Note: Descriptions are shown in the official language in which they were submitted.
CA 02826593 2013-09-12
HYDRAULIC OIL WELL PUMPING SYSTEM, AND
METHOD FOR PUMPING HYDROCARBON FLUIDS FROM A WELLBORE
BACKGROUND OF THE INVENTION
This section is intended to introduce various aspects of the art, which may be
associated
with exemplary embodiments of the present disclosure. This discussion is
believed to assist in
providing a framework to facilitate a better understanding of particular
aspects of the present
disclosure. Accordingly, it should be understood that this section should be
read in this light,
and not necessarily as admissions of prior art.
Field of the Invention
The present disclosure relates to the field of hydrocarbon recovery
operations. More
specifically, the present invention relates to hydraulically actuated pumping
units for the
production of hydrocarbon fluids and for dewatering gas wells.
Technology in the Field of the Invention
In the drilling of oil and gas wells, a wellbore is formed using a drill bit
that is urged
downwardly at a lower end of a drill string. After drilling to a predetermined
depth, the drill
string and bit are removed and the wellbore is lined with a string of casing.
An annular area is
thus formed between the string of casing and the surrounding formations.
To prepare the wellbore for the production of hydrocarbon fluids, a string of
tubing is run
into the casing. A packer is set at a lower end of the tubing to seal an
annular area formed
between the tubing and the surrounding strings of casing. The tubing then
becomes a string of
production pipe through which hydrocarbon fluids may be lifted.
In order to carry the hydrocarbon fluids to the surface, a pump may be placed
at a lower
end of the production tubing. This is known as "artificial lift." In some
cases, the pump may be
an electrical submersible pump, or ESP. ESP's utilize a hermetically sealed
motor that drives a
multi-stage pump. More conventionally, oil wells undergoing artificial lift
use a downhole
CA 02826593 2015-01-27
reciprocating plunger-type of pump. The reciprocating downhole pump is
relatively long and
thin to avoid restricting oil flow up the well. The pump has one or more
valves that capture fluid
on a down stroke, and then lift the fluid on the upstroke. This is known as
"positive
displacement." In some designs such as that disclosed in U.S. Patent No.
7,445,435, the pump
may be able to both capture fluid and lift fluid on each of the down stroke
and the upstroke.
Conventional positive displacement pumps have a barrel that is reciprocated at
the end of
a "rod string." The rod string comprises a series of long, thin joints of pipe
that are threadedly
connected through couplings. The rod string is pivotally attached to a pumping
unit at the
surface. The rod string moves up and down within the production tubing to
incrementally lift
production fluids from subsurface intervals to the surface.
Most pumping units on land are so-called rocking beam drive units. Rocking
beam units
typically employ electric motors or internal combustion engines having a
rotating drive shaft.
The shaft turns a crank arm, or possibly a pair of crank arms. The crank arms,
in turn, have
heavy, counter-weighted flywheels. The flywheels rotate along with the crank
arms. Rocking
beam units also have a walking beam. The walking beam pivots over a fulcrum.
One end of the
walking beam is mechanically connected to the crank arms. As the crank arms
and flywheels
rotate, they cause the walking beam to reciprocate up and down over the
fulcrum.
The opposite end of the walking beam is a so-called horse head, The horse head
is
positioned over the well head at the surface. As the walking beam is
reciprocated, the horse head
cycles up and down over the wellbore. This, in turn, translates the rod and
attached pump up and
down within the wellbore. A drawing and further description of a walking beam
unit are
provided in U.S. Pat. No. 7,500,390.
Another type of pumping unit is a hydraulic actuator system. These systems
employ a
cylinder residing over a wellbore. The cylinder is axially aligned with the
wellbore and holds a
reciprocating piston. The cylinder cyclically receives fluid pressure through
an oil line. As fluid
is injected through the oil line and into the cylinder, the piston is caused
to move linearly within
the cylinder. This, in turn raises the connected rod string, causing the pump
to undergo an
2
CA 02826593 2015-01-27
upstroke. When fluid pressure is released from the cylinder, the rod string is
lowered due to
gravitational forces, causing the downhole pump to undergo a downstroke.
Surface hydraulic actuator systems have been used successfully for many years.
Such
systems offer a beneficially long stroke length for the downhole plunger pump.
Such systems
are also ideal for urban environments where a small footprint is demanded.
Further, such
systems offer the ability to operate more than one well from a single surface
installation.
During operation of any rod pump system for a producing well, it is desirable
to be able
to monitor the position of the rod string and specifically, the piston within
the cylinder. In this
respect, it is helpful to know when the piston is about to reach a top or
bottom of a stroke.
Knowing this position allows the operator to slow or stop the motion of the
piston and rod-string
pro-actively, eliminating the "slamming" of the piston against a plate within
the cylinder.
Further, it is desirable to be able to measure the load on the sucker rods
making up the
rod string. The load can be recorded and printed out on a so-called surface
dynamometer card.
The "dyno card" offers a plot of the measured rod loads at various positions
throughout a
complete stroke. The load is usually displayed in pounds of force, while the
position is usually
displayed in inches. The pump dynamometer card represents the load the pump
applies to the
bottom of the rod string. Dynamometer cards are displayed by predictive and
diagnostic
software for the purposes of design and diagnosing sucker rod pumping systems.
Historically, hydraulic pressure has been used to measure rod loads for
dynamometer
cards. Then, separate physical measurements have been made on the piston and
polished rod for
determining position. This requires the use of sensors at the wellhead to
directly measure piston
position. Such sensors may be either discrete position switches or more
advanced linear position
sensors. SPE Paper No. 113186 entitled "Optimizing Downhole Fluid Production
of Sucker-Rod
Pumps With Variable Speed Motor" (2009) describes some of the mathematics
behind the
dynagraph calculations.
A need exists to be able to use the hydraulic fluid data to determine not only
the load on the rod
string, but also the position of the piston using only the hydraulic fluid as
the
3
CA 02826593 2013-09-12
measurement for both position and load without the need for data gathered from
devices or
sensors at or near the wellhead. Removal of electronic or other methods of
directly attached
instrumentation from areas around the wellhead reduces risk of sparking and
also eliminates the
cost of placing and maintaining such instrumentation. Further, it is desirable
to be able to
determine the position of the piston within the cylinder on both the upstroke
and the down stroke
at a safe distance without using position sensors at the wellhead.
BRIEF SUMMARY OF THE INVENTION
An oil well pumping system is first provided herein. The pumping system uses a
set of
valves and an electrical control system to cyclically direct hydraulic fluid
into and release
hydraulic fluid from a cylinder. The pressure created by the hydraulic fluid
causes a piston and
connected rod string and downhole pump to reciprocate. This, in turn, causes
reservoir fluids to
be produced from a wellbore to the surface through positive displacement.
In one aspect, the oil well pumping system first includes an elongated
hydraulic cylinder.
The cylinder is positioned over the wellbore. The cylinder may either be over
an associated
wellhead, or inside the wellbore and below the wellhead.
The hydraulic cylinder may be placed above the wellhead, where sensors are
easily
attached, but the cylinder may also be placed inside the wellbore. This aspect
places the entirety
of the hydraulic cylinder length within the wellbore, below the wellhead.
Because the length of
the cylinder is inaccessible, it is impossible to place sensors along the
cylinder in this
configuration. The need exists for an alternate method of determining position
without the use of
direct instrumentation of the hydraulic cylinder when positioned entirely in
the wellbore and
submerged in crude oil.
The oil well pumping system also includes a piston and a polished rod. The
polished rod
defines an elongated rod that is movable with the piston between upper and
lower rod positions
within the cylinder. The piston, in turn, provides an annular seal between the
polished rod and
the surrounding cylinder. Hydraulic pressure cyclically acts against the
piston to create an
upstroke and a down stroke of the polished rod.
4
CA 02826593 2013-09-12
The oil well pumping system further has a rod string. The rod string is
mechanically
connected to the lower end of the polished rod. This means that when the
piston reciprocates,
the rod string reciprocates with it. The rod string extends downwardly from
the polished rod and
into the wellbore. The rod string has a downhole pump connected to it for
lifting fluids to the
surface in response to reciprocation of the rod string.
The oil well pumping system also includes a hydraulic pump. The pump is
powered by a
prime mover. The prime mover may be an electric motor, an internal combustion
engine, or
other driver.
The oil well pumping system further includes a directional control valve. The
directional
control valve shifts between upstroke and downstroke flow positions. When the
valve is in its
upstroke position, it directs hydraulic fluid such as oil from the pump and
into the annular area
formed below the piston between the polished rod and the surrounding cylinder.
When the
directional control valve is in its downstroke (or neutral) position, it
receives reverse flow from
the annular area and allows the gravity-induced fall of the piston and
connected rod string.
The oil well pumping system also has an oil line. The oil line connects the
pump and the
hydraulic cylinder. The control valve is positioned in the oil line so that it
can control flow
between the pump and the cylinder in response to electrical signals. The
signals are sent by an
electrical control system that shifts the directional control valve between
its upstroke and
downstroke flow positions.
A fluid reservoir is also provided. The fluid reservoir contains hydraulic
fluid to be
supplied to the pump.
The oil well pumping system next comprises a reservoir line. The reservoir
line transmits
hydraulic fluid from the cylinder back to the reservoir. Optionally, a filter
is provided along the
reservoir line to filter the return oil. Optionally, a pressure bypass line is
also provided to bypass
the filter as part of the reservoir or return line.
5
CA 02826593 2013-09-12
The oil well pumping system also includes a downstroke control valve. The
downstroke
control valve has a restricted orifice that chokes the flow of fluid from the
cylinder back to the
reservoir. The downstroke control valve limits the speed with which the piston
and operatively
connected rod string fall within the cylinder during the down stroke. This
serves to control the
rate of flow of hydraulic fluid returning from the cylinder.
As noted, an electronic control system is also provided for the oil well
pumping system.
The control system controls movement of the piston as it moves between the
upper and lower rod
positions. This is done by cycling the directional control valve between (i)
an "upstroke"
condition wherein the pump is pumping oil through the oil line into the
hydraulic cylinder to
move the piston to its upper rod position, and (ii) a "neutral" condition
wherein the pump is no
longer pumping oil into the hydraulic cylinder, but is allowing oil to flow
back through the oil
line in response to gravitational fall of the piston and connected rod string.
The electronic
control system is programmed to cycle based upon a volumetric capacity of the
hydraulic
cylinder and the volume of oil delivered to the cylinder, and without
reference to position sensors
along the wellhead.
In one aspect, the electronic control system controls movement of the piston
and polished
rod based on time. This may be based on (i) time for the "upstroke" pump
condition, (ii) time
for the "neutral" pump condition, or (iii) both. In this embodiment, the
control system is simply
a clock for turning the pump on and off at calculated or estimated time
intervals.
In another aspect, the electronic control system controls movement of the
piston based on
volume. The volume may be (i) the volume of hydraulic fluid sent to the
cylinder during the
"upstroke" valve condition, (ii) the volume of fluid returned from the
cylinder during the
"neutral" valve condition, or (iii) both. Note that flow rate and volume are
intimately associated.
Flow rate is the volume of fluid which passes through a given point in a
system per unit time.
Flow rate can be calculated as the product of a given cross sectional area for
flow and an average
flow velocity. A series of flow rate measurements over a cross sectional area
taken over a period
of time may be used to determine fluid volume passing through the cross
section over the time
period. Accordingly, direct measurements of total volume and a series of
instantaneous
measurements of flow rate over time provide equivalent volume information.
6
CA 02826593 2013-09-12
A method of pumping oil from a wellbore is also provided herein. The wellbore
has a
bore extending into an earth surface. The method employs a unique pumping
system that uses a
set of valves and an electrical control system. The valves cyclically direct
hydraulic fluid into a
cylinder. The pressure created by the hydraulic fluid causes the piston and a
connected rod
string and downhole pump to reciprocate. This, in turn, causes reservoir
fluids to be produced
from a wellbore to the surface through positive displacement.
In one aspect, the method first comprises providing an elongated hydraulic
cylinder. The
cylinder is positioned over the wellbore. The cylinder may either be over an
associated
wellhead, or inside the wellbore and below the wellhead.
The method also includes providing a piston and a polished rod. The piston and
connected polished rod are movable between upper and lower rod positions
within the cylinder.
The piston creates an annular seal above the polished rod and the surrounding
cylinder.
Hydraulic pressure cyclically acts against the piston to create an upstroke
and a downstroke.
The method further includes mechanically connecting the piston and polished
rod to a rod
string. This means that when the piston reciprocates, the rod string
reciprocates with it. The rod
string extends downwardly from the piston and into the wellbore. The rod
string has a downhole
pump connected to it for lifting fluids to the surface in response to
reciprocation of the rod string.
The method also includes providing a hydraulic pump. In one aspect, the pump
is a
positive displacement pump. The pump is powered by a prime mover. The prime
mover may be
an electric motor, an internal combustion engine, or other driver.
The method also has the step of connecting the pump and the hydraulic cylinder
with an
oil line. The oil line transmits hydraulic fluid from the pump to the
cylinder.
Still further, the method includes providing a directional control valve that
moves
between open upstroke and downstroke flow positions. When the valve is in its
upstroke flow
position, it directs hydraulic fluid such as oil from the pump, through the
oil line and into the
annular area formed between the polished rod and the surrounding hydraulic
cylinder below the
7
CA 02826593 2013-09-12
piston. When the valve is in its downstroke flow position, it allows hydraulic
fluid to bleed from
the cylinder.
The method also has the step of providing a fluid reservoir. The reservoir
contains
hydraulic fluid to be supplied to the pump.
The method next includes providing a reservoir line. The reservoir line
transmits
hydraulic fluid from the cylinder back to the reservoir. Optionally, a filter
is provided along the
reservoir line. It is understood that the term "reservoir line" may mean more
than one line, such
as a pressure bypass line.
The method also has the step of providing a down stroke control valve. The
down stroke
control valve chokes the flow of fluid from the cylinder back to the
reservoir. This, in turn,
limits the rate of flow of hydraulic fluid during the down stroke of the
piston.
The method also offers the step of controlling movement of the piston as it
moves
between upper and lower rod positions. This is done by using an electronic
control system. The
control system controls the valves and the pump to cycle the pump between (i)
an "upstroke"
condition wherein the pump is pumping oil through the directional control
valve, through the oil
line and into the hydraulic cylinder to move the piston to its upper rod
position, and (ii) a
"neutral" condition wherein the pump is no longer pumping oil into the
hydraulic cylinder, but is
allowing oil to flow back through the oil line and the down stroke control
valve in response to
gravitational fall of the piston and connected polished rod. The electronic
control system is
programmed to cycle based upon a volumetric calculation of the capacity of the
hydraulic
cylinder and the oil delivered to, or received back from, the cylinder without
reference to
position sensors located in the wellhead environment.
Preferably, the electronic control system controls movement of the piston
based on
volume. The volume may be (i) the volume of hydraulic fluid sent to the
cylinder during the
"upstroke" pump condition, (ii) the volume of fluid returned from the cylinder
during the
"neutral" pump condition, or (iii) both. In another aspect, the electronic
control system controls
movement of the rod based on (i) time for the "upstroke" valve condition, (ii)
time for the
8
CA 02826593 2013-09-12
"neutral" valve condition, or (iii) both. Time on the downstroke or "neutral"
pump condition
may be limited, as the next upstroke may take place at a fixed interval.
Optionally, the control system may send a signal to cause the pump to vary its
output, to
cause a valve to adjust its proportional flow, or to change an operating speed
of the prime mover
based upon either (i) a relative volume of fluid that has moved into the
hydraulic cylinder, or (ii)
an absolute volume of fluid that has moved into the hydraulic cylinder, during
the "on" pump
condition.
Also, the method includes reciprocating the piston and mechanically connected
rod string
in order to pump oil from the wellbore.
BRIEF DESCRIPTION OF THE DRAWINGS
So that the manner in which the present inventions can be better understood,
certain
illustrations, charts and/or flow charts are appended hereto. It is to be
noted, however, that the
drawings illustrate only selected embodiments of the inventions and are
therefore not to be
considered limiting of scope, for the inventions may admit to other equally
effective
embodiments and applications.
Figure lA is a side view of a hydraulic oil well pumping system of the present
invention,
in one embodiment. The hydraulic oil well pumping system is used for producing
reservoir
fluids from a subsurface formation to the surface. Portions of the system are
shown
schematically.
Figure 1B is a perspective engineering view of a portion of the hydraulic oil
well
pumping system of Figure 1A. Here, the cylinder is seen over the wellhead. The
reservoir and
the valving are also shown in an integral tank.
Figure 2A is a cross-sectional view of the hydraulic cylinder of Figure IA in
an enlarged
view. The cylinder is again positioned above a wellhead and has a
hydraulically actuated piston
therein.
9
CA 02826593 2013-09-12
,
,
Figure 2B is a photographic view of the hydraulic cylinder of Figure 1A, in
one
embodiment.
Figure 3 is an engineering model showing a side, cut-away view of a cylinder
having a
hydraulically actuated piston therein. Here, the cylinder is disposed below
the wellhead, inside
the wellbore.
Figure 4A is a perspective view of a skid having certain components of the
hydraulic oil
well pumping system of Figure 1. An internal combustion engine is shown as the
prime mover
for powering a hydraulic pump.
Figure 4B is a perspective view of a skid having components of the hydraulic
oil well
pumping system of Figure 1, in an alternate embodiment. Here, an electric
motor is shown as the
prime mover for powering a hydraulic pump.
In each of Figures 4A and 4B, a novel two-chambered tank is provided. Valves
and
hoses are housed in an upper chamber, while working oil is housed in a lower
chamber.
Figure 5 is an exploded perspective view of the valve stack from Figures 4A
and 4B.
This valve stack includes a directional control valve and a downstroke control
valve.
Figure 6 is an engineering diagram showing illustrative hydraulic circuitry of
the
hydraulic oil well pumping system of Figure 1, in one embodiment. Fluid lines
and certain
components for the system are shown schematically.
Figure 7 is a flow chart showing steps that may be performed for a method of
pumping
oil from an oil well, in one embodiment.
Figure 8A and Figure 8B are another flow chart. Here, steps are shown for a
method of
determining the position of a hydraulically actuated piston within a cylinder.
CA 02826593 2013-09-12
DETAILED DESCRIPTION OF CERTAIN EMBODIMENTS
Definitions
For purposes of the present application, it will be understood that the term
"hydrocarbon"
refers to an organic compound that includes primarily, if not exclusively, the
elements hydrogen
and carbon. Hydrocarbons may also include other elements, such as, but not
limited to,
halogens, metallic elements, nitrogen, oxygen, and/or sulfur. Hydrocarbons
generally fall into
two classes: aliphatic, or straight chain hydrocarbons, and cyclic, or closed
ring hydrocarbons,
including cyclic terpenes. Examples of hydrocarbon-containing materials
include any form of
natural gas, oil, coal, and bitumen that can be used as a fuel or upgraded
into a fuel.
As used herein, the term "hydrocarbon fluids" refers to a hydrocarbon or
mixtures of
hydrocarbons that are gases or liquids. For example, hydrocarbon fluids may
include a
hydrocarbon or mixtures of hydrocarbons that are gases or liquids at formation
conditions, at
processing conditions or at ambient conditions (15 C and 1 atm pressure).
Hydrocarbon fluids
may include, for example, oil, natural gas, coalbed methane, shale oil,
pyrolysis oil, pyrolysis
gas, a pyrolysis product of coal, and other hydrocarbons that are in a gaseous
or liquid state.
As used herein, the terms "produced fluids," "reservoir fluids" and
"production fluids"
refer to liquids and/or gases removed from a subsurface formation, including,
for example, an
organic-rich rock formation. Produced fluids may include both hydrocarbon
fluids and non-
hydrocarbon fluids. Production fluids may include, but are not limited to,
oil, natural gas,
pyrolyzed shale oil, synthesis gas, a pyrolysis product of coal, carbon
dioxide, hydrogen sulfide
and water (including steam).
As used herein, the term "fluid" refers to gases, liquids, and combinations of
gases and
liquids, as well as to combinations of gases and solids, combinations of
liquids and solids, and
combinations of gases, liquids, and solids.
As used herein, the term "wellbore fluids" means water, mud, hydrocarbon
fluids,
formation fluids, or any other fluids that may be within a string of drill
pipe during a drilling
operation.
11
CA 02826593 2013-09-12
,
As used herein, the term "gas" refers to a fluid that is in its vapor phase at
1 atm and 15
C.
As used herein, the term "subsurface" refers to geologic strata occurring
below the earth's
surface.
As used herein, the term "formation" refers to any definable subsurface region
regardless
of size. The formation may contain one or more hydrocarbon-containing layers,
one or more
non-hydrocarbon containing layers, an overburden, and/or an underburden of any
geologic
formation. A formation can refer to a single set of related geologic strata of
a specific rock type,
or to a set of geologic strata of different rock types that contribute to or
are encountered in, for
example, without limitation, (i) the creation, generation and/or entrapment of
hydrocarbons or
minerals, and (ii) the execution of processes used to extract hydrocarbons or
minerals from the
subsurface.
As used herein, the term "wellbore" refers to a hole in the subsurface made by
drilling or
insertion of a conduit into the subsurface. A wellbore may have a
substantially circular cross
section, or other cross-sectional shapes. The term "well," when referring to
an opening in the
formation, may be used interchangeably with the term "wellbore." The term
"bore" refers to the
diametric opening formed in the subsurface by the drilling process. (Note that
this is in contrast
to the term "cylinder bore" which may be used herein, and which refers to a
hydraulic cylinder
over a wellbore.)
Description of Selected Specific Embodiments
Figure 1A is a side view of a hydraulic oil well pumping system 100 of the
present
invention, in one embodiment. The hydraulic oil well pumping system 100 is
used for producing
reservoir fluids from a subsurface formation (not shown) to the surface 101.
Portions of the
system 100 are shown schematically.
In Figure 1A, it is first seen that the system 100 includes an elongated
cylinder 150. In
this arrangement, the cylinder 150 resides over a wellhead 105. The wellhead
105 serves to
12
,
CA 02826593 2013-09-12
support a string of production tubing 110 that extends from the surface 101
and down into a
wellbore 115.
Above the wellhead 105 is a set of control valves. The valves are part of a
"Christmas
tree," shown at 108. The Christmas tree 108 generally supports the cylinder
150. The valves of
the Christmas tree 108 direct the flow of production fluids and also permit an
operator to inject
treatment chemicals or otherwise access the production tubing 110.
Residing within the wellbore 115 is a rod string 120. The rod string 120 is
comprised of
a plurality of long, slender joints of steel, known as sucker rods. Each
sucker rod is typically 25
or 30 feet in length. The rod string 120 supports a pump (not shown) downhole.
The pump, in
turn, moves production fluids from the subsurface formation, up the production
tubing 110, and
to the wellhead 105 through positive displacement. The pump is generally
positioned next to a
perforated zone of the wellbore 115. The production fluids then flow out of a
valve in the
Christmas tree 108 where they may undergo some initial fluid separation and
are then directed
into a flow line or a gathering tank (not shown).
Each sucker rod includes a coupling. In Figure 1A, a coupling 122 is shown
above the
rod string 120. In this view, the coupling 122 connects the rod string 120 to
a polished rod 160.
The polished rod 160, in turn, extends up through the wellhead 105, through
the Christmas tree
108, and into the cylinder 150. The polished rod 160 defines an elongated
cylindrical body.
At an upper end of the polished rod 160 is a piston 165. The piston 165 seals
an annular
area 155 formed between the polished rod 160 and the surrounding cylinder 150.
The piston 165
prevents the hydraulic oil from migrating into a chamber above the piston 165.
The annular area
155 is filled with a working fluid, typically a clean hydraulic oil.
The piston 165 and connected polished rod 160 reciprocate within the cylinder
150
between two heads. A first or upper head 142 is at a distal end of the
cylinder 150, while a
second or lower head 144 is at a proximal end of the cylinder 150. The second
head 144 has an
internal bore to slidably receive the polished rod 160.
13
CA 02826593 2013-09-12
The hydraulic oil well pumping system 100 also includes a pair of fluid lines
170, 175. A
first fluid line 170 is an oil line. The oil line 170 is in fluid
communication with the annular area
155 of the cylinder 150 just above the second (or lower) head 144. The oil
line 170 injects and
receives oil from the annular area 155 in order to move the piston 160 up and
down within the
cylinder 150. In this way, an up stroke and a downstroke are created for the
piston 165 and
mechanically connected rod string 120 and downhole pump.
The second fluid line 175 is essentially a vent line. The vent line 175
receives air and
any leaked oil from the piston 165 during the upstroke. The vent line 175 is
supported by one or
more brackets 156 disposed along the outer wall of the cylinder 150.
Figure 1B is a perspective view of a portion of the hydraulic oil well pumping
system
100 of Figure 1A. Here, the cylinder 150 is seen over the wellhead 105. The
two fluid lines
170, 175 are seen along with the supporting brackets 156.
Returning to Figure 1A, additional components of the hydraulic oil well
pumping system
100 are shown schematically. These include a prime mover 182, a hydraulic pump
184, a valve
stack 190, and a fluid reservoir 195. These components are optionally
supported together on a
skid 180.
The prime mover 182 provides power to the pump 184. The prime mover 182 may be
a
gasoline engine, a diesel engine, or other internal combustion engine. Such a
prime mover is
shown at 482A in Figure 4A and is discussed more fully below. Alternatively,
the prime mover
182 may be an electric motor as shown at 482B in Figure 4B and discussed
below. When the
prime mover 182 is started, it activates the hydraulic pump 184. Beneficially,
changing the
operating speed of the prime mover 182 will vary the output of the pump 184.
Alternatively,
different types of controlled valving can be used to vary the hydraulic output
with a fixed RPM
in the pump.
The pump 184 serves to pump fluid into the oil line 170. The pump 184 is
preferably a
vane style pump. However, other types of pumps such as a piston-type pump may
be employed.
The pump 184 may be a fixed displacement pump or a variable displacement pump.
14
CA 02826593 2013-09-12
Oil is directed from the pump 184 and into the oil line 170 by means of a set
of valves
190. The valves 190 preferably include a discrete four-way valve. Such a valve
is shown in
detail at 500 in Figure 5 as part of a valve stack. Alternatively, the valves
190 may include a
proportional valve or even a variable speed prime mover as the valve.
In one preferred embodiment, the valves 190 are discrete valves housed
together with the
reservoir 195 in a dual-chambered tank. Such a tank is shown generally at 190'
in Figure 1B.
The tank is shown in greater detail in Figures 4A and 4B.
Moving now to Figures 2A and 2B, Figure 2A is a cross-sectional view of the
hydraulic
cylinder 150 of Figure 1A, shown in an enlarged view. Figure 2B is a
perspective
(photographic) view of the hydraulic cylinder 150 of Figure 2A, in one
embodiment.
Referring primarily to Figure 2A, the hydraulic cylinder 150 is again seen
residing over a
wellhead 205 and a Christmas tree 208. The wellhead 205 and the Christmas tree
208 are shown
somewhat schematically. The cylinder 150 is secured to the Christmas tree 208
and connected
wellhead 205 by means of a coupling 290. The wellhead 205, in turn, is secured
over a wellbore
215.
The wellbore 215 is formed by a string of casing 210. Within the casing 210 is
the string
of production tubing 110. The production tubing 110, in turn, holds the rod
string 120 and
receives production fluids.
At a top of the cylinder 150 is a threaded connector 280. The threaded
connector 280 is
optionally used to pick up the cylinder 150 during installation over the
wellhead 205. The
connector 280 is part of the upper head 142.
In some embodiments, a frame or a tripod (not shown) are used to stabilize the
cylinder
150 over the wellhead 205. This optional feature is most commonly used in
windy locations.
In Figure 2A, the oil line 170 is seen entering the annular area 155 above the
lower head
144. Further, the vent line 175 is seen in fluid communication with the
annular area 155 below
CA 02826593 2013-09-12
the upper head 142. In addition, the piston 160 is seen residing within the
cylinder 150, forming
the annular area 155.
The polished rod 160 has a distal end 162 and a proximal end 164. The distal
end 162
connects to the piston 165. In Figure 2A, one or more steel or composite rings
266 can be seen
along the piston 165, providing the needed seal to keep hydraulic oil within
the annular area 155.
In addition, a seal 244 comprised of "Vee" packing or other material is
preferably provided along
the lower head 144 to provide fluid sealing along the polished rod 160.
The cylinder 150 shown in Figures 1A and 1B and Figures 2A and 2B reside above
the
wellhead 105, 205. However, it is possible to place the cylinder (and housed
piston) inside the
wellbore and below the wellhead. This may be of benefit on offshore production
platforms
where vertical height is a concern.
Figure 3 is an engineering model showing a side, cut-away view of a cylinder
350 having
a hydraulically actuated piston 360 therein. Here, the cylinder 350 is
disposed below a
Christmas tree 308 and a wellhead 305. Of interest, a vent line (not shown)
comes directly out of
the upper head (as in the above ground cylinder). The oil line also goes into
the upper head, but
is directed down through a double walled cylinder to the lower head.
Moving now to Figures 4A and 4B, each of Figures 4A and 4B presents certain
components of the hydraulic oil well pumping system 100 of Figure 1A. These
components are
supported on the skid 180. First, each figure shows a unique dual-chamber tank
490. Working
oil is housed in a lower chamber 495, while valves and hoses are housed in an
upper chamber
492. A lid 494 is provided over the upper chamber 492.
The valves are not clearly seen in Figures 4A and 4B; however, Figure 5 shows
an
exploded view of the valves, or valve stack 500. The valve stack 500 generally
includes a valve
body 510, a downstroke control valve 520, and a sub-plate manifold 530. These
components
work together to form a four-way valve that allows hydraulic oil to be pumped
from the pump
184 to the annular area 155 through oil line 170. The four-way arrangement
also allows the
operation and control of two wells stroking alternately.
16
CA 02826593 2013-09-12
As another feature, the valve stack 500 permits oil to return to the fluid
reservoir chamber
495 via a restricted orifice. In this arrangement, the restricted orifice is
referred to as a
downstroke control valve, shown at 520. Oil returns to the fluid reservoir
chamber 495 through
the downstroke control valve 520 in response to gravitational forces applied
to the piston 160 by
means of the rod string 120 and connected downhole pump.
In Figure 5, various components of the valve stack 500 are shown in
perspective view.
First, the valve body 510 is seen. The valve body 510 serves as the
directional control valve,
which controls fluid flow during the upstroke. A pair of four-way valve end
caps 512 are placed
at either end of the valve body 510. The end caps 512 are secured in place via
a plurality of head
cap screws 513. 0-rings 517 are seen placed between the end caps 512 and the
valve body 510
to prevent oil leakage. These end caps 512 also allow for the insertion of a
four-way spool 590,
discussed below.
The valve body 510 includes additional components. These include a four way
valve
spring 514, studs 515, and insert nuts 516. The studs 515 and insert nuts 516
are used to connect
the valve body 510 to the downstroke control valve 520 and the sub-plate 530.
The valve spring
514 serves the purpose of returning the four-way spool 590 to a neutral
position in the absence of
an explicit control signal.
The downstroke control valve 520 represents an essentially rectangular block
that is
located between the sub-plate manifold 530 and the valve body 510. The
downstroke control
valve 520 has various passages allowing unrestricted flow in one direction
(the upstroke
direction), and restricted flow in the other direction (the downstroke
direction). The downstroke
control valve 520 includes a pair of valve cartridges 522. The cartridges 522
are mechanically
adjustable to restrict the return flow during a downstroke. In this way, the
cartridges 522 serve
as restricted orifices to limit the return flow of hydraulic fluid, e.g., a
refined oil or a clean
aqueous fluid, from the cylinder during a downstroke. One cartridge 522 may
control one well
("Well A"), while another cartridge 522 limits the rate of flow of oil from
the cylinder of another
well ("Well B").
17
CA 02826593 2013-09-12
As noted, the valve stack 500 also includes a sub-plate 530. The sub-plate 530
represents
a rectangular block having various openings. These openings receive hydraulic
pressure from
the high-pressure discharge of the hydraulic pump The openings also interface
the hydraulic
lines 170, 175 that are in fluid communication with the cylinder. The openings
further interface
with various ports on the rest of the valve stack 500, starting with the
downstroke control valve
520.
In the arrangement of Figure 5, the sub-plate 530 receives a high pressure
bypass
cartridge 532 at one end. The cartridge 532 serves the purpose of limiting
pressure delivered to
the valve stack 500 and to the cylinder via line 170. Under normal operating
conditions, the high
pressure bypass cartridge 532 should not activate -- it is merely a safety
precaution if, for
example, the valve stack 500 is compromised by a foreign object.
It is also seen that the sub-plate 530 has four ports 534. The oil line 170
comes in at two
of the ports 534 ¨ one for one well ("Well A") and one for another well ("Well
B"). In addition,
the vent line 175 exits at two of the ports 534 ¨ one for one well ("Well A")
and one for another
well ("Well B"). The sub-plate 530 also includes head cap screws 535. The head
cap screws
535 mechanically secure components of the valve stack 500 together as a
unitary tool.
Other parts of the valve stack 500 are also seen in Figure 5. These include an
optional
soft shift body 540 with an opposing pair of soft shift cartridges 542. When
used, the soft shift
cartridges 542 serve the purpose of reducing shock while shifting the four-way
valve 510.
A pilot valve 550 is also provided. The pilot valve 550 receives an opposing
pair of pilot
solenoid coils 552. Further, the pilot valve 550 has a body seal plate 554.
The pilot valve 550
utilizes a small and manageable amount of hydraulic fluid, controlled by the
solenoid coils 552,
to shift the much larger four-way valve 510. Pilot pressure is directed from
the pilot valve 550 to
the valve body 510 to shift the spool 590. This pilot pressure acts on either
end of the spool 590
and against the end caps 512 to force the spool 590 and to shift the valve
position. Once the
spool 590 is shifted, the main hydraulic flow path through the valve body 510
is redirected.
18
CA 02826593 2013-09-12
An alignment plate 545 is seen between the soft shift body 540 and the pilot
valve 550.
The alignment plate 545 receives a plurality of screws 555, and insures
alignment of the soft
shift body 540 and the pilot valve 550.
Returning to Figures 4A and 4B, the dual-chamber tank 490 presents a unique
arrangement for the valve stack 500 and a fluid reservoir. Because the valve
stack 500 resides in
the upper chamber 492 over the fluid reservoir, any nuisance leaks from the
valve stack 500 will
drip into the lower chamber 495. At the same time, because the valve stack 500
is isolated from
the hydraulic oil in the lower chamber 495, the electronics need not be
explosion-proof
As an additional feature, the dual-chamber tank 490 employs a pair of inhale
and exhale
lines (not shown). The inhale and exhale lines create something of a bellows
approach to pump
fresh air into the tank 490 and to purge the air and potentially explosive gas
from the fluid
reservoir chamber 490 by way of the fluctuating fluid level. Because the
hydraulic cylinder 150
mounts directly in the production line, that is, over the wellhead 105, there
is a possibility of
migrating gas from the wellbore 115 to the hydraulic oil reservoir chamber 495
via seal 244.
In operation, the hydraulic fluid level will rise and fall in the reservoir
chamber 495 on
each stroke of the piston 160. Two check valves are placed in the bulkhead
(not shown)
separating the upper 492 and lower 495 chambers. One check valve allows air
(and residual oil
drips) to flow from the upper chamber 492 in to the lower chamber; the other
check valve allows
air from the lower (fluid reservoir) chamber 495 to be safely vented outside
the cabinet 490.
Optionally, a vent line (not shown) may be run from the upper chamber 492,
where applicable, to
the outside of a building or other enclosure. In this way, the fluctuating
hydraulic fluid level is
used to "pump" fresh air from the upper chamber 492, through the lower
reservoir chamber 495,
and then safely directed outside.
As noted above, each of Figures 4A and 4B show a prime mover. The prime mover
is
designed to provide working power to a pump (seen at 184 in Figure 1). In
Figure 4A, the
prime mover 482A is shown as an internal combustion engine 482A. In Figure 4B,
the prime
mover 482B is shown as an electric motor.
19
,
CA 02826593 2013-09-12
Also seen in each of Figures 4A and 4B is an electronics cabinet 484A, 484B.
The
illustrative cabinets 484A, 484B present two separate chambers -- one for 480
volt AC motor
controls, and one for programmable logic controller (low voltage) wiring. In
the case of
electronics cabinet 484A (for the gasoline engine), the cabinet 484A may
optionally have only
one box.
Figure 6 is an engineering diagram showing illustrative hydraulic circuitry
600 of the
hydraulic oil well pumping system 100 of Figure 1, in one embodiment. Fluid
lines and certain
components for the system 100 are shown schematically.
First, a motor is shown at 682. The motor 682 is an electric motor that serves
as a prime
mover for powering a pump. It is understood that the prime mover may
alternatively be an
internal combustion engine. Alternatively, the motor 682 may utilize pneumatic
cylinders,
weight or gravity-driven cylinders, mechanical spring-driven cylinders or
other source of fluid
power.
Next, a hydraulic pump is shown at 684. The illustrative pump 684 is a vane
pump.
However, it is understood that the pump 684 may be any type of fixed or
variable displacement
hydraulic pump. The hydraulic discharge of the vane pump 684 is directed under
the control of a
programmable logic controller, either to the cylinder 155 or back to the tank
490.
The pump 684 pumps a working fluid such as a clean or refined oil from a
reservoir 695.
The reservoir may be, for example, the lower chamber 495 of Figures 4A and 4B.
A line 686 is
shown pulling oil from the reservoir 695 into the pump 684. The oil is then
delivered through
line 672 and then to lines 670 to a pair of wells 615A, 615B.
Each well 615A, 615B employs a hydraulic cylinder 650. Each cylinder 650, in
turn, has
a piston 665 and polished rod 660 that together reciprocate in response to
fluid pressure applied
by the cyclic injection of oil through lines 670. An annular area 655 is
formed below the piston
660 and between the polished rod 660 and surrounding cylinders 650. Each
piston 665 has a
piston ring (seen in Figure 2A at 266) that provides a seal for holding fluid
pressure within the
CA 02826593 2013-09-12
cylinders 650. The cylinders 650 are illustrative of cylinder 150 described
above, while the oil
lines 670 are representative of oil lines 170 from Figures 1A and 2A.
En route to the cylinders 650, the oil will travel through a directional
control valve 692.
The control valve 692 may be, for example, the discrete four-way valve stack
500 of Figure 5.
Alternatively, the control valve 692 may be a proportional valve or may be
part of a variable
speed prime mover. In any embodiment, the control valve 692 allows hydraulic
oil to be
pumped from the pump 684 to the annular area 655 through oil line 670. Pumping
is controlled
by a programmable logic controller (not shown).
The hydraulic circuitry 600 also includes a downstroke control valve 694. The
down
stroke control valve 694 may be part of the discrete valve stack 500 of Figure
5. To this end, the
directional control valve 692 and the downstroke control valve 694 are shown
in Figure 6 by a
common bracket at 690. The down stroke control valve 694 permits oil to return
to the fluid
reservoir 695 via a restricted orifice, and then through reservoir line 688.
This takes place when
the directional control valve 692 is in its "neutral" position. Since pressure
no longer forces the
piston 660 upwardly, it begins to drop in response to gravitational forces
applied to the pistons
660 by means of the rod string 120 and connected downhole pump.
Several additional components are seen in Figure 6 as part of the hydraulic
circuitry 600.
These include a vent line 675, a heat exchanger 676, and an oil filter 678.
The vent line 675 is
comparable to line 175 of Figures 1A and 2A. The heat exchanger 676 is,
preferably, an air-
over-oil heat exchanger that utilizes a fan for cooling oil. The oil filter
678 filters return oil
before it is deposited into the reservoir 695. A 25 psi bypass valve may
optionally be provided
so that excess pressure is not applied to the filter media in the filter 678.
The four-way valve 692
or the bypass valve 673 directs return oil through the heat exchanger 676 and
filter 678.
It is again noted that the hydraulic circuitry 600 of Figure 6 shows two
different
cylinders 650 in two different wells 615A, 615B. The valve stack 690 is
capable of driving two
different wells concurrently, provided the requirements of the two wells are
similar. The system
can only operate one upstroke at a time, but can operate two wells alternating
upstrokes. While
one well 615A is upstroking, the other well 615B is downstroking. However, the
valve stack
21
CA 02826593 2013-09-12
690 may be used to drive a piston 660 in only a single well should the
operator so choose.
Operating two wells is a capability, not a requirement.
In either design, it is desirable for the operator to know where the piston
665 is within the
cylinder 650 during any given part of the cycle. One reason is so that speed
control may be
applied to the pump 684. Specifically, the operator may wish to decrease the
speed of the pump
684, and thus decelerate the piston 665 and rod string at the ends of the
upstrokes and
downstrokes.
As noted above, hydraulically actuated reciprocating sucker rod pump systems
have
historically employed sensors along the wellhead. The sensors may be
mechanical, hydro-
mechanical, pneumatic, pneumatic-mechanical, acoustic, electronic or electro -
mechanical
position indicating devices to detect the position of the piston. For example,
U.S. Patent No.
7,762,321 teaches the use of a plurality of "proximity switches" along the
actuation cylinder to
detect the location of an object along the piston. When a proximity switch
detects the object, a
limit switch is activated that de-energizes a valve. Sensors have also been
used to detect travel
speed or direction and are used to control piston position, speed or
direction.
Position feedback on hydraulically actuated rod pumping systems has been
required to
intelligently react to, control, monitor, or record the effects of dynamic
load changes to the
bottom-hole equipment. For example, it is known to mount the cylinder above
the wellhead with
the cylinder's rod exposed to the atmosphere for attachment of position
indicating devices or
linear position transducers. However, it is desirable to employ a simplified
system that does not
require the presence of sensors at or above the wellhead. Placing exposed
electrical components
in such an environment is undesirable. Furthermore, the wellhead is an area
that sees much
activity during well work and the small sensor components and cabling could be
easily damaged.
Thus, it is proposed herein to employ a rod pumping system and method that
mathematically
infer the piston position from a remote location. This is done by measuring
cumulative or
volumetric flow of the hydraulic working fluid into and out of the cylinder.
22
CA 02826593 2013-09-12
In connection with a hydraulic oil well pumping system, it is possible to use
the hydraulic
pressure in the annular area 155 to measure load on the piston 160. Generally,
hydraulic
pressure may be calculated as:
L = F x A
where: L = load on the piston (pounds);
F = Force against the piston (psi); and
A = Annular area (in2).
However, it is believed by the inventors herein that hydraulic fluid dynamics,
in addition
to the load calculation, may also be used to determine the relative position
of the piston 165
within the cylinder 150. This may be done by measuring the total fluid volume
or flow rate of
fluid going into, and returning from, the annular area 155 of the hydraulic
cylinder 150 during
the upstroke and the down stroke. The position of the piston 165 within the
cylinder 150 is then
inferred from the volumetric measurements, all at a safe distance from the
wellhead 105.
Various techniques may be employed for measuring fluid flow. In one aspect,
differential pressure measurements may be used to measure the flow rate of
hydraulic fluid. A
cumulative series of flow rate measurements over a known cross sectional area
is equivalent to a
total fluid volume over that time period. The pressure measurements are made
at the valve stack
500 and not at the wellhead 105 or cylinder 150. Preferably, pressure sensors
and transmitters
are located along the sub-plate 530, but could be placed anywhere along the
main hydraulic (or
oil) line 170 as well.
In another aspect, a flow meter such as a paddle wheel may be used. A paddle
wheel has
a shaft that is turned in response to hydraulic forces on a paddle. A
correlation can be made
between the number of rotations of the shaft at or near the valve stack 500
during a given period
of time and a volume of fluid that passes across the paddle wheel during that
time period. Of
course, the present system and methods are not limited to the technique used
for measuring
volumetric flow unless expressly stated in the claims.
23
,
CA 02826593 2013-09-12
Next, the volume of the annular area is calculated:
VA Ls X AA
where: VA = Volume of the annular area (gallons);
Ls = Stroke length of the piston (inches);
and
AA = Annular area [Cylinder area - piston area] (in2)
From this, it is possible to calculate gallons of fluid pumped per stroke
inch:
VA / Ls
where: F = Fluid pumped (gallons per stroke
inch);
VA = Volume of the annular area (gallons);
and
L = Stroke length of the piston (inches).
By way of example, assume the effective volume of the cylinder (the annular
area 155
under the piston 165) is 10 gallons, and the stroke is 288 inches:
10 gallons / 288 inches
0.035 gallons / stroke inch.
In a pumping cycle, the volume of hydraulic oil pumped into a cylinder and the
corresponding rod piston position are linearly related. Thus, F (gallons /
stroke inch) is not
dependent on the velocity at which the piston is traveling or the pump
pressure applied. It is also
noted that a fixed displacement pump offers a unique advantage in that it is
known how long it
takes to fill the annular area V.. Thus, if the pump is pumping at 10
gallons/minute, the annular
area Va will be filled in 10 minutes when V. is 10 gallons. Of course, the use
of the fixed
displacement pump is only of benefit on the upstroke. On the down stroke, the
velocity of the
piston will be dependent on the free-fall of the piston 160 and the size of
the restricted orifice in
the downstroke control valve 520 or 694. Therefore, the calculations
concerning F are critical to
knowing the position of the piston 160 on the down stroke.
24
CA 02826593 2013-09-12
Another advantage to the present method is that no sensors are needed at the
wellhead to
determine piston location. Downhole well conditions may be monitored remotely
by combining
the cylinder's piston load and position without attaching devices on or near
the wellhead. This
enables remote monitoring and control of the cylinder's position, load and
acceleration, while
remotely monitoring the effects of the downhole dynamics on the fluid power
system.
It is noted that diagnosis of a rod-pumped well based upon surface parameters
was first
presented by Gibbs in U.S. Pat. No. 3,343,409. Surface load and piston
position are measured at
consistent time intervals during the complete stroke cycle at the surface. The
dynamics of the
rod string and fluid are known, and from these pieces of information, it is
possible to calculate
the downhole load and position. This is a known procedure. However, this
procedure requires
that the operator or system know both the load and position of the polished
rod at the surface.
This further requires directly attached pressure and load sensors in the
wellhead environment. It
should be noted that directly attached sensors may not be used in the
configuration where the
hydraulic cylinder is placed inside the wellbore and submerged in crude oil.
The operator may wish to monitor hydraulic fluid pressure during the upstroke.
For
example, a pressure limit switch may be employed to cut off the pump in the
event pressure
spikes above a certain value. This is a safety feature that comes into play
if, for example, the
pump becomes stuck downhole. If excess pressure is detected along oil line
672, a relieve valve
673 may be used to release oil from line 672.
In one aspect, the absolute volume value (VA) is not required; rather, a
relative volume,
or flow rate, value may be used. Using a measurement of fluid volume pumped,
the operator can
correlate the amount of fluid volume injected into a cylinder (annular area
155) to push the
piston to the top of its stroke length and the position of the piston ring.
Thus, for example, if a
cylinder (annular area 155) has received 10 gallons for a full stroke length,
then the operator
knows that the piston is half way up the cylinder (144 inches) when 5 gallons
have been pumped
into the annular area 155. This relation between position and volume within
the cylinder is
linear. This also assumes little to no piston ring leakage during the stroke.
If there is piston ring
leakage, that oil is recovered through the vent line 175. This limits the
effect of any consistent
piston ring leakage to individual strokes; the effects are not cumulative.
CA 02826593 2013-09-12
Figure 7 is a flow chart showing steps that may be performed for a method 700
of
pumping oil from a wellbore, in one embodiment. The wellbore has a bore
extending into an
earth surface. The method 700 employs the unique pumping system described
above, including
the set of valves shown in Figure 5 that are controlled by an electrical
control system. The
valves cyclically direct hydraulic fluid into a cylinder. The pressure created
by the hydraulic
fluid causes a piston and connected rod string and downhole pump to
reciprocate. This, in turn,
causes reservoir fluids to be produced from a wellbore to the surface through
positive
displacement.
Referring to Figure 7, the method 700 first comprises providing an elongated
hydraulic
cylinder. This is shown at Box 710. The cylinder is positioned over the
wellbore. The cylinder
may either be over an associated wellhead as shown in Figure 2A, or inside the
wellbore below
the wellhead as shown in Figure 3.
The method 700 also includes providing a piston. This step is provided at Box
715. The
piston may be in accordance with the piston 165 of Figure 1A. The piston is
movable between
upper and lower rod positions within the cylinder. The piston creates an
annular seal below the
piston between a connected polished rod and the surrounding cylinder.
Hydraulic pressure acts
against the piston.
The method 700 further includes mechanically connecting the piston to a rod
string, such
as through a threaded coupling. This may be done through a polished rod
between the piston and
the rod string. When the piston reciprocates, the polished rod and connected
rod string
reciprocate with it. This is shown at Box 720. The rod string extends
downwardly from the
piston and into the wellbore. The rod string has a downhole pump connected to
it for lifting
fluids to the surface in response to reciprocation of the rod string.
The method 700 also includes providing a hydraulic pump. This is seen at Box
725.
Preferably, the pump is a fixed displacement pump. The pump is powered by a
prime mover.
The prime mover may be an electric motor, an internal combustion engine, or
other driver.
26
CA 02826593 2013-09-12
The method 700 also has the step of connecting the pump and the hydraulic
cylinder with
an oil line. This is indicated at Box 730. The oil line transmits hydraulic
fluid from the pump to
the cylinder.
Still further, the method 700 includes providing a directional control valve.
This is given
at Box 735. The directional control valve moves between upstroke and
downstroke (neutral)
flow positions in response to signals from an electrical control system. The
electrical control
system may be, for example, a programmable logic controller. When the valve is
in its open
position, it directs hydraulic fluid such as oil from the pump, through the
oil line and into an
annular area formed between the piston and the surrounding cylinder. In the
neutral position, the
control valve allows oil to flow back from the cylinder to the reservoir
through a downstroke
control valve.
It is understood that the downstroke control valve need not be a discrete
valve. The
downstroke control valve may be a nitrogen accumulator or any other device
that captures the
energy from the gravitational fall of the piston and connected polished rod,
rod string and
downhole pump.
The method 700 also has the step of providing a fluid reservoir. This is shown
at Box
740. The reservoir contains hydraulic fluid to be supplied to the pump.
The method 700 next includes providing a reservoir line. This is seen at Box
745. The
reservoir line transmits hydraulic fluid from the cylinder to the reservoir.
An example of a
reservoir line is seen at line 688 of Figure 6. Optionally, a filter is
provided along the reservoir
line. A filter is seen at 678 of Figure 6.
The method 700 also has the step of providing a down stroke control valve.
This is
shown at Box 750 of Figure 7. The down stroke control valve chokes the flow of
fluid from the
cylinder back to the reservoir. This, in turn, limits the rate of flow of
hydraulic fluid. An
example of a down stroke control valve is shown schematically at 694 in Figure
6.
27
CA 02826593 2013-09-12
The method 700 also offers the step of controlling movement of the piston as
it moves
between upper and lower rod positions. This step is provided at Box 755. The
step of Box 755
is done by using an electronic control system. The control system controls the
valves and the
pump to cycle the pump between (i) an "upstroke" condition wherein the pump is
pumping oil
through the control valve, through the oil line and into the hydraulic
cylinder to move the piston
to its upper rod position, and (ii) a "neutral" condition wherein the pump is
no longer pumping
oil into the hydraulic cylinder, but is allowing oil to flow back through the
oil line in response to
gravitational fall of the piston. The electronic control system is programmed
to cycle based upon
a volumetric calculation of hydraulic fluid in the cylinder and without
reference to position
sensors along the wellhead.
Preferably, and as noted above, the electronic control system controls
movement of the
rod based on (i) the volume, or rate, of hydraulic fluid sent to the cylinder
during the "upstroke"
valve condition, (ii) the volume, or rate, of hydraulic fluid returned from
the cylinder during the
"neutral" valve condition, or (iii) both. Optionally, the control system may
send a signal to cause
the pump to vary its output, to cause a valve to adjust its proportional flow,
or to change an
operating speed of the prime mover based upon either (i) a volume of fluid
that has moved into
the hydraulic cylinder during the "upstroke" valve condition, or (ii) a volume
of fluid that has
returned from the hydraulic cylinder during the "neutral" valve condition.
In one aspect, the electronic control system sends a signal to cause the valve
to change
flow paths and to initiate a down stroke of the piston based upon (i) a
relative measurement of a
volume, or rate, of fluid that has moved into the hydraulic cylinder, or (ii)
an absolute volume of
fluid that has moved into the hydraulic cylinder, during the "upstroke" valve
condition. The
measurement of fluid volume may be based upon (i) pressure differential across
a fixed orifice,
(ii) a flow meter such as a paddle wheel, or (iii) fluid level in the
reservoir. Alternatively, some
combination of these approaches, or other methods of measuring a moving fluid
volume may be
used.
Also, the method 700 includes reciprocating the piston and mechanically
connected rod
string in order to pump oil from the wellbore. This is indicated at Box 760.
The step of Box 760
is the natural result of operation of the control system and pump over time.
28
CA 02826593 2013-09-12
It is noted that by taking volumetric measurements over time, the operator can
plot the
position of the piston during the strokes. In addition, velocities, and
accelerations can be
calculated. Using a programmable logic controller, the system may be
controlled to operate at a
constant speed during the upstroke of the piston. Further, the pump speed may
be altered prior to
and during changes of direction to reduce load on the rod string and connected
pump. In this
respect, the surface stroke velocity can be proactively altered to minimize
the stress on the sucker
rod string and pump. This can be done by controlling the pump speed, and by
controlling the
bleed-down rate for the relief line 675 through the down stroke control valve
694. This helps to
reduce fatigue of the sucker rod string 120 and to minimize fluid or gas
pounding effects upon
the bottom hole pump.
In one aspect, the operator sets the cycle for the down stroke based on time.
The operator
estimates how long it takes the piston 660 to fall to the bottom of the
cylinder 650. The pumping
of hydraulic fluid is not resumed until a designated period of time for the
down stroke has lapsed.
By monitoring volume, or rate, of flow out of the cylinder 650, the system may
make small
adjustments or change valve states in order to minimize stress on the
mechanical system.
Figures 8A and 8B are another flow chart. Here, steps are shown for a method
800 of
determining the position of a piston within a hydraulic cylinder. The piston
is a hydraulically
actuated piston that resides within a cylinder. The cylinder, in turn, is
positioned over a
wellbore.
The method 800 first includes determining a volume of hydraulic fluid needed
to fill the
cylinder. In one aspect, the volume is an annular area below the piston and
between a connected
polished rod and a surrounding hydraulic cylinder. This is shown at Box 810.
The method 800 also includes determining a rate for filling the cylinder
during the
upstroke of the piston. This is provided at Box 820. The annular area is
filled using a pump
along with an oil line that provides fluid communication between the pump and
the annular area.
The rate at which the cylinder can be filled is a function of the hydraulic
pump output and the
speed at which that pump is driven.
29
CA 02826593 2013-09-12
The method 800 further has the step of determining a first time. This first
time is the
time it takes to fill the annular area (or cylinder) during the upstroke. This
is seen at Box 830.
The step of box 830 is based upon the determined volume and rate from the
steps of Boxes 810
and 820. This provides a baseline to which subsequent strokes can be
calibrated against. In
general, the theoretical time to fill the cylinder is a minimum. Other factors
such as degraded
pump efficiencies or piston ring leakage may increase the time required to
fill the cylinder.
The method 800 still further includes determining a second time. This second
time is the
time it takes to drain the fluid from the cylinder through a down stroke
control valve. This is
shown at Box 840. The down stroke control valve has a restricted orifice for
reducing or
restricting a rate at which the piston falls during draining. The rate at
which the downstroke
occurs is not constant. Downhole loads fluctuate significantly depending on
changing conditions,
and as the loads shift during a downstroke, the rate at which fluid is allowed
to pass through the
orifice also changes. It is therefore critical to closely monitor both of
these changing loads and
position measurements to apply Gibbs' method for calculating the conditions
during the full
stroke cycle.
The method 800 also has the step of controlling movement of the piston as it
reciprocates
between upper and lower rod positions. This step is provided at Box 850. The
step of Box 850
is done by using an electronic control system. The control system causes the
pump to cycle
between (i) an "upstroke" condition wherein the pump is pumping oil through
the control valve,
through the oil line and into the hydraulic cylinder to move the piston to its
upper rod position
over the first time, and (ii) a "neutral" condition wherein the pump is no
longer pumping oil into
the hydraulic cylinder, but is allowing oil to flow back through the oil line
and through the down
stroke control valve in response to gravitational fall of the piston over the
second time. Of
interest, the cycling is performed without reference to position sensors along
the wellhead.
The method 800 further includes monitoring hydraulic fluid pressure in the oil
line. This
is shown at Box 860. The pressure is monitored during the first time and the
second times. In
one aspect, monitoring is conducted at regular intervals to correlate to the
position samples.
CA 02826593 2013-09-12
The method 800 then includes reciprocating the piston and mechanically
connected rod
string in order to pump oil from the wellbore. This is provided at Box 870. In
practical effect,
the step of Box 870 is the result of the step of Box 850 over time.
In one aspect, the method 800 further includes calculating a position of the
piston during
the upstroke. This calculation is based upon (i) the relative volume, or rate,
of hydraulic fluid
injected by the pump during the "upstroke" condition, (ii) the absolute volume
of fluid injected
by the pump during the "upstroke" condition, or (iii) a full scale calibration
from the ratio of a
pressure reading in the oil line to a baseline pressure representing a
pressure value just before the
piston has reached a mechanical top of its upstroke. This is provided at Box
880. The method
800 may then include the step of sending a signal from the electronic control
system to cause the
pump to vary its output, to cause a valve to adjust its proportional flow, or
to change an operating
speed of the prime mover based upon the location of the piston during its
upstroke. This is
shown at Box 885.
In another aspect, the method 800 further includes calculating a position of
the piston
during the downstroke based upon (i) the relative volume, or rate, of
hydraulic fluid drained from
the hydraulic cylinder during the "neutral" condition, (ii) the absolute
volume of hydraulic fluid
drained from the hydraulic cylinder during the "neutral" condition, or (iii)
when the pressure
reading in the oil line has reached a value of substantially 0, indicating a
mechanical bottom of
the down stroke. This is provided at Box 890. When the piston noticeably hits
the bottom of the
stroke, the volumetric measurements can be reset, allowing each stroke to be
measured
independently without influence from previous strokes. The method 800 then
includes the step
of sending a signal from the electronic control system to cause the pump to
vary its output, to
cause a valve to adjust its proportional flow, or to change an operating speed
of the prime mover
based upon the location of the piston during its down stroke. This is shown at
Box 895.
As can be seen, a method for measuring and controlling the position of the
hydraulic
piston in a linear stroking fluid power cylinder, used specifically for
actuating a sucker rod string
and bottom hole plunger pump in oil or gas wells is offered herein. The system
and method
provide the ability to remotely measure or control a piston's position, speed
and direction in the
absence of direct measurements of position and/or load at the wellhead.
31
CA 02826593 2013-09-12
Beneficially, the operator will be able to stop or slow the piston and
connected rod string
at various positions during the upstroke or downstroke. This allows the
operator to run various
down-hole valve tests. This is in addition to the slowing of the piston at the
ends of the strokes
to minimize mechanical stresses on the complete system.
Under one embodiment of the systems and methods described herein, differential
pressure measurements taken at a given orifice (which corresponds to square of
the fluid velocity
through a give orifice) may be used to "calibrate" a system onto itself. Under
such embodiment,
there would be no need to account for certain parameters including location of
pressure taps
relative to fixed orifice, hydraulic fluid viscosity, oil temperature, orifice
diameter, or even
cylinder volume, etc, because all such factors may be corrected for in a
calibration operation.
Under this embodiment, it is known that the piston within a hydraulic system
always starts from
position zero, and that full stroke length can be periodically detected
through a spike in hydraulic
pressure. Although the goal is to prevent hitting the mechanical top of a
piston upstroke on each
stroke, such piston position may be periodically probed to perform the
calibration operations
described below. Data samples of differential pressure before and after a
given orifice (and
therefore data samples of fluid velocity through a give orifice) may be logged
and scaled
according to a percentage of the full stroke length. The known piston stroke
length can be
applied to this percentage to derive the unitized measurement of actual piston
position. The
process yields a calibration factor, which may be pro-actively used to
determine real-time
position of a piston on subsequent strokes, or between calibration cycles.
Note that differential
pressure measurements may be taken across a fixed orifice, or by other such
flow rate
measurement techniques, located at or near the valve stack or along an oil
line to or from the
cylinder, but embodiments are not so limited.
The calibration approach described above may be implemented using the
following steps.
assuming a data sampling rate of 10ms:
= Calculate the square root of sampled differential pressure data (which
corresponds to the fluid velocity through the orifice)
32
'
CA 02826593 2013-09-12
= Multiply that instantaneous fluid velocity data by a 10ms sample interval
and
add result to a running total (a preferred method would be to use the
trapezoidal rule to
calculate the average velocity over this sample period)
= Assume "System performs X units of velocity for 10ms"
= Subsequent data samples sweep out the area under a velocity curve which is
equivalent to position data of a piston (i.e. data samples capture information
of a piston's
position, velocity, and acceleration, as all three are related over time)
= At any given point, a running total register holds what amounts to a
cumulative
position reading of the piston; note that such values are scaled by a yet
unknown factor
(unknown until the end of stroke, where we can derive it from the stroke
length)
= Samples from the running total register (along with the piston load) may
be read,
and logged for later processing, from the register at a more reasonable sample
rate than
the high frequency data sampling rate; note that since differential
pressure/velocity is
being processing at a very high sample rate, the position value derived (or
more
accurately, integrated) from the velocity data at any given point should be
nearly as
precise as the inputs
= At the end of piston upstroke, the position value of the piston is
assumed to be
100% of the stroke length which is to be mechanically calibrated/verified
periodically by
deadheading the piston
= Gathered position samples over the total stroke (logged from the high
frequency,
velocity over time, register) may then be scaled according to a calibration
percentage/factor and known overall stroke length to yield actual piston
position in inches
= The same procedure as described above starts over for the piston
downstroke,
which might have some different fluid dynamics in the return path; such
difference
should not matter since upstroke and downstroke are treated independently
33
CA 02826593 2015-01-27
= Starting with an assumed top of piston stroke, as previously determined,
bottom
of stroke may be detected when the hydraulic pressure effectively drops to
zero, meaning
the piston is resting on the mechanical bottom of stroke.
Under this embodiment, a relatively simple sensor and method may be used to
measure
differential pressure across a given orifice. One does not need to know
anything about certain
parameters including location of pressure taps relative to fixed orifice,
hydraulic fluid viscosity,
oil temperature, orifice diameter, or even cylinder volume, etc, because they
are more or less
constants embedded in the "position" data. Those details all become irrelevant
once end of the
stroke is determined. These variable factors are all contained in a single
calibration factor that,
along with the stroke length, will scale the individually calculated position
samples into familiar
units such as inches. This process yields a calibration factor which may be
pro-actively used to
determine real-time position of the piston (and that scaling/calibration
factor will most likely be
different from upstroke to downstroke).
It is understood that the hydraulic oil well pumping system 100 of Figure 1
and the
method 700 for pumping oil of Figure 7 are merely illustrative. Other
arrangements may be
employed in accordance with the claims set forth below. The scope of the
claims that follow is
not limited by the embodiments set forth in the description. The claims should
be given the
broadest purposive construction consistent with the description and figures as
a whole.
34
