Note: Descriptions are shown in the official language in which they were submitted.
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DEVICE AND PROCESS FOR STIMULATION AND CLEANING OF A LIQUID-FILLED WELL
Description
The present invention relates to a device for cleaning a liquid-filled well
comprising a tubular
vessel, the interior of which contains at least one combustion chamber and at
least one hollow
chamber arranged in longitudinal succession, the combustion chamber being at
least partly
filled with a fuel and having an igniter, and the vessel having at least one
inflow orifice through
which well fluid can flow from the outside into the vessel. The invention
further relates to a
process for stimulating and cleaning a liquid-filled well using the inventive
device.
In the production of fluids such as mineral oil or natural gas from
underground rock strata, the
productivity of a production system depends to a high degree on the
permeability of the rock
strata which adjoin the well. The more permeable these rock strata, the more
economically a
deposit can be operated. Both in the development and during the production
from a deposit,
there may be a reduction in permeability and hence adverse effects.
In the production of wells, both for production and for injection wells, there
may be slurrying of
the porous rock strata during the drilling and cementing operation, such that
the permeability
falls. Moreover, there is a change in the stress, pressure and deformation
state of the rock in the
course of drilling, the result of which is that zones of elevated density and
low permeability form
in a circle around the well. During the operating phase of the well,
paraffins, asphaltenes and
high-viscosity tars are frequently deposited in the rock, these reducing the
productivity of the
well.
The best-known methods for counteracting a reduction in the permeability of
the well region
include various perforation technologies, vibration and heat treatment, the
use of chemically
active substances and swabbing. In one kind of perforation technology, gas
generators which
are operated with solid fuels are used. They are designed as encased or
unencased explosive
charges and, after ignition, generate hot gases which result in a pressure
rise in the well and the
adjacent rock strata. Typically, gas generators are used in the well at the
level of the production
zone in order to cause new perforations in the rock or widen existing
perforations owing to the
pressure rise.
Russian patent specification RU 2311529 02 discloses a process for well
stimulation by means
of a gas generator in oil and gas production. The device includes tubular
cylindrical explosive
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charges, ignition charges and a geophysical cable, called a logging cable,
with securing
elements for the explosive charges. The burnoff of the cylindrical explosive
charges in the well
results in thermal gas treatment and compressed air treatment of the rock. If
a perforation has
been conducted beforehand, the perforation channels are widened and cleaned,
and cracks
form in the rock.
The document RU 2178065 Cl discloses a further gas generator which is used in
liquid-filled
wells. The gas generator comprises fuel charges which, when they burn off,
generate hot gas
which escapes into the well fluid surrounding the gas generator. The liquid is
heated and begins
to boil. On completion of the thermal gas treatment, valves in the gas
generator are opened,
such that liquid can flow rapidly into the hollow interior thereof. This
causes a rapid pressure
drop in the already boiling liquid, resulting in explosive vaporization of the
liquid. This generates
new orifices in the rock and widens existing orifices.
The document RU 2211313 Cl likewise describes a hollow gas generator which is
intended,
after a thermal gas treatment of the well fluid surrounding it, to accommodate
the latter in the
hollow interior thereof. The interior of this gas generator is divided into
several chambers by
membranes. The well fluid first flows into a first chamber. The pressure which
builds up destroys
the membrane, and the liquid flows into the next chamber. This causes a
sequence of pressure
pulses which lead to the formation of new and widened cracks and orifices in
the rock.
Even though several approaches to well stimulation are already known, there is
still a need for
improvement and enhanced efficiency in the production of mineral oil or
natural gas from
underground deposits.
It was an object of the present invention to provide a device and a process
for well stimulation,
by means of which the permeability of the rock can be improved in a targeted
and efficient
manner around a region of the well. The device should be producible in a
simple manner in
terms of construction and inexpensively.
This object is achieved by the subject matter of the invention as described in
claim 1. Further
advantageous embodiments of the invention can be found in the dependent
claims. A further
part of the subject matter of the invention is specified in process claim 11
and the claims
dependent thereon.
The inventive device for cleaning a liquid-filled well comprises a tubular
vessel, the interior of
which contains at least one combustion chamber and at least one hollow chamber
arranged in
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longitudinal succession, the combustion chamber being at least partly filled
with a fuel and
having an igniter. The vessel has at least one inflow orifice through which
well fluid can flow
from the outside into the vessel. The at least one inflow orifice is provided
with a closure device
comprising a closure element which loses its integrity on exceedance of a
given temperature,
such that the closure device opens.
The process according to the invention for stimulation and cleaning of a
liquid-filled well
comprises the following steps:
(a) introducing an inventive device into the well,
(b) igniting the fuel in the at least one combustion chamber,
(c) thermally opening the closure element of the at least one inflow orifice,
such that well
fluid can flow into the at least one hollow chamber,
(d) depending on the specific configuration of the device, optionally closing
the at least one
inflow orifice, and
(e) withdrawing the device from the well.
The vessel is preferably secured to a geophysical cable, which is also
referred to as a "logging
cable". With the aid of this, the vessel can be lowered from the surface of
the well into the well
by known means such as a hoist, and be removed again therefrom.
In a preferred embodiment of the process according to the invention, in step
(a), the device is
positioned in the well such that the combustion chamber is at the level of the
perforation region
of the production zone. The perforation region is understood here and
hereinafter to mean the
region of a production zone in which perforation holes and perforation
channels are already
present. Frequently, the axial extent of the perforation region corresponds to
the thickness of
the rock stratum from which the fluid, for example mineral oil or natural gas,
is to be produced.
It is additionally preferable when, step (c) is preceded by positioning of the
device in the well
such that the at least one inflow orifice is at the level of the perforation
region of the production
zone.
In a further advantageous embodiment of the process according to the
invention, step (c) is not
initiated until the temperature of the outer wall of the inventive device in
the region of the at least
one combustion chamber has cooled to the boiling temperature of the well fluid
in this region.
The time interval between the ignition of the fuel in the combustion chamber
and the cooling of
the outer wall below the boiling temperature of the well fluid can already be
estimated prior to
the use of the device. An exact temperature determination is not required.
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The tubular vessel may have a one-piece or a multipart design. The outer wall
thereof is
manufactured from a material which withstands the pressure and temperature
stresses during
the burnoff of the fuel. The choice of the material and configuration
parameters, such as the wall
thickness, depend on factors including the conditions in the well provided for
the use, and on the
properties and the amount of the fuel used.
Firstly, the vessel should be stable under the use conditions required;
secondly, very good heat
transfer is desired from the interior of the vessel to the outer wall thereof,
in order to be able to
utilize the energy generated by the burnoff of the fuel in a very efficient
manner.
In a preferred configuration of the invention, the outer wall of the vessel is
manufactured from a
steel, especially from a high-strength, ductile steel. The inventive vessels
used are more
preferably pipes as typically used for production of oil or gas. Such pipes
are usually
manufactured from steel with an internal diameter of 8 to 40 cm and a length
of 1 to 15 m. The
wall thickness thereof is typically 1 to 10 mm. The diameter is advantageously
selected such
that it is 10% to 30% less than the internal diameter of the well in the
region in which the device
is used.
The vessel preferably has a circular cross section. However, the invention
also covers other
cross-sectional shapes, in which case the external diameter is understood to
mean the greatest
distance between two points on the cross-sectional area.
In the interior of the vessel, there is at least one combustion chamber at
least partly filled with a
fuel. The fuel may be present in the combustion chamber in different forms,
for example as a
solid body, pasty mass or finely divided bulk material. The solid body may
have been produced,
for example, by pressing with or without binder.
In preferred configurations of the invention, the fuel used is a
metallothermic mixture.
"Metallothermic mixtures" refer here and hereinafter to mixtures of metals
with metal oxides
which, after activation of the redox reaction, are converted exothermically to
form the metal
originally present in the metal oxide. According to the fuel used, the burnoff
in the interior of the
combustion chamber can give rise to temperatures well above 1000 C.
Particularly preferred
fuels are a subgroup of the metallothermic mixtures in which aluminum is used
as a reaction
partner of the metal oxides. Such mixtures are referred to hereinafter as
"aluminothermic".
Especially preferred are mixtures comprising aluminum as a reducing agent and
CuO, Fe0,
Fe203, Fe304, Ti02, Cr203 and/or Si02 as an oxidizing agent. Such
aluminothermic mixtures are
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inexpensive compared to other metallothermic mixtures and cover a wide use
range with
respect to the ignition temperature, the maximum temperature which evolves in
the course of
burnoff of the fuel, and the burnoff rate.
"Thermite" refers hereinafter to a mixture of iron(III) oxide and aluminum
which is produced by
and can be purchased from, for example, Elektro-Thermit GmbH & Co. KG
(Halle/Saale). The
temperature range which arises as the thermite reaction proceeds and the
reaction enthalpy
which is released can be adjusted by appropriate selection of the reaction
partners and
optionally the addition of additives. Patent specification RU 2291289 02
discloses, as well as
the abovementioned thermite mixtures, further metallothermic mixtures such as
nickel(11) oxide
and magnesium, iron(II1) oxide and silicon, chromium(III) oxide and magnesium,
molybdenum(VI) oxide and silicon and aluminum, vanadium(V) oxide and silicon.
The burnoff of
these mixtures can give rise to temperatures up to 2500 C. A further class of
metallothermic
mixtures including iron oxide, aluminum powder, alumina and a metal phosphate
binder is
known from document RU 2062194 Cl. These mixtures have a comparatively low
specific
exothermicity and a maximum temperature in the course of burnoff of about 1930
C.
In the combustion chamber, there is additionally at least one igniter for
ignition of the fuel. The
choice of igniter depends on the fuel used. For example, it is possible to use
electrical igniters
such as electrical light arc igniters or spiral igniters, or chemical
igniters, provided that they have
sufficient activation energy. Suitable chemical igniters are, for example,
mixtures ignitable at
temperatures below the ignition temperature of the fuel. Examples of suitable
igniters are
mixtures of (proportions by mass in percent in brackets):
- Si02/ Mg (55 / 45),
- Mn02/ Al dust / Al dust / Mg (68 / 7.5 / 7.5 / 17),
- Ba02/ Mg (88 / 12).
These mixtures are ignited with the aid of electrical pulses, for example by
the abovementioned
electrical igniters. The electrical igniters are preferably activated by means
of a conductive cable
which is conducted from the surface of the well to the electrical igniter
along the logging cable or
integrated within the logging cable.
The longitudinal dimension of the combustion chamber is more preferably
selected such that it
corresponds to the axial dimension of the well through the perforation region.
In addition, within the vessel, there is at least one hollow chamber suitable
for accommodating
well fluid. The combustion chamber and hollow chamber are arranged in
longitudinal
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succession, "longitudinal" being understood to mean the direction of the axis
of the tubular
vessel. Terms used hereinafter such as "top", "above", "bottom", "below"
relate to the alignment
of the vessel in typical vertical wells. The hollow chamber and combustion
chamber may directly
adjoin one another, with or without a separating element between them. It is
also possible for
further chambers to be provided between the combustion chamber and the hollow
chamber.
The examples are used to illustrate preferred embodiments in detail below.
According to the invention, the tubular vessel has at least one inflow orifice
through which well
fluid can flow into the vessel from the outside. The inflow orifice is
provided with a closure
device which in turn comprises at least one closure element. In terms of its
construction and
material selection, the closure element is designed such that it loses its
integrity on exceedance
of a given temperature, such that the closure device opens.
In a preferred configuration of the invention, the closure device comprises,
as well as the
closure element, a further component which closes the inflow orifice, more
particularly a plug
present in the inflow orifice. The closure element connects the inflow orifice
to the further
component. As soon as the closure element is exposed to a temperature
exceeding a given
limit, the closure element loses its integrity, and the further component can
move out of the
inflow orifice under the pressure of the adjacent well fluid, such that the
liquid passes into the
vessel. In this configuration, the closure element is preferably a weld seam
or an adhesive
bond.
In a further preferred configuration of the invention, the closure device
consists merely of the
closure element, preferably in the form of a plug which closes the inflow
orifice, loses its integrity
on exceedance of a given temperature limit and as a result opens the inflow
orifice. Such a
closure element is advantageously manufactured from a plastic or a metal, and
the material is
selected such that its melting point corresponds to the given temperature
limit. Suitable
materials are, for example, plastics having a melting temperature within the
range from 150 C to
500 C or aluminum alloys having melting temperatures within the range from 600
C to 800 C.
In embodiments of the invention in which several inflow orifices are present,
each is provided
with a closure device. The closure devices may also have a coherent design,
for example in the
form of a lining of the inner wall of the vessel which extends over several
inflow orifices and is
manufactured from a material which, on exceedance of the given temperature
limit, loses its
integrity. The number of inflow orifices is preferably from 1 to 10. The total
cross-sectional area
of all inflow orifices together is preferably at least as great as the cross-
sectional area of the
interior of the hollow chamber.
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In some embodiments of the inventive device, separating elements are used to
separate
adjacent chambers from one another. The separating elements preferably extend
over the
entire inner cross section of the vessel and run essentially at right angles
to the longitudinal axis
of the vessel. Particularly preferred separating elements are disk-shaped or
cylindrical
structures made of plastic or metal, the external diameter of which is
slightly greater than the
internal diameter of the vessel. A combustion chamber in this case can be
produced, for
example, by first introducing fuel into the vessel and then pressing a
separating element into the
vessel, such that the combustion chamber is closed.
In one configuration of the invention, the entire separating element is
manufactured from a
material which, on exceedance of a given temperature, loses its integrity. The
effect of the
thermal evolution in the course of burnoff of the fuel in this case is that
the entire separating
element loses its integrity. In a further configuration, only the means by
which the separating
element is secured in the tubular vessel are manufactured from such a
material. In this case, in
the course of burnoff of the fuel, only the securing of the separating element
loses its integrity,
such that the separating element is freely mobile within the vessel. Materials
suitable for
production of the separating elements or of the securing means thereof for
this embodiment are,
for example, plastics having a melting temperature within the range from 150 C
to 500 C or
aluminum alloys having melting temperatures in the range from 600 C to 800 C.
In a preferred configuration of the inventive device, the vessel is configured
as a one-piece pipe
in which the chambers are separated from one another by separating elements
extending over
the entire pipe cross section within the pipe.
In a further preferred configuration of the inventive device, the vessel
comprises two or more
tubular vessels which form the chambers or parts of the chambers and the ends
of which are
connected via connecting elements. The vessels may be connected via connecting
elements in
different ways at the ends thereof. A manner which is simple to implement
involves screwing the
vessels together by means of the connecting elements, for example by providing
the vessels
with an outer screw thread onto which a tubular connecting element with an
inner screw thread
is screwed. A further means of connection results from provision of each of
the ends of the
vessels to be connected with a flange as a connecting element, and connection
of the flanges to
one another, for example by screw connection. It is also easily possible to
use swivel nuts or a
bayonet mount, for example, to establish connections between the tubular
vessels.
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To perform the process according to the invention for stimulation and cleaning
of a liquid-filled
well, an inventive device is first introduced into the well. The device is
preferably positioned in
the well such that the combustion chamber is at the level of the perforation
region of the
production zone. Subsequently, the fuel in the combustion chamber is ignited.
Proceeding from
the igniter, the fuel in the combustion chamber burns off, forming a reaction
front which passes
through the combustion chamber in the course of burnoff. In a preferred
variant of the process
according to the invention, the vessel is pulled upward or lowered downward
continuously at a
speed corresponding to the speed of the reaction front in the segment of the
vessel in the
process of burnoff. The evolution of heat strongly heats the well fluid
surrounding the device in
the region of the combustion chamber in the process of burnoff, preferably
within temperature
ranges of the boiling point thereof. The hot fluid and the vapor which forms
clean the adjoining
perforation region of the well.
As soon as the reaction front reaches the region of the combustion chamber
where the closure
element is present, the closure element loses its integrity due to the
increase in temperature in
the environment thereof. This thermal opening of the closure element opens the
at least one
inflow orifice of the vessel, and well fluid flows into the vessel, more
particularly into the hollow
chamber. Finally, the device is withdrawn from the well. The arrangement and
configuration of
the inflow orifices and optionally the closure elements thereof ensures that
the well fluid
accommodated within the vessel remains enclosed within the vessel while it is
being withdrawn
from the well.
In a preferred embodiment of the inventive device, the combustion chamber is
at the lower end
of the tubular vessel. The inflow orifice with its closure device is arranged
at the lower end of the
tubular vessel. The hollow chamber is arranged above the combustion chamber;
it preferably
reaches upward as far as the upper end of the vessel. In this configuration of
the device, it is
advantageous when the igniter is arranged within or at the fuel at the upper
end of the
combustion chamber. The igniter is more preferably present in the upper
quarter of the fuel-filled
volume of the combustion chamber. The hollow chamber may directly adjoin the
combustion
chamber. The hollow chamber is preferably separated by a separating element
from the
combustion chamber, said separating element being manufactured from a material
which, when
the fuel burns off, loses its integrity. In both cases, after the burnoff, in
addition to the hollow
chamber, the part of the combustion chamber not filled with burnoff residues
is also available for
accommodation of well fluid.
In a further preferred variant of this embodiment, the inflow orifice is
configured so as to narrow
from the inside outward, more preferably in the form of a cone. The closure
device comprises a
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plug whose shape is matched to the inflow orifice and which is provided with a
securing device
which restricts the axial movement thereof away from the inflow orifice. The
plug is connected in
a thermally releasable manner to the inside of the end by virtue of a closure
element, especially
a weld seam or adhesive bond. The plug is manufactured from a material which
withstands the
temperatures that exist in the course of burnoff of the fuel. Only the closure
element loses its
integrity when the fuel is burnt off and releases the plug.
In a particularly preferred configuration, the securing device comprises a
connecting element
and a weight element which is outside the vessel. The connecting element is
fixed to the weight
element and the plug. The connecting element may be rigid or flexible and is
manufactured from
a material which withstands the temperatures which exist in the course of
burnoff of the fuel. A
rigid connecting element used is preferably a pole, and a flexible connecting
element used is
preferably a chain or a rope. The connecting element is preferably
manufactured from a high-
strength steel. The radial extent of the weight element at least in one
spatial direction is greater
than the diameter of the inflow orifice on the outside of the lower end of the
vessel. This ensures
that the weight element cannot get inside the vessel.
To perform the process according to the invention according to this
configuration, the tubular
vessel is first introduced into the well and preferably positioned such that
the combustion
chamber is at the level of the perforation region of the production zone.
Subsequently, the fuel
in the combustion chamber is ignited. Proceeding from the igniter, the fuel
burns off within the
combustion chamber, forming a reaction front which runs downward through the
combustion
chamber in the course of burnoff. If a separating element is present between
the combustion
chamber and the hollow chamber, it loses its integrity owing to the thermal
evolution in the
course of burnoff of the fuel. As soon as the reaction front reaches the lower
region of the
combustion chamber where the closure element is present, the latter loses its
integrity owing to
the temperature increase in the environment thereof. The plug becomes detached
from the
inflow orifice and opens it, such that well fluid can flow into the hollow
chamber. On completion
of the inflow operation, the vessel is withdrawn from the well in the upward
direction. Under the
action of gravity, the plug falls back into the inflow orifice under its own
weight and closes it.
This effect may be enhanced by the weight of the weight element, which pulls
downward on the
plug during the withdrawal of the vessel. The well fluid which has flowed into
the vessel is
enclosed therein and can be conveyed to the surface. This inventive
configuration is particularly
suitable for cleaning the well bottom.
In a further preferred embodiment of the inventive device, the combustion
chamber is at the
lower end of the tubular vessel. Above the combustion chamber is arranged the
hollow
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chamber. Above the hollow chamber in turn is arranged an orifice chamber which
is separated
from the hollow chamber by a separating element. In the wall of the orifice
chamber, there is at
least one inflow orifice with its closure device. In the orifice chamber, a
further igniter and further
fuel are present, said fuel, when it burns off, generating a temperature at
which both the at least
one closure element and the separating element from the hollow chamber lose
their integrity.
In this variant, the combustion chamber is more preferably filled completely
with fuel, and the
igniter is present in or at the fuel at the upper end of the combustion
chamber. The hollow
chamber may directly adjoin the combustion chamber. The hollow chamber is
preferably
separated from the combustion chamber by a separating element manufactured
from a material
which, when the fuel burns off, loses its integrity. In both cases, after the
burnoff, in addition to
the hollow chamber, the part of the combustion chamber not fulfilled by
burnoff residues is
available for accommodation of well fluid. More preferably, the orifice
chamber is at the upper
end of the tubular vessel and the at least one inflow orifice is provided at
the upper end of the
orifice chamber. Most preferably, several inflow orifices are provided.
To perform the process according to the invention, the inventive device is
first introduced into
the well and preferably positioned such that the combustion chamber is at the
level of the
perforation region of the production zone. Subsequently, the fuel in the
combustion chamber is
ignited. Proceeding from the igniter, the fuel burns off in the combustion
chamber, forming a
reaction front which passes downward through the combustion chamber in the
course of
burnoff. If a separating element is present between the combustion chamber and
the hollow
chamber, it loses its integrity owing to the thermal evolution in the course
of burnoff of the fuel.
On completion of the burnoff in the combustion chamber, the further fuel is
ignited with the aid
of the further igniter in the orifice chamber. The burnoff generates a
temperature at which both
the closure elements and the separating element from the hollow chamber lose
their integrity.
The inflow orifices are opened as a result, and well fluid flows into the
interior of the vessel. In
this embodiment, the closure of the inflow orifices after the inflow of the
well fluid is not required,
since the inflow orifices are at the upper end of the vessel. The well fluid
is enclosed within the
vessel and can be withdrawn from the well in the upward direction with the
vessel.
In preferred configurations, the igniters of the combustion chamber and of the
orifice chamber
are ignitable independently of one another. This enables offset phases of well
stimulation by
burnoff of the fuel in the combustion chamber on the one hand and of cleaning
of the well by
inflow of dirty well fluid on the other hand. The two phases can be matched
flexibly to the
respective local circumstances. The heat released to the well fluid during the
burnoff phase
generally leads to heating of the well fluid above its boiling point and
commencement of boiling
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thereof. In a preferred embodiment of the process according to the invention,
the thermal
opening of the inflow orifices is not initiated until the temperature of the
outer wall of the device
in the region of the at least one combustion chamber has cooled down to the
boiling
temperature of the well fluid in this region.
In a further preferred embodiment of the inventive device, the at least one
inflow orifice with its
closure element is within a middle region of the vessel. A stop element is
arranged below the at
least one inflow orifice on the outside of the vessel. A shell tube which is
arranged around the
vessel at the upper end of the vessel is secured by a thermally releasable
securing element on
the outer wall of the vessel. An upper combustion chamber present at the level
of the securing
element in the vessel comprises a further igniter and further fuel which, when
it burns off,
generates a temperature at which the securing element loses its integrity.
For performance of the process according to the invention, the inventive
device is first
introduced into the well and is preferably positioned such that the combustion
chamber is at the
level of the perforation region of the production zone. Subsequently, the fuel
in the combustion
chamber is ignited. Proceeding from the igniter, the fuel burns off in the
combustion chamber.
After the burnoff of the fuel in the combustion chamber, the closure element
of the at least one
inflow orifice is thermally opened, such that well fluid flows into the
interior of the vessel. Since
the at least one inflow orifice is in the middle region of the vessel, it is
advantageous to close the
inflow orifice prior to the withdrawal of the device from the well. This is
done by igniting the
further fuel in the upper combustion chamber. The burnoff of the further fuel
heats the outer wall
of the vessel in the region of the upper combustion chamber to such an extent
that the securing
element on the outer wall loses its integrity. The outer tube is released and
slides downward
owing to gravity along the outer wall of the vessel down to the stop element.
The length of the
shell tube is such that all inflow orifices are closed when the shell tube
rests on the stop
element. Since the upper combustion chamber is equipped with its own fuel and
igniter, the
inflow orifices can be closed independently in time from the burnoff operation
and the inflow of
the well fluid. After the closure of the inflow orifices, the well fluid is
enclosed in the interior of
the vessel and can be withdrawn from the well in the upward direction with the
vessel.
The securing element which secures the shell tube on the outer wall of the
vessel may be
applied to the outer wall on the outside, for example as an adhesive bond or
weld bond. In a
further configuration, the securing element is at least one pushfit or screw
connection between
the shell tube and the wall of the vessel, which is manufactured from a
material which, on
exceedance of a given temperature limit, loses its integrity, for example a
plastic. In a further
configuration, a support ring is secured in or on the outer wall of the
vessel, which holds the
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shell tube. In this case, the support ring is manufactured from a material
which, on exceedance
of a given temperature limit, loses its integrity, for example a plastic.
The stop element is fixed to the outer wall of the vessel, for example by
screw connection, rivet
connection or weld connection. It is configured such that it can absorb the
forces which act on it
on impact of the shell tube sliding downward, without damage to the stop
element. The stop
element is preferably manufactured from a steel. In a preferred configuration,
the stop element
is a component which extends radially outward in the form of a collar from the
outer face of the
vessel. The collar may consist of individual components or be configured as a
surrounding
component.
In a first variant of this embodiment, the combustion chamber and the hollow
chamber are
arranged from the bottom upward between the lower end of the vessel and the
upper
combustion chamber, the combustion chamber being separated from the hollow
chamber by a
separating element. In addition, the at least one inflow orifice is arranged
at the upper end of the
combustion chamber and the igniter at the lower end of the combustion chamber.
The fuel is
selected such that, after ignition, it burns off from the bottom upward and
the burnoff of the fuel
at the upper end of the combustion chamber generates a temperature at which
both the at least
one closure element and the separating element from the hollow chamber lose
their integrity. In
this variant, the inflow orifices are opened owing to the burnoff of the fuel
in the combustion
chamber as soon as the reaction front reaches the region of the inflow
orifices.
In a second variant of this embodiment, the combustion chamber, a separation
chamber, an
orifice chamber and the hollow chamber are arranged from the bottom upward
between the
lower end of the vessel and the upper combustion chamber. The hollow chamber
is bounded at
the top and bottom by separating elements. The orifice chamber is arranged at
the level of the
at least one inflow orifice and has a further igniter and further fuel which,
when it burns off,
generates a temperature at which both the at least one closure element and the
at least one
separating element from the hollow chamber lose their integrity. In this
variant, the burnoff of the
fuel in the combustion chamber and the opening of the inflow orifices can be
controlled
independently in terms of time. This is enabled by the separation chamber
comprising no fuel,
thus ensuring thermal decoupling between fuel in the process of burnoff and
the further fuel in
the orifice chamber. The separation chamber can be separated by separating
elements from the
combustion chamber and the orifice chamber. The separation chamber may also be
a region of
the combustion chamber not filled with fuel.
CA 02893313 2015-06-01
13
In a third variant of this embodiment, the hollow chamber, the combustion
chamber and a
separation chamber are arranged from the bottom upward between the lower end
of the vessel
and the upper combustion chamber. The hollow chamber is separated from the
combustion
chamber by a separating element. The at least one inflow orifice is arranged
at the lower end of
the combustion chamber. The fuel in the combustion chamber is selected such
that, when it
burns off in the lower end of the combustion chamber, it generates a
temperature at which both
the at least one closure element and the separating element from the hollow
chamber lose their
integrity. As in the aforementioned variant, the separation chamber may be a
separate chamber
separated with separating elements, or be implemented as part of the
combustion chamber
unfilled with fuel. In this variant, the separation chamber fulfills the
function of thermal
decoupling of the combustion chamber and of the upper combustion chamber.
In a development of the invention, the thermal opening of the inflow orifices
is brought about by
an explosive charge. The explosive charge may be embedded within the fuel and
may ignite
owing to the evolution of heat. In a preferred embodiment, the explosive
charge is used instead
of the fuel and is ignited by a separate igniter. This configuration variant
is advantageous
especially in the case of embodiments with a separate orifice chamber. In
configurations of the
inventive apparatus with an explosive charge, the at least one inflow orifice
and the closure
device thereof are configured such that the closure element is forced out of
the inflow orifice by
the pressure and temperature rise after the explosion. In an advantageous
configuration, the
inflow orifice is configured so as to widen from the inside outward, more
preferably in the form of
a cone. Any separating elements present should be configured such that they
lose their integrity
after the explosion owing to the pressure and temperature rise.
The inventive device can be manufactured beforehand in individual parts and be
transported to
the well, for example individual pipe sections which are filled with fuel or
which form hollow
chambers. On site, the individual parts can simply be assembled and matched to
the specific
demands, for example by screwing together an appropriate number of pipe
sections as
required. Lengths of individual pipe sections from one to three meters are
preferable from a
manufacturing point of view and with regard to simple transport to the well.
The total length of
the device depends on the respective demands and may, for example, be from two
to about fifty
meters. The device can be introduced into the well and withdrawn again
therefrom by known
means such as a hoist and logging cables.
As well as the preferred embodiments mentioned, the invention also encompasses
further
configurations, for example combinations or modifications of the embodiments
described.
CA 02893313 2015-06-01
14
The inventive device is notable for a simple construction, which is
inexpensive to produce and
easy to employ. A majority of the components can be reused repeatedly. The
device can be
manufactured in advance, optionally in individual parts, and be stored over a
prolonged period
without any problem. Especially in the case of use of an aluminothermic
mixture as a fuel, no
potentially harmful gases escape in the course of burnoff of the fuel.
In the course of performance of the process according to the invention, the
well fluid which
surrounds the device in the region of the combustion chamber in the process of
burnoff is
strongly heated. The well fluid begins to boil and at least partly vaporizes.
The hot liquid and the
vapor which forms penetrate into the perforation channels and generate
turbulences and
pressure pulses in the rock. This leaches encrustations and/or high-viscosity
deposits out of the
rock and thus cleans the perforation channel. This effect is enhanced as soon
as the inflow
orifices are opened and the pressure in the region close to the inflow
orifices falls drastically.
The soil detached is discharged from the perforation orifices into the well
fluid, absorbed into the
interior of the inventive device and transported from the well to the surface.
The process according to the invention brings about controlled and efficient
stimulation and
cleaning of the perforation region of the production zone. As a result, the
fluids to be produced,
such as mineral oil or natural gas, can again flow and be produced more easily
through the
perforation channels into the well.
The drawings hereinafter further illustrate the invention, though the drawings
should be
understood as schematic diagrams. They do not constitute any restriction of
the invention, for
example with respect to specific dimensions or configuration variants of
components. For the
sake of better illustration, they are generally not to scale, particularly
with respect to length and
width ratios. The figures show:
fig. 1: embodiment of an inventive device with an inflow orifice at the
lower end of the vessel
fig. 2: embodiment of an inventive device with an inflow orifice at the
upper end of the vessel
fig. 3: embodiment of an inventive device with an inflow orifice in the
middle region of the
vessel
fig. 4: variant of the embodiment with an inflow orifice in the middle
region of the vessel
fig. 5: variant of the embodiment with an inflow orifice in the middle
region of the vessel
List of reference numerals used
... well
CA 02893313 2015-06-01
11 ... lining
12 ... perforation orifices
13 ... perforation channels
14 ... production zone
15 ... well bottom
16 ... well fluid
... logging cable
21 ... tubular vessel
22 ... pipe segment
23 ... segment connector
24 ... separating element
... hollow chamber
26 ... separation chamber
... combustion chamber
31 ... fuel
32 ... igniter
33 ... reaction front
34 ... residue
... orifice chamber
41 ... inflow orifice
42 ... closure device
43 ... closure element
44 ... plug
... securing device
46 ... weight element
47 ... connecting element
48 ... further fuel
49 ... further igniter
... upper combustion chamber
51 ... further fuel
52 ... further igniter
53 ... shell tube
54 ... securing element
... stop element
Figs. 1 to 5 show schematic section drawings of a well in an underground
deposit. The well 10
is provided with a lining 11, for example a steel pipe. The lining 11 prevents
loose rock adjoining
CA 02893313 2015-06-01
16
the well from falling into the well and formation fluids which are typically
under pressure, such as
formation water, from breaking through into the well in large volumes. The
lining 11 has several
perforation orifices 12. Known processes such as ball perforation or jet
perforation produced
perforation channels 13 in the production zone 14. Through the perforation
channels 13, fluids
to be produced, for example natural gas or mineral oil, flow through the
perforation orifices 12
into the well 10 and can be produced to the surface.
The inner wall of the lining 11 has a cylindrical or stepwise cylindrical
configuration with a
circular cross section. In the case of a stepwise cylindrical configuration,
the diameter of the
circular cross section decreases stepwise in the axial downward direction. The
tubular vessel 21
is connected via a suspension system to the logging cable 20, which can be
moved by means of
a hoist at the surface. The latter is not shown in the figures; corresponding
devices are known to
those skilled in the art. The hoist can be used to move the vessel 21 in the
well 10 in axial
direction. The outer diameter of the vessel 21 is preferably 10% to 30% less
than the internal
diameter of the lining 11 in the region of the production zone 14.
Figs. la to 1d show a first preferred embodiment of an inventive device for
cleaning a liquid-
filled well. A tubular vessel 21 is secured by means of a suspension system to
a logging cable
20. The vessel 21 is configured as a multipart pipe, of which the figure shows
two pipe
segments 22. The pipe segments 22 are connected to one another via segment
connectors 23,
for example by flange connections or screw connections. The pipe segments 22
can be
produced from steel pipes as typically used in mineral oil production and
referred to as "tubing",
for example of the H-40, C-75, N-80 or P-105 type.
From the inner face of the lower end, a combustion chamber 30 extends in the
upward direction,
this being filled by a fuel 31 and being concluded at the top by a separating
element 24. The fuel
is preferably an aluminothermic mixture which comprises the components Al,
FeO, Fe203,
Fe30.4 and/or Si02 and is present as a bed or pressed blocks in the combustion
chamber.
Particular preference is given to a thermite bed or pressed thermite blocks.
The amount of the
fuel 31 may be from a few kilograms up to several hundred kilograms and is
fixed according to
how great the amount of heat to be introduced into the well fluid is to be.
The separating
element 24 extends over the entire pipe cross section and is manufactured from
a material
which loses its integrity when the fuel burns off. Suitable materials are, for
example, plastics,
aluminum or an iron alloy with low melting point. The separating element
concludes the
combustion chamber 30 and thus protects the fuel, for example, from moisture.
The space
above the separating element 24 up to the upper end of the vessel is not
filled with fuel and
forms a hollow chamber 25. At the upper end of the combustion chamber 30, an
igniter 32
CA 02893313 2015-06-01
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17
which has been arranged within the fuel is suitable for igniting the fuel 31,
for example an
electric igniter such as a light arc igniter or spiral igniter, or a chemical
igniter. The activation or
ignition temperature depends on the composition of the fuel and may, in the
case of an
aluminothermic mixture, for example, be from 600 C to 1300 C. The igniter can
be ignited using
a wire which is conducted from the igniter through the logging cable 20 up to
the surface.
At the lower end of the tubular vessel 21 is arranged an inflow orifice 41
with its closure device
42. Fig. lb shows a more detailed view of the lower end of the vessel. In the
example shown,
the inflow orifice 41 is configured as a cone narrowing from the inside
outward. The closure
device 42 comprises a plug 44 which has a shape matched to the inflow orifice
and which has
been provided with a securing device 45 which limits the axial movement
thereof away from the
inflow orifice. The securing device 45 comprises a weight element 46 which is
outside the
tubular vessel 21 and is fixed to the plug via a steel rope as the flexible
connecting element 47.
The weight element in this example consists of a frustoconical base body on
which three rods
are mounted in homogeneous distribution over the circumference, protruding
radially outward.
The length of the rods is such that the diameter of the circle surrounding the
rod ends is greater
than the external diameter of the inflow orifice 41.
The weight element 46 can also be configured in other ways, for example with a
spherical or
disk-shaped base body with or without lateral projections. The base body may
also consist of
rods fixed to one another in a preferably crossed manner. The weight element
is preferably
manufactured from a metal, especially iron or steel, and has a mass of 20 to
40 kg. The flexible
connecting element 47, especially a steel rope, preferably has a length of 0.5
m to 2 m.
The plug 44 is connected in a thermally releasable manner to the inside of the
end by a closure
element 43. The closure element 43 preferably takes the form of a weld seam or
adhesive bond.
With regard to integrity, the closure element 43 is preferably designed such
that the connection
between the inside of the end and the plug 44 at least withstands the
hydrostatic pressure of the
well fluid surrounding the vessel, provided that the fuel in the combustion
chamber is not ignited.
In this case, the weight that the fuel mass exerts on the plug 44 may be taken
into account. The
plug 44 itself is manufactured from a material which withstands the
temperatures which exist in
the course of burnoff of the fuel.
For performance of the process according to the invention, the tubular vessel
21 is first
introduced into the well. If the cleaning of the well bottom 15 is the main
aim, the vessel is
positioned such that the lower end thereof is from 0.5 m to 5 m above the well
bottom. The
connecting element 47 in this case is preferably such that the weight element
46 after the
CA 02893313 2015-06-01
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positioning of the vessel rests on the well bottom. If, in contrast, the
cleaning of the perforation
region of the production zone 14 is the main aim, the vessel 21 is positioned
such that the
combustion chamber 30 is at the level of the perforation region of the
production zone 14. In the
example shown, both demands are present in combination; the well bottom 15 is
just below the
production zone 14. The weight element 46 of the securing device 45 rests on
the well bottom
15.
After the positioning of the vessel 21, the fuel 31 in the combustion chamber
30 is ignited.
Proceeding from the igniter 32, the fuel burns off in the combustion chamber,
forming a reaction
front 33 which passes downward through the combustion chamber in the course of
burnoff.
During the burnoff of the fuel in the upper region of the combustion chamber
30, temperatures
are attained which lead to the separating element 24 losing its integrity,
more particularly being
thermally destroyed. Due to the evolution of heat, the well fluid which
surrounds the device in
the region of the combustion chamber 30 in the process of burnoff is strongly
heated, such that
it at least partly begins to boil. The hot liquid and the vapor which forms
penetrate through the
perforation orifices 12 into the perforation channels 13 and generate pressure
pulses in the
rock. This leaches encrustations and/or high-viscosity deposits out of the
rock and thus cleans
the perforation channels. As a result, the fluids to be produced, such as
mineral oil or natural
gas, can again flow more easily through the perforation channels into the
well. The turbulences
excited transport the soiling detached from the perforation channels into the
well, and they are
present in the well fluid.
As soon as the reaction front 33 reaches the lower region of the combustion
chamber 30 in
which the closure element 43 is present, this too loses its integrity owing to
the temperature
increase in the environment thereof. The plug 44 is released from the inflow
orifice 41 and
opens it, such that well fluid can flow into the hollow chamber. This state is
shown in Fig. 1 c.
The plug 44 is forced upward by the flow. The axial motion thereof away from
the inflow orifice,
however, is limited by the connecting element 47. The residue 34 resulting
from the burnoff of
the fuel is entrained with the flow and is distributed in the interior of the
vessel 21. For
absorption of well fluid, the entire volume of the combustion chamber 30 and
of the hollow
chamber 25 is available, minus the volume taken up by the residue 34. With the
well fluid,
particles released from the perforation channels, and also sand and sludge
from the well
bottom, are transported into the interior of the vessel. Depending on the
dimensions of the
vessel and the pressure difference between the inside of the vessel and the
well fluid, the inflow
operation may take from one to about ten minutes.
CA 02893313 2015-06-01
19
In one variant of the invention, the total length of the vessel 21 is selected
such that the
uppermost segment projects above the liquid level of the well fluid. In the
liquid-free portion of
the vessel, an orifice is provided, through which the interior of the vessel
is connected to the
ambient air, such that atmospheric pressure exists within the vessel. During
the inflow
operation, the air present within the vessel can escape, as a result of which
the inflow time is
shortened.
In a further variant, the inventive vessel 21 takes the form of a tubing
string. This variant is used
advantageously when the liquid column in the well is more than 100 meters in
height. In this
case, it is additionally advantageous, just above the perforation zone of the
production zone 14,
to use a packing around the vessel 21, this extending in the radial direction
from the outer
vessel wall up to the inner well wall. This restricts the region of the well
fluid stimulated by the
burnoff of the fuel in the combustion chamber, which leads to more intense
stimulation of the
perforation channels.
In one variant of this embodiment for cleaning of the well bottom, the mass of
the weight
element 46 is such that the weight is greater than the flow forces, such that
the weight element
remains lying on the well bottom during the inflow operation. In an
alternative variant, the total
mass of plug 44, connecting element 47 and weight element 46 is selected such
that, after the
thermal release of the closure element 43, the plug and the weight element
secured thereto by
the connecting element are pulled in the direction of the inside of the vessel
21 by the pressure
of the adjoining well fluid. Since the radial extent of the weight element 46
in at least one spatial
direction is greater than the diameter of the inflow orifice 41 on the outside
of the lower end of
the vessel, the weight element cannot get into the vessel. As a result, the
axial movement of the
plug away from the inflow orifice is limited. In this case, the weight element
46 is configured
such that it does not completely block the inflow orifice 41, but allows the
well fluid to flow
around the weight element adjoining the inflow orifice into the vessel.
On conclusion of the inflow operation, the vessel 21 is withdrawn from the
well in the upward
direction. Under the action of gravity, the plug 44 falls back into the inflow
orifice 41 under its
own weight and closes it. This effect is enhanced by the weight of the weight
element 46 which,
during the withdrawal of the vessel 21, pulls downward on the plug. This
situation is shown
schematically in Fig. 1d. The well fluid which has flowed into the vessel 21,
with the soil particles
and/or sand and sludge present therein, is enclosed therein and can be
conveyed to the
surface. This operation can be repeated several times if required. In this
way, the perforation
channels 13 and the well bottom 15 are effectively cleaned.
CA 02893313 2015-06-01
Figs. 2a and 2b show a second preferred embodiment of an inventive device for
cleaning a
liquid-filled well. A tubular vessel 21 configured as a multipart pipe is
secured on a logging cable
20 by means of a suspension system, the figures showing two pipe segments 22
thereof. The
pipe segments 22 are connected to one another via segment connectors, for
example by flange
connections or screw connections. The two ends of the vessel 21 are closed and
are
manufactured from a material which withstands the temperatures which arise in
the course of
burnoff of the fuel.
A combustion chamber 30 which is filled with a fuel 31 and is completed in the
upward direction
by a separating element 24 extends upward from the inner face of the lower
end. Preference is
given to using the same fuels as described above for Fig. 1. The separating
element 24 extends
over the entire tube cross section and is manufactured from a material which
loses its integrity
when the fuel burns off. The separating element concludes the combustion
chamber 30 and
thus protects the fuel, for example, from moisture. At the upper end of the
combustion chamber
30, an igniter 32 is arranged in the fuel, this being suitable for igniting
the fuel, for example an
electrical igniter such as a light arc igniter or spiral igniter, or a
chemical igniter. The igniter can
be ignited by means of a wire which is conducted from the igniter through the
logging cable 20
up to the surface. The length of the combustion chamber preferably corresponds
to the axial
dimension of the perforation region of the production zone 14 and may be
several meters.
The space above the separating element 24 is not filled with fuel and forms a
hollow chamber
25. The length thereof may be much longer than the length of the combustion
chamber and
may, for example, be from a few meters up to approx. 50 meters. The hollow
chamber 25 is
closed at the top by a further separating element 24. The space above the
further separating
element up to the upper end of the vessel 21 is provided with further fuel 48,
especially a
thermite mixture, and a further igniter 49, and forms the orifice chamber 40.
The length thereof
may be up to about one meter. In the outer wall of the vessel 21, in the
region of the orifice
chamber 40, several inflow orifices 41 are arranged with their closure devices
42. In the
example shown, the inflow orifices 41 are arranged in two rows one on top of
the other,
distributed homogeneously over the circumference of the vessel. Each inflow
orifice 41 is
configured as a cone narrowing from the inside outward. The closure devices 42
in this example
each comprise only one connecting element whose shape is matched to the inflow
orifice in the
form of a plug and which is manufactured from a material which loses its
integrity when the
further fuel 48 is burnt off. The closure devices may also be configured
analogously to the
embodiment according to Fig. 1 as a plug with an additional closure element
which is connected
in a thermally releasable manner to the inside of the wall of the orifice
chamber and the plug.
CA 02893313 2015-06-01
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21
To perform the process according to the invention, the tubular vessel 21 is
first introduced into
the well and positioned such that the combustion chamber 30 is at the level of
the perforation
region of the production zone 14. Subsequently, the fuel 31 in the combustion
chamber 30 is
ignited. Proceeding from the igniter 32, the fuel in the combustion chamber
burns off, forming a
reaction front which passes downward through the combustion chamber in the
course of
burnoff. During the burnoff of the fuel in the upper region of the combustion
chamber 30,
temperatures are attained which lead to thermal destruction of the separating
element 24
between the combustion chamber and the hollow chamber 25. Depending on the
case, the
amount of fuel may be from 10 kg to 300 kg. In the case of use of a thermite
mixture as the fuel,
this reacts within a few minutes to form liquid metal and a slag as a residue.
The heat stored in
the metal and the slag is released to the well fluid over a period of one to
about five hours.
Owing to this evolution of heat, the well fluid which surrounds the device in
the region of the
combustion chamber 30 in the process of burnoff is strongly heated, such that
it at least partly
begins to boil. The hot liquid and the vapor which forms penetrate through the
perforation
orifices 12 into the perforation channels 13 and clean them.
On conclusion of the burnoff in the combustion chamber 30, the further fuel 48
is ignited with the
aid of the further igniter 49 in the orifice chamber 40. In a preferred
variant, this ignition is
delayed until the outside temperature of the vessel has again gone below the
boiling
temperature of the well fluid. The burnoff generates a temperature at which
both the closure
elements and the separating element 24 from the hollow chamber 25 lose their
integrity. The
inflow orifices 41 are opened as a result, and well fluid with the soil and/or
sand particles
present therein flows into the interior of the vessel 21. As well as the
volume of the hollow
chamber 25, the volume of the combustion chamber 30 not filled with residues
34 from the
burnoff is also available for accommodation of well fluid. Fig. 2b shows the
inventive device after
conclusion of the inflow operation. In this embodiment, the closure of the
inflow orifices 41 after
the inflow of the well fluid is not required, since the inflow orifices are at
the upper end of the
vessel 21. The well fluid is enclosed in the interior of the vessel and can be
withdrawn from the
well with the vessel in the upward direction.
By raising or lowering the vessel 21 in the well prior to the opening of the
inflow orifices or
during the inflow phase, it is possible in a controlled manner to influence
the region of the
production zone 14 from which the well fluid is drawn off. The process
according to the invention
enables controlled and efficient stimulation and cleaning of the perforation
region of a well.
Figs. 3a to 3c show a third preferred embodiment of an inventive device for
cleaning a liquid-
filled well. A tubular vessel 21 configured as a multipart pipe is secured on
a logging cable 20 by
CA 02893313 2015-06-01
22
means of a suspension system, the figure showing two pipe segments 22 thereof.
The pipe
segments 22 are connected to one another via segment connectors, for example
by flange
connections or screw connections. Both ends of the vessel 21 are closed and
are manufactured
from a material which withstands the temperatures which arise in the course of
burnoff of the
fuel.
A combustion chamber 30 which is filled with a fuel 31 and is concluded at the
top by a
separating element 24 extends upward from the inner face of the lower end of
the vessel 21.
The separating element 24 extends over the entire pipe cross section and is
manufactured from
a material which loses its integrity when the fuel is burnt off. The
separating element 24
concludes the combustion chamber 30 and thus protects the fuel, for example,
from moisture.
Below the separating element, at the upper end of the combustion chamber 30,
there are
several inflow orifices 41 with their closure devices 42. With regard to the
axial extent of the
vessel 21, the inflow orifices 41 are in the middle region of the vessel 21.
In the example shown, the inflow orifices 41 are arranged in two rows one on
top of another,
distributed homogeneously over the circumference of the vessel 21. Each inflow
orifice 41 is
configured as a cone narrowing from the inside outward. The closure devices 42
in this example
each comprise just one closure element whose shape is matched to the inflow
orifice in the form
of a plug and which is manufactured from a material which loses its integrity
when the fuel 31 in
this region is burnt off. The closure devices 42 may also be configured
analogously to the
embodiment according to Fig. 1 as a plug with an additional closure element
which is connected
in a thermally releasable manner to the inside of the wall of the vessel and
the plug.
At the lower end of the combustion chamber 30, an igniter 32 is arranged in
the fuel, this being
suitable for igniting the fuel, for example an electrical igniter such as a
light arc igniter or spiral
igniter, or a chemical igniter. The igniter can be ignited via a wire which is
conducted from the
igniter through the logging cable 20 up to the surface. The length of the
combustion chamber
preferably corresponds to the axial extent of the perforation region of the
production zone 14
and may be several meters. The fuel 31 is selected such that, after ignition,
it burns off from the
bottom upward and, when it burns off at the upper end of the combustion
chamber, generates a
temperature at which both the closure elements of the closure devices 42 and
the separating
element 24 lose their integrity.
The space above the separating element 24 is not filled with fuel and forms a
hollow chamber
25. The hollow chamber is closed in the upward direction by a further
separating element 24.
The space above the further separating element up to the upper end of the
vessel 21 is
CA 02893313 2015-06-01
23
provided with further fuel 51, especially a thermite mixture, and a further
igniter 52, and forms
the upper combustion chamber 50. The axial extent of the upper combustion
chamber is
preferably from 0.5 m to 1 m.
At the upper end of the vessel 21, a shell tube 53 is arranged around the
vessel, this being
secured on the outer wall of the vessel with a thermally releasable securing
element 54. Within
the vessel, the upper combustion chamber 50 is at the level of the securing
element 54. The
fuel 51 in the upper combustion chamber 50, when it burns off, generates a
temperature at
which the securing element loses its integrity. In the example described, the
securing element
54 is a number of point weld connections which hold the shell tube 53 in its
axial position at the
upper end of the vessel 21. The weld points are designed so as to melt at the
temperatures
which prevail when the fuel 51 in the upper combustion chamber 50 is burnt
off.
Below the inflow orifices 41, a stop element 55 is arranged on the outside of
the vessel 21 and
is fixed thereto. The stop element 55 in this example is designed as a
surrounding steel collar
welded to the outer wall of the vessel.
To perform the process according to the invention, the tubular vessel 21 is
first introduced into
the well and positioned such that the combustion chamber 30 is at the level of
the perforation
region of the production zone 14. Subsequently, the fuel 31 in the combustion
chamber 30 is
ignited. Proceeding from the igniter 32, the fuel in the combustion chamber
burns off, forming a
reaction front which passes from the bottom u'pward through the combustion
chamber in the
course of burnoff. During the burnoff of the fuel in the upper region of the
combustion chamber
30, temperatures are attained which lead to thermal destruction of the
separating element 24
between the combustion chamber and the hollow chamber 25. Depending on the
case, the
amount of fuel may be from 10 kg to 300 kg. In the case of use of a thermite
mixture as the fuel,
this reacts within a few minutes to form liquid metal and a slag as a residue.
Owing to the
evolution of heat by the burnoff, the well fluid which surrounds the device in
the region of the
combustion chamber 30 in the process of burnoff is strongly heated, such that
it at least partly
begins to boil. The hot liquid and the vapor which forms penetrate through the
perforation
orifices 12 into the perforation channels 13 and clean them.
As soon as the reaction front reaches the upper end of the combustion chamber
30, the closure
elements of the closure devices 42 are thermally opened. The inflow orifices
41 are opened as a
result, and well fluid with the soil and/or sand particles present therein
flows into the vessel 21.
As well as the volume of the hollow chamber 25, the volume of the combustion
chamber 30 not
CA 02893313 2015-06-01
24
filled with residues 34 from the burnoff is also available for accommodation
of well fluid. Fig. 3b
shows the inventive device after conclusion of the inflow operation.
Since inflow orifices 41 are present in the middle region of the vessel 21, it
is advantageous to
close the inflow orifices prior to the withdrawal of the device from the well.
This is done by
igniting the further fuel 51 in the upper combustion chamber 50. The burnoff
of the further fuel
51 heats the outer wall of the vessel in the region of the upper combustion
chamber to such an
extent that the securing element 54 on the outer wall loses its integrity. The
shell tube 53 is
released and it slides downward owing to gravity along the outer wall of the
vessel down to the
stop element 55. This state is shown in Fig. 3c. The length of the shell tube
53 is such that all
inflow orifices 41 are closed when the shell tube rests on the stop element.
The length of the
shell tube is preferably 1.5 times to twice the axial extent of the inflow
orifices on the outside of
the vessel, for example two meters in the case of an extent of the inflow
orifices of one meter.
Since the upper combustion chamber 50 is equipped with its own fuel 51 and
igniter 52, the
inflow orifices can be closed independently in terms of time from the burnoff
operation and the
inflow of the well fluid. After the closure of the inflow orifices, the well
fluid is enclosed within the
vessel and can be withdrawn from the well in the upward direction with the
vessel. By raising or
lowering the vessel 21 in the well prior to the opening of the inflow orifices
or during the inflow
phase, it is possible to influence in a controlled manner the region of the
production zone 14
from which the well fluid is drawn off. The process according to the invention
enables controlled
and efficient stimulation and cleaning of the perforation region of a well.
Fig. 4 shows a variant of the third preferred embodiment, in which are
arranged, between the
lower end of the vessel 21 and the upper combustion chamber 50, from the
bottom upward, the
combustion chamber 30, a separation chamber 26, an orifice chamber 40 and the
hollow
chamber 25. The hollow chamber 25 is bounded at the top and bottom by
separating elements
24. The orifice chamber 40 is arranged at the level of the inflow orifices 41
and has a further
igniter 49 and a further fuel 48. The separation chamber 26 in this example is
separated by
separating elements from the combustion chamber 30 and the orifice chamber 40.
It can also be
implemented in other ways, for example by virtue of an upper section of the
combustion
chamber not being filled with fuel.
Below the lower inflow orifices 41, a stop element 55 is mounted on the
outside of the vessel 21.
At the upper end of the vessel 21, at the level of the upper combustion
chamber 50, a shell tube
53 is arranged around the vessel, which is secured on the outer wall of the
vessel with a
thermally releasable securing element 54.
CA 02893313 2015-06-01
The process is performed in a similar manner to that described by Figs. 3a to
3c. The difference
is that, in the embodiment according to Fig. 4, the phases of the fuel burnoff
in the combustion
chamber 30 and the phase of inflow of well fluid into the vessel 21 are
controllable
independently in terms of time. First of all, with the aid of the igniter 32,
the burnoff of the fuel 31
in the combustion chamber is started. This thermally destroys the separating
element from the
separation chamber 26. The dimensions of the separation chamber are such that
the heat which
arises in the course of burnoff of the fuel 31 is insufficient to also destroy
the separating element
from the orifice chamber 40 or to ignite the further fuel 48 in the orifice
chamber.
Only after conclusion of the burnoff in the combustion chamber 30 is the
further fuel 48 in the
orifice chamber 40 ignited with the aid of the further igniter 49. In a
preferred variant, this ignition
is delayed until the outside temperature of the vessel again goes below the
boiling temperature
of the well fluid. The burnoff generates a temperature at which both the
closure elements of the
closure devices 42 and the separating elements from the hollow chamber 25 and
from the
separation chamber 26 lose their integrity. The inflow orifices 41 are opened
as a result, and
well fluid with the soil and/or sand particles present therein flows into the
vessel 21. As well as
the volume of the hollow chamber 25, the volume of the combustion chamber 30,
of the
separation chamber 26 and of the orifice chamber 40 not filled with residues
34 from the burnoff
is available for accommodation of well fluid. The closure of the inflow
orifices 41 and the
withdrawal of the device from the well are effected as described for Figs. 3a
to 3b.
Fig. 5 shows a further variant of the third preferred embodiment, in which are
arranged, between
the lower end of the vessel 21 and the upper combustion chamber 50, from the
bottom upward,
the hollow chamber 25, the combustion chamber 30 and a separation chamber 26.
The hollow
chamber 25 is separated from the combustion chamber 30 by a separating element
24. At the
lower end of the combustion chamber are arranged inflow orifices 41 with their
closure devices
42. Below the lower inflow orifices 41 is mounted a stop element 55 on the
outside of the vessel
21. At the upper end of the vessel 21, at the level of the upper combustion
chamber 50, a shell
tube 53 is arranged around the vessel, this being secured by a thermally
releasable securing
element 54 on the outer wall of the vessel.
The performance of the process according to the invention corresponds
essentially to that
described by Figs. 3a to 3c. The difference is that the burnoff of the fuel 31
in the combustion
chamber 30 in the present example proceeds from the top downward.
CA 02893313 2015-06-01
26
In all embodiments with a shell tube 53 which is provided for closure of the
inflow orifices 41, it
has to be ensured that the shell tube can slide unhindered from its starting
position down to the
stop element 55. If the tubular vessel 21 is composed of several pipe
segments, the segment
connectors 23 therefore have to be selected accordingly, for example as screw
connections.
