Note: Descriptions are shown in the official language in which they were submitted.
34~5
Back~round of the Invention. This invention relates
generally to apparatus Eor logging earth boreholes and specifi-
cally to metho~ls and apparatus which utilize means in addition
to, or wh~ch aid gravity in causing the well logging instruments
to traverse the high angled earth boreholes.
It has become relat:ively common within the last few
years to drill wells in the search for oil and gas and the like
with a portion of the bore devia-ting from the usua] ver-tical
orientation thereof. The deviation or inclination may extend
for a considerable distance at angles ranging to 70, sometimes
returniny 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 ar-t of drilling such wells
to attempt the logging of the formations surrounding such bore-
holes with logging instruments run into the well bore on a wire-
line and/or a cable to perform various operations. Such tools
usually depend upon the force o~ gravity to permit positioning
of the well tool at the desired formation in the well bore.
~25 lYanifestly, the relatively hcjrizontal angle of the
deviated portion of the well bore will not permit the wireline
actuated tools to move into the lower portion of the well bore
since friction of the well tool in the deviated portion works
acJainst the force of gravity. Thus it has become essential to
provide some means of causing the weIl logging instrument to
pass through the deviated portions of the well bore.
Another pxohlem associated with such boreholes relates
--1--
..~,~
3~i
~o the instability of some formations penetrated by the well
bore, thus causing borehole di,ameter changes, some very abrupt.
Ledges are formed, and the logging instrument lodg~s against
them.
Yet another problem exists because the hoist drum keeps
. rotatlng after the well logging instrument slows down, sometimes
- to a complete stop, and too much cable is payed out.
It is therefore the primary object of the present
invention to provide new and improved methods and apparatus for
: 10 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 dif~icult for the well logging instrument to
traverse the borehole. ':
The above object is met by the present invention which
broadly provides a method for.logg.ing the formations surrounding
an earth borehole, comprising: causing a well logging instrument
to traverse an earth borehole by meaDs of a well logging cable
from the earth's surface; measuP.ing the velocity of the cable
- 20 at the earth's surface; measuring the velocity of the'well
logging ins~rument; comparing the cable velocity with the
instrument velocity and generating a signal indicative of the
comparision; and activating means within the instrument respon-.
sive 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 formations surrounding an earth borehole~ com-
prising: an elongated well logging instrument c~nnected to the
earth's surface by a well logging.cable and adapted to traverse
,: 30 an earth borehole, the instrument having therein an accelero-
meter and means to convert the acceleration of the instrument
into an indication of instrument ~elocity, the instrument also
.
'. 5d/~ -2-
. .
.
3~
.aving means therein acti~atable 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 earth's surface and
to generate a signal indicative of the comparison, the
activatable means within the instrument being responsive to the
comparison signal.
These and other objects, features and advantages of
the present invention will be apparent rom the following
detailed description taken with reference ~o 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;
FI~. 2 schematically illustrates a prior art well
logging system encountering some of the problems associa-ted
with logging a highly deviated earth borehole;
~'"~` .
. *
sd/~ 2A-
.
.
`
~ G~ 3 schemat~cally illu~tr~te~ a P~i~r ~rt well
lQ~ing syste~ ~hich has been used in ~n attempt to o~erco~e
some of the pro~lems as ~raphically illustrated in FIG. 2;
FIG. 4 is an eIevated v~ew, partly in cros~ section,
of the apparatus according t~ 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
siect~on, showing the reversing mechanism for changing the direc-
tion of the slant of the vanes;
FIG. 7 is a top plan view, partly in cross sectionr
taken along the lines 7-7 of FIG~ 6;
FIG~ 8 is an eIevated 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 accordance with the apparatus
according to FIG. 8;
~IG. lO illustrates in block diagram por-tions of the
~unctions accomplished by the system illustrated in FIG. 9;
FIG. 11 illustrates schematically, partly in block
diagram, an alternative embodiment of the invention; and
FIG. 12 illustrates schematically, partly in block
diagram, yet another embodiment o~ the invention.
Re~erring now to the drawing in more detail, especially
to FIG. 1, thexe is illus~rated schematically a conventional
system for drillin~ an earth borehole having a high degree of
de~iation ~ro~ true vertical. As is wall known in the art, it
~'s com~on pract~ce to dr~ll suc~ slanted weIls from offshore
platforms~ A drilling plat$or~ 10 having a plurality of legs 11
.
--3-
:. , : . .
. ~
- - - . : .
'$~
anchored on the ocean ~loor 12 h~s ~n ea~th borehQle 13 drilled
therefrq~, Wi~hin ~he borehole 13 i~ a pipe str~ng 14r to the
lower end of wllich is ~ttached a drill ~it 15. A suxface casin~
25 maintains the inte~rity of the borehole 13 as is well known
in the art. A derrick 16 with it~ conventional drawworks 17 is
mounted on the platform 10. The dr~11 string 14 comprises a
number of joined sections of pipe term~nating at its upper end
in a kelly 18, followed by a swivel 19~ a hook 20 and a traveling
block 21 suspended by a dr~ ng line 22 ~rom a crown block 23
The drawworks also drive a rotar~ table 24 wh~ch in turn trans-
m.itS the drive ~o the kelly 18. One end of the 11ne 22, namely
the fast line 22a, is connected to the drawworks 17 which con-
tains the motor or motors for manipulating the drill string.
~lthough not illustrated, the other end of the drill line is
secured to an anchor on the platform floor, that portion of the
line extendin~ to the anchor from the crown block being generally
referred to as the dead l~ne. Again not illustrated, such an
anchor member normally would include a winding-on drum and can
also, if desired, conta~n a dead line senso~ for monitoring the
weight on the bit, for example, as shown in U. S~ Patent No.
3,461,978 to ~. Whittle, issued Augu~t l9r 1969~
In the operation of the system according to FIG. 1, it
is quite conventional in drilling wells from such offshore plat-
for~s to drill the initial portion of the well substantially
along a vertical l~ne from the plat.~orm and then to angle off in
the further drilling of the weIl~ Such wells after angling off
will oftentimes be inclined at an angle of 60 to 70 from
~ertical. It:is with these types of h~.ghly deviated wells that
the problem presents itself as to providing a log of the forma~
tions surroundin~ the well bore~
Re~erring now to FIG. 2, there is illustrated schemati- ;
cally a weI1 logs~ng operation conducted in accordance with the
3~;
prior art in which a portion of the e~rth~s su~face 12 is shown
in vert~cal sect~on~ ~ weIl 13, ~hich has been drilled as illus-
trated in FIG. 1, penetrates the earth~s surface. Disposed with~
in the weIl is subsurface instrument 30 o~ the well logging
system. The subsurface instrument 30 may be of any con~entional
type, for example, one'whic~ is adapted to conduct an induction,
electric, acoustic, or any other of the conventional logs well
known in the art~ It shoulrl be appreciated~ moreover, that the
particular type o~ weIl logg~n~ instrument 30 forms no part of
the present invention~
Cable 32 suspends the instru~ent 30 in the'well and
contains the required conductors for electrically connecting
t~e instrument 30 with the surface electronics~ The cable is
~ound on or unwound from drum 33 in raising and lowering the
Lnstrument 30 to traverse'the well. During the traversal, 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 the surface
eIectronics 36. A recorder 37 c~nnected to the surface elec-
tronics 36 is driven through the'transmission 38 by the measuringreel 3~ over which the cable 32 is drawn, so that the recorder 37
associated with the surface'eIectronics 36 moves' in correlation
with depth as instrument 30 tra~erses 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 weIl.
- 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 against another such
ledge'at the point a3, the ledge 43 making it exceedingly diffi-
cult, if not impossible, for tlie instrument 30 to traverse the
earth bbrehble merely by its own ~eight due to the force of
gravity.
-5-
~eferxin~ now to ~IG~ 3~, the~e is illus,tra,ted schemati~
call~ ~ ~eIl log~ing operation which has been used by those in
the prior a.rt in an attempt to traverse highly deviated earth
boxeholes in which'a portion of t~e'earth's surface 12 is shown
in vert~cal section. ~ weIl 13 which has been drilled as illus-
trated in FIG. l penetrates the` earth ~5 surface. Disposed within
the well is subsurface instrument 30 of the well logging system.
Subsurface instrument 30 includes' a logging module 31 which may
be of any conventional type. For example,' it may be an induction,
eIectric, acoustlc or any oth~er o~ the conventional 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 ~nd lowering
the in trument 3a to traverse'the well, During the traversalj the
signals from the weIl 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'suxface electronics
36. A recorder (not illustrated) within the sur:~ace electronics
36 is driven through the trans~ission 38 by the measuring reel 39t
over which the cable 32 is drawn, so that the recorder within the
suxface electronics moves in correIation with depth as instrument
30 traverses the well.
~s illustrated in FIG~ 3~ the instrument 30 has a
pluxality 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 highIy
deviated borehole.'
It should be''noted that the cable~32 is resting against
a ledge 42 ~h.i'ch'als~ hinders the tool 3Q from being lowered into
t~e e~rth'borehole simply ~y the force'of gravity~
~eferring now to F~G. 4, there is schematically
~h~
illustr~ted a well logging operation in acco~dance ~th the
present invention wh.~ch ut~lizes a weIl lo~ing instrument 30
constr~c~ed suhstantiall~ a$ the'instrument 30 in accordance
wi~h FIG. 3 but which also has an acceIerometer 47 ~or measuring
the acceleratlon of the we:Il logg~ng instrument 30'. In addition,
the surface eIectronics section 36 has incorporated therein a
velocity indicator circuit 46 w~i'ch measures the veIocity of
either the drum 33 or the cable 32 by means o~ a sensor 44 which
is connacted to the veIocit~ indicator circuit 46 by means of
lQ the conductor 45, all o;~ which'will be 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 eIectromagnets 50 which are fixedly attached to the
support mandreI o~ the instrument housing 30' by the spacer
eIement 51, and by a similar such element 52 between each of
the el'ectromagnets. A floating sleeve ~3 constructed, for
example, from a hard plastic material or some other such material
: , which will not substantially a~ect the magnetic characteristics
2~ o~ the'electromagnets and the permanent ring magnets 54 which
are embedded t~erein, is adapted to slide up and down around
the ~andreI containing the electromagnets.
The spacer 51 is attached to an end plate 60 which in
turn is attached to a spring 61 acting against an additional end
plate 62.
In a similar manner, the'spacer 52 at the lower end of
the mandreI is attached to an end plate~63 against which a spring
64 rides which is attached to an additi,onal 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 between the various eIectromagnets and the control
r3~
electronics incorporated with~n the logging module 3I for pulsing
the electrom~gnets, This, of course ! can be done'~r3m the earth's
sur~ace or in response to some'predetermined occurrence to cause
the electromagnets to be pulsed~ In the'preferred embodiment o
the invention, however, the predetermined 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 accompllshed by the use of an
acceIerometer 47 wlthin 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 direction uphole. The permanent ring
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, mo~es the'tool up or down, depending
upon the position of the rever~ing actuator discussed hereinafter
with respec~ to ~IGS. 6 and 7.
It should be appreciated that the sleeve 53 is effec-
tiveIy $10ating around the eIectromagnets because of the springs
61 and 64 at opposite ends of the assembIy. However, the inven-
tion also contemplates the use of neither of the springs 61 and
64 and ha~ng a truly ~loating 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 xesponse'to an adverse comparison of
the two veIocities, the'~anes 40 will engage the mud cake or the
~orehble ~all and thus generate a force opposite to the direction
of the vane slant. This in turn will enable the apparatus in
.
3~
accordance with FIG. 5 to move alon~ the hlghIy deviated bore-
holes.
Referring now to FIG. 6, the`reversing actuator is
schematically illustrated and is shown as having a solenoid 70
through which a rod 71 is actuated by the solenoid. The lower
end of the rod 71 is coIlnected to a spring 72 which in turn is
anchored to the end plate 63 illustr~ted 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
~0 8~ which axe ~ixedly attached to the sliding sleeve 53~ Each
of the flexible vanes has an eIongated 510t 81 through which
pivot pins 82 ride and which are fixedly attached to the solenoid
xod 71.
In the operation o~ 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 be in the
, position illustrated.
Whenever it is desired to bring the instrument 30' out
of the borehole,' the soleno~d 7Q is actuated, preferably from the
earth's surface~ and the rod 71 moves up against the spring 72.
This causes the vanes 40 to 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 30' from the boxehole.
Referring now to FIG. 7, there is illustrated a top
plan view taken along the cross section lines 7-7 of FIG. 6~ As
, ' shown in FIG~ 7, the vane 40 is adapted to be rotated around the
pi~ot pin 80 ~nd is attached to the solenoid rod 71 by the pin 82
which slides wit~in the slot 81 i,llustrated in FIG. 6.
Referring now to FIG. 8, there is illustrated a well
logging instrument 90 which is suspended within the earth borehole
3~i
98 by means o~ a well loggin~ cable'91., The wel'l log~ing ~nstru-
ment 90 includes an upper well log~ing instrumentation sectlon 92
which may be of any convent~onal type~ The instru~ent also con~
tains an accelerometer 93 and a valve'control electronics section
94. The valve control eIectronic6 se:ct~on is connected by means
of one or more wires 101 through'a conduit 100 to a valve 99
which is located within the ori~ice 97 within the body 95 of the
lower section o~ the well log~ing apparatus 90. The apparatus 90
also includes a ~luid chamber 96 within which a friction~reduction
lQ a~ent is located. The'chamber g6 conta~ns a piston 102 having an
O-ring or other sea`ling member 103. The'piston 102 is forced
against the fluid within the chamber 96 by means of a spring 104.
Pressure equalizing port 105 maintains the upper portion of the
chamber 96 in contact with the pressurized fluid within the
borehole 98.
~n the operation of the apparatus illustrated in FIG. 8, ~:
as the weIl logg~ng instrument 90 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
chamber 96 beneath the piston 102 is ported into the borehole to
reduce the friction around the weIl logging instrument 90. The
action Qf the valve'control electronics 94 will be more readily
appreciated from the descriptions hereinafter relating to FIGS.
9 and 10. It should be'understood, howevert that the embodiment
o~ FIG. 8 contemplates that the ~riction-reduction agent is ported
into the borehole through the valve 99 only upon a command from
the valve control electronics section 94.
Referring now to FIG. 9, the well logging instrument 90
illustrated in FIG. 8 is shown in eIevated view within an earth
borehole and is suspended by a we:Il logging ca~le 91 from the
earth's surface and which passes over a measuring sheave 39 to
the drum 33 as is illustrated in Fr~ 2~ However, in addition
10-
f.~
to the s,ur~ace apparatus illu$trated ~n FI~G e 2r the sur~açe
apparatus o~ FIG~ 9 include~ ~ sensor 4~ which'monitors the
velocity o~ the drum 33 as it rotates as an indicatiQn of the
veIocity of the logging cable 91. The'si~nal from the sensor 44
passes over a conductor 45 to a conventional vel'ocit~ indicator
circuit 46. As was illustrated in FIG~ 8, the'well logging
instrument 9Q includes an acceIer'ometer 93 which, together with
the signal ~rom the'velocity indicator circuit 46 at the surface,
controls the fluid which is caused to be ported rom the orifice
97 in the lower portion of the well logg~ng instrument 90.
~', Referring now to FIG. 10, the ~unctions o~ the appara-
`, tus illustrated and described with respec't to FIGS. 8 and 9 are
shown in block diagram. The block 110 is indicative of a signal
', relating to the surface vel'ocity of the weIl logging cable, and
: 15 this signal is passed along a conductor within the weIl logging
cable, sho~n generally by the numeral 114f to a comparator cir-
cuit 112 ~hich is located within the valve'control electronics
secti,on 94 in the subsurface'instrument 90. The line 113 is
, ~unctionally reIated to the'separat~on between the surface elec-
tronics and the subsur~ace eIectronics. The output from the
acceIerometer 93 is passed into a conventional velocity ci,rcuit
111 whi'ch converts the acceIerometer signal into a velocity
signal in a manner well known in the art~ The velocity signal
from the'subsurface velocit~ circult 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 ac-tuator circuit
99, ~ox example, the valye 99, within the orifice 97 to thereby
port the fluid within the chamber 96 into the borehole.
It should be appreciated that whQn the weIl logging
instrument 90 is being caused to traverse the borehole by means
of the cable 91, the well logging cable'at the'surface will not
3S
always be traveling at the exact velocit~ as that o~ the borehole
~nstrument. This is caused by var~ous reasons, such ~5 the
stretch of the well lo~ging ca~le and the encounter of the well
logging instrument ~ith ledges: a~d other deviated portions within
the earth borehole, However, it may not ~e:`desirable to actuate
the valve 9~ upon every minute difference'indicated by the com-
parator 112. Thus d 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'difference between the two velocity
lQ signals exceeding some predetermined magnitude, for example, a
S~ or 10% di.~Eerence.
Referring now to FIG. 11, an alternative embodiment of
the present invention is schematically illustrated, partly in
block diagram. A subsurface acceIerometer 120 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 subsurface velocity
circu~t 121 within the well logging tool which has .its output .
conducted to the surface'eIectronics through the conductor 122
within the weIl logging cable 123. The line 113 symbolically
illustxates the delineation between the surface and subsurface
equ~pment. The weIl 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
~elocity indicator circuit 127 havin~ its input connected to a
veloci-ty sensor (not illustrated) such as is illustrated in
FIG. 9 and which is indicative of the veIocity of the weIl logging
cable at the surface, has its output connected to a comparator
circuit 128. The electrical signals indicative of the subsurface
velocity which i5 conducted along the: eIectrical conductor 122
is taken off the slip rings 129 on the'end of the hoist drum 124 .-
and are'conducted along tIIe'connector 13G to another input of
the compara-tor circu~t 128,
-12-
In the oper~tion o~ the'a~paratus and ci~cuitry illus~
trated in FIG 11, as the'weIl lo~ing ~nstrument traverses the
earth borehole, the acceIerometer 120 provides a signal to the
subsurface veIocity circuitry 121 and a signal indicative of the
veIocity of the weIl log~ing instxument is thus applied to the
comparator circuit 128. The veIocity of the weIl 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 here~nbefore'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 down-
ward at varying velocities, depending on the local mud and bore-
hole conditions~ Assuming that the well logging instrument does
not become f~nally stuc}- 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 o~ overrunning the well logg;ng instrument with too
much cable. In this event, by comparing the velocity of the sub-
surface'instrument and the veIocity o~ the weIl logging cable atthe surface in the'comparator circui-t 128, an output signal is
produced ~rom the comparator circuit 128 to the cable hoist
control circuitry to thexeby drive the motor and gear box 125 and
hence the hoist drum 124 to slowly unreel the logging cable 123~
By so doing, the weIl logging instrument is encouraged to continue
to move along through the borehole,' however slowly, by paying out
the well logging cable at the appropriate velocityO By way of
further example, when the difference signal produced by the com-
parator 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 be~ins to go toward zero r the cable hoist control
=13-
circuit 126 gener~tes a larger sig.nal t~ thus make the:'hoist
drum 124 turn faster and pay out more ~el'l lo~in~ cable to keep
up with the ~ncr~ased velocit~ o~ the well lo~gin~ instrument.
Referri,ng now to FIG~ 12, an alternati~e embodiment of
the present invention is described which tnCorporates the features
of FIG. 10 with those of FIG. 11. The'subsurface accelerometer
124 located w~thin the weIl logging instrument (not illustrated)
has its OUtpll~ connected to A subsurface veIocity circuit 141
whose output in turn is connected to the'input of a comparator
lQ circuit 142 which drives an actuator 143, for example, the valve
99 within the orifice 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
: 15 weIl log~ing cable 146 to the earth's surface~ ~ surface velocity
circuit 15Q which provides' a signal indicative'of the velocity of
the well logging cable at the surface as he'reinbefore described
has its output connected to a comparator circuit 151. The surface
., veIocity output signal is also conducted' by means o~ conductor 153
which passes through the sl~p rlngs 154 on the end of the hoist
.: :
drum 147 and is conducted to the subsurface instrument by means
o~ the weIl logging 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
ls taken off the slip rings 154 and is connected into another
input of the comparator circuit 151 by means of the conductor 152.
The output of the comparator circuit 151 is connected into the
cable holst control circuit 149 which'drives the motor and gear
box 148 which in turn drives the'hoist drum 147.
In the'o~er~tion o.~ the apparatus and circuitry illus-
trated in FIG. 12, it should be appreciated that as the accelero-
meter 140 measures the'acceIerat~on of the weIl logging
-14-
instr~lment and which consequently produces a slgnal indicati~e of
the subsurface velocity through'the'circuit 141, the'subsurface
veIocity is thus compared witK'the'veIocity of the cable at the
surface by means of the comparatox 142. ~henever a significant
di~ference i~5 exhibited betwee`n the'two veIocities', 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 veIocity of the well logging instrument
is also compared with'the veloc~t~ of the` cable at the earth's
surface in the comparator circuit 151 to control the movement of
the hoist dr~ 147 as was discussed ~ith respect to the embodiment
of FIG. 11. Thus, if the well logging instrument continues to
slo~ down, even though the actuaf,or 143 has been providing addi~ '
tional motivation for the weIl logging instrument, the comparison
circuit 151 will produce a greater output signal ~hich causes a
reduction in the rotat.ional movement of the drum 147 and thus
will cause less well logging cable to pay out~ Through the
combined apparatus and circuitry illustrated in FI~. 12, the well
logging instrument wIll strive'to motivate itself whenever it
starts to slow down because'of the borehole conditions and even
should it start to slo~l down, despite the activation of the :
actuator 143, the cable hoist will also 510w down in order to
avoid too much cable being payed out. Whenever the instrument
starts to speed up, the comparator circuit 151 will produce a
le,sser signal which will in turn cause the hoist dru~ to speed
up and stay with the weIl logging instrument~
Thus there have been illustrated and described herein
the preferred embodiments of the present invention which provide
methods and apparatus ~ox activating mea`ns to facilitate the
~ovement of t~e'weIl logg~ng apparatus through'the'borehole and
for preventing too much pay out of the logg.ing cable. ~Iowever,
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those skilled in the`art will recoyn~ze. that obv~ous modi~ications
can be made to the`preferred embod~ments w~thout dep~rting ~rom
the`spirit of the invention. For example, instead o using a high
molecular weight polymer for th~'frict~on-reduction agent, other
such well-known friction~reduct~on agenks can be utilized.
F~lrthermore, instead of using a valve'dependent upon changes in
veIocity, other parameters can be'measured and the valve or other
such device`for porting the friction-reduction agent into the
~rehole can be activated as a response to such parameters. Still
~urther, instead o~ mea`suring the'veIocity of the drum at the
earth~s surface, the velocity of the cable can ~e measured in
other conventional manners. In addition, a strain gauge can be
used on the cabIe head at the top of the weI1 logging instrument
to provide an indication of changes in the velocity of the
instrument.
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