Note: Descriptions are shown in the official language in which they were submitted.
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METHOD AND APPARATUS FOR OPTIMIZING DETERMINATION
OF THE ORIGINATING DEPTH OF BOREHOLE CUTTINGS
BACXGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates in general to a
new and improved method and apparatus for use in
drilling boreholes into subsurface formations. More
particularly, the present invention relates to a new
and improved method and apparatus for use in
determining and monitoring the downhole depth from
which borehole cuttings are removed and are being
received at the surface of the drilling location.
2 Description of the Prior Art
It is known that when drilling a well,
particularly those related to the rotary drilling of an
oil or a gas well, a fluid - often called "drilling
mud" - is injected into the drill pipe aæsembly from
the surface of the earth. The fluid, or mud, is pumped
downwardly through the drill pipe assembly to the
bottom of the borehole, where it passes through the
orifices in the drill bit and then flows upwardly
toward the surface of the earth through the annular
space between the drilling pipe assembly and the wall
of the borehole. Upon the return of the mud to the
surface of the earth, the mud is passed through a
shaker screen which momentarily retains the stony
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refuse material (borehole cuttings) for evaluation and
the mud is gathered in a storage tank from which the
mud is reintroduced to the drilling pipe assembly. The
drilling mud is commonly circulated and partially
retained in the borehole for various reasons, as for
example, to exert hydrostatic pressure to keep the
subsurface pressure substantially sealed in the
borehole and to remove the borehole cuttings from the
bottom of the borehole up to the surface of the earth.
When an oil well is being drilled, one of the
first methods of evaluating the exploratory activity is
to look at the borehole cuttings and examine them from
a geological point of view, as for example, what age
are the cuttings, what type of rock is in the cuttings,
do the cuttings contain a hydrocarbon, etc. When
examining and evaluating the borehole cuttings, it is
important to know the depth from which the borehole
cuttings were removed from the earth. It will be
appreciated that the borehole cuttings at the bottom of
the borehole do not instantly appear at the surface of
the earth but appear at the surface at some later time
depending upon such things as the depth of the drill
bit at the time the borehole cuttings are brought into
existence from the action of the drill bit against the
earth, the rate of the flow of the drilling mud, etc.
In the prior art, one method used to determine
the depth from which the borehole cuttings originated
is to stop the descent of the drill bit, introduce a
predetermined amount of carbide into the downhole flow
of drilling mud, record the time of the introduction of
the carbide, monitor the discharge of the drilling mud
at the surface of the earth for the presence of
acetylene gas and record the time at which the presence
of the acetylene gas occurs. The total elapsed time
provides the time required for the drilling mud to
traverse the round trip to the bottom of the borehole
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and back to the surface of the earth. Since the inside
volume of each section of drill pipe is known, the
total inside volume of the drill pipe down to any depth
is known or can be easily calculated. The output of
the mud pump at certain predetermined speeds is known
(or may be determined at any particular speed of
operation) so the amount of time required for the mud
pump to pump the carbide down to the drill bit (and the
borehole cuttings) may be calculated. The amount of
time can also be considered as the time necessary for
the mud pump to pump sufficient mud to fill the inside
volume of the drill pipe down to the drill bit. The
time required for the borehole cuttings at the drill
bit to travel to the surface of the earth from the
drill bit (or place of origination) is equal to the
total elapsed time minus the time required for the
carbide to travel down to the drill bit. If the round
trip for the drilling mud took one hour and twenty
minutes at a depth of five thousand feet and the
calculated time for the carbide to reach the drill bit
was twenty minutes, then the borehole cuttings from
that general depth would take approximately one hour to
travel from the bottom of the borehole to the surface
of the earth where the borehole cuttings could be
observed. The time required for the borehole cuttings
at the bottom of the borehole to reach the surface of
the earth is known as the lag time. Obviously, this
method depends on constant and continuous pumping of
the mud pump.
The present invention as claimed is intended
to provide a method and apparatus which eliminates many
of the prior art deficiencies which include the
necessity to operate the mud pump or mud pumps at the
same speed at all times which includes during the
calibration or initialization of the determination of
the lag time, during the time borehole cuttings are
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being brought to the surface of the earth to be
evaluated, etc. If the mud pump or mud pumps are not
operated at the same speed at the times associated with
the determination of the lag time then error will be
introduced into the determination of the lag time. In
the prior art, it is necessary to monitor and maintain
a record, mental or written, of the time or times
associated with the determination of lag time. In the
prior art, lag time is a function of time and requires
the measurement of time.
Summarv _ the Invention
The present invention provides a method and
apparatus for determining when and providing an
indication of when the borehole cuttings from
preselected depths arrive at the surface of the earth
for examination and evaluation. Switches provide
inputs representing the lag strokes and the
predetermined drilling depth increment. A signal
representative of the actual drilling depth i5 provided
to a computer circuitry. Counter circuitry accumulates
a count of the strokes of the positive displacement mud
pump. Adder circuitry sums the lag strokes and the
accumulated count of the mud pump. Comparator
circuitry provides an output when the compared values
of the accumulated number of strokes of the positive
displacement mud pump equals the sum of the lag strokes
and the strokes of the positive displacement mud pump
at a predetermined depth plus the depth increment.
Visual and audio indications provide notification of
the arrival of borehole cuttings from preselected
depths.
Among the advantages offered by the present
invention are circuitry which automatically determines
when and automatically provides an indication when the
borehole cuttings from preselected depths arrive at the
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surface of the earth for examination and evaluation.
The present invention eliminates the need to operate
the mud pumps at the same speed during the drilling
operation. The present invention allows any necessary
number of mud pumps to be operated during the drilling
operation. It is not necessary to keep a record of
time during the operation.
Examples of the more important features and
advantages of this invention have thus been summarized
rather broadly in order that the detailed description
thereof that follows may be better understood and in
order that the contribution to the art may be better
appreciated. There are, of course, additional features
of the invention that will be described hereinafter and
which will also form the subject of the claims appended
hereto. Other features of the present invention will
become apparent with reference to the following
detailed description of a presently preferred
embodiment thereof ln connection with the accompanying
drawing, wherein like reference numerals have been
applied to like elements in which:
BRIEF DESCRIPTION OF THE DRAWING
FIGURE 1 shows schematically a well
installation during the drilling operation and
represents the locations of the various conventional
elements of the drilling mud system;
FIGURE 2 shows the front panel of the unit
encompassing the present invention; and
FIGURE 3 is a simplified block diagram
schematic of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring now to the drawing wherein like
reference numerals designate like or corresponding
elements throughout the several views, lag-determining
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apparatus is referred to generally by the reference
numeral 10. The lag-determining apparatus 10 is shown
in FIGURE 1 in conjunction with a typical drilling mud
system. With reference to FIGURE 1, a typical well
installation is illustrated and comprises a
conventional derrick 12 with a drilling pipe assembly
14 which is provided at its lower end, at the bottom of
the borehole or well, with a drill bit 16. At the
upper end of the drilling pipe assembly 14 is located
a swivel 18 which is suspended at the hook 20 of a
movable block 22. The drilling mud 24 is injected into
the drill string at the swivel 18 through a stand pipe
26 and a Kelly hose 28. The drilling mud 24 being
transported by mud pump or pumps 30 which are located
at the upstream side of the stand pipe. The drilling
mud 24 flows downwardly within the drill pipe assembly,
passes through the orifices in the drill bit 16 and
then flows upwardly through an annular space 32 toward
the head 34 of the well. The drilling mud 24 then
flows through a so-called "flo line" 36 which dumps
into a small mud reservoir called a "possum belly" and
then flows onto shaker screen 40. From the shaker
screen 40, the drilling mud 24 passes into a fluid pit
or pits 42 which are sized to store a predetermined
volume of drilling mud 24 and have an outlet pipe or
conduit 44 to the suction side of the mud pump or pumps
30. The lag-determining apparatus 10 is operatively
connected by cable 46 to pump stroke sensor or sensors
48 which are operatively connected to the mud pump or
pumps 30. The lag-determining apparatus 10 is also
operatively connected by cable 50 to the depth sensor
52. The borehole cuttings 53 are momentarily retained
on the surface of the shaker screen 40. It will be
appreciated that the lag-determining apparatus 10 is
not required to be located on the derrick 12 but could
be placed at a remote location as long as the apparatus
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could be connected by appropriate cables.
FIGURE 2 shows the front panel 54 of the
lag-determining apparatus 10 as seen by an operator
using the apparatus. The front panel 54 includes a
pump stroke display 56 which provides a read-out of the
total strokes of the mud pump or pumps 30. Also
included is a cutting depth or drill bit depth display
58 which provides a read-out of the depth in feet of
the drill bit 16 at time of desired sampling. Thumb
wheel entry switches and display 60 allows the operator
to enter and display ~ predetermined number of lag
strokes into the lag-determining apparatus 10. Lag
strokes are defined as being the number of strokes of
the mud pump or pumps 30 which are required to displace
the volume of drill string well bore annulus or to
cause the drilling mud to lift the borehole cuttings at
the bottom of the borehole up to the surface of the
earth where the borehole cuttings may be identified as
originating from the depth selected and be examined and
evaluated. The mud pump or pumps 30 are positive
displacement type pumps in which the amount of
displacement per stroke is the same and is independent
of the speed of the pump. Depth increment switches
62-68 are arranged vertically on the front panel 54 to
allow the designation of intervals of drill bit depth
of thirty feet, ten feet, five feet and one foot,
respectively. A visual or light alarm display 70 and
an audio alarm device 72 are included on the front
panel 54.
FIGURE 3 shows a simplified block diagram
schematic of the present invention for determining when
and providing an indication of when the borehole
cuttings from preselected depths arrive at the surface
of the earth for examination and evaluation. The lag-
determining apparatus 10 is externally interconnected
with pump stroke sensors 48 and 49, depth sensor 52 and
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computer 74. In the preferred embodiment, computer 74
comprises a personal computer but it will be
appreciated that the computer and computing function
could be incorporated as an integral portion or element
of the lag-determining apparatus 10. The outputs of
pump stroke sensors 48 and 49 are provided as a pulse
for each positive stroke of each pump and are input to
BCD (Binary Coded Decimal) counter 76 and to binary
counter 78 through gating device 80. The scD output of
the BCD counter 76 drives pump stroke display 56 which
displays the total pump strokes of the multiple number
of pumps. It will be appreciated that if only one mud
pump is being utilized, then the total pump strokes
displayed will be for that one pump. The output of
binary counter 78 is provided as one binary input to
adder circuitry 82 and as one binary input to the
comparator 84.
The BCD output from the thumb wheel entry
switches and display 60 represents the predetermined
number of lag strokes entered therein and is input to
the BCD/binary converter 86 whose output is provided as
another binary input to adder circuitry 82. Adder
circuitry 82 sums the binary representation of the
total pump strokes to the binary representation of the
lag strokes. The output of the adder circuitry 82 is
input to RAM (Random-Access Memory) circuitry 88 which
also receives another input from the timing and logic
circuitry 90 which determines and controls when the
value received from the adder circuitry 82 will be
stored in RAM circuitry 88. The value from the adder
circuitry 82 will be stored in the RAM circuitry 88 at
the initiation of the process for determining when the
borehole cuttings will arrive at the surface from a
particular depth or increment of depth for observation
and evaluation. The output of RAM circuitry 88 is
provided as another binary input to comparator 84 which
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compares the binary output from RAM circuitry 88 with
the binary representation of the total pump strokes
received from binary counter 78. The output of
comparator 84 is provided as one input to the timing
and logic circuitry 90 when the value of the total pump
strokes is equal to the value of the sum of the
predetermined number of lag strokes entered into the
thumb wheel entry switches and display 60 and the
number of pump strokes at the initiation of the process
for determining when the borehole cuttings will arrive
at the surface of the earth.
The binary output of depth sensor 52 is
provided as an input to the computer 74 and also to BCD
counter 92 whose output is provided as one input to RAM
circuitry 94 which also has another input from the
timing and logic circuitry 90. The input from the
timing and logic circuitry 90 determines and controls
when the input value from the BCD counter 92 will be
stored in RAM circuitry 94. The output of RAM
circuitry 94 drives the cutting depth display 58 and
updates the display with each new value stored in the
RAM circuitry 94. Timing and logic circuitry 90
receives an input store signal from computer 74 which
provides the command for the timing and logic circuitry
90 to provide an input store signal to RAM circuitry 88
and RAM circuitry 94 at the appropriate times. Timing
and logic circuitry 90 also provides an output to the
visual alarm circuitry 96 and an output to the audio
alarm circuitry 98. The outputs of depth increment
switches 62-68 are provided to computer 74 through
interface circuitry 100 which in the preferred
embodiment is multiplexer circuitry. The necessary
voltages for operation of the present invention are
supplied by power supply 102. Computer 74 is provided
with a state-of-the-art program to perform the
necessary calculations and provide the necessary
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control signals to the lag-determining apparatus 10.
With respect to the operation of the present
invention and with reference to FIGURES 2 and 3, the
operator must initialize or calibrate the
lag-determining apparatus 10 prior to the usage thereof
in the drilling process. The operator must obtain the
value of lag strokes for the particular drilling depth
when the lag-determining apparatus 10 is to be
initially brought on-line to be used with the dril]ing
system. This initialization information may be
obtained by the prior art carbide method but with one
primary difference wherein the number of lag strokes
are counted rather than keeping a record of the amount
of time involved. The volume of mud pumped for each
lS stroke of the positive displacement mud pump is known.
It will be appreciated that any identifiable material
could be substituted for the prior art carbide, e.g.
colored rags, etc. in the obtaining of the number of
lag strokes.
When the number of lag strokes have been
determined, the operator will enter the number of lag
strokes into the lag-determining apparatus 10 by
operation of the thumb wheel entry switches and display
60. Let it be assumed that the number of lag strokes
is one thousand. The operator will then place one of
the depth increment switches 62-68 to the on position.
Generally the depth increment switches for the greater
increments (thirty feet and ten feet) are used at
shallow drilling depths since the drilling proceeds at
a fast rate of drilling depth at the shallow depths
while the small increments tfive feet and one foot) are
used at the deeper drilling depths. Let it be assumed
that the operator places the depth increment switch 64,
which represents ten foot increments, in the on
position which results in a signal being sent to the
computer 74 that the ten foot increment has been
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chosen. Let it be assumed that the drill bit 16 is at
four thousand feet, which value will be sent from the
depth sensor 52 to BCD counter 92 and to the computer
74. Let it be assumed that the pump stroke display 56
shows twenty thousand. Upon receipt of the value of
the depth of the drill bit, the computer 74 reads the
input depth value and divides that input depth value by
ten. When the input depth value is divisible by ten,
which occurs at four thousand and ten feet, the
computer 74 sends a store signal to the timing and
logic circuitry 90. The timing and logic circuitry 90
then sends a store signal to RAM circuitry 88 which
will store the value which is received from adder
circuitry 82. The timing and logic circuitry 90 also
sends a store signal to RAM circuitry 94 which will
store the value of the drill depth received from sCD
counter 92.
It will be appreciated that while the drilling
depth has increased by ten feet the pump strokes have
also increased during this drilling period. It will be
assumed that the pump strokes read twenty thousand five
hundred at the time the store signal was received by
RAM circuitry 88; therefore, the value stored in the
RAM circuitry 88 will be twenty one thousand five
hundred which is the sum of the total pump strokes and
~he lag strokes.
The binary representation for twenty one
thousand five hundred is provided by RAM circuitry 88
as one input to comparator 84. The other input to
comparator 84 is the binary input from binary counter
78 which represents the total pump strokes of twenty
thousand five hundred. Binary counter 78 will continue
to increment upwardly as the total number of pump
strokes increase until the total number of pump strokes
equal twenty one thousand five hundred. At that time
the comparator 84 will provide an output to the timing
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and logic circuitry 90 which will then provide an
output to the visual alarm circuitry 96 resulting in
the visual alarm display 70 being activated. An output
from the timing and logic circuitry 90 is also provided
to the audio alarm circuitry 98 resulting in the
activation of the audio alarm device 72 which along
with the visual alarm display 70 will provide an
indication that borehole cuttings from the depth of
four thousand ten feet have arrived at the surface of
the earth. At this time, the value of the drill depth
stored in RAM circuitry 94 will be passed to and
displayed by cutting depth display 58.
This determination process continues for each
drill depth value which is divisible by ten and the
cycle described above is repeated so that the drill
operator may observe the borehole cuttings at every ten
foot interval of drill depth. It will be appreciated
that the cycle will be the same for the other depth
increments of thirty, five and one.
Although the present invention has been
described in conjunction with specific forms thereof,
it is evident that many alternatives, modifications and
variations will be apparent to those skilled in the art
in light of the foregoing disclosure. Accordingly,
this description is to be construed as illustrative
only and is for the purpose of teaching those skilled
in the art the manner of carrying out the invention.
It is understood that the forms of the invention
herewith shown and described are to be taken as the
presently preferred embodiment. Various changes may be
made in the shape, size and arrangement of parts. For
example, equivalent elements may be substituted for
those illustrated and described herein, parts may be
reversed, and certain features of the invention may be
utilized independently of other features of the
invention. It will be appreciated that various
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modifications, alternatives, variations, etc., may be
made without departing from the spirit and scope of the
invention as defined in the appended claims.
