U.S. patent number 3,608,653 [Application Number 04/859,938] was granted by the patent office on 1971-09-28 for method and apparatus for controlling a well.
This patent grant is currently assigned to Dresser Industries, Inc.. Invention is credited to William A. Rehm.
United States Patent |
3,608,653 |
Rehm |
September 28, 1971 |
METHOD AND APPARATUS FOR CONTROLLING A WELL
Abstract
A method and apparatus for controlling a well to prevent a
blowout and an accompanying loss of the drilling mud which utilizes
the change in volume of the drilling mud in the mud pits. This
change in volume is converted to a corresponding pressure change
necessary to compensate for the volume change in the relationship
of the gas and drilling mud in the well bore to make such
compensation as is necessary to maintain the pressure constant at
the bottom of the well bore.
Inventors: |
Rehm; William A. (Houston,
TX) |
Assignee: |
Dresser Industries, Inc.
(Dallas, TX)
|
Family
ID: |
25332114 |
Appl.
No.: |
04/859,938 |
Filed: |
September 22, 1969 |
Current U.S.
Class: |
175/25; 175/38;
175/218 |
Current CPC
Class: |
E21B
21/08 (20130101) |
Current International
Class: |
E21B
21/00 (20060101); E21B 21/08 (20060101); E21b
021/00 (); E21b 041/00 () |
Field of
Search: |
;175/24,25,38,40,48,65,218 ;166/75 ;73/151,155,308,311-313 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Bell, Frank S. High Pressure Drilling and Blowout Prevention. In
Oil & Gas J., Oct. 14, 1957. pp. 147-151 and 160-163 relied on.
(Copy in 175-65).
|
Primary Examiner: Calvert; Ian A.
Claims
The embodiments of the invention in which an exclusive property or
privilege is claimed are defined as follows:
1. A method for controlling a well to prevent a blowout or lost
circulation wherein said well contains a drill pipe and casing with
an annulus therebetween and said well contains mud, and there is a
mud pit communicating with the annulus, comprising
measuring any change of volume of mud in the mud pit from the
volume of mud present under normal drilling conditions,
converting the volume change measured to a pressure change needed
to compensate for the volume change according to the formula:
##SPC2## and,
changing the pressure in the well bore an amount substantially
equal to the pressure change determined thereby compensating for
said volume change and maintaining the pressure in the well bore
substantially at the normal operating value.
2. The method according to claim 1 wherein said volume change is
measured in U.S. barrels, said annular volume is measured in U.S.
barrels per foot of length of the well bore, and said mud weight is
expressed as pounds per square inch per foot of length of the well
bore, the pressure change obtained in pounds per square inch, and
the pressure in the well bore increased the amount of said pressure
change if said volume change was an increase or the pressure in the
well bore decreased the amount of said pressure change if said
volume change was a decrease.
3. The method according to claim 2 wherein said mud weight is
converted to pounds per square inch per foot of length of the well
bore by the formula: (mud weight in pounds per U.S.
gallon).times.(0.052).
4. A method according to claim 1 where said volume change is
displayed and said change of the surface pressures is made as
dictated by said display.
5. A method according to claim 1 wherein said surface pressure
change is made automatically.
6. Apparatus for controlling a well to prevent a blowout or lost
circulation wherein said well contains a drill pipe and casing with
an annulus therebetween and said well contains mud, and there is a
mud pit communicating with the annulus, comprising in combination,
means for measuring mud volume change in the mud pit, means for
receiving and converting said measured volume change to a pressure
change needed to compensate for the volume change according to the
formula: ##SPC3##
and means for changing the pressure in the well bore an amount
substantially equal to said pressure change to maintain the
pressure in the well bore substantially at the normal operating
value.
7. The apparatus according to claim 6 wherein said volume change
measuring means is a pneumatic means which employs a float means
that floats on the surface of the mud in said mud pit, said
receiving and converting means is a multiplier means, and said
means for changing the pressure in the well bore is a choke which
controls the output of mud from the well bore.
Description
BACKGROUND OF THE INVENTION
In drilling a well, high-pressure gas from the underground
reservoir pierced by the well bore sometimes enters the well bore.
The entry of the gas is controlled by the pressure exerted by the
drilling mud and/or extra pressure exerted at the surface by
closing in the top of the well bore. The intrusion of gas is
manifested by the forcing of an equivalent amount of drilling mud
out of the well bore into the mud pits. The removal of mud from the
well bore decreases the pressure opposite the underground reservoir
and allows more gas to enter the well bore.
A blowout can then occur when the gas blows most of the mud out of
the hole and the gas itself appears at the surface. Fire and
accompanying loss of life and property can result from the
uncontrolled blowing of gas at the surface. On the other hand, if
too much pressure is exerted upon the well bore while controlling
the gas, fracturing of the protective casing in the well bore or of
the earth can occur and the gas will then escape in an uncontrolled
manner into the earth. This may manifest itself by blowing in an
uncontrolled manner around the drilling rig where it has worked its
way to the surface. Also, the gas may repressure other reservoirs
within the earth. In either case, there is an economic loss from
the loss of potential fuel.
Heretofore three types of blowout-control procedures have been
used.
1. Historically an attempt has been made to control subsurface
pressures by holding the volume of mud in the pits constant. This
approach has not been satisfactory because, due to the nature of
the gas laws and the length of the column of intruding fluid of the
gas or oil, this method impressed such great pressures upon the
well bore that the casing or the earth was fractured causing
uncontrolled loss of the reservoir material to the earth. This also
causes the hazards listed above.
2. A method has been attempted whereby the calculation of the
expansion of gas by means of the general gas law was attempted. The
result of this calculation was a theoretical surface pressure that
should be maintained as the intruding fluid was pumped to the
surface. This was unsatisfactory because the intruding fluid was
not totally understood and the theoretical calculations were not
sufficiently accurate.
3. Another approach involves using not the pressure on the annulus
of the well, but the drill pipe pressure to maintain a constant
bottom hole pressure. This method is simple and accurate. However,
this method is usable only when the drill pipe is at the bottom of
the hole.
The method and apparatus of this invention employ a technique that
is simple and accurate and that is usable when there is no drill
pipe in the well bore or the drill pipe does not extend to the
bottom of the well bore. Thus, it provides a method and apparatus
for killing a well and preventing a blowout when the constant drill
pipe pressure method of subparagraph 3 above is unusable.
SUMMARY OF THE INVENTION
It has now been discovered that potential blowouts and accompanying
lost mud circulation problems can be controlled by measuring only a
single parameter related to the operation of the well and by making
only a single calculation in determining the change in pressure
required to be impressed on the well bore to compensate for the
volume change of drilling mud in the well bore displaced by the
intruding material. This maintains the pressure at the bottom of
the well bore substantially at the desired value.
According to this invention there is provided a method which
comprises measuring the change of volume in the mud in the mud pits
during the potential blowout and relating this measured-volume
change to the pressure change in the well bore. It is then possible
to increase or decrease the pressure in the well bore according to
this relationship of volume on the surface versus pressure in the
well bore. In this way, the pressure at the bottom of the well bore
can be maintained at substantially the desired operating
pressure.
This invention also relates to apparatus which employs a
combination of means for measuring mud volume change in the mud
pits, means for receiving and converting this measured volume
change to a pressure change, and means for changing the pressure in
the well bore in amounts substantially equal to the determined
pressure change to maintain the pressure at about the bottom of the
well bore substantially at the desired normal operating
pressure.
Other aspects, objects, and advantages of the invention will be
apparent to those skilled in the art from the disclosure and the
appended claims.
DETAILED DESCRIPTION OF THE INVENTION
In the drawings: FIGS. 1 and 2 show schematic drawings of a well
bore and its associated apparatus. For reasons due to the operation
of the drilling procedure, the drill pipe is not at the bottom of
the hole.
More specifically FIG. 1 shows a well bore 1 lined with casing 2,
and containing a drill pipe 3 which does not extend to the bottom 6
of well bore 1. Casing 1 does not extend to the bottom of the hole
so that the open well bore is in communication with the underground
reservoir formation 4. The annulus 5 of the open hole and around
the partial length of drill pipe 3 contains drilling mud from
bottom 6 of well bore 1 upwards and through the return line 7,
choke 8, and into one or more mud pits 9.
Mud is removed from the mud pits by pump 10 and pumped through
pipes 11 and 12 into the interior of the drill pipe 3. The mud then
passes down to bottom 22 of drill pipe 3 and upwardly in annulus 5
to the return line 7. Thus, there is no controlled circulation
below bottom 22 of drill pipe 3. Gas from formation 4 can enter
annulus 5 and thereby collect in the well bore. A gas bubble 13 is
shown in FIG. 1. Gas bubble 13, however, could, for example, be
water, oil, or any combination of the three.
The introduction of gas bubble 13 into annulus 5 causes a
corresponding volumetric displacement of drilling mud into pit 9.
This causes an increase in the volume (and therefore liquid level
14) of the mud in pit 9.
This initial displacement of mud can be quite small in terms of the
volume of mud present since the pressure at the bottom of the well
bore is very high and gas bubble 13 will initially be quite
compressed. However, as the bubble rises towards the surface of the
well, as it will do since it is lighter than the drilling mud, it
increases in volume because the pressure on the bubble decreases as
the bubble progresses towards the surface of the earth. This is
shown in FIG. 2. Thus, as gas bubble 13 progresses upwardly in
annulus 5, it will expand, if allowed to do so, and displace larger
and larger volumes of mud into mud pit 9.
The increase of volume of mud in pit 9 is sensed by a conventional
mud pit volume totalizer mechanism 15. For example, a pneumatic
mechanism such as that disclosed in U.S. Pat. No. 3,086,397 can be
employed. This mechanism uses a float 16 that rides on the mud
surface 14. This can also be done by replacing the pneumatic
totalizing circuitry with electric totalizing circuits.
The volume change measured by mechanism 15 is transmitted to a
conventional and commercially available pneumatic multiplier or
electric multiplier 17 by means of line 18 wherein the volume
change is converted to equivalent pressure needed to compensate for
the loss of mud in the well bore caused by bubble 13.
The pressure change determined by device 17 then can be transmitted
by way of line 19 to the choke controller 20 which adjusts through
line 21 the opening in choke 8 to the proper pressure.
The method of this invention therefore comprises measuring the
change of volume of mud in the mud pit, converting the volume
change thus measured to a pressure change needed to compensate in
the well bore for the mud displaced by the expanding gas according
to the formula: ##SPC1##
and changing the pressure in the well bore in amounts substantially
equal to the pressure change thus determined thereby compensating
for the volume change and maintaining the pressure in the well bore
substantially at the normal operating value.
In the above formula the volume change can, as a nonlimiting
example, be measured in barrels (U.S.), the annular volume being
the volume of annulus 5 measured in barrels (U.S.) per foot of
length of the well bore, and the mud weight being expressed in
pounds per square inch per foot of length of the well bore.
The formula would then be:
.DELTA.P=(.DELTA.V) (0.052 WtM/AV)
where:
.DELTA.P = Change in pressure on the bottom of the well bore,
p.s.i.
.DELTA.V = Change in volume in the mud pits, barrels (U.S.).
wtM = Mud weight, pounds/gallon.
0.052 = Conversion factor to change mud weight pounds/gallon to mud
weight, p.s.i./ft. of length of well bore.
AV = Effective volume of the hole, barrels (U.S.)/ft. of length of
well bore.
This formula then shows that the change in pressure at the bottom
of the hole (.DELTA.P) is dependent upon the change in volume of
the surface pits, since in the drilled hole the volume and mud
weight may be regarded as a constant.
The result of this formula (.DELTA.P) can then be used to either
manually correct the surface pressure by means of a hand operated
choke control or may be used to automatically control choke by
means of raising or lowering the surface pressure at the choke
according to the value .DELTA.P. The manual control is obvious to
one skilled in the art. The automatic control is commonly used in
industry where a change of pressure is sensed from some source and
the change of pressure is used to change a control or throttle in
the valve.
Thus, by way of further example, a drilling mud weighing 10
pounds/gallon in the apparatus in FIG. 1, when displaced in part by
the intrusion of gas bubble 13 into annulus 5, will be indicated by
an increase in the volume of mud in the mud pit 9, and will be
detected by mechanism 15 and transmitted to device 17. Device 17
will perform the appropriate mathematical processes as described in
the above formula and either display the result for manual
correction or transmit the result to throttling valve 8 to
automatically exert the proper change in pressure upon the well
bore.
Reasonable variations and modifications are possible within the
scope of this disclosure without departing from the spirit and
scope of this invention.
* * * * *