Abstrict A well has a downhole flow meter that is installed in a sub in
a string of tubing. The flow meter has a body having an external
profile that lands on a landing profile in the sub. The body has
a passage with a throat area of reduced diameter. Upstream and downstream
body ports in a side wall of the body are in fluid communication
with the throat area and a downstream portion of the passage downstream
of the throat area. Seals are located between the body and the sub,
defining an upstream annular chamber and a downstream annular chamber
surrounding the body, the chambers being in communication with the
upstream and downstream body ports. Upstream and downstream sub
ports in a side wall of the sub are in fluid communication with
the upstream and downstream chambers. A sensor circuit is in operative
engagement with the sub ports for determining a flow rate based
on a pressure difference sensed between the throat area and the
downstream portion of the passage in the body.
Claims I claim:
1. A well flow meter assembly, comprising: a tubular sub having
threaded ends for connection into a string of well tubing, the sub
having a bore with a landing profile; a flow meter body that lands
on the landing profile, the flow meter body having a passage therethrough;
upstream and downstream sub ports in a sidewall of the sub that
are in fluid communication with the passage at upstream and downstream
points, respectively, in the passage; and a sensor circuit in fluid
communication with the sub ports for determining a flow rate of
fluid flowing through the passage based on a pressure difference
between the upstream and downstream points.
2. The flow meter assembly according to claim 1 wherein the upstream
point in the passage is located within a throat of reduced diameter.
3. The flow meter assembly according to claim 1 further comprising
an upstream tube extending from the upstream sub port to the sensor
circuit to communicate fluid pressure at the upstream point to the
sensor circuit, and a downstream tube extending from the downstream
sub port to the sensor circuit to communicate fluid pressure at
the downstream point to the sensor circuit.
4. The flow meter assembly according to claim 1 further comprising
a fishing neck on a upper end of the flow meter body for engagement
by a fishing tool to retrieve the flow meter body from the sub.
5. The flow meter assembly according to claim 1 further comprising
a seal that seals an exterior portion of the flow meter body to
the sub.
6. The flow meter assembly according to claim 1 further comprising:
an upstream body port extending from the passage through a sidewall
of the flow meter body adjacent to the upstream point; a downstream
body port extending from the passage through the sidewall of the
flow meter body adjacent to the downstream point; and a plurality
of seals on the exterior of the flow meter body that seal the body
to the sub, the seals being axially spaced apart to define an upstream
chamber in fluid communication with the upstream sub port and a
downstream chamber in fluid communication with the downstream fluid
port.
7. The flow meter assembly according to claim 1 wherein the landing
profile comprises a tapered surface.
8. The flow meter assembly according to claim 1 wherein the passage
comprises: a converging section; a throat area joining and downstream
of the converging section; a diverging section joining and downstream
of the throat area; wherein the upstream sub port is in fluid communication
with the throat area; and the downstream sub port is in fluid communication
with the diverging section.
9. In a well having a casing and a string of tubing, the improvement
comprising: a sub in the string of tubing, the sub having a bore
containing a landing profile; a flow meter body having an external
profile that lands on the landing profile and a passage therethrough,
the passage having a throat area of reduced diameter; upstream and
downstream body ports in a side wall of the body that are in fluid
communication with the throat area and a downstream portion of the
passage downstream of the throat area; seals located between the
body and the sub defining an upstream annular chamber and a downstream
annular chamber surrounding the body, the chambers being in communication
with the upstream and downstream body ports, respectively; upstream
and downstream sub ports in a side wall of the sub that are in fluid
communication with the upstream and downstream chambers, respectively;
and a sensor circuit in operative engagement with the sub ports
for determining a flow rate based on a pressure difference sensed
between the throat area and the downstream portion of the passage
in the body.
10. The well according to claim 9 further comprising: an upstream
tube extending from the upstream sub port to the sensor circuit
to communicate fluid pressure at the upstream chamber to the sensor
circuit, and a downstream tube extending from the downstream sub
port to the sensor circuit to communicate fluid pressure at the
downstream chamber to the sensor circuit.
11. The well according to claim 9 wherein the sensor circuit is
located at an upper end of the well, and wherein the well further
comprises: an upstream tube extending alongside the tubing from
the upstream sub port to the sensor circuit to communicate fluid
pressure at the upstream chamber to the sensor circuit; a downstream
tube extending alongside the tubing from the downstream sub port
to the sensor circuit to communicate fluid pressure at the downstream
chamber to the sensor circuit.
12. The well according to claim 9 further comprising a fishing
neck on a upper end of the flow meter body for engagement by a fishing
tool to retrieve the flow meter body from the sub.
13. The well according to claim 9 wherein the landing profile
comprises a tapered surface.
14. The well according to claim 9 wherein the passage comprises:
a converging section upstream from and joining the throat area;
a diverging section joining and downstream of the throat area; wherein
the downstream sub port is in fluid communication with the diverging
section.
15. The well according to claim 9 further comprising: an electrically
driven submersible pump suspended below the sub, the pump discharging
into the sub.
16. A method of measuring flow rate within a well, comprising:
(a) connecting a tubular sub into a string of well tubing, the sub
having a bore with upstream and downstream sub ports extending through
its side wall; (b) placing a flow meter body in the sub, the flow
meter body having a passage therethrough; (c) lowering the tubing
into the well; (d) flowing well fluid upward through the sub, the
passage in the body and the tubing, the body being positioned in
the sub such that the upstream and downstream sub ports are in fluid
communication with the well fluid flowing through the passage at
upstream and downstream points, respectively; and (e) sensing a
difference between the fluid pressures at the sub ports and determining
a flow rate of the fluid flowing through the passage based on the
pressure difference sensed.
17. The method according to claim 16 further comprising lowering
a wireline through the tubing, engaging the body and retrieving
the body to the top of the well for repair or replacement.
18. The method according to claim 16 further comprising connecting
tubes from each of the sub ports to a sensor circuit located exterior
of the sub; and step (e) comprises fluid communicating the pressures
at the sub ports to the sensor circuit.
19. The method according to claim 16 further comprising connecting
a tube to each of the sub ports and extending the tubes alongside
the tubing to a sensor circuit located at the top of the well; and
step (e) comprises fluid communicating the pressures at the sub
ports to the sensor circuit.
20. The method according to claim 16 further comprising connecting
an electrically driven submersible pump to the tubing below the
sub; and step (d) comprises rotating the pump to pump fluid through
the flow meter body.
Description FIELD OF THE INVENTION
[0001] This invention relates in general to oil well production,
and in particular to a downhole flow meter for monitoring the flow
of production fluid flowing up the tubing.
BACKGROUND OF THE INVENTION
[0002] Many oil wells employ electrically driven submersible pumps
to pump the well fluid to the surface. In a typical well, the pump
and motor are suspended on a string of production tubing, and the
pump discharges the well fluid into the tubing. The pump may be
a centrifugal pump ("ESP") having a large number of impeller
and diffuser stages. A power cable extends alongside the tubing
to the motor for supplying three-phase power. Progressing cavity
pumps driven by downhole electrical motors are also used in some
wells.
[0003] It is common for an ESP unit to have pressure and temperature
sensors that transmit to the surface downhole pressure and temperature
while the ESP is operating. Usually the pressure and temperature
signals are superimposed on the motor power cable, and a surface
electronic unit will detect the signals and provide readings.
[0004] Another useful parameter for an operator of an ESP driven
well or a naturally flowing well is the flow rate of the well fluid.
A variety of different flow meters exist that can be used at the
surface for determining the flow rate at the surface. Downhole flow
meters for wells have been employed with well surveys or production
logging operations, particularly for natural pressure driven wells.
In production logging, typically a downhole flow meter is lowered
into the tubing on a cable. In one type, power is supplied to the
flow meter through a conductor in the cable, and signals are transmitted
to the surface while the well is allowed to flow. The downhole unit
could be battery powered. Typically, a well survey using a flow
meter is only performed periodically and for a short period of time.
Normally, operators do not install downhole flow meters for continuous
long term operation in ESP driven wells
[0005] The flow rate at the surface is easily measured, but may
differ from a flow rate measured downhole Downhole, free gas produced
by the well is more likely entrained in the well fluid or is in
solution, thus will not affect a downhole flow meter reading. At
the surface, much of the gas typically comes out of solution because
of the lower pressure. Gassy fluid flow rates can not be accurately
or easily monitored once the gas has come out of solution.
SUMMARY OF THE INVENTION
[0006] In this invention, a flow meter is installed within a sub
in the production tubing. The sub has a bore with a landing profile
for receiving the flow meter body. The flow meter body has a passage
therethrough. The sub has upstream and downstream ports in its sidewall
that are in fluid communication with the flow meter passage at upstream
and downstream points. A sensor circuit is in fluid communication
with the sub ports for determining a flow rate of fluid flowing
through the flow meter passage based on a pressure difference between
the upstream and downstream points.
[0007] In the embodiment shown, the sensor circuit is located at
the surface of the well. A small diameter tube extends from each
sub port alongside the production tubing to the surface for communicating
the pressure differential. Alternately, the sensor circuit could
be located downhole and transmit its signals on the power cable.
[0008] Preferably, the passage in the flow meter body has a throat
area and a diverging area that joins and is downstream from the
throat area. A port extends through the side wall of the flow meter
body at the throat area. Another port extends through the side wall
of the flow meter body in the diverging area. Seals are located
on the exterior of the body for sealing to the bore of the sub.
The seals are positioned to define an annular upstream chamber surrounding
the throat port and a downstream chamber surrounding the port in
the diverging area.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] FIG. 1 is a schematic view illustrating an electrical submersible
pump assembly located within a well and having a downhole retrievable
flow meter in accordance with this invention.
[0010] FIG. 2 is an enlarged sectional view of the flow meter of
FIG. 1.
DETAILED DESCRIPTION OF THE INVENTION
[0011] Referring to FIG. 1 the well has a casing 11 containing
a set of perforations 13 to allow fluid flow from an earth formation
into casing 11. An electrical submersible pump assembly ("ESP")
15 is suspended in casing 11.
[0012] ESP assembly 15 includes a pump 17 which is typically a
centrifugal pump having a large number of stages of impellers and
diffusers and an intake 18. Alternately, pump 17 could be a progressive
cavity pump utilizing a helical rotor that rotates within a helical
elastomeric stator. Pump 17 is connected on its lower end to a seal
section 19. An electrical motor 21 mounts to the lower end of seal
section 19. Motor 21 rotates a shaft that is coupled to shafts (not
shown) in seal section 19 and pump 17 for driving pump 17. Motor
21 is filled with a dielectric lubricant, and seal section 19 equalizes
the lubricant pressure with the hydrostatic pressure in well casing
11.
[0013] A string of tubing 23 extends from ESP assembly 15 to the
surface. Tubing 23 is typically production tubing made up of sections
of tubing about thirty feet in length that are secured together
by threads. A flow meter sub 24 is mounted in the string of tubing
23 preferably at the upper end of pump 17. Flow meter sub 24 contains
a retrievable flow meter 25 for determining the flow rate of the
well fluid being discharged by pump 17. Flow meter 25 is preferably
a venturi-type. Upstream and downstream capillary tubes 27 29 extend
alongside tubing 23 and monitor a pressure drop through flow meter
25 to calculate the flow rate. Tubes 27 29 communicate with a sensor
circuit 30 that is shown at the surface in this embodiment. Sensor
circuit 30 provides a display of the flow rate based on the pressure
difference sensed.
[0014] Referring to FIG. 2 flow meter 25 has a tubular body 31
that lands within flow meter sub 24. Body 31 has a flow passage
extending through it that has a first section 33 that is conical,
with a minimum diameter or throat 34 at its upper or downstream
end. Throat 34 joins a second section 35. Second section 35 is conical,
but diverges from throat 34 in a downstream direction. In this embodiment,
second section 35 has a length much shorter than first section 33.
A third section 37 extends from second section 35 and is cylindrical
in this embodiment. Optionally, the passage could also include a
fourth section 39 that is slightly flared.
[0015] A landing profile 41 comprising an upward facing tapered
shoulder is located in flow meter sub 24. Body 31 has a mating landing
profile 43 that lands on profile 41. The engagement creates a wedging
fit that is sufficient to resist body 31 being dislodged by upward
flowing fluid being discharged from pump 17. A fishing neck 45 at
the upper end of body 31 allows flow meter 25 to be engaged by a
fishing tool and pulled to the surface.
[0016] A throat pressure port 47 extends laterally through the
sidewall of body 31 from throat 34. A downstream pressure port 49
is located above throat pressure port 47 in third portion 37 of
the passage.
[0017] A first seal 51 seals between the outer diameter of body
31 and the exterior of flow meter sub 24 at a point upstream or
below first pressure port 47. A second seal 53 seals between the
outer diameter of body 31 and flow meter sub 24 at a point between
pressure ports 47 49. A third seal 55 seals between body 31 and
the inner diameter of flow meter sub 24 at a point above downstream
pressure port 49 and below seating profile 43.
[0018] Seating profiles 41 43 are located for communicating tube
27 with throat pressure port 47 and the annular chamber created
between first and second seals 51 53. Similarly, second tube 29
communicates with downstream pressure port 49 and the annular chamber
created by seals 53 55. Tubes 27 29 convey the pressure difference
to sensor circuit 30 which is located at the surface in this embodiment.
[0019] During installation, an operator lowers ESP assembly 15
on tubing 23. The operator also lowers pressure sensing tubes 27
29 at the same time. Preferably, flow meter 25 will be installed
within tubing 23 while still at the surface, then lowered along
with tubing 23. Alternately, flow meter 25 could be lowered into
tubing 23 on a wireline and landed in profile 41.
[0020] During operation, the operator supplies electrical power
to pump motor 21 via a power cable (not shown), leading from motor
21 to a power supply at the surface. Pump motor 21 rotates pump
17 causing fluid from perforations 13 to flow up tubing 23. As
the well fluid flows through the passage of flow meter 25 a pressure
drop will occur between throat 34 and third passage section 37.
The pressure drop is communicated to sensor circuit 30 via tubes
27 29. Circuit 30 senses the pressure difference and computes a
flow rate based on the pressure difference and various parameters
provided. Sensor circuit 30 provides a readout and optionally may
include a transmitter that transmits the information in digital
or analog format to a central location.
[0021] As another alternative, pressure sensing tubes 27 29 could
lead to a downhole circuit that converts the pressure difference
to an electrical signal that is superimposed on the power cable
and transmitted to the surface. For example, the downhole circuit
could be located in a housing (not shown) on the lower end of motor
21. The housing might also contain pressure and temperature monitoring
sensors and circuitry. At the surface, the signal could be picked
off the power cable and transmitted to a central location.
[0022] The invention has significant advantages. The downhole flow
meter provides more accurate readings of flow rate than a surface
flow meter, particularly for gassy well fluids. The flow meter operates
continuously, and in the preferred embodiment, has no moving parts.
There is no requirement for a cable to extend down the tubing to
supply power to the flow meter. The flow meter can be retrieved
on wireline for maintenance or replacement without having to pull
the tubing or pump.
[0023] While the invention has been shown in only one of its forms,
it should be apparent to those skilled in the art that it is not
so limited but is susceptible to various changes without departing
from the scope of the invention. For example, although shown with
an ESP unit, the flow meter could be employed in a natural pressure
driven, or flowing well. |