U.S. patent number 3,651,871 [Application Number 05/029,469] was granted by the patent office on 1972-03-28 for drilling rig depth control.
This patent grant is currently assigned to Automatic Drilling Machines, Inc.. Invention is credited to Palmer G. Greene.
United States Patent |
3,651,871 |
Greene |
March 28, 1972 |
DRILLING RIG DEPTH CONTROL
Abstract
A system which monitors the depth at which a drilling rig is
operating and indicates when a predetermined depth is reached by
recording the length traveled by the drill pipe supporting member
in a predetermined direction within the mast of the drilling rig,
comparing the length traveled with a predetermined length, distance
or measurement and producing a signal when the two are equal. This
may be a prealarm signal or a final alarm signal. Preferably the
signal sounds an alarm and automatically interrupts power to the
drill pipe supporting member.
Inventors: |
Greene; Palmer G. (Dallas,
TX) |
Assignee: |
Automatic Drilling Machines,
Inc. (Dallas, TX)
|
Family
ID: |
21849176 |
Appl.
No.: |
05/029,469 |
Filed: |
April 17, 1970 |
Current U.S.
Class: |
173/21; 33/739;
175/40; 340/686.6 |
Current CPC
Class: |
E21B
47/04 (20130101) |
Current International
Class: |
E21B
47/04 (20060101); E21b 047/04 () |
Field of
Search: |
;33/132-134 ;73/151.5
;173/21 ;175/40 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Purser; Ernest R.
Claims
What is claimed is:
1. In a drilling rig having a mast, and a drill pipe supporting
member mounted for vertical movement within said mast for elevating
and lowering drill pipe into a hole beneath the mast, a system for
monitoring the depth at which the drilling rig is operating and
indicating when a predetermined depth is reached, which system
comprises:
first means operably associated with said drill pipe supporting
member for recording the length traveled by said member in a
predetermined direction;
second means operably associated with said first means for
comparing the length traveled by said drill pipe supporting member
in a predetermined direction with a predetermined distance; and
third means for producing a signal when the length traveled by said
drill pipe supporting member in the predetermined direction is
equal to the predetermined distance.
2. The system of claim 1 including fourth means operably associated
with said third means for interrupting power to said drill pipe
supporting member when the length traveled by the drill pipe
supporting member is equal to the predetermined distance.
3. The system of claim 1 wherein said first means comprises:
means for generating a pulse each time the drill pipe supporting
member travels a unit of length in a predetermined direction;
a pulse counter;
means connecting said pulse generating means with said pulse
counter; and
means for visually indicating the number of pulses generated and
thereby the number of units representing the length traveled by the
drill pipe supporting member.
4. The system of claim 1 wherein said third means includes:
means for sounding an alarm when the length traveled by said drill
pipe supporting member in a predetermined direction is equal to the
predetermined distance.
5. The system of claim 4 including fourth means responsive to the
signal from said third means for stopping the drill string
supporting member.
6. The system of claim 1 including fourth means responsive to the
signal from said third means for stopping the drill string
supporting member.
Description
BACKGROUND OF THE INVENTION
This invention relates to drilling rig control, and more
particularly to a determination of the depth at which the drilling
rig is operating.
In drilling through earth formations various conditions can occur
which may damage the equipment employed in the drilling operation.
For example, during the drilling operation there may develop
"bridges," "ledges" or "keyseats" which, upon withdrawing or
inserting the drill bit from or into the borehole may cause damage
to the drilling equipment. A "keyseat," which is a slot formed in
the borehole by a drill string which is exerting a lateral pressure
on the formation can cause the drill string to part as it is
retrieved from the hole. More particularly, as the drill bit is
commonly wider than the drill string, it can wedge in the slot or
"keyseat" upon being retrieved from the hole creating a tension on
the drill string which, if undetected, can cause the drill string
to sever, collapse the mast of the drilling rig or damage the drill
string lifting mechanism.
The present invention provides means for indicating when a drilling
rig has reached a predetermined depth at which danger areas are
known to exist and for generating an alarm signal and for shutting
down the drill string lifting mechanism when the predetermined
depth is reached.
The invention may be generally described as a system for monitoring
the depth at which a drilling rig is operating. The system includes
first means which are operably associated with the drill pipe
supporting member of the drill rig to record the length traveled by
the member in a predetermined direction. Second means are provided
for comparing the length traveled by the drill string supporting
member with a predetermined distance. Third means produce a signal
when the length traveled by the drill pipe supporting member is
equal to the predetermined distance. Means are also preferably
provided for interrupting power for stopping movement of the drill
pipe supporting member when the third means produce a signal
indicating that a predetermined depth has been reached.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic of a drilling rig and four subsystems for
detecting off-normal drilling operation;
FIG. 2 is an electrical schematic of a system for indicating to a
rig operator off-normal operation and for shutting down a drilling
rig when a predetermined depth has been reached; and
FIG. 3 is a more detailed electrical schematic of a portion of the
depth control means of FIG. 1.
DESCRIPTION OF A PREFERRED EMBODIMENT
As the present invention is preferably utilized in conjunction with
means for monitoring and indicating when a drill string has
encountered an off-normal condition, it is illustrated and
described in connection with such equipment. Specifically, once
other means have, on a trip in or out of the borehole, detected
areas where conditions occur that could be injurious to the
equipment, the present invention may be utilized to indicate the
depth at which this condition occurs and be also utilized to warn
the operator on the next trip in or out that he is about to reach
one of these trouble areas.
More specifically, and with reference to FIG. 1, there is shown an
application of the present invention to an automatic hydraulic
drilling rig of the type described in U. S. Pat. No. 3,158,213. The
drilling rig 10 includes a mast 12 within which is slidably carried
a vertically movable drill head assembly 14. Drill head assembly 14
supports a drill string 16, only a portion of which has been
illustrated, that may be several thousand feet in length, by means
of elevators (not shown) or a threaded spindle 76 which extends
from assembly 14. Movement of the drill head assembly 14 relative
to the mast 12 is accomplished by a suitably braced tower 18 fixed
to the top of the mast 12. The tower 18 includes cylinders 20 and
22, more than two may be used, which are braced by struts 24. Rods
26 and 28, which are mounted to pistons within the cylinders 20 and
22, respectively, effect vertical movement of the drill head upon
introduction of hydraulic fluid into the cylinders through pipes 30
and 32.
Fluid flow rates within the pipes 30 and 32 may be controlled by a
hydraulic system of the type described in the copending U.S. Pat.
application of Raymond J. Bromell, et al., Ser. No. 782,231, filed
Dec. 9, 1968, and assigned to the assignee of the present
invention. As described in this copending application, the yoke of
a variable displacement pump is stroked to various positions to
establish flow rates in the pipes 30 and 32 and thus vary the speed
of raising and lowering the drill head assembly 14. The pressure
maintained in the cylinders 20 and 22 by the variable displacement
pump will be at a level established by the weight of the drill
string 16.
Pressure transducers 34 and 36 are coupled to the pipes 30 and 32,
respectively, and produce electrical signals proportional to the
pipe pressure. Since there are two or more cylinders lifting the
drill head assembly 14 and drill string 16, a pressure in the pipes
30 and 32 will be proportional to only a portion of the total
weight of the drill head and drill string. Thus, the electrical
signals from the transducers 34 and 36 are added in a summing
amplifier 38 to produce a signal on a line 40 proportional to the
weight of the drill string 16. The electrical signal on the line 40
is coupled to an indicating meter 42. This meter 42 has a scale 44
calibrated in drill string weight and a pointer 46 for indicating
instantaneous drill string weight. In addition to the meter 42, the
signal on line 40 connects to a recorder 48 which produces a
permanent record of drill string weight for further analysis.
In addition to generating electrical signals representing drill
string weight by converting pressure in the cylinders 20 and 22,
other transducers may be employed. For example, strain gauges may
be mounted on the rods 26 and 28 to produce electrical signals
representing the drill string weight. Further load cells may be
mounted under the rig to produce electrical signals that vary with
drill string weight.
The signal on line 40 is tied to an alarm controller 50. A typical
controller 50 may include a potentiometer circuit coupled to a knob
52 for establishing a signal representing the calculated weight of
the drill string 16. The alarm controller may also include an
amplifier having a first output when the drill string weight is
above a calculated value, a second output when the actual weight is
at the calculated value, and a third output when the actual weight
is below the calculated value. The first and third outputs of the
amplifier energize a relay 54 to complete various alarm circuits
and shut down the drilling rig operation, as will be described
shortly. When the first output energizes the relay 54, a "high"
alarm condition exists such as would occur when a reduced hole,
sloughing shale or "keyseat" is encountered when removing the drill
string from a hole. Energizing the relay 54 from the third output
indicates a "low" alarm condition such as would occur for a drill
string "twist-off" or when encountering a ledge or bridge when
lowering the drill string into a hole.
A signal on line 40 is also coupled to a pressure v. time rate
amplifier 56 which energizes the relay 54 when the rate of change
of the drill string weight exceeds an established level. Many rate
amplifier circuits are available and additional description is not
deemed necessary.
To indicate off-normal drilling rig operation with the weight alarm
circuit described above, the knob 52 is set at a drill string
weight calculated to be slightly less than the weight being
supported. Pressure in the pipes 30 and 32 will be maintained at a
level to support the drill string and will remain at some
reasonably constant value for a given weight. Assume the drill
string 16 is about 2,000 feet long and a "twist-off" occurs at
about the 1,000 foot level, then the pressure in pipes 30 and 32
will be readjusted by means of automatic controls (not shown) to
support the new weight and prevent the drill head assembly from
running to the top of and damaging the tower. A lower pressure in
the pipes 30 and 32 produces a signal of lower magnitude on the
line 40 that will be less than a signal established by the knob 52.
As a result, the alarm controller 50 energizes the relay 54,
thereby closing a contact 54-1 in series with an indicating light
60 shown in FIG. 2. The light 60 will be connected to a source of
voltage at the terminals 62 and 64 through a contact 66. The
contact 66 has previously been closed in the normal sequence of
operation. In addition to turning on the light 60 by closing the
contact 54-1, energizing the relay 54 closes a contact 54-2 to
energize a horn 68 to produce an audible alarm.
In addition to giving a visual and audible indication of a change
in drill string weight, energizing the relay 54 also opens a
contact 54-3 which de-energizes a relay 70, thereby shutting down
the drilling rig. The relay 70 is energized at the start of the
drilling operation by closing the switch 72 and pushing the reset
button 74. This completes a circuit to the terminals 62 and 64
through a normally closed contact 66-2. Contact 66-2 is opened
after the sequence of activating the drilling rig has been
completed. The relay 70 will be energized through other normally
closed contacts, to be described. Energizing the relay 70 closes
contacts 70-1 and 70-2. Contact 70-1 completes a holding circuit
for the relay 70 and the contact 70-2 connects drilling rig control
circuitry 72 to the terminals 62 and 64.
For the alarm controller 50 to properly control the relay 54, the
knob 52 must be adjusted for each additional length of drill pipe
added to the drill string 16. This can be accomplished by hand or
automatically by a computer. However, should adjustment of the knob
52 be overlooked, the weight alarm circuitry will give an
indication of off-normal rig operation by means of the rate
amplifier 56. The rate amplifier 56 energizes the relay 54 when the
rate of change of drill string weight exceeds an established value.
Under normal operating conditions for the drilling rig, that is,
during the drilling operation or when lowering the drill string
into a hole, the rate of change will be below the established
level. When a drill string "twist-off" or other malfunction occurs,
however, the rate of change of drill string weight will be high,
thereby energizing the relay 54. Energizing the relay 54 closes
contacts 54-1 and 54-2 to activate the light 60 and the horn 68,
respectively. In addition, energizing the relay 54 opens a contact
54-3, thereby de-energizing the relay 70. This, as explained, shuts
down the drilling rig operation.
In addition to indicating drill string "twist-off," the weight
alarm circuitry will indicate a "ledge" condition before any
damaging amount of weight has been applied to a drill bit when
lowering a string into a previously formed hole. The knob 52 is
set, by hand or automatically, at a drill string weight slightly
lower than the pickup weight, that is, the hanging weight of the
string. If the drilling bit comes in contact with a "ledge," the
pressure in the pipes 30 and 32 will suddenly decrease, thereby
setting up the same conditions that were described previously with
regard to a "twist-off." The light 60 and the horn 68 will be
activated and the relay 70 de-energized to shut down the drilling
rig, thus preventing bending of the drill string and damage to the
drill bit. This additional feature of the weight control circuitry
shuts down the rig before an excessive amount of weight damages the
drill string or the drill bit.
Still another feature of the weight alarm circuitry, the drilling
rig will be shut down before the drill bit binds in a "tight" hole
or "keyseat" when removing the drill string from a hole. For this
feature, the knob 52 is set at a drill string weight slightly
higher than the pickup weight of the string. The setting of the
knob 52 should not, however, be at a level such that the relay 54
will be energized. A "tight" hole or "keyseat" condition will be
detected when removing the drill string by the "high" alarm (the
third output) signal from the controller 50 which energizes the
relay 54. As the drill bit encounters a "keyseat" or "tight" hole,
the pressure in the pipes 30 and 32 will rapidly increase, thereby
generating the high alarm signal from the controller 50. Energizing
the relay 54 will activate the light 60 and the horn 68 by closing
contacts 54-1 and 54-2, respectively. The relay 70 will be
de-energized by opening the contact 54-3 to shut down the rig, thus
minimizing the possibility of pulling the drill string in two or
collapsing the mast.
Another variable that provides an indication of off-normal drilling
rig operation is the torque required to rotate the drill string.
The drill head assembly 14 includes one or more fluid motors 73
coupled through pinion and gear mechanisms to a pipe gripper
section 76. A complete description of the drill head assembly 14
will be found in the U.S. Pat. No. 3,158,213. Hydraulic fluid for
operating the motors 73 will be provided through flexible hoses,
such as the input hose 78 and the return hose 79. The torque alarm
circuit includes a transducer 80 for converting the pressure in the
hose 78 to an electrical signal on a line 82. The signal on line 82
therefore represents the pressure in the hose 78 and in turn the
torque produced by the hydraulic motor 73. The signal on line 82 is
coupled to an indicating meter 84 having a scale 86 calibrated in
units of torque. A recorder 88 also connects to the line 82 and
produces a permanent record of the torque required for rotating the
drill string 16.
To indicate an off-normal operation, e.g., a probability of drill
string "twist-off," the signal on line 82 connects to an alarm
controller 90 which may include an amplifier having a first output
when the signal on line 82 is above a minimum setting and a second
output when this signal drops below the setting. The alarm
controller 90 includes a knob 92, which may be set by a computer,
for setting a minimum and maximum value of torque to be developed
by the hydraulic motor 73. Any change in torque produced by the
motors 73 above or below the setting on controller 90 will energize
a relay 94.
Energizing the relay 94 closes a contact 94-1 to connect a light 96
to the terminals 62 and 64. Energizing the relay 94 also closes a
contact 94-2 and opens a contact 94-3 in the circuit for the horn
68 and relay 70, respectively. Note, closing the contact 94-2 does
not activate the horn 68 and opening the contact 94-3 does not
de-energized the relay 70. Since a decrease in torque is not a
positive indication of a drill string "twist-off" with the system
illustrated, only the light 96 is turned on to indicate to the
operator a probable "twist-off" or that some other malfunction has
occurred.
In addition to indicating a drill string "twist-off", a change in
torque may also indicate a dull drill bit. As the drill bit wears
with usage, additional torque will be required to penetrate the
subsurface layers. When this increase in torque exceeds the value
set by the knob 92, the relay 94 will be energized, thereby
indicating an off-normal operation.
For a sudden decrease in torque to activate the horn 68 and
de-energize the relay 70, there must be an accompanying
non-programmed decrease in mud pump pressure. Drilling mud may be
pumped into the drill string 16 via a mud tube 98 and a hollow
portion of the section 76. A hose 100 connects to the mud tube 98
and a mud pump (not shown). The mud pump pressure alarm circuit
includes a transducer 102 connected in the hose 100 to convert the
mud pump pressure to an electrical signal on line 104. Usually, the
transducer 102 will be installed in an oil chamber which is
separated from the drilling mud by a flexible diaphragm. Such
transducers are readily available and additional description is not
deemed necessary.
The electrical signal representing mud pump pressure on the line
104 connects to an indicator/alarm meter 106 or to a controller,
such as controller 90. An indicator/alarm meter suitable for the
system shown includes an indicating needle 108 and a set point
needle 110. When these two needles coincide, they operate
electrical contacts to energize a relay 112 from an electrical
power source 114. Energizing the relay 112 closes a contact 112-1,
as shown in FIG. 2, to connect a light 116 to the terminals 62 and
64. Energizing the relay 112 also closes a contact 112-2 and opens
a contact 112-3 for the horn 68 and the relay 70, respectively.
Closing the contact 112-2 will not actuate the horn 68 and opening
the contact 112-3 will not de-energize the relay 70 unless the
relays 94 and 112 are energized at the same time. If the relays 94
and 112 are energized together, then the contacts 94-2 and 112-2
will be closed and the horn 68 will be energized to give an audible
signal to an operator that a drill string "twist-off" has occurred.
Opening the contacts 94-3 and 112-3 at the same time will
disconnect the relay 70 from the terminals 62 and 64, thereby
shutting down the drilling rig by opening the contact 70-2.
By monitoring mud pump pressure, off-normal operations other than a
drill string "twist-off" bay be detected. For example, if the drill
string develops holes, the drilling mud will be lost through these
holes and the mud pump pressure will drop. By substituting the
controller 90 for the meter 106, a high mud pump pressure will
cause an energization of the relay 112. High mud pump pressure will
result when the drill bit becomes plugged or when a sloughing shale
condition develops. When a drill bit becomes plugged, it is
important that the drilling be stopped to avoid damaging the bit.
Not all deviations of mud pump pressure from a normal setting,
however, require a complete shutdown of the rig operation. In fact,
it may be desirable to continue the flow of drilling mud at some
nominal value. In a sloughing shale condition, the mud pump
pressure will be reduced to avoid damage to the hole through
fracturing by excessive pressure, but some drilling mud flow is
desirable to prevent the shale from packing around the drill
string.
Although the circuit of FIG. 2 illustrates that a drill string
weight change is an indication of a drill string "twist-off"
independent of the other variables, it should be understood that by
modifying the contact arrangement, a "twist-off" indication may not
be given unless there was a change in drill string weight
accompanied by deviation of one of the other variables from their
established levels. By various contact arrangements, an indication
of drill string "twist-off" can be made to be dependent upon a
deviation from established levels of any combination of two of the
three variables described. Thus, it should be understood that the
contact arrangement described illustrates only one embodiment and
is not intended as a limitation to the system shown.
The drilling rig which is partially illustrated in FIG. 1 includes
means for indicating the depth at which the drilling rig is
operating when the drill bit encounters a "ledge," "bridge" or
"keyseat" as well as at what level the rig is operating when a
"twist-off" occurs.
More particularly, these means take the form of a footage switch
116 mounted on the drill head assembly 14. Upon vertical movement
of drill head assembly 14, switch 116 is actuated by a plurality of
cams 117 spaced at 1-foot intervals along leg 118 of mast 12. Drill
head assembly 14 also has attached thereto a direction switch 119
which is adapted to be actuated by cams 121 and 122 which are
slightly larger than cams 117.
Both of the switches 116 and 119 communicate through conductor
bundle 123 with a depth indicator and controller 124 which is
coupled to a recorder 125 for preserving in permanent form a record
of the depth of the rig as a function of time and is also coupled
to a relay 126, the purpose of which will be explained hereinafter.
Depth controller 124 and the switches which are responsible for
admitting signals thereto are illustrated in more detail in FIG. 3.
In FIG. 3, the footage switch 116, which is for example a
single-pole double-throw toggle switch, has an arm 127 for
engagement with cams 117. As drill head assembly 14 moves down the
mast 12 arm 16 will engage cams 117 and move upward to engage
contact 128. Conversely, when drill head assembly 14 moves up the
mast 12, arm 127 will, upon encountering one of the cams 117, move
downward to engage contact 129. Arm 127 is spring biased to the
center position, as illustrated in FIG. 3 so that it returns to
this position after engaging each of the cams 117 regardless of the
direction of travel of the drill head assembly 14.
Switch 119 is a single-pole double-throw non-centered switch having
an arm 131 which, upon engagement with cam 121, at which point
drill head assembly 14 will be at its uppermost elevation, will be
deflected to engage contact 132, as illustrated in FIG. 3.
Conversely, when drill head assembly 14 reaches its lowermost
position, arm 131 will engage cam 122 and be moved upwardly to
engage contact 133. Switches 116 and 119 serve, in cooperation with
a double-pole single-throw switch 134 to complete a circuit to a
pulse counter 136, such as a Veeder-Root counter, Series 1847
manufactured by the Veeder-Root Company, Hartford, Connecticut. The
pulse counter is provided with first and second registers 137 and
138. Second register 138 is provided with a set of manually
adjustable knobs 139 to permit entry within the register 138 of a
desired number. The output of register 137 is coupled by conductor
141 to the recorder 125 and a comparator 142. Comparator 142 also
receives an input through conductor 143 from register 138 to
compare the relative magnitude of the numbers in registers 137 and
138 and to generate an output signal in conductor 144 when the
values of the two registers 137 and 138 are equal for energizing
the relay 126.
The register 137 communicates through conductor 145 with contacts
128 and 129 of switch 116. Thus, a signal in conductor 145 will be
transmitted, upon contact of center arm 127 with either of contacts
128 or 129 due to engagement of arm 127 with one of the cams 117,
to conductor 146 which communicates with center arm 131 of switch
119. A signal transmitted through contact 132 or contact 133 will
pass through conductor 147 or conductor 148, depending upon the
position of arm 131, to arms 149 and 151 of switch 134.
When the drilling rig is making a trip into the hole with drill
pipe, switch 134 is manually set to the position indicated in FIG.
3, in which event arm 149 will communicate with register 137
through conductor 152 whereas arm 151 only communicates with an
open contact. With switch 134 in the second position, as for
example when the device is making a trip out of the borehole, the
signal in conductor 148 and arm 151 will communicate through
conductor 153 with register 137 whereas the signal and arm 145 will
be to an open contact.
In operation, if the operator of the drilling rig wishes to count
the number of feet of drill pipe in the hole on a trip into the
hole, switch 134 is manually moved to the position indicated in
FIG. 3 and drill head 14 is moved (by means not shown) to the top
of mast 12. As drill head assembly 14 reaches the top of mast 12
cam 121 will engage arm 131 moving it into engagement with contact
132, as illustrated in FIG. 3. As drill head assembly 14 is lowered
to admit pipe to a borehole, arm 127 will, upon engaging the cams
117, momentarily engage contact 128 completing the circuit through
conductor 145, switches 116 and 119 to conductor 147, arm 149 and
conductor 152. The closed circuit will cause register 137 to enter
a unit in the register for each pulse caused by closing of arm 127
against contact 128. Register 137 will, as cams 117 are spaced at
1-foot intervals, register the number of feet admitted to the
borehold. When drill head assembly 14 reaches the bottom of the
mast 12, center arm 131 of switch 119 will engage cam 122 moving
the arm 131 into engagement with contact 133. As drill head
assembly 14 is then elevated upward in mast 12 to receive another
joint of drill pipe the pulse which is generated upon the contact
of arm 127 with contact 129 will not be counted as the signal will
communicate through conductor 148 with the arm 151 which engages an
open contact. Upon reaching the uppermost position drill head
assembly 14 will again move arm 131 into engagement with contact
132 so that the pulses are again counted as drill head assembly
moves downward. If a "ledge" or the like has been detected on the
trip out of the hole or on a previous trip, for example, the
300-foot level, the operator may, on the trip back into the hole,
set register 138 by manually inserting the digits 290 of the first
three positions in register 138. The register 138 may be set by
turning of manually adjustable knobs 139. When the register 137
indicates 290, a signal is transmitted through conductor 141 which
is equal in magnitude to the signal in conductor 143. This equality
will be sensed by the comparator 142 causing comparator 142 to
transmit a signal through conductor 144 to energized relay 126.
Energization of relay 126 will warn the operator of the drilling
rig in a manner to be later described. The operator may then assume
manual control of the drilling rig and slowly move drill head
assembly downwardly while closely observing gauges 42 and 84 to
assure that the rig is not damaged by this "ledge". Once the danger
area is passed, register 138 may be set to a lower desired depth
and the drilling rig again placed on automatic operation.
If the number of feet of the pipe remaining in the borehole is to
be determined on a "trip out", switch 134 is moved to the "out"
position in which event, after clearing of register 137 by
manipulation of adjustable knobs 140, the number of feet of pipe
withdrawn from the hole may be observed as center arm 131 of switch
119 will have been moved into engagement with contact 133 by
movement of drill head assembly 14 to its lowermost position
causing pulses created by movement of center arm 127 into
engagement with contact 129 to be admitted through arm 151 and
conductor 153 to register 137. By setting of register 138 in the
same manner as described above on a trip into the borehole the
values in registers 137 and 138 may be compared and a signal
generated by comparator 142 when the signal from registers 137 and
138 are equal for stopping the rig at known "ledge" areas or other
danger areas.
With reference to FIG. 2, a signal from comparator 142 will
interrupt power to drill head assembly 14 as energization of relay
126 closes contacts 126-1 and 126-3 to ignite lamp 120 and sound
alarm 68 in the manner described before. Energization of relay 126
also opens normally closed relay 126-2 to the energized relay 70
thereby open contacts 70-2 terminating power from drilling rig
control 72.
With the system described above, it is possible, once a danger area
is found to exist at a particular point in a borehole to program
the depth indicator and controller 124 to stop the drilling rig at
a predetermined depth to permit the operator to manually control
the rig past the danger to assure that no damage is done to the
equipment or stop prior to reaching existing total depth of the
hole to permit slow washing to bottom.
It is also possible to determine at what point a "twist-off" occurs
as the length of pipe removed from the hole after "twist-off" may
be measured to assist in subsequent fishing operations as the point
at which the fish may be located within the hole may be fairly
accurately determined by the use of the depth indicator and
controller.
While specific embodiment of the invention has been illustrated and
described, the invention is not limited to that embodiment, but is
defined by the following claims.
* * * * *