U.S. patent application number 11/634587 was filed with the patent office on 2008-06-12 for method and apparatus for disposal of well flare gas in oil and gas drilling and recovery operations.
Invention is credited to Matt Cugnet, Tim Cugnet.
Application Number | 20080135238 11/634587 |
Document ID | / |
Family ID | 39496616 |
Filed Date | 2008-06-12 |
United States Patent
Application |
20080135238 |
Kind Code |
A1 |
Cugnet; Matt ; et
al. |
June 12, 2008 |
Method and apparatus for disposal of well flare gas in oil and gas
drilling and recovery operations
Abstract
A wellhead gas recovery system and method for the generation of
power from wellhead gas is provided. A gas conduit is used to
direct wellhead gas from a wellhead casing or wellhead bore to a
stirling engine where the wellhead gas is used as the fuel source
for the stirling engine. The wellhead gas is ignited and the
burning wellhead gas is used as the heat source for the stirling
engine. The thermal energy from the burning wellhead gas is
converted transferred into motion by the stirling engine and the
output of the stirling engine can be used to drive devices at the
wellsite, generate electricity or other use.
Inventors: |
Cugnet; Matt; (Weyburn,
CA) ; Cugnet; Tim; (Weyburn, CA) |
Correspondence
Address: |
LADAS & PARRY LLP
224 SOUTH MICHIGAN AVENUE, SUITE 1600
CHICAGO
IL
60604
US
|
Family ID: |
39496616 |
Appl. No.: |
11/634587 |
Filed: |
December 6, 2006 |
Current U.S.
Class: |
166/256 |
Current CPC
Class: |
E21B 41/005
20130101 |
Class at
Publication: |
166/256 |
International
Class: |
E21B 43/243 20060101
E21B043/243 |
Claims
1. A wellhead gas recovery system for the generation of power, the
system comprising: a stirling engine, comprising a combustor; and a
gas conduit operative to route wellhead gas from a wellhead to the
stirling engine, wherein the wellhead gas routed to the stirling
engine is ignited by the combustor and the ignited wellhead gas
acts as a heat source to drive the stirling engine.
2. The system of claim 1 wherein the stirling engine comprises at
least one combustion chamber and wellhead gas is directed to the at
least one combustion chamber by the gas conduit and the wellhead
gas is ignited in the at least one combustion chamber by the
combustor.
3. The system of claim 2 wherein the at least one combustion
chamber is operably removable whereby the at least one combustion
clamber can be removed and replaced when the at least one
combustion chamber becomes corroded from the wellhead gas.
4. The system of claim 2 wherein the at least one combustion
chamber comprises a corrosion resistant material.
5. The system of claim 1 wherein power generated by the stirling
engine is used to drive an output shaft.
6. The system of claim 1 wherein power generated by the stirling
engine is used to drive an electrical generator to output
electrical energy.
7. The system of claim 6 wherein the electrical generator is
operatively connected to an electrical power grid and wherein
electrical energy produced by the electrical generator is supplied
to the electrical power grid.
8. The system of claim 1 further comprising: a compressor located
inline on the gas conduit and operative to compress wellhead gas
passing through the gas conduit to a predetermined pressure; a
pressure vessel located inline on the gas conduit and downstream
from the compressor, the pressure vessel operative to store
wellhead gas pressurized by the compressor; and a pressure
regulator valve, located inline on the gas conduit and downstream
from the pressure vessel, the pressure regulator valve operative to
allow a regulated flow of pressurized wellhead gas at a
predetermined pressure from the pressure vessel to the stirling
engine.
9. The system of claim 1 comprising: a first stirling engine
connectable to the gas conduit by a first pressure regulator valve;
and a second stirling engine connectable to the gas conduit,
wherein wellhead gas is supplied to both the first stirling engine
and the second sterling engine and wherein wellhead gas is ignited
in the first stirling engine and second stirling engine to drive
the first stirling engine and second stirling engine,
respectively.
10. A method of using a stirling engine to recover energy from
wellhead gas, the method comprising: routing wellhead gas to a
stirling engine; igniting the wellhead gas; using the ignited
wellhead gas as a heat source to drive the stirling engine.
11. The method of claim 10 wherein the wellhead gas is directed to
at least one combustion chamber of the stirling engine and ignited
in the at least one combustion chamber.
12. The method of claim 11 comprising replacing the at least one
combustion chamber when the at least one combustion chamber has
become corroded.
13. The method of claim 11 wherein the at least one combustion
chamber comprises a corrosion resistant material.
14. The method of claim 10 comprising using power generated by the
stirling engine to drive an output shaft.
15. The method of claim 10 comprising using power generated by the
stirling engine to generate electricity.
16. The method of claim 15 wherein the electricity generated by the
stirling engine is supplied to an electrical grid.
Description
[0001] This invention is in the field of wellhead gas recovery and
more specifically generating power using wellhead gas collected as
a by-product of oil collection.
BACKGROUND
[0002] Natural gas occurs in the collection of oil from an oil
well, typically referred to as wellhead gas, because it
concentrates at a wellhead during oil collection. Typically, this
gas dealt with by either piping it to a collection system, shutting
it in the well head, or in many cases venting or flaring it
off.
[0003] Ideally, this gas is collected for later processing because
the gas can often be processed into a saleable commodity. However,
because many well sites are in relatively remote locations and the
amount of gas collected is often relatively small, the requirements
of collecting and transporting the gas for further processing is
often uneconomical.
[0004] Raw wellhead gas (wellhead gas that has not been treated)
typically comprises a mixture of methane, ethane, propane nitrogen
carbon-dioxide, helium, and other compounds. In addition, the raw
wellhead gas may contain small quantities of water vapor and/or
significant amounts of hydrogen sulfide (H.sub.2S) making the
wellhead gas "sour gas".
[0005] Wellhead gas with a hydrogen sulfide content exceeding 5.7
milligrams per meter of gas is typically considered to be "sour
gas". The pressure of the raw wellhead gas collected from the
wellhead is typically 2 pounds per square inch (psi) or slightly
higher, although the pressure of the raw wellhead gas leaving the
wellhead can vary quite significantly.
[0006] One way of dealing with this wellhead gas produced as a by
product of the oil recovery process at a well site, is to simply
seal up the wellhead gas in the wellhead and prevent it from
escaping into the atmosphere. However, by shutting the gas in the
wellhead, the pressure in the well bore is increased and the
production of oil from the well can be detrimentally affected
because the flow of oil out of the well will often decrease as a
result of the increased pressure created by the shut in gas.
[0007] The easiest solution to deal with this gas is to simply vent
the gas to the atmosphere. To vent the gas, the wellhead gas is
simply directed out of the wellhead casing and straight into the
atmosphere. Venting the gas reduces the back pressure in the well
bore, which can increase the production of the well as compared to
shutting the gas in the well head. However, this vented gas,
because of its composition contains many harmful elements and can
be detrimental to the environment, especially if the gas is sour
gas, and in many jurisdictions venting is strictly regulated, if
allowed at all.
[0008] In an attempt to lessen some of the environmental problems
associated with vented gas, the gas is often flared rather than
vented (if the gas can support stable combustion). By flaring (or
burning) the gas, the back pressure in the well head is reduced
just as it is with venting, however, the flaring somewhat lessens
the environmental problems that can occur with straight vented gas
because the products of combustion of the gas are somewhat less
harmful than the straight vented gas. For example, by burning the
gas some of the hydrogen sulfide is converted to less harmful
sulphur dioxide.
[0009] Although it is often not economically viable to collect and
transport the gas to a location for further processing, the gas is
still often a useful source of energy and it has been recognized
that it is often desirable to recover some of the energy in the gas
at the well site. Often these wellhead gases are of a sufficient
quality to allow stable combustion (which is required for flaring)
and these gases can be used as a fuel source. It is simply the
economics of collection and transport that often makes it
undesirable to attempt to collect these wellhead gases at a well
site. Microturbines and other internal combustion engines or
sometimes utilized to recover energy from these waste gases at the
well site. Rather than simply venting or flaring the wellhead gas,
the gas is directed to the microturbine or other combustion engine
to serve as a fuel for the internal combustion engine. The power
generated by the combustion engine using the wellhead gas as fuel
can be used to power devices at the well site, generate electricity
or any other suitable purpose.
[0010] However, using combustion engines to recover energy from
wellhead gas is not without problems. The quality of the gas is
often not ideal for use in a combustion engine and is often highly
corrosive. Because of the corrosiveness of some of the gases, the
combustion of these gases in an internal combustion often either
quickly corrodes the internal components of the internal combustion
engine requiring extensive maintenance and/or repair of the engines
or the internal components of the internal combustion engine need
to be made from high quality materials with very good corrosion
resistance which are not highly susceptible to the corrosive gas.
This makes it necessary for internal combustion engines using
wellhead gas as a fuel to either be made from relatively costly
high quality corrosion resistant materials or to have substantially
shortened the service lives and/or require more regular and
extensive maintenance if the internal combustion engines are made
from more conventional materials.
[0011] In addition, internal combustion engines often require a
relatively narrow range of air/fuel mixtures in order to operate,
which can be hard to maintain with wellhead gas which may vary in
supply and quality causing an internal combustion engine, fuelled
with wellhead gas, to operate poorly or require extensive
preconditioning of the wellhead gas in order to maintain an
operable air/fuel mixture.
SUMMARY OF THE INVENTION
[0012] It is an object of the present invention to provide a system
and method that overcomes problems in the prior an.
[0013] In a first embodiment of the invention, a wellhead gas
recovery system for the generation of power is provided. The system
comprises: a stirling engine, comprising a combustor and a gas
conduit operative to route wellhead gas from a wellhead to the
stirling engine. The system operates by routing wellhead gas the
stirling engine and igniting the wellhead gas with a by the
combustor and the ignited wellhead gas acts as a heat source to
drive the stirling engine.
[0014] In a second embodiment of the invention, a wellhead gas
recovery system for the generation of power is provided. The system
comprises: a stirling engine, comprising a combustor; a gas conduit
operative to route wellhead gas from a wellhead to the stirling
engine, a compressor located inline on the gas conduit and
operative to compress wellhead gas passing through the gas conduit
to a predetermined pressure a pressure vessel located inline on the
gas conduit and downstream from the compressor, the pressure vessel
operative to store wellhead gas pressurized by the compressor; and
a pressure regulator valve, located inline on the gas conduit and
downstream from the pressure vessel, the pressure regulator valve
operative to allow a regulated flow of pressurized wellhead gas at
a predetermined pressure from the pressure vessel to the stirling
engine. The system operates by routing wellhead gas the stirling
engine and igniting the wellhead gas with a by the combustor and
the ignited wellhead gas acts as a heat source to drive the
stirling engine.
[0015] In a third embodiment of the invention, a wellhead gas
recovery system for the generation of power is provided. The system
comprises: a gas conduit operative to route wellhead gas from a
wellhead to the stirling engine, a first stirling engine
connectable to the gas conduit by a first pressure regulator valve;
and second stirling engine connectable to the gas conduit. Wellhead
gas is supplied to both the first stirling engine and the second
sterling engine and the wellhead gas is ignited in the first
stirling engine and second stirling engine to drive the first
stirling engine and second stirling engine, respectively.
[0016] In fourth embodiment of the invention, a method of using a
stirling engine to recover energy from wellhead gas is provided.
The method comprises routing wellhead gas to a stirling engine;
igniting the wellhead gas; and using the ignited wellhead gas as a
heat source to drive the stirling engine.
[0017] The present invention provides a system and method wherein
raw wellhead gas obtained as a by-product from an oil producing
well is used as the fuel source for a stirling engine. The wellhead
gas is typically collected from the wellhead during the pumping of
oil at the well site, however, it could also be collected from the
well bore during the drilling of the well bore. The wellhead gas is
routed from the wellhead casing to a stirling engine where it is
ignited by a combustor and used to drive the stirling engine. The
power generated by the stirling energy can then be converted to
either: kinetic energy, to provide mechanical power at the website
for driving the oil pump and/or other mechanical devices: or
electrical power, to power devices on the website or be fed back
into an electrical grid.
[0018] In a stirling engine, heat is typically created by using a
combustor to burn an incoming fuel. The heat generated by the
burning fuel is then transferred to a working fluid circulated
within the stirling engine and this working fluid undergoes a
thermodynamic cycle, specifically a carnot cycle, and the thermal
energy contained in the working fluid is converted into mechanical
energy. This mechanical energy can be then be utilized to drive an
output shaft, generate electricity, etc.
[0019] In contrast to an internal combustion engine where the
combustion of the incoming fuel occurs inside the pistons of the
engine, the combustion in a stirling engine occurs outside of the
pistons. The working fluid inside the pistons and the internal
workings of the stirling engine do not come into contact with the
wellhead gas used as the fuel source and therefore the internal
components of the stirling engine are not subjected to the
corrosiveness of the wellhead gas. Because the internal components
of the stirling engine do not come into contact with the corrosive
wellhead gas, these internal components do not have to be made from
high quality materials to prevent corrosion as a result of the
combusting wellhead gas and can have a substantially extended
service life, relative to internal combustion engines, using
materials of lower quality.
[0020] In addition, the fuel supply does not need to be as exact as
it does for an internal combustion engine. Unlike internal
combustion engines that often require a relatively narrow range of
air/fuel mixture in order to operate, stirling engines only require
the incoming fuel to be able to maintain a relatively stable
combustion because the incoming fuel is merely ignited to provide
heat to the stirling engine. Minor fluctations in the heat output
from the burning fuel typically do not significantly affect the
operation of the stirling engine. The air/fuel mixture, pressure,
and other variable in the fuel supply do not have to be regulated
as strictly as in an internal combustion engine making the
operation of the stirling engine on the wellhead gas more reliable
because fluctuations in the composition and supply of the wellhead
gas to the stirling engine will not have as detrimental an effect
as these fluctuations would have on an internal combustion
engine.
[0021] Even though many stirling engines typically have combustion
chambers in which the fuelling source is combusted, these
combustion chambers need to merely contain the combustion of the
fuel while the heat of the combustion is being transferred to the
stirling engine and do not contain any moving parts. Therefore, the
combustion chambers in stirling engines do not need to have the
same tolerances that combustion chambers in internal combustion
chambers require. The combustion chambers themselves can be made of
more corrosive resistant materials or be more frequently replaced
without having to tear down and rebuild the entire stirling
engine.
[0022] In addition, by burning the wellhead gas, some of the
hydrogen sulfide which is very harmful and may be present in the
wellhead gas is converted into less harmful sulfur dioxide. Because
the stirling engine will allow a much wider operating range for the
ignited wellhead gas, the air/fuel mixture and temperate can be
optimized to try to enhance the conversion of the hydrogen sulfide
to sulfur dioxide; allowing more hydrogen sulfide in the wellhead
gas to be converted to sulfur dioxide.
[0023] In a further embodiment, a system and method is provided for
allowing a stirling engine to be fueled by wellhead gas where the
supply of wellhead gas from the wellhead is relatively unstable. In
this embodiment, the raw wellhead gas is directed to a compressor
where the wellhead gas is compressed and stored in a pressure
vessel. A pressure regulator valve allows a steady flow of wellhead
gas from the pressure vessel to the sterling engine, where the
wellhead gas is ignited to supply heat to drive the stirling
engine.
[0024] In this manner, when the raw wellhead gas from the wellhead
drops below a suitable pressure, the compressed wellhead gas stored
in the pressure vessel can compensate for the reduce pressure in
the supply or raw wellhead gas from the wellhead. The length of
time that this system can compensate for a fluctuating supply of
raw wellhead gas will vary depending on the amount of compression
of the wellhead gas, the size of the pressure vessel and the
pressure level allowed by the pressure regulator valve.
[0025] In a further embodiment, two or more- stirling engines are
supplied with raw wellhead gas for situations where the pressure of
the raw wellhead gas is sufficient to supply fuel to more than one
stirling engine. The stirling engines are connected to a gas
conduit in series with pressure regulating valves regulating the
supply of the wellhead gas in the gas conduit to each of the
stirling engines. In this manner, well sites that produce
substantial amounts of wellhead gas can be used as the fuel source
for multiple stirling engines.
DESCRIPTION OF THE DRAWINGS
[0026] While the invention is claimed in the concluding portions
hereof, preferred embodiments are provided in the accompanying
detailed description which may be best understood in conjunction
with the accompanying diagrams where like parts in each of the
several diagrams are labeled with like numbers, and where:
[0027] FIG. 1 is schematic diagram of a system for recovering
energy from wellhead gas, in accordance with the present
invention;
[0028] FIG. 2 is a schematic diagram of a stirling engine in
accordance with the present invention, connected to an output
shaft;
[0029] FIG. 3 is a schematic diagram of a stirling engine, in
accordance with the present invention connected to an electrical
generator, supplying electrical power to a power grid;
[0030] FIG. 4 is a schematic diagram of a further embodiment of a
system in accordance with the present invention comprising a
compressor and a pressure vessel; and
[0031] FIG. 5 is a schematic diagram of a further embodiment of a
system in accordance with the present invention wherein a plurality
of stirling engines are fueled with wellhead gas.
DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS
[0032] FIG. 1 is a schematic illustration of a system 10 for
recovering energy from wellhead gas. The energy recovery system 10
comprises a gas conduit 25 and a stirling engine 30. The gas
conduit 25 transfers raw wellhead gas, collected as a by-product
from oil producing wells, from a wellhead 20 to the stirling engine
30.
[0033] The raw wellhead gas is collected from the top of the
wellhead as is known in the art and typically comprises a mixture
of methane, ethane, propane, nitrogen, carbon-dioxide, helium, and
other compounds. In addition, the raw wellhead gas may contain
small quantities of water vapor and/or significant amounts of
hydrogen sulfide (H.sub.2S) making the wellhead gas "sour gas".
Typically, wellhead gas with a hydrogen sulfide content exceeding
5.7 milligrams per meter of gas is typically considered to he "sour
gas". The pressure of the raw wellhead gas collected from the
wellhead is typically 2 psi or slightly higher allowing the raw
wellhead gas to move through the gas conduit 25 without requiring
additional compression, although the pressure of the raw wellhead
gas leaving the wellhead can vary quite significantly.
[0034] The stirling engine 30 is a stirling engine as is
conventionally known and could have various configuration, however,
stirling engine 30 typically comprises: at least one combustion
chamber 32; a combustor 33; one or more pistons 34; a heater
portion 35; typically a regenerator 36; a cooling portion 37 and a
power collecting unit 38. Although the stirling engine 30 is
illustrated as a beta configuration stirling engine, stirling
engine 30 could be any type of configuration, as is know for
stirling engines, including alpha, beta, gamma, rinia alpha
configuration or other stirling engine configuration.
[0035] In operation, the raw wellhead gas is transferred from
wellhead (not shown) through the gas conduit 25 and into the
combustion chamber 32 of the stirling engine 30. Once the wellhead
gas enters the combustion chamber 32, the raw wellhead gas is
ignited by the combustor 33. This ignited wellhead gas is used as
the heat source for the stirling engine 30.
[0036] Typically, the wellhead gas will be collected from a
wellhead casing (not shown) as a by-product of the collection of
oil from the well, however, wellhead gas can also be released
during the drilling and preparation of the well for the production
process and wellhead gas collected during the drilling and/or
preparation of the well could also be used and supplied through the
gas conduit 25 to the combustion chamber 32 where it is ignited and
used as the heat source to drive the stirling engine 30.
[0037] As is typical for stirling engines, the heat source is used
to transfer thermial energy to a heating portion 35 containing a
working fluid. Wellhead gas, ignited in the combustion chamber 32
by the combustor 33, forms the heat source and a portion of the
thermal energy released by the burning of the wellhead gas is
transferred to working fluid in the heating portion 35 of the
stirling engine 30. The heated working fluid then drives the
pistons 34 and the working fluid is then recirculated through the
cooling portion 37. Although the stirling engine 30 in FIG. 1 is
illustrated with a single piston 34, it is known by those skilled
in the art that some configurations of stirling engines contain
multiple piston arrangements and stirling engines with more than
one piston could be used in the present invention.
[0038] Although it is not necessary for a stirling engine to
comprises a regenerator 36, many do to improve their operation,
such as sterling engines in the beta configuration and a stirling
engine 30 may be used that does not have a regenerator 36.
[0039] The fluid in the heating portion 35, cooling portion 37 and
piston 34 is not in fluid communication with the combustion chamber
32 so the corrosive wellhead gas being ignited by the sterling
engine 30 does not to affect the internal workings of the pistons
34 of the stirling engine 30 and no combustion of gases occurs in
the pistons 34 or any other part of the stirling engine 30, with
the exception of the combustion chamber 32.
[0040] The stirling engine 30 is driven by the heat source created
by the ignited wellhead gas and the output of the stirling engine
is harnessed by the power collecting unit 38. FIG. 2 illustrates a
stirling engine 30, in accordance with the present invention, where
the displacement of the piston 34 is harnessed mechanical energy,
such as by rotating a output shaft using a rombic drive 39,
although other devices could be used to harness the mechanical
power such as a swash plate drive (not shown).
[0041] FIG. 3 illustrates a stirling engine 30, in accordance with
the present invention, wherein the displacement of the piston 34 is
harnessed to drive a generator 40 and output electrical energy. The
generator 40 introduces a load in the form of a linear alternator
coils 42, wherein the passing of magnets 44 past the linear
alternator coils 42 create an electrical current. This electrical
current can then be used either to power devices onsite or, as
shown in FIG. 3, processed through a transformer 50 and connected
to an electrical grid 55, to pass the electrical energy back to the
electrical grid 55.
[0042] FIG. 4 illustrates a further embodiment of the present
invention, for use when the supply of wellhead gas is relatively
unsteady. Energy recovery system 100 comprises: a gas conduit 25, a
compressor 110; a pressure vessel 115; a pressure regulator valve
120; and a stirling engine 30.
[0043] Some oil producing wells may produce a relatively unsteady
supply of raw wellhead gas, wherein the pressure of the wellhead
gas exiting the wellhead casing can fluctuate substantially. The
supply of raw wellhead gas can fluctuate from pressures above 2 psi
to much lower; so low that the raw wellhead gas will not move
through the gas conduit 25 or allow adequate combustion by a
combustor (not shown) of the stirling engine 30.
[0044] The raw wellhead gas is transported from the well head or
well bore (not shown) through the gas conduit 25 to the compressor
110. The compressor 110 compresses the wellhead gas to a higher
pressure and passes the pressurized wellhead gas to the pressure
vessel.
[0045] A pressure regulator valve 120 is provided in proximity to
the exit of the pressure vessel 115 to allow wellhead gas at a
predetermined pressure to be transported into a combustion chamber
(not shown) of the stirling engine 30, where the compressed
wellhead gas is ignited to drive the stirling engine 30 and the
power generated by the stirling engine 30 can be harnessed, as
described above.
[0046] Using the power recovery system 100, raw wellhead gas can be
used when the raw wellhead gas is supplied at a relatively unsteady
rate. The pressure vessel 115 stores compressed wellhead gas so the
supply of wellhead gas to the stirling engine 30 is regulated. The
size of the pressure vessel 115, tie pressure the wellhead gas is
compressed to by the compressor 110 and/or the settings of the
pressure regulator valve 120 will determine the amount of time the
stirling engine 30 can be supplied with a sufficient flow of
wellhead gas when the raw wellhead gas supplied from a wellhead
(not shown) drops below a suitable pressure.
[0047] FIG. 5 illustrates a further embodiment of the present
invention, wherein the pressure of the raw wellhead gas is greater
than required for the operation of a single stirling engine 30.
System 200 comprises a gas conduit 25; a first pressure regulator
valve 210; a first stirling engine 30A; a second pressure regulator
valve 220; and a second stirling engine 30B.
[0048] Wellhead gas is supplied to the first stirling engine 30A
and second stirling engine 30B by the gas conduit 25. The first
pressure regulator valve 210 controls the flow of wellhead gas to
the first stirling engine 30A. The remaining flow of wellhead gas
that does not pass through the first pressure regulator valve 210
will flow through the second regulator valve 220 and to the second
stirling engine 30B. In this manner, wellhead gas can be supplied
to multiple stirling engines 30A and 30B and multiple stirling
engines 30A and 30B can he used to generate power using the
wellhead gas as fuel.
[0049] Although FIG. 5 illustrates two stirling engines 30A and
30B, it will be apparent to a person skilled in the art that more
than two stirling engines could be used in the same manner
providing the supply of wellhead gas is sufficient to fuel the
additional stirling engines.
[0050] The foregoing is considered as illustrative only of the
principles of the invention. Further, since numerous changes and
modifications will readily occur to those skilled in the art, it is
not desired to limit the invention to the exact constriction and
operation shown and described, and accordingly, all such suitable
changes or modifications in structure or operation which may be
resorted to are intended to fall within the scope of the claimed
invention.
* * * * *