Note: Descriptions are shown in the official language in which they were submitted.
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SYSTEM, APPARATUS AND METHOD FOR PRODUCING A WELL
CROSS REFERENCE TO RELATED INVENTIONS
[001] This application claims priority to and relates to an earlier filed
United States
provisional application S.N. 61/524,596 which was filed in the United States
Patent and
Trademark Office on August 17, 2011.
FIELD OF THE INVENTION
[002] The invention is directed to a system, apparatus and method for
producing fluids and
gas from a wellbore.
BACKGROUND OF THE INVENTION
[003] A problem in the production of oil and gas from subsea wellbores is the
undesirable
formation of gas hydrates. A gas hydrate is a crystalline solid consisting of
molecules of gas,
usually methane, surrounded by a "cage" of water molecules. Gas hydrates have
the visual
appearance of ice. Methane hydrate is stable in ocean floor sediments at water
depths of
greater than about 300 meters. Certain temperature and pressure conditions
encourage the
formation of gas hydrates.
[004] Gas hydrates pose a problem for the oil and gas industry as more
deepwater gas enters
the supply stream. Gas hydrates may form inside pipelines or in wellbores,
slowing or
completely blocking flow of hydrocarbons. Hydrate formation is a serious
problem for
producers moving gas from offshore wells to onshore processing facilities.
Clearing plugged
lines is expensive and time-consuming, and may take as long as twenty days. It
has been
estimated that controlling and preventing gas hydrate formation costs the
industry hundreds
of millions of dollars annually. It is very important to make changes or
adjustments in
wellbores to reduce the likelihood of gas hydrate formation.
[005] In the production of oil and gas, it is sometimes necessary to employ
downhole
electrical submersible pumps to assist in moving oil from the formation to the
surface in the
wellbore. Submersible pumps are used in such operations to provide a
relatively efficient
form of "artificial lift". By decreasing the pressure at the bottom of the
well, more oil can be
produced from the well when compared with natural production. Such pumps
typically are
electrically powered and may be referred to as Electrical Submersible Pumps
("ESP").
[006] ESP systems may be subject to undesirable cavitation if excess gas is
present in the
flow stream being pumped. Shock waves caused by cavitation in pumps may damage
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moving parts within the pump. It is desirable to avoid entrained gas in
production fluids that
are to be pumped by a downhole ESP to avoid damage to pumps.
SUMMARY OF THE INVENTION
[007] A system, apparatus and method is provided for producing oil and gas
from a
wellbore within a subterranean formation. The system comprises a wellbore
lined with a
casing, the wellbore having an upper end and a lower end, the lower end of the
wellbore
being adjacent the subterranean formation. The casing is tubular in shape with
an interior
cavity. Casing is installed in sections when the well is constructed, with
each successive
section of casing installed in the drilled well being slightly smaller in
diameter than the prior
section of casing. Production tubing is positioned within the interior cavity
of the casing. A
pump may be connected to the production tubing, the pump being adapted for
lifting
hydrocarbons within the production tubing.
[008] An isolation sleeve may be positioned circumferentially outside of the
production
tubing and within the interior cavity of the casing. An inner space may be
located between
the isolation sleeve and the production tubing. An outer space also may be
positioned
between the isolation sleeve and the casing. The isolation sleeve may be
configured to
facilitate the upward movement, within the outer space, of production fluids
and gas towards
the upper end of the wellbore. Gas is separated from the production fluids,
and the isolation
sleeve may be configured to facilitate the downward movement, within the inner
space, of
production fluids toward the lower end of the wellbore.
[009] A pump may be adapted for transmission of heat to the production fluids
in the inner
space, thereby elevating the temperature of the production fluids. The system
may be
configured for transferring heat carried by the production fluids to the lower
end of the
wellbore to reduce the formation of gas hydrates in the wellbore. In general,
adding heat to
the lower end of the wellbore assists in inhibiting undesirable gas hydrate
formation.
[0010] In one specific aspect of the invention the system also comprises a
heating element
positioned to contact production fluids in the inner space. Further, a ported
bushing sub may
be employed to receive production fluids and gas from the outer space and
facilitate the
movement
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of the production fluids to the inner space. The ported bushing sub may be
positioned
adjacent a gas collection space. Production fluids and gas from the inner
space may proceed
through the ported bushing sub for separation, so that gas is accumulated in
the gas collection
space while production fluids are provided to the inner space for transport
further down into
the wellbore.
[0011] In yet another embodiment of the invention, an annular seal locator sub
may be
positioned above the gas collection space. The annular seal locator sub may be
configured
for releasing gas from the gas collection space towards the upper end of the
wellbore. A
safety valve may be positioned upon the annular seal locator sub for
controlling gas release
from the gas collection space. The ported bushing sub may be adapted for
sealed engagement
with a polished bore receptacle (a "PBR").
[0012] In one embodiment of the invention, at least one heating element is
provided upon or
adjacent the production tubing. The method may include the additional step of
transferring
heat from the heating element to the production fluids and applying such heat
towards the
lower end of the wellbore. Further, production fluids may be pumped through
the production
tubing towards the upper end of the wellbore.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] Fig. 1 shows a cross sectional view of one embodiment of the system of
the invention.
DETAILED DESCRIPTION OF THE INVENTION
[0014] A system, apparatus and method is provided that is capable of providing
heat across a
produced interval during oil and gas production that may serve to minimize or
reduce
undesirable formation of gas hydrates in the wellbore. In one embodiment the
configuration
provides a means to recycle and conserve heat generated by an electrical
submersible pump
("ESP"). Also, it may be possible in some applications to provide additional
heat downhole
by the use of one or more heating elements to apply heat to produced fluids
that are circulated
downhole, thereby minimizing the undesirable formation of gas hydrates within
or adjacent
to the wellbore interface. An isolation sleeve may be employed that extends
across the
completion interval and is sealed near the bottom in a seal receptacle,
causing the flow stream
from the wellbore to flow up the outside of the isolation sleeve. The fluids
and gas may be
separated, as further described herein. Also, such heat could assist in
producing heavy oil in
some applications, by making the heavy oil less viscous and more capable of
flow.
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[0015] In one embodiment, the configuration is capable of providing for
downhole separation
of the gas to reduce or eliminate gas from being produced through an ESP.
Producing gas
through an ESP is undesirable, as it may damage the pump by way of cavitation
or "gas
lock". The system in one embodiment may provide for the safe containment and
selective
release of gas within the wellbore by the utilization of an annular safety
valve.
[0016] Turning to Fig. 1, an example of the invention is shown. A subterranean
formation 28
contains a wellbore upper end 20 and wellbore lower end 26 (seen at the upper
and lower
portions of Fig. 1). A casing 22 extends into the wellbore and is cemented in
place with
cement 24. Production tubing 32 is shown in the central portion of Fig. 1,
extending through
the annular seal locator sub 34 and the ported bushing sub 56. The annular
seal locator sub
34 mates with polished bore receptacle 36 in a gas tight seal. A cement plug
38 seals against
the inside surface of the casing 22 circumferentially around the periphery of
casing 22.
Further, inner casing 23, is cemented in place by cement 25. The inner casing
23 mates with
polished bore receptacle 36 to form a seal.
[0017] An optional heating element 40 may be provided as shown in association
with the
production tubing 32 and in position to contact production fluids to transfer
heat to
production fluids. Electrical submersible pump (ESP) 42 also is provided in
association with
production tubing 32 and is provided to provide pumping pressure to assist in
moving
production fluids upwards within production tubing 32. An isolation sleeve 44
is provided,
and it is associated with the ported bushing sub 56. The isolation sleeve 44
separates and
defined an outer space 46 from inner space 48. The outer space receives
commingled
production fluid comprising gas and liquids, while the inner space contains
primarily only
liquid production fluids. The separation of the gas from the production fluids
will occur in
the gas collection space 58, as further discussed herein. Gas may be released
through gas
release line 60 upon opening of valve 49.
[0018] The flow of production fluids begins in subterranean formation 28 and
proceeds
through perforations 57 in lower casing joint 55. The pathway of production
fluids proceeds
along arrow 54a within inner space 48 towards the wellbore upper end 20. At
gas collection
space 58, the gas portion of the production fluids is collected, while the
liquid portion of
production fluids proceeds through the ports (not shown) of the ported bushing
sub 56
downwards towards the wellbore lower end 26 along arrow 54b into inner space
48. At point
50, the liquid portion of the production fluids within inner space 48 is in
position to collect
heat generated by the optional heating element 40 and proceed further
downwards within the
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inner space 48 to point 52. At point 52, the liquid portion of the production
fluids receive
heat from the ESP and continue to travel downwards towards arrow 54c and then
to arrow
54d. The heated liquid portion of the production fluids transmit heat to the
wellbore lower
end 26 to assist in preventing the formation of gas hydrates in the wellbore
lower end 26.
Fluids travel along the path of arrow 54e, where they change direction and
then proceed
upwards along arrow 54f into the production tubing 32. Production tubing 32
contains
release valve 47. Fluids are produced from the wellbore upper end 20 through
production
tubing 32.
[0019] In the practice of the invention, many different equipment sizes may be
employed.
However, one embodiment of the invention, as shown, employs a polished bore
receptacle 36
having a 15 inch internal diameter in the bottom of an 18 5/8 inch casing 33.
Further, the
production tubing 32 may be 4 1/2 inch in diameter in the embodiment shown in
Fig. 1.
[0020] The ported bushing sub 56 may be a triple bushing sub, also known as a
triple
connection bushing. Such a bushing comprises three connections -- a washpipe
connection
and two drillpipe connections. The ported bushing sub 56 may be run in
connection with a
backoff or packer retrieving assembly. The triple connection bushing sub may
be employed
for a bottom hole assembly requiring an inside and outside assembly. The
outside diameter is
built per specifications of the washpipe connection and the internal diameter
is determined by
the specifications of the smaller drillpipe connection.
[0021] One example of a suitable isolation sleeve 44 is of a size 11 3/4 inch
X 8 5/8 inch. A
gravel pack with perforations 57 is commonly used in such an application. A
sump packer 62
is shown near the lower portion of Fig. 1.
[0022] The invention is shown by example in the illustrated embodiments.
However, it is
recognized that other embodiments of the invention having a different
configuration but
achieving the same or similar result are within the scope and spirit of the
claimed invention.
