable 24 and the remaining parts of the clamped detector 10. Connecting means 236 comprises a commercial cable termination 238 which is provided with a housing and which is nested within an adapter sheath 240. A plurality of set screws 242 are provided in the side of sheath 240 to bear against multiple connector 238. The upper end of sheath 240 is beaded as at 244, which bead cooperates with a shoulder 246 formed on the lower end of a flexible stress relief member 248 having a central axial opening within which the cable 24 is located. Member 248 is preferably made of rubber or the like resilient material to protect the cable 24 from flexing damage at its connection to the clamped detector 10 while at the same time permitting a substantial degree of flexibility at this location. In the successfully constructed embodiment, four set screws were used to hold the parts 238 and 240 together. Below sheath 240, a protective cover 250 has a plurality of tabs on each end which are peened over as at 252 to secure the split halves of the lower section of the commercial connecting means 238 together. The commercial cable termination 238 had several undesirable features as originally supplied. The split halves of the lower part were originally provided with strap clamps having outward projections, and this undesirable structure was replaced by the protective cover 250. The flexible member 248 was added to the commercial device to better protect the cable at its junction to the upper unit. No such protection was provided at this location originally. The armor on the cable 24 terminates at the device 238 so that the armor and not the electrical and other utility lines carry the weight of the clamped detector. The original termination was purchased from Boston Insulated Wire Corporation. Below the connecting means 236 the upper unit 20 proper comprises a top connector assembly 254. At its lower end, assembly 254 is joined to an electrical unit interconnector member 256. The electrical cables delivered to the upper unit contained within composite cable 24 terminate at a connector member 258 which cooperates with a plurality of pins 260, only one of which pins is shown in the drawing for the sake of clarity. Each pin 260 is sealed in the transverse wall of electrical connector member 256 by means of a commercial glass to metal seal or the like 262. Another plug type electrical connector, not shown, is housed within a tubular central cup member 264 for cooperation with all of the pins 260. The upper end of cup 264 is threadedly sealed into the lower end of member 256 by means of an adapter sleeve 266 tightly press fitted into the recess in the lower end of connector member 256. A seal is provided by an "O" ring or sealing means 270 described further below. Versatility at this juncture is provided since different suitable pairs of connectors in the opposite ends of connector member 256 can be mounted to thereby accommodate various different cable terminations in the upper part. Thus, many different cable terminations can be used by simple suitable adjustments and modifications of the parts 256, 258 and 264. Means are provided to interconnect the members 256, 264, other members described below, and to provide a location for mounting a protective outer sheath over the remainder of the upper unit 20. To this end, an adapter member 268 is positioned with its upper end bearing against the lower end of member 256 with sealing means 270 being provided at the interface between these two members. A second adapter member 272 is threadedly connected to the upper end of member 268, and has instepped shoulders to cooperate with suitably formed mating structure on connector 256. A protective pressure resistant tube or sheath 274 is threadedly connected to the lower end of adapter member 268 and sealing means 276 in the form of "O" rings are provided at this juncture. The protective tube or sheath 274 runs over the entire length of the utilities portion 20, which is thereby sealed away from the fluid in the borehole, and terminates at locations closely spaced to the lower end of the utilities unit 20, see the middle segment of FIG. 12 and FIG. 1. This sealed part of the upper unit is divided into a plurality of separate compartments, three such compartments were provided in the successfully constructed embodiment being described herein. The upper two compartments are defined by divider members 278, 280 and 282, see FIGS. 9 and 10, are quite similar to each other, and are designed to be electrical equipment bays. Means are provided to cushion or protect the divider members or bulkheads 278, 280 and 282. To this end, a resilient ring 286 and 287 is provided in a suitably formed groove in the outside periphery of members 278 and 280 respectively, and a similar resilient ring, not shown, is provided in a similar manner in the periphery of divider member 282. The third compartment, between the divider member 282 of FIG. 10 down to the bulkhead 284 in the middle of FIG. 12, is filled with mechanical equipment for various purposes which will be described below. Thus, bulkhead 284 separates the open bays or parts below and the fluid tight bays or parts within unit 20 above. Divider member 278, see FIG. 9, is formed with a central opening which receives the plug portion 288 of the electrical connecting means 290 which extends between the central opening in the divider 278 and a suitably formed opening in the lower end of cup member 264. A set screw or the like securing means 292 is provided to hold the connector 290 in the cup member 264. The upper and lower electrical bays between the members 278 and 280, and 280 and 282, respectively, are quite similar to each other and each is made up of a bottom wall 294 secured by means not shown to the undersides of the divider members, a pair of "U" channel shaped members 296 secured by means of the screws 298 to the divider members, and a top strap 300 having slotted ends as at 302 for cooperation with screws 304 in the divider members to permit rapid connection and disconnection of the top straps 300. Each bottom member is formed with a transverse slot 306, and with a plurality of central longitudinal slots 308 aligned with the top strap 300. These slots 306 and 308, along with the through openings 310 in the lower two divider members 280 and 282, provide complete freedom for wiring between the various components in these two electrical bays. The bays are shown empty to simplify the drawing, and much of the space therein is provided for future uses. In the successfully constructed embodiment, the electrical components were secured into the bays by connection to any of the walls 294, 296 or 300, and/or the slots therein, and these electrical components included and could in the future also include seismic pre-amplifiers, transformers, switching relays, a timing device to record elapsed operating time, amplifiers, power regulators, an analog computer for computing driving point mobility, and similar such devices well known to those skilled in the art. The next section of the upper unit between divider 282 and the adapter member or bulkhead 284 is filled with the mechanical portions of the utilities unit which produces the hydraulic pressurized fluid needed to operate the pistons 38 and 40. This portion of the invention is diagrammatically illustrated in FIG. 2, to which reference may be had as the description of FIGS. 11 and 12 progresses, the same parts being indicated by the same reference numerals throughout. A plurality of studs 312 interconnect the lowermost divider member 282 with a top spacer or bracket 314. The space between the bracket 314 and divider 282, defined by the length of the studs 312, was provided in assembling this portion of the invention. The space between members 282 and 314 could be used to house a gyroscope which would be useful in providing azimuth data of the upper unit as it is moved up and down in the borehole. A lower motor mounting plate 316 is held in spaced relation to spacer 314 by a plurality of structural studs 318, and a reversible electric motor 320 is mounted on the plate 316 by suitable screws or other securing means, not shown. Means are provided to change the rotational motion of the motor shaft 322 into a translational motion for use in operating a cylinder to pump hydraulic oil, as will appear below. To this end, the motor shaft 322 is connected by a flexible coupling 324 to the shaft 326 of a linear friction roller actuator device 328. In the successfully constructed embodiment an actuator marketed by Barry Controls of Watertown, Mass., their Model No. 3-005 marketed under the registered trademark "ROH'LIX" was used. Such devices are well known and need not be described here in any further detail. A linear actuator of this or a competing type is preferred over a simple elongated screw and trapped nut arrangement because the screw type is positive and thus subject to binding and locking, whereas the slip force in commercial linear actuators can be adjusted so as to avoid this problem. This adjustment of force is desirable to assure smooth operation and avoid locking, and also to adjust the magnitude of the force of the pistons against the borehole wall. The upper end of the shaft 326 is mounted in a bearing 330 mounted in a frame member 332 which is held in position with relation to the lower motor plate 316 and studs 318 by means of a second set of structural studs 334 and an array of headless screws 336 and bolts 338. For purposes of carrying wires and the like, frame member 332 is provided with a plurality of openings 340, and a number of protective tubular conduits 342 are also provided in this section through which the linear actuator 328 moves, in order to protect such electrical conductors from harm which might be caused by the moving parts. A plurality of structural spacer rods 343 are provided to securely interconnect the frame members 332 and 344 (described below). These rods 343 are subject to the thrust of the actuator and prevent the actuator 328 from rotating. The conduits 342 are relatively thin walled and serve to protect the electrical wiring in the zone of actuator motion. In the successfully constructed embodiment of the invention, four rods 343 and two protective tubes 342 were provided. Other embodiments of the invention could, of course, provide different quantities of these kinds of members. The actuator shaft 326 terminates in a transverse wall 344 and is mounted in a suitable bearing, now shown. The front end of the actuator 328 carries a shaft adapter member 346, which accommodates slight shaft misalignments, and a tab 348 in which is adjustably mounted the end 350 of the moveable member of an elongated variable resistor assembly or potentiometer 352. The resistor 352 is wired into other equipment in the instrument van at the surface such that the resistance thereof is indicative of the physical position of the actuator on its shaft 326, all in a well-known manner. The other side of adapter 346 is connected to the shaft 354 of a first hydraulic piston 356. Piston 356 is connected in double actuator mode and therefore has its rear end connected to a line 358 and its front end connected to a similar line 360 by means of conventional hydraulic hardware. The drawings have been simplified from considerably more complex shop assembly drawings from which the successfully constructed embodiment of the invention was built. In this process many relatively minor details have been omitted, mostly relating to openings, conduits through which wires pass, and structural members tying together the various transverse walls described, which transverse walls carry said openings. Such details are easily within the expertise of skilled designers and mechanics in the art. Some of these details are shown where necessary, and others where no undue confusion results. Thus, transverse wall 344 is joined to the next transverse wall 362 by another plurality of structural members which serve to support the piston 356, one of said structural members being indicated at 364. A clamp 366 supports both line 360 and resistor 352 with respect to support 364. Referring now to FIG. 12, the transverse wall 362 is joined to the next two transverse walls 368 and 370 by means of suitable structural supports indicated at 372. As an optional feature, a pair of batteries 374 are mounted between a suitable clamp 376 fixed to one of the supports 372 and by means of another clamp 378 fixed to wall 362. The batteries 374 are a "fail safe" device for operating the motor 320 in the direction necessary to release the pistons from the borehole in the event of any malfunction in the tool or in the power supply via the cable. A pair of brackets 380 are fixed to another of the supports 372 and serve as a location on which to mount an electrical terminal board, which terminal board is omitted in order to more clearly show the underlying structure. This terminal board is used to connect the batteries and the monitoring detector 382 into the remaining electrical circuitry. The additional detector 382 is provided in the upper unit to monitor the mechanical coupling between the lower clamped unit and the upper unclamped unit when the invention has been emplaced and used to record the elastic waves propagating in the ground. A manually operated on/off valve 384 is connected across the hydraulic lines 358 and 360 as indicated diagrammatically in FIG. 2. The various hydraulic lines themselves only appear partially in the left hand side of FIG. 12, but the manner of connection is clear from the diagram of FIG. 2. From FIG. 2 it can be seen that opening valve 384 will isolate the piston 356 from the remaining hydraulic system and closing said valve will stop the bypass flow and cause piston 356 to drive the operating piston 386. As mentioned above, the pressure tight portion of the utilities unit 20 ends at bulkhead 284. Pressure protective tube 274 also terminates at the upper flange of said bulkhead 284 and is sealed therein by means of the "O" rings 388. The hydraulic lines 358 and 360 pass through the transverse wall of bulkhead 284 and are silver soldered in place to provide an adequate seal. One tube sealing member 390, which is the vent for the hydraulic fail-safe, is indicated in the middle segment of FIG. 12. Similarly, the various electrical leads are carried through the bulkhead by means of conventional electrical pressure and fluid tight hardware, one of which is indicated at 392. The remainder of the utilities unit 20 below bulkhead 284 including the main piston 386 and associated parts are exposed to the well fluid, a perforated protective sheath 394 being provided over this segment, see FIG. 1. All other parts of the utilities unit 20, including the prime mover electric motor and the first piston 356, are not exposed to the well fluid in that they are inside of pressure tube 274 above bulkhead 284. The parts are so arranged to compensate the clamping pistons 38 and 40 for the hydrostatic pressure of the borehole fluid. This lowermost bay or segment of the utilities unit 20 containing the active hydraulic parts is located between bulkhead 284 and another bulkhead 396, three intermediate support walls 398, 400 and 402 being provided between the two bulkheads. The intermediate walls 398, 400 and 402 are spider-like in that they have many clearance openings and mounting openings and the like to allow clearance for the various hydraulic and electrical lines, to mount the various parts, and to themselves be held together by the various support elements, all of which support elements are generally indicated by reference numeral 404. It will of course be understood by those skilled in the art that other specific structure could be built embodying the invention, and that the specific showing of the drawings is by way of example only. The support elements throughout the entire length of the upper unit 20 are generally of a triangular pattern since this configuration is highly efficient of material and of the crowded space within the tool, while at the same time being quite sturdy. The invention, of course, is not so limited. Similarly, sometimes the support elements are solid rods and sometimes they are hollow members depending upon the design and manufacturing considerations. Other simple modifications of this nature will present themselves to those skilled in these arts. The main operating piston 386 is mounted between the walls 398 and 400 by conventional means not shown. Means are provided to equalize the pressure of the well fluid on the active piston member within assembly 386 so that said assembly will be responsive to only pressures delivered to it from the first cylinder 356. To this end, the rod in the cylinder 386 is of the double ended variety, see FIG. 2 in conjunction with FIG. 12. The upper end of rod 406 is provided with a pressure balancing piston rod end 408, whereby an equal cross-sectional area is presented at each end of the piston to thereby negate any undesirable effect the hydrostatic pressure of the borehole fluid might have on the operation of the tool. Balance rod end 408 is a commercial item. The lower end of piston rod 406 is connected to an adapter member 410 which connects the cylinder 386 in driving relationship to a hydraulic chamber 412. Chamber 412 is mounted between walls 402 and bulkhead 396 as indicated by the right hand side of FIG. 12. Chamber 412 comprises an active surface area of predetermined size, which, with respect to the surface area of pistons 38 and 40 exposed to the well fluid, is such as to equalize and cancel the hydrostatic forces acting on these members. The fluid from the chamber 412 is delivered via a hydraulic fail safe device 414 to hydraulic line 126 forming part of composite cable 22, and then to pistons 38 and 40 as described below. Thus there is provided two separate hydraulic systems; one including pistons 356 and 386, and the prime mover motor 320 protected in the fluid tight bay; and the second including chamber 412 in the open bay for operating the pistons 38 and 40 and to balance the hydrostatic pressure in the hole. The double ended cylinder 386 is self-pressure balanced as described above. Pressure chamber 412 comprises a body portion 416 having its front end shouldered and mounted on bulkhead 396 by means of a snap ring 418 fitted into a suitable groove in a projecting portion of the body 416. Thus, the transverse wall of bulkhead 396 is held firmly between snap ring 418 and a shoulder formed in the body portion. A piston assembly 420 is slidably mounted in the body 416 and comprises a central plug member 422 having a snap ring 424 at its front end and an annular projecting shoulder 426 at its rear end. A ring 428 and a counterbored ring 430 are arranged in tandem between the ring 424 and shoulder 426. A wiper 432 is provided in a suitably formed annular seat at the rear end of the body portion 416 to exclude debris from the sliding seal between the flanged ring 430 and the body portion. "O" rings 434 are provided at the three planes of juncture between the parts 422, 428, 430 and 416. A stud 436 interconnects adapter member 410 and piston member 422. This structure is provided to facilitate assembly and accommodate to space limitations. The rings 428 and 430 could be made into one piece to further simplify the structure. Standard hydraulic fittings 438 interconnect the discharge end of the chamber 412 with the supply end of fail safe 414. The relatively large surface area presented by the rear flange on piston 420 serves to aid in pressure balancing to overcome any hydrostatic force differential, as described above. Fail safe 414 is provided for the purpose of assuring that the hydraulic fluid operating the pistons 38 and 40 can be relieved so as to permit the pistons to be retracted in the event of a power failure in the upper unit 20 or some other breakdown in said unit which would prohibit normal operation. More generally, fail safe 414 could be used in any environment of the character described between a source of fluid under pressure and a utility being serviced by that fluid. The fail safe comprises a main body portion 440 in which is mounted a piston 442 by means of an "O" ring 444. Piston 442 is sealingly fixed to a hollow shaft 446 by means of a snap ring 448 and an "O" ring 450. The upper end of the shaft 446 is normally seated in a suitably formed chamber forming part of a passageway 452 which transmits the hydraulic fluid from pressure chamber 412 to the central passageway in the hollow shaft 446. An "O" ring 454 seals the juncture of the end of the shaft 446 to its chamber and to body 440. A closure plate 456 is mounted at the lower end of body 440 by means of a plurality of screws 458 and an "O" ring 460. Closure 456 is provided with a pair of "O" rings 462 to slidingly and sealingly receive the shank of the hollow shaft 446. The closure plate 456 is formed with an annular flange 464 in forwardly spaced relation to its main body. An intermediate split member 466 is formed with an annular flange 468 which mates with flange 464 in overlying relationship. Intermediate member 466 is nested within a split flanged sleeve member 470 and is joined thereto by a plurality of shear pins or shear bolts 472. The upwardly extending flange of the sleeve 470 underlies a flange 474 formed on shaft 446 in closely spaced relation to the front end thereof. Thus, the parts 468 et. seq. define an array of overlapping flanges. For ease of manufacture and assembly, the parts 468 and 470 are of split construction. A cage member 469, provided with slots or openings to clear shear members 472, is therefore provided to hold these split halves assembled, and this cage retainer is held onto closure plate 456 by a plurality of screws 471. The open bottom end of the cage 469 allows the broken parts of the fail safe to separate and fall away if the safety device should come into operation. The space on the underside of piston 442 and within the body 440 communicates with a passageway 476 which extends through the body 414 and terminates at a fitting 478. A tube 480 has an end connected to fitting 478 and in turn extends upwardly through the bulkhead 284 to terminate at a location inside the protected space above said bulkhead within the sheath 274. Ports 476 and ports 478 and 480 serve as a vent for the space between piston 442 and closure plate 456 in the event it is necessary to operate the failsafe 414. The operation of the failsafe 414 depends upon the fact that the shear pins 472 support the entire weight of the lower unit below and including composite cable 22. In the event of a power failure in the upper unit or a fouling of the cable 22 or some other difficulty which will not permit retraction of the pistons 38 and 40, then it is merely necessary to pull on the cable 24 until the shear pins 472 break. Prior to this time normal operation was maintained through the central opening in shaft 446 communicating passageway 452 with hydraulic line 126. When the pins 472 break the piston 442 will descend because of the upward pull on the upper unit. The air below the piston vents via passageway 476, fitting 478, and tube 480 up into the protected and sealed space in the unit 20 above bulkhead 284. Simultaneously, seal 454 is withdrawn and an equal space is created above the piston which creates a vacuum, which vacuum pressure in turn literally draws the hydraulic fluid up through line 126 to thereby withdraw the pistons. This motion of piston 442 does not cause any motion of piston assembly 420 in that no change of condition has occurred within the main piston 386 and the other parts thereabove. To further enhance the action of the failsafe in retracting the clamping pistons upon relief of the hydraulic pressure, said pistons 38 and 40 may be provided with springs to normally urge the pistons to the retracted position. The upper end of the hydraulic line 126 in composite cable 22 is connected to the lower end of the flanged hollow shaft 446 by means of a tandem array of fittings 482. Means are provided within this array to provide a seal between line 126 and shaft 446. Fittings 482 include an enlarged nut 484 on which is mounted a split anchor block 486 in which is fitted the upper beaded ends 488 of the strong thin strain member wires 166 described above. While the invention has been described in detail above, it is to be understood that this detailed description is by way of example only, and the protection granted is to be limited only within the spirit of the invention and the scope of the following claims.

Claims

We claim:

1. In a geophysical exploration tool, the combination comprising a generally elongated body member to facilitate movement of said tool in a borehole in the earth, a pair of piston assemblies mounted one piston assembly in closely spaced relation to each end of said elongated body member, means for supplying hydraulic fluid under pressure to said piston assemblies, open conduit means for said hydraulic fluid interconnecting said piston assemblies, whereby said pistons operate in a differential mode of operation, and disconnect means for connecting the assemblage of said piston assemblies and said conduit means into said tool body member, whereby the assemblage of said two piston assemblies and said conduit means may be readily moved from one tool to another.

2. The combination of claim 1, each of said piston assemblies comprising a piston housing block having a cross-sectional shape similar to the cross-sectional shape of said elongated body member, a piston member slidably mounted in said housing block on an axis disposed generally perpendicular to the axis of said elongated body member, said piston member comprising a hollow piston shaft having a flanged inner end communicating with said open conduit means, whereby said piston shaft may have a length substantially equal to the diameter of said elongated body member and access may be had by said hydraulic fluid to said piston shaft via said flanged inner end in the retracted position of said piston.

3. The combination of claim 2, and a bead around the outside end surface of said flanged inner end to define the limit of extent of said piston out of said piston housing block.

4. The combination of claim 1, and spring means biasing said piston to the retracted position of said piston within said elongated body.

5. The combination of claim 1, and spring means disposed inside said hollow piston shaft for biasing said piston to the retracted position within said housing block.

6. The combination of claim 1, and a second hollow piston shaft nested within said first mentioned piston shaft, whereby a telescoping piston shaft is provided to extend the reach of said piston assemblies in a borehole.

7. The combination of claim 1, failsafe means interposed in said hydraulic fluid supply means for retracting said pistons in the event of a power failure in said hydraulic fluid supply means.

8. The combination of claim 7, said failsafe means comprising a piston member mounted on a hollow shaft, means to mount said elongated body member on one end of said hollow shaft, means to normally flow said hydraulic fluid through said hollow shaft from said supply to said piston assemblies, said mounting means including selectively destructible means, means to move said hollow shaft with said piston member thereon upon destruction of said destructible mounting means to create a vacuum pressure at the second end of said hollow shaft opposite said one end, whereby hydraulic fluid is drawn away from said piston assemblies through said failsafe hollow shaft by said vacuum pressure.

9. The combination of claim 8, said moving means comprising a failsafe body member comprising a chamber in which said piston member is mounted for axial motion with respect to said hollow shaft, a closure member secured to said body member defining said chamber, and means to vent said chamber from that side of said piston member associated with said one end of said hollow shaft, whereby the motion of said hollow shaft and piston member from the side of said second end to the side of said one end to create said vacuum pressure is facilitated.

10. The combination of claim 8, wherein said selectively destructible means comprises an array of overlapping flanges mounted partly on said hollow shaft and partly on said failsafe, whereby said destructible means may be destroyed by pulling on the cable attached to the upper end of said borehole tool in the event said tool should become stuck in said borehole.

11. The combination of claim 1, and jettisonable weight means removably attached to the lower end of said elongated body, said jettisonable weight means including spring means having a portion adapted to grasp cooperating portions in said geophysical exploration tool, and said spring means including a portion cooperable with the lower one of said pair of piston assemblies, whereby extension of said lower piston assembly acts on the associated portion of said spring means to cause said grasping portion of said spring means to release and disengage said jettisonable weight means from said geophysical exploration tool.

12. A system for generating pressurized hydraulic fluid in an elongated geophysical exploration tool for use in a borehole, the combination comprising a fluid and pressure tight bay of said tool and an open bay of said tool, a bulkhead separating said bays, an electrical motor in said fluid and pressure tight bay, rotational to translational motion transducer means driven by said motor in said fluid and pressure tight bay, a first dual acting hydraulic piston in said fluid and pressure tight bay driven by said transducer means, means to pass the hydraulic lines from said first piston through said bulkhead in said tool separating said fluid and pressure tight bay and said open bay, a second dual acting hydraulic piston in said open bay directly driven from said hydraulic lines from said first piston, and a pressure chamber in said open bay driven by said second piston to supply hydraulic fluid to a portion of said tool being serviced, whereby the hydraulic fluid from said pressure chamber is in a hydraulic system separate from the hydraulic system which includes said first and second dual acting pistons.

13. The combination of claim 12, and bypassing means interconnecting the hydraulic lines between said first and second dual acting hydraulic pistons, said bypassing means including a manually operable on-off valve and being located in said fluid and pressure tight bay, whereby said second dual acting piston and said pressure chamber may be cut off from said electric motor and said first dual acting hydraulic piston.

14. The combination of claim 12, said pressure chamber including a piston assembly therein, said piston assembly comprising a portion of predetermined area exposed to the environment in said open bay, whereby the hydrostatic pressures on that side of said pressure chamber having said portion of predetermined area in said open bay is substantially equal to the hydrostatic pressures on the moving parts of said tool serviced from the other side of said chamber to thereby equalize said hydrostatic pressures and eliminate the need to supply energy from said motor to overcome any difference in said pressures.

15. Th combination of claim 12, wherein said portion of said tool being serviced comprises piston means located below said first and second hydraulic systems, and failsafe means interconnecting said pressure chamber and said piston means.

16. The combination of claim 15, wherein said failsafe means comprises a piston member mounted on a hollow shaft, a body member defining a closed chamber for movement of said piston member therein, means to normally flow pressurized hydraulic fluid from said pressure chamber to the upper end of said hollow shaft and through said hollow shaft and to said piston means, destructible mounting means interconnecting said hollow shaft and said piston means, means to vent the space normally below said piston member to said fluid and pressure tight bay through said bulkhead, whereby a failure in at least one of said hydraulic systems and destruction of said mounting means and concommitant motion of said piston member from the upper end towards the lower end of said chamber will create a vacuum pressure at the upper end of said hollow shaft to thereby relieve the hydraulic pressure on said piston means.

17. The combination of claim 15, said piston means comprising a pair of piston assemblies mounted in tandem in said exploration tool in closely spaced relation one to each end of said tool, an open conduit for said pressurized hydraulic fluid from said pressure chamber interconnecting said piston assemblies, and rapid disconnect means hydraulically connecting the assemblage of said pair of piston assemblies and said conduit into said tool.

18. The combination of claim 17, each of said piston assemblies comprising a piston housing block having a cross-sectional shape similar to the cross-sectional shape of said elongated body member, a piston member slidably mounted in said housing block on an axis disposed generally perpendicular to the axis of said elongated body member, said piston member comprising a hollow piston shaft having a flanged inner end communicating with said open conduit, whereby said piston shaft may have a length substantially equal to the diameter of said elongated body member and access may be had by said hydraulic fluid to said piston shaft via said flanged inner end in the retracted position of said piston.

19. The combination of claim 18, and spring means disposed inside said hollow piston shaft for biasing said piston to the retracted position within said housing block.

20. A failsafe for use in a hydraulic system between a source of pressurized hydraulic fluid and a utility being serviced by said hydraulic fluid, the combination comprising a piston member mounted on a hollow shaft, means to mount the utility being serviced on one end of said hollow shaft, said mounting means comprising selectively destructible means, means to normally flow the hydraulic fluid through said hollow shaft from said source to said utility, means to move said hollow shaft with said piston member thereon upon destruction of said destructible mounting means to create a vacuum pressure at the second end of said hollow shaft opposite said one end, whereby hydraulic fluid is drawn away from the utility being serviced by said vacuum pressure.

21. The combination of claim 20, said moving means comprising a failsafe body member comprising a chamber in which said piston member is mounted for axial motion with respect to said hollow shaft, a closure member secured to said body member defining said chamber, and means to vent said chamber from that side of said piston member associated with said one end of said hollow shaft, whereby the motion of said hollow shaft and piston member from the side of said second end to the side of said one end to create said vacuum pressure is facilitated.

22. The combination of claim 20, wherein said hollow shaft is oriented substantially vertically, said utility being serviced comprises a cable mounted borehole geophysical exploration tool, said hydraulic fluid source comprises a portion of said tool located above said failsafe, said utility being serviced comprises a portion of said tool mounted below said failsafe, and said selectively destructible means comprises an array of overlapping flanges mounted partly on said hollow shaft and partly on said failsafe, whereby said destructible means may be destroyed by pulling on the cable attached to the upper end of said borehole tool in the event said tool should become stuck in said borehole.

23. The combination of claim 22, said array of overlapping flanges comprising an outwardly extending annular flange mounted on said hollow shaft adjacent the lower end thereof, an outwardly extending annular flange mounted on a portion of said failsafe, and an intermediate member and a flange sleeve nested together and interconnecting said hollow shaft flange and failsafe flange, and said destructible means further comprising a plurality of shear members interconnecting said nesting portions of said intermediate member and said flanged sleeve.

24. The combination of claim 23, said intermediate member and said flanged sleeve being of axially split construction, a cage retainer member on said intermediate member and said flanged sleeve to hold the split halves of said intermediate member and said flanged sleeve together, said cage retainer member having an open bottom end, and means to hold said cage retainer member on said failsafe, whereby said flanged sleeve is free to fall out of the open bottom end of said cage retainer member upon destruction of said shear members.

25. A jettisonable weight for use with a borehole tool having a portion which can be selectively extended radially outwardly of the tool, the combination comprising an adapter member having connection means at its lower end for connecting weight increasing thereto, the upper end of said adapter member having an internal cross-sectional shape adapted to receive the lower end of said tool, spring means on said adapter member having a portion adapted to grasp cooperating portions in said tool, and said spring means including a portion cooperable with said selectively extensible means, wherein extension of said extensible means acts on the associated portion of said spring means to cause said grasping portion of said spring means to release said adapter member with said weight increasing means thereon from said tool.

26. The combination of claim 25, said extensible means comprising a hydraulic piston located closely adjacent the lower end of said tool, said spring means comprising a pair of elongated flat springs mounted in suitably formed slots in said adapter member, said grasping portion of said spring means comprising a pair of blocks extending radially inwardly from the upper ends of said flat springs, and said cooperating portion in said tool comprising openings adapted to receive said blocks.

27. The combination of claim 25, said weight increasing means comprising weighted conduit means.