CA1109292A - Method and apparatus for logging inclined earth boreholes using the measured acceleration of the well logging instrument - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
A method and apparatus for use in logging inclined earth boreholes is disclosed, The well logging instrument is connected to one end of a well logging cable, the other end of which is connected to a rotatable hoist drum at the earth's surface. The cable is wound on the drum which in turn controls the pay out of the cable as the instrument traverses the bore-hole. The instrument carries an accelerometer and circuitry to convert instrument acceleration into an indication of instrument velocity, The velocity of the well logging cable at the earth's surface is determined and that velocity is compared with the indicated velocity of the instrument in the borehole.
The resulting comparison signal is used to control rotation of the hoist drum and hence the pay out of the cable so as to avoid the risk of overrunning the well logging instrument with too much cable.

Description

~This is a divisio~ of-Canadian Appllcation ~erial No. 310,68Z
filed September 6j 1978.' ,- ' , , Background of the Invention. This invention relates generally to apparatus for logging earth boreholes and spe'cifi- ~
c~lly to methods and apparatus which utilize means in addition to, or which aid gravi-~y in causing the''weIl logging instruments to traverse 'the high an~led earth boreholes.
It has become relative~y common within the last few years to drill wells in the search for oil and gas and the, like ` with a portion o~ the bore deviating from the usual vertical orien~ation thereo~. The deviation or inclination may extend-for a'considerable'distance at an~les ranging to 70, sometimes -returning to the usual vertical orientation. In some instances, '' such boreholes may even extend past 90 from the vertical and - .
actually be extending in the up direction for some distance.
It is also weIl known in the'art of drilling such wells to attempt the logg~ng of the ~ormations surrounding such bore-'holes' with logging'instr~men~s run into the well bore on a ~ire-- -.
-- line-and/or a cable to perform various operations~ Such tools usuall~ depend upon the'~orce o~ gravity to permit positioning ,~ o~ the well tool at the desired *ormation in the well bore.-'S , , Manifestly, the rela~ively horizontal angle of the - - . . .
~ deviated poxtion of the' well bore will not permit the wireline - ., ~ , , ~ actuated tools to move into the'lower portion o~ the well bore - . . , ,, ~ . .
since friction of the well tool,in the deviated pvrtion works against the force o gravity. Thus it has hecome essential to O provide so~e means o~ causing the well logging instrumen~ to pass through the deviated portions of the well bore.
Another problem associated with such boreholes relates .

' ' , ' ,: '`:' ' ~ '' to the instability of some formations p~netrated by the well bore, thus causing borehole diameter changes, some very abrupt.
Ledges are formed, and the logging instrument lodges against them.
Yet another problem exists because the hoist drum keeps rotating after the well logging instrument slows down, sometimes to a complete stop, and too much cable is payed out.
~' This problem was recognized by Bowers in U.S. Patent No. 3,490,149 of January 20, 1970 wherein he taught a device to correct the cable length indications for making an accurate `determination of depth in the borehole. In the Bowers patent a ~ ' ~;~ subsurface accelerometer generates a first function representa-~;~ tive of instrument asceleration. A second function representa-`~ ;tive of the amount of cable movement at the surface is generated ,, .
'and subsequently corrected by the first function. The resultant signal is utilized in driving the surface recorder unit for more accurate depth correlation of the recorded electrical signals.
The present invention, as defined in the parent -~
application and in the present divisional application differs considerably from Bowers in that the instrument is controlled in its downward movement either through instrument control, or control of the surface hoist, or both.
It is therefore the primary object of the present invention to provide new and improved methods and apparatus for logging earth boreholes.
It is also an object of the present invention to pro-vide methods and apparatus for logging deviated boreholes in which it is difficult for the well logging instrument to traverse the borehole.
The above objects are met by the invention of the parent application which broadly provides a method for logging the ormations surrounding an earth borehole, comprising:
causing a well~logging instrument to traverse an earth borehole ,, .
sd/~ 2-rh~

by means of a well logging cable from the earth's sur~ac~;
measuring the velocity of the cable at the earth's surface;
measuring the velocity of the well logging instruments; com-paring the cable velocity with the instrument velocity and generating a signal indicative of the comparison; and activating means within the instrument responsive to the signal which facilitates the movement of the instrument through the borehole.
The above method may be carried out by way of apparatus - for logging the formatio~s surrounding an earth borehole, com-prising: an elongated well logging instrument connected to theearth's surface by a well logging cable and adapted to traverse an earth borehole, the instrument having therein an accelero-meter and means to convert the acceleration of the instrument into an indication of instrument velocity, the instrument.also - -having means therein activatable to facilitate the movement of the instrument through deviated portions of the borehole;
means at the earth's surface for providing an indication of the velocity of the well logging cable at the earth's surface;
and means for comparing the velocity of the instrument with the velocity of the well logging cable at the ear~h's surface and to generate a signal indicative of the comparison, the activatable means within the instrument being responsive to the comparison signal.
On the other hand, the invention of the present application may be seen-as broadly ~roviding a method for logging the formations surrounding an earth borehole, comprising:
causing a well logging instrument to traverse an earth borehole by means of a well logging cable wound around a rotatable cable hoist drum at the earth's surface; measuring the velocity of the cable at the earth's surface; measuring the velocity of the well logging ins~rument; comparing the cable velocity with the instrument velocity and generating signals indicative of the comparison; and controlling the rotation of the cable hoist drum sd/~ 2A-- ~a~$~

in response to the comparison signals.
The above method may be carried out by way of apparatus for logging the formations surrounding an earth bore-hole, comprising: a rotatable.hoist drum at the earth's surface;
a well logging cable wound around the hoist drum; an elongated well logging instrument connected to the earth's surface by the well logging cable and adapted to traverse an earth borehole, the pay out of the cable being controlled by the rotation of the hoist drum, the instrument having therein an accelerometer and means to con~ert the acceleration of the instrument into an indication of instrument velocity; means at the earth's surface for providing an indication of the velocity of the well logging cable at the earth's surface; and means for comparing the velocity of the instrument with the velocity of the well logging cable at the earthis surface and to generaté signals indicative of the comparison, the rotation of the hoist drum being responsive to the comparison signals~
These and other objects, features and advantages of the present invention will be apparent from the following .0 detailed description taken with reference to the figures of the accompanying drawing, wherein;
FIG. 1 is a schematic view illustrating the drilling of a deviated earth borehole from an offshore platform;
FIG. 2 schematically illustrates a prior art well logging system encountering some of the problems associated with logging a highly deviated earth borehole;

~d/~ 2B-F~G,. 3 sch~matically illust~ates a prio~ a~t ~ell logging s~stem wh~ch h~s been used in an attempt to overcome some of the problems as graphically illustrated in FIG. 2;
FIG. 4 is an elevated v~ew, partly in cross section, ; 5 of the apparatus according to the present invention for logging an earth borehole;
FIG. 5 is an enlarged schematic view, partly in cross section, illustrating the well log~ing instrument in accordance with the present invention;
. FIG. 6 is an enlarged schematic view, partly in cross section, showing the reversing mechani~m for changing the direc- :
tion o~ the slan~ of the vanes;
FIG. 7 is a top plan view, partly in cross section, taken along the lines 7 7 of FIG~ 6;
FIG. 8 is an elevated view, partly in cross section, of an apparatus according to an alternative embodiment of the present invention;
FIG. 9 is an elevated view, partly in block diagram, of the logging system used in accordanc~ with the apparatus according to FIG. 8;
FIG. lO illustrates in block diagram portions of the ~unctîons accomplished by the system illustrated in FIG. 9;
FIG. ll illustrates schematically, par~ly in block diagram, an alternativP embodiment o the invention; and FIG. 12 illustrates schematically, partly in block - diagram, yet another embodiment of the invention.
Referring now to the drawing in more detail, especially to FIG. l, there is illustrated sche~atically a conventional system for drilling an earth borehole ~aving a high degree of - 30 deviat~on fro~ true vextic~l. As is well known in the art, it is common practice to dr~ll such slanted weIls from offshore platforms~ A drllling plat~or~ lO having a plurality o~ legs ll ; -3-. .

~,t~ ~c~

anchored on the ocean floor 12 h~s ~n earth boreh.~le 13 drilled therefro~. ~ithin the borehol~'13 is ~ pi~pe string 14~ to the lower end of which is attached a drill bit 15. A surface casing 25 maintains the integrity of the borehole 13 as is well known S in the art, A derrick 16 with its conventional drawworks 17 is mounted on the platform 10. The drill string 14 comprises a number of joined sections of pipe terminating at its upper end în a kelly 18, followed bv a swivel 19, a hook 20 and a traveling b'lock 21 suspended by a drilling line 22 from a crown block 23.
The`drawworks also drive a rotary table 24 which in turn trans-mits the drive to the 'kelly 18. One end of the l~ne 22, namely the fas~ line 22a, is connected to the drawworks 17 which con-tains the motor or motors for manipulating the drill string.
Although not illustrated, the other end of the drill line is secured to an anchor on the platform floor, that portion of the line extending to the anchor from the crown block being generally referred to as the'dead line. Again not illustrated, such an anchor member normally would include a winding-on drum and can ~lso, if desired, contain a dead line senSor for monitoring the weight on the bit, for example,' as shown in U. S. Patent No.
3,461,978 to F. Whittle, issued August 19, 1969.
: In ~he operation o~ the system according to FIG. 1, it is quite conventional in drilling wells from such offshore plat-forms to drill the initial portion o the well substantially along a vertical line from the platform and then to angle'off in the'~urther drilling of the weIl. Such wells after angling off will oftentimes be inclined at an angle of 60 to 70 ~rom vertical. It is with these types of highly deviated wells that the'problem Presents itself as to providing a log of the forma-tions surrounding the well bore, Re~errin~ no~ to FIG. 2, t~ere'is illustrated schemati-cally a well logging operation conducted in accordance with the -4~

prior art in which a portion of the earth~s surface 12 is shown in vert~cal section~ A weIl 13,' wh~ch h~s been drilled as illus-trated in FIG. l, penetrates the''earth~s surface. Disposed with~
in the well is subsurface instrument 30 of the well logging S system. The subsurface instrument 30 may be of any conventional type, for example, one which is adapted to conduct an induction, electric, acoustic, or any other of the conventional logs well known in the art~ It should be appreciated, moreover, that the particular type of weIl loyging instrument 30 forms no part of the present invention.
Cable 32 suspends the instrument 30 in the well and contains the required conductors for el~ctrically connecting the instrument 30 wlth the surface electronics. The'cable is wound on or unwouna from drum 33 in raising and lowering the 1~ instrument 30 to traverse the well. During the travexsal, the signals from the well logging instrument 30 are sent up the cable 32. Through slip rings and brushes 34 on the end of the drum 33~ the s~gnals are'conducted by the lines 35 to ~he surface electronics 36. A recorder 37 connected to the surface elec-20 ~ tronics 36 is driYen through the transmission 38 b~ the measuringreel 3~ over wh~ch the cabls 32 is drawn, so that the recorder 37 assosiated w~th the surface'eIectronîcs 36 moves in correlation with depth as instrument 30 traverses the well, It is also to be understood that instruments such as the'instrument 30 are general-ly constructed to withstand the pressures and mechanical andthermal abuses encountered in logging a deep well.
- In the operation of the system illustrated in FIG. 2, the cable 32 is touching one'ledge of the formation at the point 42 and the instrument 30 has come to rest agains~ another such ledge ~t the point 43l tI~e'ledge'43 making it exceedingly diffi-cult, if not impossible, for tT~e' instrument 30 to traverse the earth bsrehole merely by its own weight due to the force of gxavi~y.

JI~

~eferring now to FIG, 3, the~e is illustra,ted schemati-cally a weIl logging operation which has been us~d by those in the prior art in an attempt to traverse highly deviated earth boreholes in which a portion of t~e'earth's surface 12 is shown S in vertical section. A well 13 which has been drilled as illus-trated in FIG. 1 penetrates the earth''s surface. Disposed within the well is subsurface instrument 30 of the weIl logging system.
Subsurface instrument 30 includes a logging module 31 which may be of any conventional type. ~or example, it may be an induction, 1,0 electric, acoustic or any other of the convenkional logs well known in the art. Cable 32 suspends the instrument 30 in the well and contains the required conductors for electrically connecting the instrument 30 with the surface apparatus. The cable is wound on or unwound from drum 33 in raising and lowering the instrument 30 to traverse the well. During the traversal, the signals from the well logging module 31 are sent up the cable 32.
Through'slip rings and brushes 34 on the end of the drum 33, the signals are conducted by the lines 35 to the surface electronics 36. A recorder (not illustrated) within the surface electronics 36 is driven through the transmission 38 by the measuring reel 39, over which the cable 32 is drawn, so that the recorder within the surface electronics moves in correlation with depth as instrument 30 traverses the well.
~s illustrated in FIG, 3, the'instrument 30 has a plurality of flexi~le vanes 40 which are slanted in the upward direction and which, as will be explained in more detail herein-after, help the instrument 30 to be'lowered into the highly deviated borehole.
It should be'noted that the cable,32 is resting against a iedge 42 which also hinders the''tool 3Q from being lowered into the'earth'borehole'simply by the ~orce'of gravity~
,Referring now to FIG. 4, there is schematically illustrated a ~ell lo~ging opexation in acc~rdance with the present inv~ntion which ut~lizes a weIl logging instrument 30' constructed substantially as the'instrument 30 in accordance with FIG. 3 but w~ich also has an accelerometer 47 for measuring the acceleration of the weIl logging instrument 30'. In addition, the surface electronics section 36 has incorporated therein a yelocity indicator circuit 46 which measures the velocity of either the drum 33 or the cable 32 by means of a sensor 44 which is connected to the velocity indicator circuit 46 by means of 1~ the'conductor 45, all of which will ~e discussed in more detail hereinafter~
Referrin~ now to FIG. 5, the instrument 30' is illus-trated in greater detail. The instrument 30' has a plurality of pulsed electromagnets 50 which are fixedly attached to the support mandrel of the instrument housing 30' by the spacer eIement 51, and by a similar such element 52 between each of the elec'tromagnets. A floating sleeve 53 constructed, for example, from a hard plastic material or some other such material which will not substantially affect the ~agnetic characteristics of the electromagnets and the permanent ring magnets 54 which are embedded therein, is adapted to slide up and down around the mandrel containing the el'ectromagnet's.
The spacer 51 is attached to an end plate 60 which in turn is attached to a spring 61 acti-ng against an additional end plate 62.
In a similar manner, the'spacer 52 at the lower end of the mandrel is attached to an end plate 63 against which a spring 64 rides whicll is attached to an additional end plate 65. Passing through the center of the various end plates' and the electro-ma~nets is an electrical cable'66 which is connected to the cable32 and also to the''logging module 31, Electrical conductors are also connected bet'ween the various eI~ctromagnets and the control electronics incorporated within the'logging module 31 for pulsing the electromagnets, This, o~ course,' can be done from the earthls surf~ce or in response to s~me predetermined occurrence to cause the electromagnets to be pulsedp In the preferred embodiment of the invention, however, the predeter'mined occurrence is the adverse comparison of the instrument velocity with the velocity of the well logging cable at the earth's surface. The measure-ment of the instrument velocity is accomplished by the use of an accelerometer 47 within the'instrument 30'.
In the operation of the apparatus according to FIG. 5, it should be appreciated that the assembly comprises, effectively, a linear reciprocating motor. The motor powers a sleeve 53 to which the vanes 40 are attached and having a particular slant, in this case slanted in a direc~ion uphole. The permanent ring -15 magnets are all oriented in the same direction. As the coils are pulsed alternatively, the magnets are either repulsed or attracted which thus generates a reciprocating motion which, transferred to the vanes 40, moves the tool up or down, depending upon the position of the reversing actua~or discussed hereinafter with respect to FIGS. 6 and 7.
It should be appreciated that the sleeve 53 is effec-tively floating around the el0ctromagnets because o the springs 61 and 64 at opposite ends of the assembly. However, the inven-tion also contemplates the'use of nei~her of the springs 61 and 64 and ha~ing a truly floating sleeve. The invention also con-templates the use of a single spring against which the motor will operate in alternating cycles.
In any event, in the operation of the apparatus in accordance with FIG. 5, in response'to an adverse comparison of the two velocities, the'vanes 40 will engage the mud cake or the borehole wall and thus generate'a force opposite to the dixection of the vane slant. This in turn will enable the apparatus in accordance with FI~. 5 to move ~long the highly deviated bore- ~
holes.
Referring now to FIG. 6, the reversing actuator is schematically illustrated and is shown as having a solenoid 70 S through which a rod 71 is actuated by the solenoid. The lower end of the rod 71 is connected to a spring 72 which in turn is anchored to the end plate 63 illustrated in FIG. 5. It should be appreciated that the reversing mechanism is carried by the sleeve 53. Each of the vanes 40 is pivoted about pivot points 8Q which are fixedly attached to the sliding sleeve 53. Each of the flexible vanes has an elongated slot 81 through which pivot pins 82 ride and which are fixedly attached to the solenoid - rod 71.
In the operation of the apparatus in accordance with FIG. 6, whenever it is desired to have the instrument 30' travel downhole, the solenoid 70 is not actuated, and the spring 72 pulls the rod 71 down and thus causes the vanes 40 to ~e in the position illustrated.
Whenever ~t is desired to br;ng the instrument 30' out ~f the borehble, the solenoid 70 is actuated, preferably from the earth's surface~ and the rod 71 moves up against the spring 72.
This causes the vanes 40 tQ rotate around the pivot point 80 and while the pivot points 82 are sliding through the slots 81, the outer ends of the vanes will pivot down in the direction to facilitate removal of the apparatus 30l from the borehole.
Referring now to FIG. 7, there is illustrated a top plan ~iew taken along the cross section lines 7-7 of FIG. 6. As sho~n in FI~ 7, the vane 40 is adapted to be rota~ed around the piVot pin 80 and is attached to the solenoid rod 71`by the pin 82 which slides within the slot 81 illustrated in FIG~ 6.
~ eferring now to FIG. 8, there is illustrated a well loggin~ instrument 90 which is suspended within the earth borehole _g_ ~$~

98 by ~eans o~ ~ wel'l logging cable'91, The'wel'l logging instru-ment 90 includes an upper weIl logging instrumentation section 92 which may be of any convention~l type. The instrument also con-tains an accelerometer 93'and a valve'control electronics section ~4. The'valve control el'ectronics sect~on is connected by means of one or more wires 101 through a conduit 100 to a valve 99 which is located within the orifice g7 within the body 95 of the lower section of the well logging apparatus 90. The apparatus 90 also includes a fluid chamber 96 within which a friction-reduction agent is locatedO The chamber 96 conta~ns a piston 102 having an O-ring or other sealing member 103. The piston 102 is forced against the fluid within the chamber 96 by means of a spring 104.
A p~essure equalizing pQrt 105 maintains the upper portion of the chamber 96 in contact with the pressurized fluid within the borehole 98.
In the operation o~ the apparatus illustrated in FIG. 8, as the well logging instrument 30 traverses the earth borehole 98, upon a command from the valve control eIectronics section 94, the valve 99 is actuated and the ~riction-reduction agent within the 2Q chamber 96 beneath the piston 102 is ported into the borehole to reduce the friction around the well logging instrument 90. The action Qf t~e valve'control electronics 94 will be more readily appreciated from khe des'criptions hereinafter relating to FIGS
9 and 10. It should be'understood, however, that the embodiment o~ FIG, 8 contemplates that the friction-reduction agent is ported into the borehole through the valve'~9 only upon a command from the valve control electronics section 94.
Referring now to FIG. 9, the well lo~ging instrument 90 illustrated in FI~. 8 is shown in elevated view within an earth borehole'and is suspended b~ ~ weIl loyg~ng ca~le 91 from the earth's surface and w~ich passes over a measuring sheave 39 to the drum 33 as is illustrated in FIG~ 2~ However, in addition to the ~urface apparatus illu$tratea in FIG~ 2~ the. sur~ace app~ra~us of FIG~ 9 includes a sensor 44 which'monitors the velocity of the drum 33 as it rotates' as an indication of the veloc~ty of the logging c~ble 91, The signal from the sensor 44 passes over a conductor 45 to a con~entional veIocity indicator circuit 46. As was illustrated in FIG, 8, the well logging instxument 90 includes an accelerometer 93 which, together with the signal ~rom the velocity indicator circuit 46 at the surface, controls the fluid which is caused to be ported from the orifice 10 . 97 in the lower portion of the well logging instrument 90.
Referring now to FIG. 10, the functions of the appara-tus illustrated and described with respect to FIGS. 8 and 9 are shown in block diagram. The block 110 is indicative of a signal relating to the surface veloci~y of the well logging cable, and this signal is passed along a conductor wlthin the well logging cable, shown generally by the numeral 114, to.a comparator cir-cuit 112 which is located with.in the valve control electronics section 94 in the subsurface instrument 90. The line 113 is functionally related to the separation between the sur~ace elec-tronics and the subsurface'electronics. The output from the ~ ' accelerometer 93 is passed into a conventional veloclty circuit 111 which converts the accelerometer signal into a velocity si~nal in a manner well known in the art~ The velocity signal ~rom the subsurface velocity c~rcuit 111 is compared with the surface velocity signal 110 in the'comparator circuit 112 and whenever a signal of predetermined magnitude from the comparator circuit 112 exists, a signal is passed to the actuator circuit ~9, or exa~ple, the valve'99, with.in the orifice'97 to thereby . port the fluid within the'chamber 96 into the borehol~.
It should be appreciated that when the well logging instrument 90 is bei'ng ~used to traverse the borehole by means o~ the cable 91, the w~l'1 logg~ng cable at the'surface will not s~

always be traveling at the exact ~elocit~ as that -of the borehole instrument. This is causea by various reasons, such as the stretch of the well logging ca~le and the 'encounter of the well logging instrument with ledges and other deviated portions within the earth borehole, However, it may not be'desirable to actuate the valve'99 upon every minute 'dif~erence'indicated by the com-parator 112. Thus~ the comparator 112 can be'set by means well known in the art to generate a signal to the valve or other actuator means 99 upon the diff~rence between the two velocity signals exceeding some predetermined magnitude, for example, a 5% or 10~ difference.
Referring now to FIG. 11, an alternative embodiment of the present invention is schematically illustrated, partly in block diagram. A subsurface accelerometer i20 which'is located within a well logging tool such as that illustrated, for example, in FIGS. 4 or 9, has its output connected to a su~surface velocity circu~t 121 within the well logging tool which has its output - conducted to the surface elec~ronics through the conductor 122 within the weIl logging cable 123. The line 113 symbolically illustrates the delineation between the surface and subsurface equipment. The well logging cable 123 is wound around the hoist drum 124 which is controlled by a conventional motor and gear box 125 driven by a cable hoist control unit 126. A surface velocity ind;cator circuit 127 having its input connected to a velocity sensor (not illustrated) such as is lllustrated in FIG. 9 and which is indicative of the velocity of the well logging cable at the surface~ has its output connected to a comparator circuit 128. The electrical signals indicative of the subsurface velocity which i~ conducted along the electrical conductor 122 is taken off the slip rings 129 on the end of the hoist drum 124 and are conducted along the'connector 130 to another input of the comparator circu~t 128~

~ ~3~

In the operation o~ the apparatus ~nd ci~cuitry illus-trated in FIG. 11, as the well logging Inst~ument traverses the earth boreholer the accelerometer 120 provides a signal to the subsurface veIocity circuitry 121 and a signal indicative of the veIocity of the weIl logging inst~ument is thus applied to the comparator circuit 128. The velocity of the well logging cable at the surface from the surface velocity circuit 127 is also applied to the comparator circuit 128~ Thus, in contrast to the embodiments hereinbefore descr~bed, there is not necessarily a subsurface source of motive power other than, for example, the stiffness of the logging cable 123 and the effect of gravity.
In such a case, the well logging instrument may be moving do~m-ward at varying velocities, depending on the local mud and bore-hole conditions. Assuming that the weIl logging instrument does not become finally stuck within the borehole, it is desirable to continue the rotational movement of the hoist drum 124 so as to push constantly on the well logging instrument without running the risk of overrunning the weIl losging instrument with too much cableO In this event, by comparing the veloci~y of the sub--20 surface instrument and the velocity of the weIl logging cable at the surface in the comparator circuit 128, an output signal is produced from the comparator circu~t 128 to the cable hoist control circuitry to thereby drive the motor and gear box 125 and hence the hoist drum 124 to slowly unreel the logging cable 123.
By so doing, the well logging instrument is encouraged to continue to move along through the borehole, however slowly, by paying out the well logging cable at the appropriate velocity. By way of further example, when the difference signal produced by the com-par~tor circuit 128 becomes too large, indicating that the well logging instrument is slowing down, the hoist drum 124 is also slowed down. Again, when the difference signal from the compara--tor circuit 128 begins t~ go toward zero, the cable hoist control circuit 126 generates a larger signal to thus m~ke the''hoist drum 124 turn faster ~nd pay out ~ore.well logging cable to keep up with the increased velocit~ of the well logging instrument.
~eferring now to ~I&, 12, an alternative embodiment of the present invention is described which incorporates the features of FIG. 10 with ~hose of FIG. 11. The'subsurface'accelerometer 124 located within the well logging instrument (not illustrated) has its outpu' connected to a subsurface velocity circuit 141 whose output in turn is connected to the'input of a comparator :: 10 circuit 142`which drives an actuator 143, for example, the valve 99 within the'oriice 97 illustrated in FIG. 8 or the control module for controlling the vanes in the embodiment illustrated in FIG. 5. The output of the subsurface velocity circuit 141 is : also connected by means of a conductor 144 located within the well logging cable 146 to the earth's surface. A s~rface velocity circuit 150 which provides a signal indicative of the'velocity of the well logging cable at the surface as hereinbefor~ described has its output connected to a comparator circuit 151. The surface velocity output signal is also conducted by means of conductor 153 which passes through the'slip rings 154 on the end of the hoist drum 147 and is conducted to the subsurface instrument by means of the weIl logg;ng cable 146 along the conductor 145 to the second input of the comparator circuit 142. The signal which passes along the conductor 144 through the well logging cable 146

2~ i5 taken off the slip rings 154 and is connected into anoth~r input o~ the comparator circuit 151 by means of the conductor 15~.
The output of the comparator circuit 151 is connected into the cable hoist control circuit 149 which drives the motor and gear box 148 which in turn drives the'hoist drum 147.
In the'operation of the apparatus and circuitry illus-trated ;n FIG. 12, it should be appreciated that as the accelero-meter 140 measures the 'acceleration of the'weIl logging instrument and which consequently produces a si~n~l indicative o~
the'subsurf~ce velocity thr'~ugh the circuit 141,,the'subsurface veIocity is thus comparea with.'the veIocit~ of the cable at the surface by means of the comparator 142, Whenever a significant difference is exhibited between the two velocities, the actuator 143 is actuated to thus make, or at least attempt to make, the well logging instrument proceed through the'borehole at a greater velocity.
. , The subsurface velocity of the well logging instrument is also compared with'the velocity o~ the cable at the earth's surface in the comparator circuit 151 ~o control ~he movement of the hoist drum 147 as was discussed with respect to the embodiment of FIG. 11. Thus, if the well logging instrument continues to slow down, even though the actuator 143 has-been providing addi-tional motivatlon for the well logging instrument, the comparison - circuit 151 will produce a greater output signal which causes a reduction in the rotational movement of the drum 147 and thus will cause less well logging cable to pay out. Through the combined apparatus and circuitry illustrated in FIG. 12, the well logging instrument w-ll strive to motivate itself whenever it starts to slow down because of the borehole conditions and even should it start to slow down, despite the activation of the actuator 143, the cable hoist will also slow down in order to avoid too much cable bein~ payed out. Whenever the instrument starts to speed up, the 'comparator circuit 151 will produce a lesser signal which will in turn cause the hoist drum to speed up and stay with the well logging instrument.
Thus there have been illustrated and described herein the preferred embodiments of the present invention.which provide ' methods and apparatus for activating means to facilitate the ~ovement o~ the'well logging apparatus through the'borehole and for preventing too much pay out of the logging cable. However, ~15- -;

those'skilled in the art will recogni.ze that o~v~ous modifications c~n be mad~ 'to the pre~erred embod~ments w~th.out departing from the'spirit of the'invention.. For example, instead of using a high molecular weight pol~mer for the f~icti.on-reduction agent, other such well-known friction-re~uction a~ents can be'utilized.
Furthermore, instead of using a valve'dependent upon changes in velocity, other parameters can be measured and the valve or other such device for porting the friction-reduction agent into the bQrehole can be activated as a response to such parameters. Still ~urther, instead of measuring the'velocity of the drum at the earth's surface, the velocity o~ the cable can be measured in other conventional manners. In addition, a strain gauge can be used on the cable head at the top of the well logging instrument t~ provide an indication of changes in the velocity of the instrument.

Claims (2)

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

1. Apparatus for logging the formations surrounding an earth borehole, comprising:
a rotatable hoist drum at the earth's surface;
a well logging cable wound around said hoist drum;
an elongated well logging instrument connected to the earth's surface by said well logging cable and adapted to traverse an earth borehold, the pay out of said cable being controlled by the rotation of said hoist drum, said instrument having therein an accelerometer and means to convert the acceleration of said instrument into an indication of instrument velocity;
means at the earth's surface for providing an indication of the velocity of said well logging cable at the earth's surface; and means for comparing the velocity of said instrument with the velocity of said well logging cable at the earth's surface and to generate signals indicative of said comparison, the rotation of said hoist drum being responsive to said comparison signals.

2. A method for logging the formations surrounding an earth borehole, comprising:
causing a well logging instrument to traverse an earth borehole by means of a well logging cable wound around a rotatable cable hoist drum at the earth's surface;
measuring the velocity of said cable at the earth's surface;
measuring the velocity of said well logging instrument;
comparing the said cable velocity with the said instru-ment velocity and generating signals indicative of the comparison; and controlling the rotation of said cable hoist drum in response to said comparison signals.