Note: Descriptions are shown in the official language in which they were submitted.
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BACKGROU~ID OF THE INVENTION
Field of the Invention
This invention concerns oil well pumping systems
in general. More specifically, it relates to an improved
deep well down hole pumping system that employs a con-
tinuous centrifugal pumping arrangement with an electric
motor drive.
Descri~tion of the Prior Art
For various reasons, including the wide variation
in actual condltions in regard to oil wells that must be
pumped for producing the fluid therefrom, the most widely
used arrangement for carrying out the pumping is the
longstanding surface controlled and powered reciprocating-
type of pumping. It has a string of so-called sucker rods
which are connected from a surface structure and extend
downhole to actuate a reciprocating pump. Such an
arrangement has practical problems, particularly where
the well is deep, which means the string of sucker rods
must be very long and heavy.
While, heretofore, attempts have been made to
employ down hole electrical submergible pumping systems,
these have been applied particularly to wells which are
considered high volume producers. So that, even though
the principle of using submergible electrical pumping
systems with high-volume fluid pumping at substantial
depths has been known, it has been found as a practical
matter that such systems are lacking in production
flexibility once they have been installed. Thus, a
submergible pump system that is designed to match a
particular production rate of fluid, will not retain the
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matching characteristics as tlle production of the well changes.
Consequently, such systems are subject to failure under pump-
off conditions and have not been found economically feasible.
Heretofore, there has been a suggestion for pumping of
deep oil wells. It is United States Patent No. 1,957,320 to
Coberly et al, issued May 1, 1934. That system employs a
hydraulic-type of fluid driven motor located down hole and power-
ing a down hole pump. There are controls applied to an electric
motor located at the surface. The motor drives a surface hydraulic
pump that applies hydraulic fluid pressure to actuate the down hole
fluid motor. That system has quite apparently not been found
particularly practical.
Thus, it is an object of this invention to provide
a deep well pumping system. It employs a centrifugal pump down
hole and includes flexible controls to vary the pumping rate
in accordance with the static fluid head down hole.
SUMMARY OF THE INVENTION
The present invention provides an improved deep well
pumping system. It comprises in combination a tubing string
for carrying pumped fluid from down hole to the surface, and a
submergible pumping unit operatively connected to said tubing
string at the down hole end thereof, The said pumping unit
comprises a three-phase AC electric motor connected for driving
a centrifugal pump. The pumping system also comprises means for
sensing static pressure of said fluid down hole, and speed
control means for automatically controlling the speed of said
motors depending upon said static pressure, in order to regulate
the pumping rate for maintaining the fluid level down hole within
predetermined limits. The said speed control means comprises
static type solid-state means for varying the frequency of said
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three-phase AC supply to said electric motor.
BRIEF DESCRIPTION OF TIIE DRAWING
The foregoing and other objects and benefits of the
invention will be more fully set forth below in connection with
the best mode contemplated by the inventor of carrying out the
invention, and in connection with which there is an illustration
provided in the drawing, wherein:
The figure of drawing is a schematic illustration of a
system for deep well down hole pumping, according to the invention.
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11~7409
3ESCRIPTION OF THE ?REFERRED EMBODI~ENT
In spite of much technical information and equip-
ment which has been available heretofore in relation to
pumping o~ fluld from oil wells and the like, there has
not been a successful system for using centrifugal
pumping in a continuous manner that could maintain the
pumping rate substantially in accordance with the produced
fluid down hole. Thus, even though the problem has been
recognized heretofore, the only known solution related to
controlling the pumping in a periodic manner in turn
related to the pumping down of the fluid level in the
well so that the pumping was stopped until well fluid had
time to rise again in the well bore.
A known tentative proposal dealt with an arrange-
ment for varylng the speed of an electric motor located
down hole with a submersible pump. However, that proposal
would employ a surface motor-generator in order to obtain
a variable frequency source of power for drivlng the
; down hole motor. Consequently, the cost of such an
arrangement would be high.
A deep well pumping system according to the in-
ventlon i8 illustrated in the figure of drawing. There
is a well 11 that has casing 12 thereln, at least near
the surface. The well 11 produces fluid 15 that must
be pumped in order to have it reach the surface. The
pumplng system accordlng to this invention includes a
tubing string 16 that has a pumping unit 19 attached at
the lower end thereof. The unlt 19 lncludes a centrifugal
pump 20 which ls driven by a three-phase AC motor 23,
attached therebeneath. There is, of course, an lntake
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24 ~or permitting the well fluid 15 to flow into the pump
and motor elements 20 and 23. It will be appreciated that
t;he intake 24 may be located be~ween the motor 23 and the
pump 20 so long as the motor 23 is able to maintain
adequate heat dissipation. These elements, per se, are
commercially available as will be indicated in greater
detail hereafter.
There is a combined temperature and pressure
sensing element 27 which is connected to the lower end o~
the unit l9. These provide control signals as part of
the system to be more fully described hereafter.
Total depth of the well 11 is indlcated by an
arrow 28, and it has been found that a system accordlng
to the invention is applicable to a producing well having
a depth on the order of 5000 ft. or more. At the surface,
there is piping 31 which is schematically indicated. This
carries the produced fluid 15 from the top of the tubing
string 16 to storage, or for other utilization.
Other surface equipment is electrical and is in-
dicated by a unit 32 that has the caption "pump motor
controller". It will be observed that there are three
electrical circuits indlcated schematically. One ls a
source of electric power 35, and another ls a clrcuit 36
whlch delivers variable frequency power to the motor 23.
Also, there ls a third circuit 37 which carrles electrlcal
signal information in connection with the pressure and
temperature that are being measured in the element 27
down hole.
A preferred system employs a three phase AC
electric motor as the motor 23 down hole. This may be one
such as a commercial motor designated by the tradename
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"Reda", manu~actured by T.R.W. Inc. Similarly, the pump
20 may be part of a commercial unit that incorporates a
motor ln the unlt with the pump, and is supplied by the
Reda Pump Company, which is a division of T.R.W. Inc., of
Bartlesville, Oklahoma.
The motor 23 is controlled by the unit 32 at the
surface. This unit 32 might take different forms, but
preferably is a solid state AC to AC power converter,
which transforms a constant voltage, fixed frequency
power source into an ad~ustable voltage, ad~ustable fre-
quency power supply. This element eliminates the need for
rotating sur~ace machinery, such as the above indicated
motor-generator combination. Thus, the element 32 may
be in accordance with the principles described in a
technical paper which was presented to the IEEE-IGA
Annual Meeting, at Cleveland, Ohio, October 18-21, 1971.
That paper was titled "Current Source Converter for AC
Motor Drlves", by Kenneth P. Phillips. Similarly, the
element 32 may be a power converter like one which is
described by a brochure of the Electric Machinery
Manufacturing Company, Minneapolls, Mlnnesota, 55413,
tltled "The E-M Ampll-Cycle". The brochure shows
copyrlght 1971, Electrlc Machinery Manufacturing Company.
The speed of the motor 23 and the pump 20, and
consequently the rate of pumping of the fluid 15, is
controlled in accordance with the static pressure at the
locatlon of the inlet 24, so that the fluid level of
fluld 15 may be malntained wlthln predetermined llmits
by pumping at a rate that ls comparable wlth the rate of
production of the fluid. The element 27 provides for
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static pressure by having a pressure-sensitive element
that develops electrical control signals 1n accordance
~i~h such pressure. A commercial unit for accomplishing
this may be employed, e.g. one manufactured by Lynes Inc.
of PØ Box 12486, ln Houston, Texas, 77017. It may be
noted that this same company manufactures a similar unit
that develops signals in accordance with temperature.
Thus, both the pressure and the temperature down hole
are measured with signals in accordance therewith and
transmitted electrically up-hole over the circuit 37.
It may be noted that a pumping system according to this
invention will operate in the absence of any temperature
information, but it is deslrable to have a temperature
signal which can be employed to shut down the pumping in
case the temperature exceeds a safe level.
It may be observed that individual elements of
the combination according to this invention have been
proposed for various uses heretofore. However, a need
for an efficient system of pumping fluid from deep wells
that can maintain a variable pumping rate automatically
over extended periods has existed for a long time and
there has been no suggestion or solution to this problem
heretofore. Also, it will be recognized that there are
difficulties involved in connection with a deep well
pumping system. Such difficulties are not only those
generally indicated above in relation to reciprocating
type pumping from the surface, but also in centriflcal
pumping arrangements the requirements are quite exacting
in regard to the necessary coollng of the pump itself,
in addition to the motor drive therefor, and these
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d~fficul~ies have now been overcome by this invention.
l,~hile a partlcular embodiment of the invention
has been described above in considerable detail in
accordance with the applicable statutes, this is not to
be taken as in any way limiting the invention, but merely
as being descriptive thereof.
