U.S. patent number 3,595,075 [Application Number 04/875,462] was granted by the patent office on 1971-07-27 for method and apparatus for sensing downhole well conditions in a wellbore.
This patent grant is currently assigned to Warren Automatic Tool Company. Invention is credited to Ethell J. Dower.
United States Patent |
3,595,075 |
Dower |
July 27, 1971 |
**Please see images for:
( Certificate of Correction ) ** |
METHOD AND APPARATUS FOR SENSING DOWNHOLE WELL CONDITIONS IN A
WELLBORE
Abstract
A method and apparatus for sensing downhole well conditions in a
wellbore having a drill string suspended therein and pump means and
conduit means for circulating drilling fluid down the well. The
apparatus includes a pressure transmitter for sensing the
circulating pressure of input drilling fluid being circulated down
the well and generating a first signal representative thereof. It
could also include means in the form of a differential pressure
transmitter for sensing a pressure drop of the drilling fluid along
a portion of the conduit means and generating a second signal
representative thereof. Readout means in the form of dual
concentric pressure gauges are provided for reading out a change
between the signals as an indication of a change in downhole well
conditions, such as loss of drilling fluids or incursion of
formation fluids into the well.
Inventors: |
Dower; Ethell J. (Houston,
TX) |
Assignee: |
Warren Automatic Tool Company
(Houston, TX)
|
Family
ID: |
25365849 |
Appl.
No.: |
04/875,462 |
Filed: |
November 10, 1969 |
Current U.S.
Class: |
73/152.19;
73/152.31; 73/152.51; 175/48 |
Current CPC
Class: |
E21B
47/06 (20130101); E21B 47/10 (20130101); E21B
21/08 (20130101) |
Current International
Class: |
E21B
21/00 (20060101); E21B 21/08 (20060101); E21B
47/10 (20060101); E21B 47/06 (20060101); E21b
047/06 () |
Field of
Search: |
;73/155,151,211,407,412,152 ;175/48 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Myracle; Jerry W.
Claims
What I claim is:
1. In a method for sensing down hole well conditions in a well bore
having a drill string suspended therein and pump means and conduit
means for circulating drilling fluid down said well, the
combination of steps comprising:
sensing the circulating pressure of input drilling fluid being
circulated down said well and generating a first signal
representative thereof;
sensing drilling fluid pressure at two points along said conduit
means with one of said points being upstream with respect to the
other of said points;
comparing the pressures at said points and generating a second
signal representative of the difference therebetween;
multiplying said second signal by a factor such that said first and
second signals are of substantially the same magnitude during
normal operations; and
monitoring said signals to detect a change therebetween as an
indication of a change in down hole well condition.
2. In a method for sensing down hole well conditions in a well bore
having a drill string suspended therein and pump means and conduit
means for circulating drilling fluid down said well, the
combination of steps comprising:
sensing the circulating pressure of input drilling fluid being
circulated down said well and generating a first signal
representative thereof;
passing at least a portion of said drilling fluid through a flow
restriction in said conduit means;
sensing drilling fluid pressure at two points along said conduit
means with one of said points being upstream and the other of said
points being downstream from said flow restriction;
comparing the pressures at said points and generating a second
signal representative of the difference therebetween;
and, monitoring said signals to detect a change therebetween as an
indication of a change in down hole well conditions.
3. The invention as claimed in claim 2 wherein:
said flow restriction is varied to thereby cause said first and
second signals to be substantially of the same magnitude during
normal operations, whereby a difference between said first and
second signals indicates an abnormal condition.
4. In a method for sensing down hole well conditions in a well bore
having a drill string suspended therein and pump means and conduit
means for circulating drilling fluid down said well, the
combination of steps comprising:
sensing the circulating pressure of input drilling fluid being
circulated down said well and generating a first signal
representative thereof;
sensing the pressure drop of said drilling fluid along a portion of
said conduit means and generating a second signal representative
thereof;
and, comparing said first and second signals and generating a third
signal representative of any change therebetween.
5. In apparatus for sensing down hole well conditions in a well
bore having a drill string suspended therein and pump means and
conduit means for circulating drilling fluid down said well, the
combination comprising:
means for sensing the circulating pressure of input drilling fluid
being circulated down said well and generating a first signal
representative thereof;
means for sensing drilling fluid pressure at two points along said
conduit means, with one of said points being upstream with respect
to the other of said points;
means for comparing the pressures at said points and generating a
second signal representative of the difference therebetween;
means for multiplying said second signal to increase the value
thereof relative to said first signal;
and, readout means for reading out a change between said first
signal and said multiplied second signal as an indication of a
change in down hole well conditions.
6. In apparatus for sensing down hole well conditions in a well
bore having a drill string suspended therein and pump means and
conduit means for circulating drilling fluid down said well, the
combination comprising:
means for sensing the circulating pressure of input drilling fluid
being circulated down said well and generating a first signal
representative thereof;
means for sensing drilling fluid pressure at two points along said
conduit means, with one of said points being upstream with respect
to the other of said points;
means for comparing the pressures at said points and generating a
second signal representative of the difference therebetween;
means for comparing said first and second signals and generating a
third signal representative of any change therebetween:
and, readout means connected to receive said third signal for
reading out a change in said third signal as an indication of a
change in down hole well conditions.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a method and apparatus for sensing
downhole well conditions in a wellbore having a drill string
suspended therein and pump means and conduit means for circulating
drilling fluid down the well. More particularly, the invention
relates to a method and apparatus for sensing a change in downhole
well conditions, such as a loss of drilling fluid to the formation
or the incursion of formation fluids into the well, for
example.
2. Description of the Prior Art
During the drilling of wellbores, as for example oil wells, it is
common practice to drill the well with a rotary bit suspended on
the end of a drill string in the wellbore. A drilling fluid, such
as mud, is circulated down the drill pipe to the bit and up the
annulus or vice versa. The drilling mud serves the purpose of
flushing cuttings from the wellbore, cooling the bit, and providing
a hydrostatic pressure to match formation pressures to thereby
prevent a possible blowout condition from developing. If the
condition should occur that the hydrostatic pressure of the mud
plus any back pressure which may be applied to the wellbore, are
not sufficient to match formation pressure, then there may be an
incursion of formation fluids into the wellbore and create what is
commonly referred to as a "kick. " Unless properly controlled and
circulated out, such a "kick" can result in a blowout and
subsequent loss of the hole and destruction of property and lives.
In the event that the hydrostatic pressure of the drilling fluid in
the wellbore is in excess of formation pressure along the uncased
portions of the wellbore, then there is a possibility of loss of
circulation wherein the drilling fluid flows into the formation and
there is no return drilling fluid to the surface.
In order to overcome the aforesaid problems, it has been common
practice in the drilling industry to pump drilling mud of the
desired weight, density and characteristics down the drill pipe and
sense the circulating drill pipe pressure. During such pumping, the
circulating drill pipe pressure is particularly useful information
when circulating out a "kick," so that the proper amount of back
pressure can be applied to the well to prevent further incursions
of drilling fluid.
The drill pipe pressure, or the pressure required to circulate the
drilling fluid through the well, can be a very important
measurement, not only in killing a well "kick," but also doing
drilling operations. Since the circulating drill pipe pressure
represents the sum total of all pressure drops through the well
circulation system, it is a good indicator of changes and
conditions in the wellbore.
One of the obstacles to the use of circulating drill pipe pressure
as an early indicator of downhole trouble is the fact that it is a
resultant of many factors and most of them are subject to change.
For example, the circulating drill pipe pressure is affected by a
number of factors, including circulation rate or the rate at which
the drilling mud is pumped down the wellbore. Increased circulation
rate increases drill pipe pressure as a function of the square of
the velocity resulting from the flow rate. Moreover, increases in
density and viscosity of the drilling mud cause increased drill
pipe pressure. Drill pipe pressure also increases with the depth
because of the increased friction inside the drill pipe, as well as
in the annulus of the wellbore. Drill pipe pressure also increases
as the annular cross-sectional area between the wellbore wall and
the drill pipe decreases. Drill pipe pressure also increases with
smaller bit nozzles.
Drill pipe pressure increases as surface back pressure is applied
to the return fluid, unless the casing pressure increases are
offset by expanding gas displacing mud from the annulus, as for
example, that which occurs during the circulation of a "kick" and
wherein the operator maintains the drill pipe pressure
constant.
Drill pipe pressure may also increase if a high pressure, high
production formation produces formation fluid into the annulus,
because the annulus flow increases and this increases annulus
friction. Drill pipe pressure may decrease after sufficient
incursion has reduced annulus hydrostatic pressure. Normally drill
pipe pressure will decrease when there is a loss of circulation, as
for example the loss of drilling fluid to the formation, as
discussed above, because this reduces annulus friction.
The largest part of the total drill pipe circulating pressure comes
from pressure drop across the bit nozzles. This may be on the order
of 80 percent of the total pressure drop. Annular friction may be
only about 10 percent or less of the total. Aside from detection of
drill pipe washouts (a hole in the drill pipe, for example) and the
loss of nozzles from the bit, both of which alter the large 80
percent figure noted above, the hole conditions changes will alter
only the small percent factor of annular friction. This small
percentage change resulting from hole conditions is difficult to
observe and correlate because of variations in circulation rate.
Small variations in circulation rate commonly occur as a result of
mud pump speed variations and variation in mud pump efficiency.
These changes in circulation cause changes in the total drill pipe
circulating pressure which are large compared to the annular
friction portion and thus mask the small but important changes
which occur in this portion of the hole.
During the killing of a "kick" it is common practice to
continuously regulate surface back pressure in a manner which
produces a constant drill pipe circulating pressure, as this
assures a correct applied bottomhole pressure, provided, of course,
that circulation rate is held constant. Here the adjustment of the
constant pump speed still leaves the variable pump efficiency as a
factor which can cause an error.
SUMMARY OF THE INVENTION
It is therefore an object of this invention to provide an improved
method and apparatus for sensing changes in downhole well
conditions, which method and apparatus are not subject to the
foregoing limitations.
Briefly stated, this invention includes a method for sensing
downhole well conditions in a wellbore having a drill string
suspended therein and pump means and conduit means for circulating
drilling fluid down the well. It includes in combination the steps
of sensing the circulating pressure of input drilling fluid,
commonly referred to as circulating drill pipe pressure, being
circulated down the well and generating a first signal
representative thereof. It also includes sensing a flow
characteristic of the drilling fluid in the conduit means, such as
the pressure drop of the drilling fluid along a portion of the
conduit means, and generating a second signal representative
thereof. It also includes monitoring these two signals to detect a
change therebetween as an indication of change in downhole well
conditions. The sensing of the pressure drop may be accomplished by
sensing circulating drilling fluid pressure at two spaced apart
points along the conduit means, comparing the pressures at said
points, and generating a signal representative of the difference
therebetween as the second signal. Further embodiments may include
the step of multiplying the second signal by a factor such that the
first and second signal are of substantially the same magnitude
during normal operations, whereby the difference between the first
signal and the multiplied second signal indicates an abnormal
condition in the well.
The apparatus of this invention is for sensing downhole well
conditions in a wellbore having a drill string suspended therein
and pump means and conduit means for circulating drilling fluid
down the well. The combination of the invention includes means for
sensing the circulating pressure of input drilling fluid being
circulated down the well and generating a first signal
representative thereof. Means are also provided for sensing a flow
characteristic of the input drilling fluid in the conduit means,
which characteristic may be of a pressure drop along the conduit
means, and generating a second signal representative thereof.
Readout means are included which are connected with the sensing
means for reading out a change between the signals as an indication
of a change in downhole well conditions.
Certain embodiments may include means for sensing pressure drops
along two points in the conduit means and means for comparing the
pressures at the two points and generating a signal representative
of the differences therebetween, as the second signal. Means may
also be provided for multiplying the second signal to increase the
value thereof relative to the first signal. Other embodiments may
include means for flowing at least a portion of the drilling fluid
therethrough. The readout means may include a pair of concentric
gauges, one of which is responsive to the first signal and one of
which is responsive to the second signal.
BRIEF DESCRIPTION OF THE DRAWINGS
Reference to the drawings will further explain the invention,
wherein like numerals refer to like parts, and in which:
FIG. 1 is a schematic diagram of one embodiment of the
invention.
FIG. 2 is a schematic diagram of another embodiment of the
invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring now to FIG. 1, the means for circulating drilling fluid
down a wellbore includes a mud pump 11 connected to flow mud
through conduit means in the form of mud line 12, which is
connected to the conventional stand pipe of the drilling rig and
which is arranged to flow the drilling mud down the bore of the
drill pipe to the drill bit and up the annulus. Means are provided
for sensing the circulating pressure of input drilling fluid being
circulated to the well and generating a first signal representative
thereof which is in the form of a pressure transducer 13 which is
connected to line 12 and is supplied with a regulated air supply on
line 14. Pressure transducer 13 is of conventional design and
provides an analog pneumatic output signal on the order of 3--15
p.s.i. on line 15. Line 15 is connected to operate one indicator
needle of dual concentric indicator gauge 16 which is appropriately
calibrated to cover the expected range of drill pipe pressures to
be encountered.
Means are also provided for sensing a flow characteristic, as for
example the pressure drop, of the drilling fluid along a portion of
the conduit means and generating a second signal representative
thereof. This includes diaphragm boxes 19 and 20 which are spaced
along mud line 12 and are respectively connected by hydraulic lines
21 and 22 to differential pressure transducer 23 which is supplied
with a regulator air supply over line 24. Differential pressure
transducer 23 is of conventional design and is arranged to have a
pneumatic output signal on the order of 3--15 p.s.i. on line 26.
Differential pressure transducer 23 is arranged to receive the high
pressure signal on line 21 and the low pressure signals from line
22. In other words, the pressure will be somewhat lower at
diaphragm box 20 than at diaphragm box 19 because of friction
losses in the mud conduit. It is to be understood that diaphragm
boxes 19 and 20 may be spaced several feet apart, on the order of
20 to 60 feet, for example. Alternatively, flow restriction means
in the form of flow restrictor 30 are connected by lines 31 and 32
to mud line 12, as shown. In this instance, meter bypass valve 33
may be interposed in mud line 12 and arranged such that at least a
portion of the input drilling fluid is flowed through flow
restrictor 30 to thereby induce a small amount of friction loss in
the conduit means for circulating the drilling fluid pressure to
the well.
The output on line 26 may sometimes be referred to as the second
signal and may be multiplied to be of the same general magnitude as
the pressure signal on line 15. This multiplication is accomplished
by a multiplier analog computer 36 which is connected to line 26
and is arranged to receive a regulated air supply on line 37. It is
also arranged to receive a 3--5 p.s.i. pneumatic pressure signal on
line 38, which is connected to pressure regulator 39 also connected
to a regulated air supply line 40. Conveniently, line 38 may be
connected to a regulator gauge 41 so that regulator 39 may be
manipulated to provide the correct multiplier to multiplier analog
computer 36. The output of multiplier analog computer 36 is to line
42 carrying a pneumatic analog signal on the order of 3--15 p.s.i.
which pressure is applied to the other needle of dual concentric
indicator gauge 16, which needle is appropriately calibrated to
cover the expected pressure variations which are to be encountered
between diaphragm boxes 19 and 20.
In operation, the apparatus would be set up as shown in FIG. 1 and
as described above. The needles of dual concentric indicator gauge
16 would be calibrated to overlay each other initially during
normal drilling operations. During subsequent drilling operations,
if there should be a change in downhole well conditions, such as a
loss of circulation or the incursion of drilling fluid into the
wellbore, for example, such changes would be reflected by the
divergence of the needles of dual concentric indicator gauge 16,
which needles would assume a spaced relationship to each other.
By this apparatus, flow changes, such as those sensed by diaphragm
boxes 19 and 20, are mathematically related to circulating pressure
during normal drilling operations and before unusual or abnormal
conditions are encountered. This apparatus greatly improves the
usefulness of drill pipe circulating pressure as an indicator of
downhole well conditions. The apparatus of this invention therefore
compares measured drill pipe pressure with a pneumatically computed
drill pipe pressure. The pressure drop which is sensed between
diaphragm boxes 19 and 20 is analogous to the drill pipe, bit
nozzle, and annulus of the wellbore. Differential pressure detected
between diaphragm boxes 19 and 20 is generally proportional to the
velocity squared, density and viscosity of the mud, the same as the
drill pipe circulating pressure is related to these items. In the
event that flow restrictor 30 is used it is to be understood that
the resistance offered thereby will be made low, as for example on
the order of only a few percentage points of drill pipe pressure.
It is kept low so that the increased load on the mud pump 11 is not
significant. The change in pressure between diaphragm boxes 19 and
20 is converted to a 3--5 p.s.i. pressure signal by differential
pressure transducer 23, which is of conventional design of the type
commonly used to meter flow. Because of the configuration of the
mud line 12 and/or flow restrictor 30, the output from differential
pressure transducer 23 would have a fixed relation to flow,
density, viscosity, etc. The restriction to flow in the wellbore is
subject to change with depth, bit nozzle size, hole size, etc., as
discussed above. Rather than alter the calibration of the flow
meter to match these changing well conditions, it may be preferable
to put the signal through a computing relay such as multiplier
analog computer 36 with an adjustable multiplier factor so that the
computer output can be fit to be exactly equivalent to drill pipe
pressure for the existing well conditions.
With multiplier analog computer 36 so adjusted, any subsequent
change in well conditions will be reflected as a change in drill
pipe pressure transmitted on line 15, but not in the computed drill
pipe pressure transmitted via lines 26 and 42. This difference is
measured and readout by dual concentric indicator gauge 16 or
alternatively by using another differential pressure transducer,
the output of which is proportional to the difference between the
first and second signals discussed above, or by appropriate record
means.
A differential transmitter is optional and may take the form of
differential pressure transducer 45, which is connected via line 46
to line 42 and by line 47 to line 15, and with the outputs thereon
connected to differential pressure gauge 48 by line 49. The output
from transducer 45 may be a pneumatic signal on the range of 3--15
p.s.i. which is proportional to the difference between the two
signals applied thereto.
Hence, any appreciable change in flow rate, density or viscosity
will alter the signals on lines 15 and 42 by like amounts and no
difference therebetween will occur or be detected. Hence, an
observer may monitor either dual concentric indicator gauge 16, or
differential pressure gauge 48 or other readout means in the form
of recorders or the like and can determine the difference in
measured and computed drill pipe pressures, and any change
therebetween is attributed to some downhole change in the
circulating system and serves as an immediate warning of
trouble.
It is to be understood that if differential pressure transducer 23
is sufficiently convenient and has sufficient range, it can be used
in lieu of multiplying analog computer 36 to set the computed drill
pipe pressure equal to the measured drill pipe pressure for
existing well conditions.
A typical example of suitable differential pressure transducers 23
and 45 is one sold by Foxboro Company of Foxboro, Mass. and bearing
Model No. 13H.
A typical example of a suitable multiplier analog computer 36 is
one sold by Foxboro Company of Foxboro, Mass. and bearing Model No.
556.
A typical example of pressure transducer 13 is one sold by Foxboro
Company of Foxboro, Mass., and bearing Model No. 11GH.
Referring now to FIG. 2, an alternate and perhaps even more
preferred embodiment will be described. In this instance, a mud
pump 50 is shown connected to a conventional mud line 51 leading to
the stand pipe of the drilling rig. Two diaphragm pressure sensor
boxes 52 and 53 are connected to mud line 51 at substantially
spaced apart positions and arranged such as to be responsive to the
pressure of mud in line 51 at the points where they are positioned.
The spacing between boxes 52 and 53 may be on the order of 20 to 60
feet and preferably at least 40 to 60 feet. Box 52 is connected by
hydraulic line 55 to pressure transducer 56 which is connected to a
source of air supply over line 57 and is arranged to have a
pneumatic output in the range of 3--15 p.s.i. on line 58, which in
turn is connected to drill pipe pressure gauge 59. It is to be
understood that gauge 59 is one part of a dual concentric indicator
gauge, such as indicator gauge 16 shown in the previous
embodiment.
Diaphragm pressure sensor box 52 is also connected by hydraulic
line 60, which in turn is connected as one of the inputs to
differential pressure transducer 61 and having an air supply input
on line 62. Differential pressure transducer 61 is connected by
hydraulic line 63 to diaphragm pressure sensor box 53 and is
arranged to have a pneumatic output signal on line 64 spanning the
range of about 3--15 p.s.i., which signal is representative of the
difference between the pressures sensed by boxes 52 and 53.
It is to be understood that pressure transducer 56 is similar to
pressure transducer 13, described in the previous embodiment, and
differential pressure transducer 61 is similar to differential
pressure transducer 23, previously described.
Line 64 connects via line 64a to adjustable proportioning valve 65,
which in turn is connected by line 64b to bleed valve 67 which is
provided with an air supply over line 68 which also connects to an
optional booster valve 69, which is applied to well circulating
pressure gauge 70 having a needle which is deflected in response to
pressure applied on line 71 from booster valve 69. It is to be
understood that gauge 70 is calibrated to cover the anticipated
range of computed well circulating pressure and is concentric with
respect to drill pipe pressure gauge 59 and is similar in
construction to dual concentric indicator gauge 16 described with
respect to the previous embodiment.
The apparatus also includes a line 73 connected between line 72 and
line 71, the purpose of which is to optionally bypass booster valve
69 which is a two-to-one multiplier. A fixed restrictor 74 is
provided in line 64 and valve 65 is a variable restrictor in line
64a. Valve 67 is a regulator connected to line 64 b. Regulator 67
is set to have an output of 3 p.s.i. which is equal to the "zero" 3
p.s.i. signal in line 64 from differential pressure transducer 61.
Regulator valve 67 will bleed off any pressure in excess of 3
p.s.i. in line 64b. The adjustment of restrictor valve 65, in
conjunction with fixed restrictor 74, modifies the pressure of line
64 as it exists in line 64a and line 72. If restrictor valve 65 is
closed, pressure in line 64a and line 72, is equal to that in line
64. This could be called the 100 percent setting. If restrictor
valve 65 is opened, it bleeds off pressure in line 64a down to near
3 p.s.i. (zero). This could be called the 10 percent setting. At
intermediate settings it can cause pressure in line 64a to be any
fraction of that in line 64, as for example 50 percent. With
booster relay 69 in operation, the 100 percent setting of
restrictor valve 65 causes a 100 percent signal in line 64a and
line 72 into the two-to-one booster relay 69 and the result is a
200 percent signal pressure in output line 71 to indicator gauge
70. With a 50 percent setting on restrictor valve 65, the 50
percent signal pressure in line 72 results in a 100 percent output
signal in line 71 to indicator gauge 70. Restrictor valve 65, in
conjunction with booster relay 69, can modify signal pressure
existing in line 64 by 20 percent to 200 percent in line 71 and
indicator 70. If booster relay 69 is bypassed by line 73, then the
pressure in line 72 is conducted directly to indicator gauge 70 and
the resultant modification range is 10 percent to 100 percent.
It is to be understood that the total assembly found within the
dotted square 75 is a Moore Products M/P ratio control apparatus
sold by Moore Products Company of Spring House, Pa., under the
Model No. 543.
In operation, valve 65 is adjustably set for well conditions so
that the pressure signal applied to well circulating pressure gauge
70 equals the pressure applied to drill pipe pressure gauge 59
during normal drilling operation.
Upon encountering abnormal well conditions, as for example an
incursion of drilling fluid into the wellbore or loss of
circulation, a difference will be noted on gauges 59 and 70. Hence,
by monitoring these gauges, any variation therebetween would
indicate a potentially hazardous condition, the same as would be
indicated by dual concentric indicator gauge 16 of the previous
embodiment.
Further modifications and alternate embodiments will be apparent to
those skilled in the art in view of this description. Accordingly,
the foregoing description is to be construed as illustrative only
for teaching those skilled in the art how to build and perform the
invention.
* * * * *