Note: Descriptions are shown in the official language in which they were submitted.
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Method for completing a borehole
The invention relates to a method for completing a borehole
before the start of production, wherein after the
introduction of the borehole the borehole wall is anchored
sealingly by means of a conveying tube and/or casing tube,
and the borehole wall is perforated at desired locations by
means of perforation units.
The object on which the invention is based is to provide a
method for completing a borehole prior to the start of
production (through tubing rotary drill bores), without the
use of cemented conveying tubes and/or casing tubes.
The method should fulfill the following conditions:
= reliable/robust connection of the formation to the
borehole
= remote control for activating the perforation guns
= the boreholes must be finished and ready for production
in the shortest possible time
= preferably, only one descent into the bore
= the system must be capable of being used above the
conductor tubing by means of which the bore is
completed
= after installation, the possibility of access to the
borehole so that maintenance work can be carried out
= it must be possible to use the system via a side
orifice in the casing tube
= allows the completion of several horizons
= allows the selective production of different horizons
= capable of being used for short and long sections up to
a few hundred meters
= use must be possible in petroleum and natural gas bores
(under dry and wet conditions)
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guarantee of compatibility with surface controlled
subsurface safety valves or other sensitive borehole
equipment
The aim is to have a simultaneous installation of the
conveying tube and/or casing tube and of the perforation
unit. The system or method must allow the sealing off of
various zones and the selective activation of each zone at
any desired position and at any desired time point.
On account of the temperature restrictions in explosive
perforation systems, long underground times are not possible
before the explosion. The flow channels in the reservoir
therefore have to be set up immediately after the
installation of the system, even when multiple-horizon
completions with different production times are required.
This object is achieved, according to the invention, in that
the conveying tube and/or casing tube are/is provided on
their/its outer face with a swellable sealing jacket, the
sealing jacket after activation swelling and anchoring the
annular gap sealingly between the conveying tube and/or
casing tube and the borehole wall and at the same time
centering the conveying tube and/or casing tube in the
borehole. This affords a method for completing a borehole
before the start of production, without cemented conveying
tubes and/or casing tubes having to be used.
In a development, the activation and swelling of the sealing
jacket are carried out after perforation. As a result, the
conveying tube and/or the casing tube are/is anchored
sealingly and at the same time centered in the borehole.
In an inventive refinement, the perforation pressure and/or
the borehole temperature and/or the liquid which is
generated in the production zone are/is used for activating
the sealing jacket for swelling purposes. These are
characteristic variables which change during and/or after
perforation.
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In one embodiment, the material used for the sealing jacket
is a viscous material and/or a rubber or thermoplastic.
In a development of the invention, the sealing jacket is
designed to be deactivatable and, after deactivation, is
permeable to liquids or gases. As a result of deactivation,
previously sealed-off regions can be opened again.
Preferably, chemical and/or thermal activation stimulators
are used for deactivation.
In one embodiment, the chemical activation stimulators used
are aggressive media, for example acids, which dissolve the
sealing jacket or parts of the sealing jacket.
In an inventive refinement, for thermal deactivation, the
activation stimulator used is a heating module which, for
activation, is brought to the desired location in the
conveying tube and/or casing tube.
In one refinement, different sealing jackets are used for
different horizons, so that, if different activation
stimulators are used, a selective opening of the sealing
jackets is achieved, and these orifices can be connected to
the conveying tube for production.
In a preferred refinement, at least one perforation unit is
inserted inside the conveying tube and/or casing tube.
In a preferred refinement, the conveying tube and/or casing
tube are/is designed in a module-like manner together with
the perforation unit, each module consisting of a section of
the conveying tube and/or casing tube and of a perforation
unit. These modules can be connected to one another, for
example via a screw connection, outside the borehole.
Preferably, all the necessary components, such as charges,
ignition cable sections and wire pieces, are preinstalled in
the module, the terminals for electrical and ballistic
contact being installed fixedly at one end of each module,
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and, at the other end, the terminals being prestressed by
means of a spring, so that, after the connection of two
modules, reliable electrical and ballistic contact between
the individual modules is ensured.
In an inventive development, the terminals of the first
module which are to be coupled are coupled to the terminals
of the contiguous second module so that the terminals lie
opposite one another in their axial direction and thus,
during use, transfer electrical and ballistic contact, the
terminals of at least one module being acted upon with force
in the direction of the terminals of the contiguous other
module, so that the end faces of the adjacent terminals
always touch one another during use.
In one embodiment, to trigger the perforation unit or
perforation units, a gas-pressure-activated ignition
mechanism is used, which is installed at the lower end of
the perforation system.
In one design variant, preferably in single-horizon
completions, the gas-pressure-activated ignition mechanism
activates an impact fuse.
In another embodiment, particularly in multiple-horizon
completions, a separate electrical detonator is used for
each perforation zone.
In this case, in a development of the invention, the
detonators are connected via wires, the ignition mechanism
containing an induction appliance, which is operated by the
gas pressure, and the induced current then igniting the
detonators.
In another embodiment, the ignition mechanism used is a
wire-operated firing head (wireline firing head) which is
installed on the top side of the conveying tubing before
installation takes place in the lower region of the
borehole. For ignition, a module on the cable is moved into
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the borehole, latches on the ignition mechanism on top and,
by the electrical connection of the borehole head to the
perforation unit, locks on the electrical signals which are
required for igniting the detonators. After detonation, the
ignition mechanism is separated from the conveying tubing
and is moved out of the borehole with the aid of the cable.
In one embodiment, the elements of the perforation unit
dissolve automatically after detonation. As a result,
production is not impeded by residues of the perforation
unit.
Since the elements of the perforation unit can be dissolved
automatically after detonation, preferably reactive
materials, such as zinc, aluminum or magnesium, are used for
the charge housings of the hollow charges.
Non-reactive sleeve materials of the charges, which generate
a fine sand-like dust, such as glass or porcelain, may also
be used for the charge housings.
A conveying tube and/or casing tube according to the
invention for carrying out the method is characterized in
that the conveying tube and/or casing tube has on its outer
face a swellable sealing jacket.
In one embodiment, the material of the sealing jacket is a
viscous material and/or a rubber or thermoplastic.
Preferably, the sealing jacket is deactivatable and, after
deactivation, is permeable to liquids.
In one embodiment, the conveying tube and/or casing tube is
designed in a module-like manner, and at least one
perforation unit is inserted in each module.
In one refinement, the terminals for electrical and
ballistic contact are installed fixedly at one end of each
module and, at the other end, the contacts are prestressed
by means of a spring, so that, after the connection of two
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modules, reliable electric and ballistic contact between the
individual modules is ensured.
In a preferred development, the terminals of the first
module which are to be coupled are coupled to the terminals
of the contiguous second module so that the terminals lie
opposite one another in their axial direction and thus,
during use, transfer electrical and ballistic contact, the
terminals of at least one module being acted upon with force
in the direction of the terminals of the contiguous other
module, so that the end faces of the adjacent terminals
always touch one another during use.
In an inventive refinement, the perforation units contain
charge housings of the hollow charges which dissolve
automatically after detonation.
Preferably, the charge housings of the hollow charges
consist of reactive materials, such as zinc, aluminum or
magnesium, or consist of non-reactive materials which, after
the detonation of the hollow charges, generate a fine sand-
like dust, such as glass or porcelain.
The invention is described in detail below.
A simultaneous perforation of all the production horizons
can easily be achieved if conventional perforation systems
are used together with the conveying tube technique. In
order to separate different horizons from one another and
seal off individual perforation ducts, a sealing-off device
on the outside of the conveying tube is proposed. The
sealing-off device used may be a slide. Preferably,
according to the invention, a sealing jacket is employed
which is installed on the conductor tube on the outside and
which is activated under specific conditions. The sealing
material of the sealing jacket preferably extends over the
entire length of the sidetrack completion, that is to say of
a side train. It is possible that the perforation horizons
which are intended for immediate production are not equipped
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with the sealing material, if this is required by the
geology or production conditions.
The perforation pressure, the borehole temperature or the
liquid which is generated by the conveying zone may be used
for activating the sealing jacket, with the result that the
material of the sealing jacket swells and closes the annular
gap between the conductor tube and the open hole. The
sealing jacket may be manufactured from a viscous material,
for example from a type of rubber or thermoplastic, which is
exposed immediately after perforation. The activation and
swelling of the sealing jacket must take place after
perforation.
After the activation of the sealing jacket, the various
zones are isolated, and all the desired perforation ducts in
the reservoir are closed and therefore separated from the
conveying tube. The ducts are tied up directly to the
conveying tube at the location where no sealing jacket has
been applied and are therefore ready for production. As
soon as the sealing material of the sealing jacket has been
swollen, it not only closes the annular gap, but also
centers the conveying tube in the open borehole.
In order to connect specific desired horizons, various types
of deactivation of the sealing material may be employed. In
particular, chemical and thermal activation stimulators may
be used. By using aggressive media, for example acids, part
of the sealing material can be dissolved. For different
horizons, different sealing materials must be employed, that
is to say, if different acids are used, a selective opening
of the perforation ducts can be achieved. To dissolve the
sealing material by the supply of heat, a heating module may
be employed which, using a wireline tractor, is brought to
the corresponding location. Depending on the position of
the heating module, horizons can be selectively opened and
connected to the conveying tube for production.
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Hydrocarbon production itself takes place directly via the
conveying tube. The conveying tube also functions as a
transport mechanism for the perforation system. A conveying
tube made from steel with a sealing jacket made from sealing
material transports the perforation unit downward in the
borehole and serves for completing the side track, that is
to say the side train. In order to obtain a free flow path
and allow access to the borehole for the purpose of
maintenance work, a self-dissolving perforation unit is
employed inside the conveying tube.
One possibility for achieving this aim is to use reactive
materials for the charge housings for the purpose of
generating a self-destructing charge (for example zinc or
magnesium). The charges are attached to locations which are
provided for production in the conveying tube. In each
individual horizon, the charges are connected via detonating
cords. A booster-booster ballistic transfer is used for
ballistic and electrical connection between various sections
of the conveying tube. Various perforation zones are
connected via wires. Each perforation zone has its own
detonator for igniting the detonation.
In order to ensure a rapid assembly of this installation at
the borehole location, all the charges, ignition cable
sections and wire pieces are preinstalled in the conveying
tube before they are transported to the borehole location.
The conveying tube has flat threaded connections (for
example, extreme line joints) at the ends. The wire and
booster connectors are fastened centrally inside the
conveying tube. One side of the terminal is always fixedly
installed, while the other side is prestressed by means of a
spring. Reliable electrical and ballistic contact between
the individual tube pieces is thereby ensured.
For triggering the perforation unit, various devices may be
employed. For use in the case of once-only descent, a ga5-
pressure-activated ignition mechanism is proposed which can
be installed at the lower end of the perforation unit. This
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ignition mechanism may activate an impact fuse for single-
horizon completions or for several horizons in which the
individual perforation regions are connected via a
detonating cord. In this application, only a single
detonator is employed.
Alternatively, a gas-initiated inductive-electrical ignition
mechanism may be used. Such an appliance would, as a result
of the movement of a piston, induce in a coil an electrical
current which is used in order to initiate the various
electrical detonators inside the conveying tube. A further
possibility for ignition would be to use a wireline firing
head at the upper end of the installation, this wireline
firing head being connected to all the detonators. In this
case, a cable has to be laid downwardly in the borehole and
connected to the ignition mechanism. The explosive impulse
is then sent downward in the borehole via the cable.
Such an ignition device would make it possible to use
electrical and electronic detonators or EFI/EBW which have
the additional advantage that they are HF-safe. As a
result, a reliable operation of the system can be achieved.
Even radio traffic does not have to be interrupted during
use. The latched cable is used in order to move out the
explosive head after the explosion. As a result, as already
mentioned, a free flow path and direct access for later
maintenance work are made possible.
The system contains in detail the following components:
Hollow charges
For the method or system according to the invention, a
standard hollow charge has to be modified so that it self-
destructs. It is proposed to use reactive materials for the
charge housings. The reactive materials used could be, on
the one hand, metals, such as zinc, aluminum or magnesium.
In the case of zinc charges, problems with specific borehole
scavengings may arise. An exact analysis of the borehole
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conditions is therefore necessary before this material can
be employed. The advantage of zinc is its easy solubility
in acid, with the result that the residues of the charges
can easily be dissolved. Furthermore, the residues of the
zinc charges normally take the form of fine dust which has a
very large surface, thus further promoting a dissolution of
the residues.
Aluminum and magnesium are highly reactive materials which
react even during the operation of detonating the hollow
charges. Moreover, magnesium reacts with water, this, in
turn, having an effect conducive to the dissolution of the
residues.
An alternative to solving the problem of a self-destructing
hollow charge would be to use reactive materials, such as
propellants or explosives, in combination with reactive
binders, in order to produce the housing of the hollow
charge. A similar solution is known from military
applications with regard to caseless ammunition.
A further solution would be to use non-reactive sleeve
materials which generate a fine sand-like dust. Glass or
porcelain are materials which may be used for hollow charge
housings and which leave behind only fine particles. These
could then be washed out of the borehole together with the
first quantities produced and be separated from the
hydrocarbons in a sand separator. As a result, as already
mentioned, a free flow path and direct access for subsequent
maintenance are made possible.
Conveying tube and connectors
A standard conveying tube with flat threaded connections
(for example, extreme line joints) at the ends is employed.
As a result, the conveying tubes can be screwed together
without sockets, with the result that a flat surface is
obtained after the tube is finished. Standard materials and
sizes of conveying tubes are employed. The desired diameter
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range amounts to 2-7/8", 3-3/8", 4", 41-~", 5" with a standard
length of 3-9 m. However, smaller and larger diameters may
also be used (min. 1-9/16"/max. 7").
Initiating device, ballistic transfer and electrical contact
Various initiating devices may be used for the system.
Three different systems are proposed.
Preferably, a gas-activated ignition mechanism is employed
which is installed at the end of the perforation system.
Installation in one operation with remote-controlled
ignition of the perforation units is thereby possible.
In the case of single-horizon completions, this gas-
activated ignition mechanism activates an impact fuse
(mechanical gas-activated ignition mechanism).
In the case of multiple-horizon completions, a separate
electrical detonator is proposed for each perforation zone.
The detonators are connected via wires. The ignition
mechanism contains an induction appliance which is operated
by the gas pressure. The induced current then ignites the
electrical detonators (electrical inductive gas-activated
ignition mechanism).
The third initiation possibility is to use a wireline firing
head. This firing head is installed on the top side of the
conveying tubing before installation in the lower region of
the borehole takes place. A snap mechanism is located on
the top side. For ignition, a module is moved into the
borehole on the cable and latches on the ignition mechanism
on top. By the borehole head being connected electrically
to the perforation unit, the electrical signals required for
igniting the detonators can be locked on. After detonation,
the ignition mechanism is separated from the conveying
tubing and moved out of the borehole with the aid of the
cable.
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The disadvantage of this solution is that an additional
descent into the borehole is required. On the other hand,
one advantage is that it is possible to use electronic
detonators or EBW/EFI initiators. These detonators are HF-
safe, and there is therefore no need to suspend radio
traffic during use. The system therefore acquires
additional safety, in particular under offshore conditions.
Each conveying tube is equipped with the charges, the
ignition cable, the detonators, wires and ballistic and
electrical transfer devices before transport to the borehole
location takes place. A connector unit, such as is
described in EP 1 828 709 Al, is installed at the end of
each conveying tube. One side is fastened and the other
tensioned by a spring. This ensures a reliable transfer of
the detonation and/or of the electrical signals between the
various sections. During the installation of the system on
site in a borehole, the threaded parts of the conveying tube
sections are screwed together. In this case, there is no
fear of any damage to the electrical and ballistic
terminals. This method allows a simple, safe, reliable and
rapid assembly of the conveying tube sections.
Sealing jacket
The sealing jacket is a central integral part of the system.
In this case, a material may be used which expands either in
conjunction with specific liquids when the perforation
pressure prevails or when there is the action of heat. The
sealing jacket is installed on the outside of the conveying
tube made from steel. The application of the material to
the outer face of the steel tube may take place by adhesive
bonding, vulcanization, thermal shrinkage, extrusion or
other robust fastening methods. The coefficient of
expansion must be carefully selected as a function of the
minimum and maximum diameter of the open hole.
In order to allow a selective opening of the perforation
ducts for production, it must be possible to deactivate and
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open the sealing material at specific locations and specific
time points by means of special methods.
The sealing material could be melted away by the action of
heat. For this purpose, a heating module may be employed
which is moved into the borehole on a cable. In this case,
a borehole tractor for horizontal boreholes may be used. By
means of this module, the required heat energy for
dissolving the sealing jacket is generated.
Another possibility for the selective opening of the sealing
jacket is to use aggressive chemicals, for example acids,
which dissolve the sealing jacket. To remove specific
regions by etching, either the use of different types of
sealing materials which react only with specific chemicals
is required or it is necessary to separate the individual
regions by means of packers.
Opening module
Depending on the type of sealing material, a heating module
must be used so that it is possible to generate in the
borehole sufficient heat with the aid of which the sealed-
off ducts can be opened again. This device is required only
when a chemical method for opening the regions is not
employed.
Shut-off of various horizons within the conveying tube
Standard shut-off devices, such as plugs or packers, can be
installed in the conveying tubing by means of standard
methods, for example by means of cables, in combination with
a tractor for horizontal boreholes. In addition, shut-off
devices may be installed on the surface during the
installation of the conveying tube. In this type of use, it
is necessary to ensure that the shut-off devices are capable
of withstanding the detonation pressure arising during
perforation. Furthermore, access to the lower-lying
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sections of the installation is restricted inside the
conductor tube on account of shut-off devices.
The proposed solution for the problem of the completion of
the through tubing rotary drill bores for boreholes, without
the use of cemented conductor tubes, constitutes a
completion which is exceedingly variable and modern.
In particular, the solution affords a reliable robust method
for connecting the production horizons to the borehole,
using standard perforation systems which are well known in
the industry. By the use of a gas-activated ignition
mechanism functioning mechanically or inductive-
electrically, remote activation of the perforation system is
possible. Since the perforation system is installed inside
the conductor tube and standard threads are used which are
screwed together at the borehole location, without in this
case the fear of damage to the electrical or ballistic
contacts, the assembly time required can be minimized, and
the borehole can be finished and put into operation in the
shortest possible time.
The system can be installed in the borehole in one
operation. The perforation system is installed inside the
conveying tubing with which the borehole is completed. By a
self-destructing perforation system being used, a free flow
path and easy access for the maintenance of the borehole are
achieved. The diameter of the system is designed so that
the system can be introduced via a side aperture in the
casing tube. In this case, the stipulated minimum
dimensions for opening regions are adhered to.
By the use of an opening device, a selective opening of the
perforation ducts in the case of multiple-horizon
completions, with selective production in different
horizons, is possible. The corresponding intervals are
limited only by the standard conveying tube technique. The
system may be used in oil and gas boreholes under wet or dry
conditions.
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On account of the super-flat outer face of the completion
section, which is coated with a sealing jacket, the
conductor tube is compatible with underground-installed
safety valves [subsurface safety valves (SCSSV)] or with
other sensitive borehole equipment located in the set-up.
The invention is further explained below with reference to
figures.
Figure 1 shows a borehole 1 as a main borehole and a
branching-off secondary track as borehole 2. In the
following figures, a completion of the borehole 2 prior to
the start of production is described. The borehole 2 is
subdivided into various zones 13a, 13b, 13c, and each zone
requires a different completion or completion at a different
time point.
Figure 2 shows a finished completion for the zones 13a and
13b which consist of modules lla, llb and llc connected to
one another. Each of the said modules lla, llb and llc
consists of a conveying tube 4a, 4b, 4c which is provided on
its outside in each case with a sealing jacket 6. The
conveying tubes 4a, 4c with their sealing jackets 6 are
perforated, so that production can take place via the
perforation ducts 14.
Figure 3 shows a conveying tube 4 which is provided on its
outer face with a sealing jacket 6. To deactivate the
sealing jacket 6, that is to say to dissolve the sealing
jacket 6 at specific locations, various methods may be
adopted. To dissolve the sealing jacket 6 by the supply of
heat, a heating module 7 may be employed which, using a well
tractor with a wireline unit, is brought to the
corresponding location. The heating module 7 heats the
sealing jacket 6 at the desired locations, with the result
that the material of the sealing jacket melts at these
locations and thereby provides opening ducts. Perforation
ducts 14 are thereby connected for production purposes.
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Figure 4 shows a conveying tube 4 which is provided on its
outer face with a sealing jacket 6. To deactivate the
sealing jacket 6, that is to say to dissolve the sealing
jacket 6 at specific locations, chemical activation
stimulators are employed here. Here, these are aggressive
acids 17 which dissolve parts of the sealing jacket 6.
Figure 5 shows a module lla consisting inter alia of a
conveying tube 4 with a sealing jacket 6 which is activated,
that is to say closed, and acts as a seal. The perforation
ducts 14 are therefore partitioned off from production. The
hollow charges have dissolved after detonation, and no
residues are present.
Figure 6 shows two modules lla, lib connected to one another
via a screw connection 18 and in each case having a
perforation unit 5. Each perforation unit 5 consists of a
tubular housing into which hollow charges 10 are inserted.
These hollow charges 10 consist in each case of a charge
housing 9 with an inserted charge. Moreover, each
perforation unit 5 has an ignition cord for initiating the
hollow charges 10 and an electrically conductive wire 19.
For coupling between these, these terminals 12 are connected
to one another between the modules lla, llb.
Each module lla, llb contains all the necessary components,
such as charges, ignition cable sections and wires 19, which
are preinstalled in the module 11, the terminals 12a for
electric and ballistic contacts being installed fixedly at
one end of each module 11, and, at the other end, the
terminals 12b being prestressed by means of a spring 8, so
that, after the connection of two modules 11, reliable
electrical and ballistic contact between the individual
modules 11 is ensured.
The terminals of the first module 11 which are to be coupled
are coupled to the terminals of the contiguous second module
so that the terminals 12a, 12b lie opposite one another in
their axial direction and thus, during use, transfer
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electrical and ballistic contact, the terminals 12b of at
least one module being acted upon with force in the
direction of the terminals of the contiguous other module,
so that the end faces of the adjacent terminals 12a, 12b
always touch one another during use.
Figure 7 shows an extract from the completion of a borehole.
The individual modules 11a, lib can be seen in the two
zones 13b and 13a. Each module consists of a conveying
tube 4 with a sealing jacket 6 (see the previous figures).
Arranged at the lower end is a gas-pressure-activated
ignition head 15 which initiates the ignition of the hollow
charges 10. The ignition signal is conducted to the
individual perforation units in the modules and ignites the
hollow charges there. Reference symbol 16 denotes a
detonator for initiating the contiguous ignition cord in the
zone 13b, which, in turn, initiates, that is to say
explodes, the hollow charges in the perforation units of the
modules in this zone. The zones in which production is to
be started by the provision of the perforation ducts can
therefore be controlled, as desired.
