Note: Descriptions are shown in the official language in which they were submitted.
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RECIPROCATING PUMPING ASSEMBLY AND METHOD WITH HOLLOW
SUCKER RODS AND NO PRODUCTION TUBING
FIELD OF THE INVENTION
The present invention relates to an assembly and method for extracting fluids,
preferably crude oil, from a drilled well within a geological formation by
means of
reciprocating pumping with hollow sucker rods. In particular, the system
comprises
the use of a string of hollow centered rods, which are able to
transport/extract the
effluents to the surface through their inner bore and, at the same time, to
impart
the reciprocating axial movement in relation to the subsurface pump.
BACKGROUND OF THE INVENTION
The economical or strategic importance of oil, is evident, therefore the
possibility
of increasing the production, as well as the usable reservoirs, is extremely
attractive. However, new oil fields have not been found, and oil and gas
reservoirs
have been reduced in the last three years. In addition, the cost reduction is
a
constant existing need in all industries in order to increase the
competitivity and
profitability of the companies. In the case of oil production, the cost
reduction
increases the economically exploitable reservoirs, since oil is extracted
provided
the income is higher than the operative costs. In Argentina, where there are
many
mature oil fields exploited by means of secondary recovery where the average
cut
(water ratio in the extracted fluids) is over 90%, the idea of a productive
alternative
for reducing costs is particularly attractive.
Typically, once an underground formation capable of containing oil and/or gas
is
located, a well is drilled, and depending on the type of ground to be passed
through and the final depth to be reached, it may begin with a diameter of
about
12.1/4" (311,15 mm) in the first 200/300 mts, of 8.1/2" (215,9 mm) at a higher
depth, capable of reaching a depth of 400 mts up to 4500 mts or more. The
greater diameter allows placing a steel line (guiding line or security line)
which will
be fixed to the ground by means of a forced introduction of cement in the
annular
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space between the tube and the ground. The blow out prevention (BOP) valve
will
be located above said tubing during the drilling with the smaller diameter.
Following this drilling of smaller diameter, it is required to introduce a
tubular steel
lining, i.e. a casing of about 5.1/2" (139,7 mm) diameter extending along the
whole
well bore. As well as with the security line, the forced introduction of
cement in the
annular space between the casing and the walls of the borehole from the bottom
to a height beyond the areas of interest will allow to fix the casing once the
cement
is forged.
Following the above operation, punctures are made at pre-selected depths, in
accordance with the nature of the reservoir, which go through both the casing
wall
and the cement sheath, allowing a free access of production fluids from the
formation to the well bore.
In some regions, the pressure of the reservoir fluids itself is sufficient to
allow the
natural lift of the fluids to the surface, rendering a flowing well. However,
reservoirs
are generally not eruptive, being necessary to extract the fluids entered into
the
well in an artificial manner by means of a pumping system.
A conventional reciprocating pumping well includes, in addition to the casing,
the
production line or tubing within which the produced fluids are passed from the
bottom to the surface. At the bottom of the well and anchored in the
production
tubing, there is a reciprocating axial pump of barrel-rod type. This pump is
mechanically actuated by an oscillating lever pivotally assembled on the
surface,
connecting in one end to a driving source and in the other to a series of
solid steel
rods connected each other to form a string which extends within the well,
being
connected by its lower end to the mobile part of the deep well pump and
imparting
it the reciprocating movement of the oscillating lever. In this way, the
pumped
fluids ascend to the surface trough the annular space defined between the
production tubing and the rod string.
The solid rods movement within the production tubing involves a frictional
contact
between both, thus producing the rod and/or production tubing break and
damages to the system. This problem increases in deviated or crooked holes.
The
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high number of interventions in holes due to this problem generates high
maintenance costs and increased production losses.
In such system, the production tubing cost is a significant part of the total
investment.
The conventional pumping system with production tubing provides low pumping
efficiency due to its stretching and shortening, which occurs with the change
of
direction of the rod string between ascending and descending movement.
Another relevant disadvantage of the system is that, whenever a service on the
pump is needed in the fixed tubing system (when due to its size the pump is
fixed
to the production tubing) it is necessary to remove the rod string and the
production tubing, thus increasing the hole intervention and interruption
times, with
the corresponding rise in costs, and loss of production.
Among the attempts to reduce costs, we can mention some patents that tend to
reduce the rods' weight in order to require less energy for its operation,
although
the energy required in this system is not directly related to the loads, since
these
regenerate energy during the ascending movement. Among these patents, we can
mention the following:
AR patent No. 230316 refers to a pumping rod, essentially made of fiber glass,
with a significantly lower weight.
AR patent No. 234862 suggests the replacement of the rod string with a
fiberglass
rod string with no mutual contact, in order to achieve a lower weight of the
rods.
Other attempts have proposed the use of continuous coiled tubing in order to
replace the solid rod string. Among them, we can mention the following:
U.S. patent No. 5,667,369 (H. Cholet) proposes the replacement of the sucker
rods with a continuous coiled tubing that has a PCP type pump rotor
(progressive
cavity pump) bound to its bottom end, and wherein the corresponding stator is
bound to the base of a production tubing. In this case, the pump activation is
carried out by means of a rotating movement of the continuous tubing, lower in
weight and easy to handie, but the use of the production tubing is maintained.
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The AR published application No. 0010430 (YPF S.A.), (US N 6,186,238)
proposes to replace the combination of solid pumping rods and production
tubing
in the conventional reciprocating pumping system by a continuous coiled
tubing.
Among its advantages, this system has a fast downloading handling as well as a
fast pump extraction. The great flexibility helps its coiling, however, it
reduces the
strength to absorb compression efforts and buckling during the ascending run,
thus increasing the possibility of friction against casing walls, particularly
in deep
wells. Consequently, this system is successfully applied in shallow and low
production wells. In addition, once broken, the continuous tubing must be
bound
by welding, thus reducing the resistance against weariness in said area. This
reduction is enhanced by the amount of splices, considerably reducing the life
of
the continuous tubing that may derive in a total change of it. The continuous
tubing
system does not allow the use of vulcanized centralizers on the tubing body;
only
bayonet centralizers may be used, with no satisfactory results.
U.S. patent No. 4.476.923 (Walling), describes a coiled, composite tubing that
allows the effluents to be conducted through its internal cavity. Such
composite
tubing supports, in its bottom end, a pump mechanically actuated by means of
an
electrical engine housed in the same deep well pump casing. The engine is
electrically actuated from the surface by means of conductors extending along
and
across the composite tubing sheaths. Therefore, the composite tubing comprises
a
complex sequence of sheaths and wrappings made of different materials able to
provide the resistance required to support this particular pumping system.
In U.S. patent No. 4,089,626, the hollow rods are used to inject chemical
products
to the bottom of the well. The possibility that the well fluids may be
produced from
its interior is not mentioned. Consequently, the production line (tubing) has
not
been removed in this patent.
U.S. patent No. 4,948,003 describes a method of taking crude samples wherein
the hollow rods are used to inject chemicals, such as surfactants, that
increase the
viscous fluids mobility. However, a conventional solid rod tubing system is
also
used in this patent.
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The Chinese Patent Application 95-104622.5 describes a production system with
hollow rods that uses a flexible tube (hose) in the well head for the
derivation of
the fluids to the production tubing, accompanying the reciprocating movement
of
the rod string to the production tubing. This arrangement increases the
environmental pollution risks due to the possibility of high pressure, several
bent
parts and harsh environments that may produce a malfunction in the flexible
tube.
OBJECTS OF THE INVENTION
The main object of the invention is to provide an assembly and method for
pumping, from the underground, an effluent produced by a drilled well within a
geological formation that replaces the combination of solid sucker rods and
production tubing of the conventional reciprocating pumping system with only
one
centered hollow sucker rod string, able to raise the effluents to the surface
and at
the same time, to transmit reciprocating axial movement to the deep well pump.
An important object of the invention is to provide a simple and robust bottom
set,
able to house and anchor reciprocating pumps of any size according to the
casing
diameter.
Another relevant object of this invention is to provide a rigid well bore head
able to
vent and pack the annular space formed between the rod string and the casing
as
well as to lubricate the external wall of a hollow rod in its reciprocating
movement.
It is also an object of the invention to provide a safe production bridge to
allow the
distribution of the fluids produced from a well to the surface pipeline while
simultaneously accompanies the axial reciprocating movement of the rod.
It is an important object of the invention to provide a robust device made
from
standard elements, easy to assemble, install and handle, able to raise high
flow
rates from very deep wells, such as 90 m3/day and 2500 m dynamic height, to
totally replace the conventional reciprocating pumping system with solid rods
and
production tubing.
A further main object of the invention is to provide a device and method for
producing an effluent from a well, preferably an hydrocarbon well, which by
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of the replacement of a conventional combination of solid rods and production
tubing with a centered hollow rod, reduces the disadvantages of the prior art
and
allows a reduction in operative costs and capital.
The assembly and method of the invention have the following advantages with
respect to the prior art:
- Reduce the intervention times (pulling): once the bottom set is fixed to the
bottom
end, the pump replacements, even those of great dimensions, are performed in
just one run, due to the lack of production tubing.
- Increase the pumping efficiency due to the elimination of the elastic
stretching of
the production tubing during the reciprocating movement of the rod string and
due
to the removal of resistance by fluid friction during the ascending run.
- Reduce the elastic stretching of the rods due to lower weight of the fluid
column
and higher stiffness of the hollow rods due to having a bigger section.
- Reduce solids accumulation due to a higher fluid speed when passing through
a
smaller section.
- Reduce fluid heat loss with surrounding elements which decreases paraffin
precipitation.
- Eliminate interventions due to production tubing breaks and fishing of
sucker rods
due to frictional wear between the rod and the production tubing.
- Eliminate interventions due to a loss between anchorage of the pump and its
seating shoe.
- Eliminate fluid losses due to failures of the gaskets of the T-press, which
significantly decreases the danger of environmental pollution.
- Reduce expenses for non destructive inspections in the production tubing and
sucker rods.
- Eliminate spending on production tubing.
- Enable the use of big diameter pumps (over 2" - 50,8 mm) in wells with
5.1/2"
(139,7 mm) diameter casings and smaller (3.1/2" - 883,9 mm slim hole), as
insertable pumps (they are lowered suspended of the rod string in one run),
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which, in the conventional mechanical pumping, are pumps fixed to the
production tubing.
- Eliminate the possibility of friction between the hollow rod string and the
casing
because there is an annular space of greater size and the use of centered rods
thus avoiding the possible friction against the casing, and the subsequent
rupture,
pollution and loss in production.
SUMMARY OF THE INVENTION
The present invention relates to an assembly for extracting a fluid from a
drilled
well within a geological formation, which walls are secured by means of a
casing
that is perforated to pre-selected depth levels, wherein the assembly
comprises:
a) a stationary bottom set that provides means to anchor a deep well pump to
the casing;
b) a deep well pump with axial reciprocating movement consisting of a
stationary member and a mobile member, an anchorage system in the
bottom part and a centralizer in the upper part, these latter being integral
to
the stationary member;
c) a series of interconnected hollow rods, forming a string that extends
within
the well, which is connected by its bottom end to the mobile member of the
deep well pump, so that the interior of the pump mobile member is in fluid
communication with the interior of the hollow rod string;
d) a hollow polished rod which connects by its bottom end to the free upper
end of the hollow rod string within the well, said hollow polished rod being
linked to a system that imparts an axial reciprocating movement to the rod;
e) a production bridge linking the upper end of the hollow polished rod to the
driving pipeline, which allows the recovery of the fluid pumped from within
the hollow rods and said hollow polished rod, and
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f) a rigid head providing a gasket that packs the annular space between the
hollow polished rod and the casing, equipped with a hollow rod lubricating
device.
According to a preferred embodiment of this invention, it is hereby provided
an
assembly to pump fluid, such as, preferably a hydrocarbon, comprising:
- a stationary bottom set that houses a deep well pump. Such set preferably
consists of, from bottom to top, an anchor that allows its fixing to the
desired
depth and provides an admission orifice whereby the fluid to be pumped will
enter, two shoes providing seats for mechanical and cup anchorage of the
deep well pump, a centralizer that in combination with the anchor allows a
perfectly concentric location of the set with respect to the casing walls and
a
connector set (on-off) that allows to carry out the descending maneuvers and
the fixing of the stationary bottom set. Filters may be installed underneath
the
anchor, if needed. Preferably, although not in a limiting way, the stationary
bottom set comprises a pump housing tube (housing) and a centralizer
thereof;
- a deep well pump (reciprocating axial conventional API type) consisting of a
stationary member and a mobile member. Said pump has, in the bottom part
and integral to the stationary member, two mechanical and cup anchorages
with admission orifice of the fluid to the pump. In the upper part, the mobile
member continues in a pull tube (hollow) adapted to bind the hollow rod string
by means of the linking flow and drain tube allowing the fluid communication
from within the pump to the interior of the hollow rods;
- a linking flow tube, preferably threaded in both ends, binding the drain
tube of
the pump to the hollow rod string. Said linking tube is such that enables the
flow circulation from the inside of the pump to the interior of the hollow rod
string, and it preferably includes a drain plug that allows to empty the rod
string during the pulling operation of the pump;
- a hollow rod string with centralizers to avoid the friction against the
casing.
Said rods, preferably formed by a tubular with female threaded ends (box-
box), are preferably interconnected by means of tubular sleeves with male
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threaded ends (pin-pin) to form a string extended towards the interior of the
well. The bottom part of the string is linked to the deep well pump mobile
member through the flow linking tube, the string upper part being connected
to a hollow polished rod, such rod being linked to the device that imparts the
axial reciprocating movement to the rod string;
a hollow polished rod consisting in a, preferably but not limited to,
chromeplated hollow rod in its external wall. Such polished rod is coupled by
its bottom end to the free upper end of the hollow rod string, preferably by
means of a connecting sleeve within the well, and it prolongs outside the well
coupling itself by its upper end to the production bridge that links the
polished
rod to the surface driving tubing. Said polished rod is connected to means
that
impart the axial reciprocating pumping movement. A lubricating device is
provided for allowing the polished rod to work lubricated, said device packing
the annular space between the polished rod and the casing. Since the
production fluid flows inside the polished rod, there is no possibility of
loosing
fluids due to failure in the gasket, which significantly reduces the
environmental pollution risk;
a production bridge formed by at least two articulate rigid tubes. Said rigid
tubes are linked to each other by one end and to the hollow polished rod
and the surface driving pipeline by the free ends. This linkage is preferably
made by means of rotating joints. This arrangement, replacing the
conventional T-press, allows the distribution of the fluids produced from
within the polished rod to the surface driving pipeline, while at the same
time accompanies the polished rod reciprocating movement;
a robust head providing a side exit that communicates the annular space
formed by the rods and casing with the exterior of the well and an adaptor
in the upper part allowing the installation of a seal box that locks the
annular
space between the polished rod and the casing. In the case of 3.1/2" - 88,9
mm casing wells (slim hole), only a conventional compact T-press coupled
to the casing which provides a side exit and the seal box which packs the
annular space between the rod and the casing, will be used. In any of the
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arrangements the seal box also has a lubricating device to lubricate the
polished rod since it works in dry conditions when the produced fluid flows
inside thereof.
In addition, a method is provided to extract a fluid from a drilled well
within a
geological formation which walls are secured by means of a casing, perforated
at
selected depth levels, by the assembly of the present invention, wherein the
stationary bottom set is lowered into the well upon its termination in an
independent run, once the desired depth is reached. Next, once the stationary
bottom set is fixed to the bottom, the deep well pump, centered coupled to the
centered hollow rod string, is carried down in one run in a concentric
position with
respect to the casing walls until the stationary bottom set is reached where,
due to
the weight of the tool itself, it enters and is attached to its respective
seats within
the set. Subsequently, a hollow polished rod is connected to the free end of
the
hollow rod string above which a surface head is placed that provides a gasket
between the polished rod and the casing while lubricating it. The polished rod
is
connected to a production bridge and is driven according to a reciprocating
axial
movement, recovering the fluid pumped by the inside of the hollow rod string
and
the hollow polished rod and delivered through the production bridge to the
driving
pipeline.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is an schematic illustration of the reciprocating axial pumping
device of
the present invention.
Figure 2 shows two schematic views for two embodiments (a) and (b) of the
stationary bottom set.
Figure 3 shows a sectional schematic view of an exemplary centralizer used in
the
stationary bottom set and in the deep well pump.
Figure 4 shows a sectional schematic view of an exemplary connector set used
to
lower and fix the stationary bottom set.
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Figure 5 shows a detail sectional schematic view of an exemplary flow linking
and
drain tube that links the pump pull tube with the centered hollow rod string.
Figure 6 shows a detail sectional schematic view of an exemplary rigid head
with
the seal box and the lubricating device that packs the annular space and
lubricates
the hollow polished rod.
Figure 7 schematically shows the positions (a), (b) and (c) of the production
bridge
according to a preferred embodiment, while it accompanies the hollow polished
rod in its axial movement, from the bottom dead point to the top one.
DETAILED DESCRIPTION OF THE INVENTION
Figure 1 shows a perforation made in an effluent producing geological
formation
containing, for instance, hydrocarbons. The borehole wall is lining by a
casing tube
1. Preferably, the tube 1 is fixed or anchored to the borehole wall by a
concrete
layer injected in the annular space between the casing external face 1 and the
borehole face. At pre-selected depths zones, according to previous geological
studies, the casing and the concrete are perforated or drilled to allow the
free entry
of fluid from the reservoir. Two fluid access layers (Fl, F2) at different
depths are
illustrated in Figure 1. In this case, a multilayer exploitation is
illustrated.
In general, as shown by the scheme of Figure 1, the reciprocating axial
pumping
system of the present invention, combines a rigid well head 22 that provides a
casing venting exit 21, a hollow sucker rod string 18 with centralizers 19, a
reciprocating axial deep well pump and a stationary bottom set that allows to
anchor the reciprocating deep well pump. Once the stationary bottom set is
fixed
to the desired depth in an independent run, the deep well pump coupled to the
hollow rod string may be removed and lowered in one single run. A production
tubing is not used since the pumped fluid will rise to the surface through the
interior of the hollow rod string.
The stationary bottom set is attached to the casing 1 by means of the anchor
3.
The anchor has the necessary attachment means of the type to allow the free
flow
of fluid, so that the fluid entering the well through the layers placed above
the
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anchor may access the admission opening 2. The mechanical and in cups seating
shoes 4 and 5, respectively, are located immediately above the anchor and
forming part of the bottom set. Then, the bottom set comprises a pump housing
tube 6 and, above it there is a centralizer 7 that together with the anchor 3
keeps
the bottom set in concentric position with respect to the casing 1 in all its
extension. Finally, in the upper part of the bottom set, there is a connecting
set 8,
that is connected by its upper end to a tubing used for the descending run.
Said
connector has a "J" pin and slot system, as shown in Figures 2 and 4 and
described below, that allows to disassemble the bottom set once it is fixed to
the
desired depth and to recover the tool used for the descending run.
The deep well pump illustrated in Figure 1, is of the axial reciprocating
movement
type. Such pump comprises a stationary valve 11, a barrel or stationary member
12 and, inside thereof it has a mobile member housing the traveling valve 13
and
the piston-pull tube set 14-15. The pump is lowered integral to the bottom end
of
string formed by a series of hollow rods 18 centered and interconnected by
means
of connecting sleeves 20. A centralizer 16 located in the upper part of the
pump
stationary member 12, allows to keep the pump in a concentric position with
the
casing walls 1 easing its entry to the bottom set. Underneath the stationary
member 12 and integral to it, the pump has two anchors, mechanical 9, and in
cups 10 which, upon reaching the stationary bottom set and due to the weight
of
the tool itself, enter into and anchor in their corresponding seats within the
set.
The pump mobile member pull tube 15, is connected to the rod string 18 by
means
of the flow linking and drain tube 17 (nipple) that allows the pumped fluid to
pass
from the inside of the pump to the interior of the hollow rod string. Said
linking tube
provides a drain plug 41 as described below referring to Figure 5.
The upper free end of the hollow rod string 18, is connected to the hollow
polished
rod 24 that extends outside the well. The connection between both is carried
out by
means of the connecting sleeve 20. Such hollow rod 24 driving the fluid along
the
inner part, is suspended by the clamp and crosspiece set 25 of the system,
which by
means of a driving force (not shown) provides the reciprocating axial pumping
movement.
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The hollow polished rod 24 is connected by its upper end to the production
bridge
through a rotating joint 26. Said production bridge formed of rigid articulate
tubes 27,
is connected by its free end to the surface driving pipeline 28. The
connection
between both tubes to the driving pipeline is also carried out through the
rotating
joints 26 that allow the production bridge to accompany the reciprocating
axial
movement of the polished rod.
At the exit of the well at the surface, a rigid head 22 is threaded to the end
of the
casing tube 1. Said head provides a side exit 21 that allows the disposal of
fluids,
gases, etc. through a valve, that may spontaneously arise from the annular
space
formed between the hollow rod string 18 and the casing tube 1.
Figure 2 shows a detail view of the stationary bottom set, that is lowered to
the well
bore in an independent run upon its termination. The anchor 3, located in the
bottom
part of the set comprises an attachment system 29 and a centralizer hub 30
provided
with friction blocks 31. The wedges 33 that will attach the anchor to the
casing tube 1
are actuated by rotating the chuck 32 clockwise and applying weight first and
then
stress. The set continues upwards with the mechanical seating shoes 4 and in
cups
respectively, the pump housing tube 6, the centralizer 7 and finally the
connecting
set 8, as shown in Figure 2 (a).
The pump housing tube 6 is formed by a portion of production tubing, for
instance,
about 2.7/8" (73 mm) in diameter and about 6,5 pounds/inch (128 kg/m) in
weight.
The length of this tube will depend on the length of the pump to be lowered.
When
big pumps, above 2" in diameter, that do not run through the interior of the
housing
tube 6 are used, this element and the next upper centralizer 7 are removed
from
the bottom set that is adapted to receive pumps of any dimension, which will
depend on the size of the casing tube 1. When the size of the pump to be
lowered
is not known for certain, or when an increase in the future production is
expected,
it is recommended to use the reduced bottom set that comprises the anchor 3,
the
mechanical 4 and in cups 5 seating shoes, and the connecting set 8 as shown in
Figure 2 (b). All the elements which are part of the bottom set are in general
provided with API threaded ends and are connected to each other by standard
API
couplings 34.
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Figure 3 shows a sectional view of a centralizer, such as those identified by
7 and
16 in Figure 1, as well as the centralizer that is part of the anchor,
mentioned
above, used to centralize the bottom set and the pump. Said centralizer is
formed
by a centralizer hub 30 equipped with friction blocks 31 which are actuated by
springs 35 that keep them in permanent contact with the casing tube wall 1 in
order to guide the descent and preserve the concentric position with the
latter.
Figure 4 shows a sectional view of the connector set 8, which is located in
the
upper part of the bottom set next to the centralizer 7 and is connected by its
upper
free end to the tubing 36 used for lowering the bottom set to the interior of
the well.
Said connecting set comprises a connecting tube 37 equipped with two pins 38
transverse to the tube, and a connecting hood 39 equipped with a "J" shaped
slot
40. The tube pins 38 engage perfectly in the hood "J" shaped slot 40 to couple
the
connecting tube-hood set 8. This connector allows to drive the anchor 3
attachment means by rotating clockwise and applying weight and stress
consecutively. Once the stationary bottom set is fixed at the desired depth,
the pin
38 and "J" 40 system allow to dismantle the connecting hood 39 from the
connecting tube 37 integral to the bottom set and to recover the tool used for
lowering it.
Figure 5 shows a sectional view of the linking flow and drain tube 17 that
links the
pump pull tube 15 with the hollow rod string 18. Such linking tube consists of
a
drain plug 41 that breaks by cut effort. A javelin 42 is released from the
surface
through the string interior to reach and break the drain plug 41. This
maneuver gives
an orifice open to the annular space that allows to empty the rod string when
removing the pump. The connection 43 between the connection tube and the pump
pull tube is of flexible type that allows to displace the bending efforts of
the last pull
tube thread, wherein the bending efforts that cause the break due to fatigue
are
mostly concentrated.
Figure 6 shows a sectional view of the rigid head 22 that is threaded to the
upper end
of the casing tube 1. Such head provides a side exit 21 allowing the venting
of the
annular space between the rods and casing and an adaptor 44 that has a thread,
such as an API 2.7/8" (73 mm) thread to assemble a seal lubricating box 23 by
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means of a standard coupling 34, such as, for instance, an API 2.7/8" (73 mm)
coupling. Such adaptor is adjusted to the head body by means of a threaded cup
45.
A ring 46, such as a rubber ring, packs the adaptor against the head body. The
internal diameter of said body head offers a continuous passage to the inside
of the
casing, therefore, all the tools lowered to the well hole are passed through
the head
without disassembling it. A set of seals 47 placed within the seal box 23 and
a
lubricating element 48 adapted thereto, allow to pack the annular space at the
rod
exit outside the well and to lubricate the friction surface between the rod
and the
seals. For wells of 3.1/2" - 88,9 mm (slim hole) casings it may only
optionally be
used a conventional compact T-press coupled to the casing that provides the
side
exit and the seal box that packs the annular space between rod and casing. In
any
of the arrangements, the seal box also has a device to lubricate the polished
rod,
since it works in dry conditions when the fluid produced flows inside thereof.
Figure 7 schematically shows the positions to be taken by the articulate
production
bridge during the reciprocating axial movement of the polished rod. Schemes
(a), (b)
and (c) depict the polished rod position in the bottom dead center, midcenter,
and top
dead center.
According to a particular embodiment, even when it is not limiting, the anchor
3
used in the stationary bottom set of the present invention, was obtained from
the
modification of a Lokset Baker packing device. Such modification includes:
the
removal of the rubber section packing against the casing 1, the removal of the
seal
packing over the mandrel, the shortening of the mandrel 32 (due to the removal
of
the packing rubber) and the modification of the mandrel thread as well as the
modification of the segments that actuate the attachment mechanism to avoid
its
interlock and blocking with sand. By this way, an anchor was obtained to allow
the
free fluid flow entering the well from the layers placed above said anchor,
and the
attachment force of which is trapped inside, therefore, it does not need to
remain
stressed as the majority of the anchors used in the conventional system. The
ability of the anchor 3 to remain still and neutral allow to disassemble the
connecting set 8 and recover the tubing 36 used for lowering the stationary
bottom
set, as shown in Figure 2. For wells with 3.1/2" - 88,9 mm (slim hole)
casings, a
useful anchor that is lowered coupled on the bottom part of the deep well pump
CA 02551315 2006-06-29
and in the same run, is the 3.1/2" - 88.9 mm anchor for insert pumps, supplied
by
Harbison-Fisher, without a packing element.
According to a particular embodiment, the connecting set 8, used for this
arrangement, shown in Figure 4, is similar to the Sealing Connector by Backer
,
2.7/8" (73 mm) in diameter, which seals have been removed between the tube 37
and the hood 39 and the top end inner cone of tube 37 has been enlarged to
ease
the entry of the pump to the bottom set.
Preferably, the seating shoes 4 and 5 used in the bottom set are standard API
mechanical and in cups type, respectively.
The centralizers 7 and 16 are obtained from the centralizing block of the
packing
Lokset Backer device, as shown in Figure 3.
The rod pump used for this embodiment is an API reciprocating axial pump with
a
hollow pull tube and double mechanical anchorage 9 and in cups 10. A
centralizer
7 was added to such pump in its top part and integral to the stationary member
12,
for guiding the descent into the well and for easing in the entry to the
stationary
bottom set, as shown in Figure 1.
According to an embodiment of the present invention, hollow rods and
connecting
sleeves made by Tenaris under the name of PCPRod may be used, although not
limited to them.
Although these rods have been developed to be used with PCP progressive
openings pumps due to their higher torsion resistance and fatigue to flexo-
torsion
with constant axial load, they have also shown to be resistant to variable
axial efforts.
Recent fatigue analysis with variable axial loads carried out over the PCPRod
rod
have shown that both the rod and the bond may stand more than 10 MM cycles
without breaking. Hydraulic estimations for load losses through the interior
of the
hollow rods and their corresponding links for different flow rates up to a
maximum of
90 m3/day have also been made, the results of which showed to be similar to
those
of conventional reciprocating pumping for production tubings of 2.7/8" (73 mm)
diameter and API solid rod strings No. 76 (double telescopic strings of 7/8"
(22,2
mm) and 3/4" (19,05 mm) in diameter and No. 86 (triple telescopic strings of
1" (25,4
16
CA 02551315 2006-06-29
mm), 7/8" (22,2 mm) and 3/4" (19,05 mm) in diameter). Even though the hollow
rod
string is, in general, heavier than a solid string, the requests about the
means that
imparts the reciprocating axial movement to the rods are not significantly
modified
due to the lower weight of the fluid column (minor section) and the lack of
relative
movement between the rod and the fluid in the ascending run that eliminates
the
load losses thus compensating the higher string weight.
Preferably, the PCPRod 1000 model without jump, with an external diameter of
48
mm (1.889"), internal diameter of 34,6 mm (1.362"), wall thickness of 6,7 mm
(0.264") and 6 Kg/m (4 pounds/feet) in weight may be used and, more
preferably, the
PCPRod 1500 model with jump, external diameter of 50 mm (1.968"), body
external diameter of 42 mm (1.653"), internal diameter of 32 mm (1.259"), wall
thickness of 5 mm (0.196") and 4,9 Kg/m (3.28 pounds/ft) in weight. The rod
centralizers 19 may be, for example, Poli Phenylene Sulfide (PPS) type,
supplied by
Tenaris, vulcanized over the rod in the requested amount and diameter, not
being
limited to them.
According to a particular embodiment, the rigid head type 22 used for this
arrangement was obtained from the API DC 200 hanging head manufactured by
ABB (ex DANCO) or similar, without clamps, to which an adaptor 44 was added.
The
seal box 23 with lubricating device 48 that is an adaptation of a box
manufactured by
TULSA .
As can be seen from the above description, and in a comparative analysis in
relation to the prior art, the total elimination of the conventional
production tubing,
as well as the elimination of the solid rod string as the axis actuating the
reciprocating axial pump is emphasized first, for its replacement by a hollow
rod
string that performs both roles simultaneously. This novel configuration,
built up
from existing elements and simple modifications made therefrom allows to
obtain a
high performance reciprocating pumping system and most relevantly, easy to
install and operate, that adapts to any casing and rod pump size, which makes
it
possible to perform drillings of significantly smaller diameter than those for
conventional wells, which usually have a diameter of about 21,6 cm (8 1/2
inches).
This reduction in the well diameter will additionally mean a reduction in the
casing
17
CA 02551315 2006-06-29
tubing diameter, which entails a reduction in the drilling costs and the
materials
used.
According to an additional embodiment of the present invention, a method of
extracting a fluid from a drilled well within a geological formation is
provided, which
walls are secured by a casing, perforated at selected depth levels, by means
of
the above disclosed assembly, comprising the following steps:
a) assembling and lowering a stationary bottom set into the well, attaching
it to the casing walls at the desired depth and recovering the tool used for
the
descent;
b) building an anchoring system in the bottom end and a centralizer in the
top end of an axial reciprocating movement rod pump stationary member,
connecting the mobile end of the pump to a centralized hollow rod, wherein
such connection is of the type that enables the pumped fluid to pass from
within the pump to the interior of the hollow rod;
c) interconnecting a centralized hollow rod string by means of sleeves, to
form a string that extends into the well, until anchoring the pump in the
bottom set;
d) connecting a hollow polished rod to the free end of the hollow rod string
by means of a sleeve and suspending said polished rod of the system that
imparts the reciprocating axial movement;
e) installing a surface head that provides a venting orifice of the annular
space formed between the casing and the polished rod and a gasket
between the casing and the polished rod extension outside the well;
f) assembling the upper end of the polished rod to a production bridge
equipped with rotating joints that allow its connection to the surface driving
tubing;
g) actuating such hollow polished rod according to a reciprocating axial
movement;
18
CA 02551315 2006-06-29
h) recovering the pumped fluid that flows up from the interior of the hollow
rod string and the hollow polished rod and deliver it through the production
bridge to the surface driving pipeline.
Considering that the minimum drilling depth for exploiting hydrocarbons is 400
mts, with the possibility of reaching up to 4500 mts, the cost reduction
achieved by
using the device of the present invention will be evident for those skilled in
the art,
even if the stationary bottom set is lowered in a separate run.
It has been found that the pumping assembly and method of the present
invention
may provide an efficient extraction service for oil wells of depths up to 2500
meters
and with average flow rates of about 90 m3 oil/day.
Preferably, the pumping assembly and method of the present invention may
provide an efficient extraction service for oil wells of depths up to 2200
meters.
Preferably, the pumping assembly and method of the present invention may be
applied to pumping flow rates of about 80 m3/day of fluid, wherein the fluid
is
preferably oil.
It must be understood that the drawings and their detailed description are not
intended to limit the invention to the particular described embodiment; but on
the
contrary, they intend to encompass all modifications, equivalents and
alternatives
comprised within the spirit and scope of the present invention, as defined in
the
annexed claims.
19
