Note: Descriptions are shown in the official language in which they were submitted.
WO 00/46484 CA 02357719 2001-07-06 PCT/EPOO/00791
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METHOD FOR CREATING SECONDARY SIDETRACKS IN A WELL SYSTEM
Background of the Invention
The invention relates to a method for creating
secondary sidetracks in a well system which comprises a
main wellbore into which one or more primary sidetracks
debouch.
Such a well system is known from International patent
application WO 98/49424.
A difficulty which arises with such a well system is
that conventional wells have a telescoping nature which
stems from the fact that a casing is inserted into the
main well at various stages of the drilling process and
casing sections which are inserted thereafter need to
have a smaller outer diameter than the inner diameter of
the previously installed casing sections, and that the
liner which is subsequently inserted into the primary
sidetrack needs to have an outer diameter which is
significantly smaller than the inner diameter of the
casing of the main wellbore at the branchpoint in order
to allow a smooth insertion of the liner from the main
wellbore into the primary sidetrack.
As a result the liner of the primary sidetrack has
such a small diameter that it is hardly feasible and
economically unattractive to drill secondary sidetracks
away from the primary sidetrack.
An object of the present invention is to provide a
method for creating one or more secondary sidetracks in a
well system in an efficient and economical manner.
Summary of the Invention
In accordance with the present invention a method is
provided for creating a secondary sidetrack in a well
system for production of hydrocarbon fluids which
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comprises a main wellbore and a primary sidetrack which
debouches into the primary wellbore, the method
comprising:
- inserting an unexpanded expandable liner into the
primary sidetrack;
- radially expanding the liner;
- creating an opening in the wall of the expanded
liner; and
- drilling a secondary sidetrack into the hydrocarbon
formation through said opening.
Preferably the expandable liner is a steel liner
which is expanded by pushing or pulling an expansion
mandrel which is provided with a conical wear-resistant
outer surface and/or rollers through the liner.
The expanded liner has an internal diameter which is
sufficiently large to allow drilling and/or kick off
equipment to be inserted into the primary sidetrack for
drilling of one or more secondary sidetrack, which also
have an internal width which is sufficiently large to
serve as a wellbranch through which hydrocarbon fluids
can flow into the well system.
Hence the method according to the invention allows to
create a root-like well system which provides an optimal
drainage of hydrocarbon fluids from a hydrocarbon bearing
formation, even if the formation has a low permeability.
In an attractive embodiment of the method according
to the invention the expandable liner is formed by a
coiled tubing through which drilling fluid is pumped
towards a downhole drilling assembly which is used to
drill the primary sidetrack and which coiled tubing is
radially expanded after the primary sidetrack has been
drilled.
Also the secondary sidetrack may be drilled using a
coiled tubing which is expanded to form an expanded liner
after completion of the drilling activities.
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Alternatively the secondary sidetrack may be lined
using an expandable slotted liner of which the slots are
staggered and open up into diamond shaped apertures upon
expansion of the liner. Such an expandable slotted line
is known from US patent No. 5,366,012. Such a slotted
liner may be surrounded in the inflow region of the
secondary sidetrack by an expandable sandscreen, such as
a sandscreen which is disclosed in International patent
application PCT/EP96/04887.
In stable reservoir formations the secondary
sidetrack may be an open uncased hole whereas if the
reservoir formation is very unstable the secondary
sidetrack may be lined with an initially unslotted
expanded or unexpanded liner into which perforations are
shot using a perforation gun which is known per se.
The invention also relates to a root-like well system
which has been created in accordance with the invention
and which comprises a main wellbore into which one or
more primary si,detracks comprising an expanded expandable
liner debouch and one or more secondary sidetracks which
debouch into the primary sidetrack or sidetracks through
one or more openings in the wall of the expanded liner or
liners.
It will be understood that the use of expandable
tubulars in a multilateral well system makes it possible
that the well tubulars in the primary or mother well and
in the primary and secondary sidetracks or well branches
have a substantially equal internal width, so that a
monobore multilateral well is created. In such a monobore
well system it is possible to drill tertiary sidetracks
away from the secondary sidetracks, which sidetracking
process can be repeated again and again so that a truly
root-like multilateral well system is created.
CA 02357719 2007-10-12
63293-3851
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In one aspect, the invention provides a method for
creating a secondary sidetrack in a well system for
production of hydrocarbon fluids from a hydrocarbon
formation, which well system comprises a main wellbore and a
primary sidetrack which debouches into the main wellbore,
the method comprising inserting an unexpanded expandable
liner into the primary sidetrack and radially expanding the
liner; characterized in that the expanded liner provides a
steel well casing, that an opening is created in the wall of
the expanded liner in the primary sidetrack; and that a
secondary sidetrack is drilled into the hydrocarbon bearing
formation through said opening.
In another aspect, the invention provides a well
system comprising at least one primary sidetrack and at
least one secondary sidetrack wherein the primary sidetrack
comprises an expanded expandable liner which provides a
steel well casing and which comprises an opening into which
a secondary sidetrack debouches.
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Brief Description of the drawings
Preferred embodiments of the method and system
according to the present invention will be described with
reference to the drawings, in which:
Fig. 1 is a schematic vertical sectional view of a
well system according to the invention; and
Fig. 2 is a schematic vertical sectional view of a
well system according to the invention, which comprises a
primary sidetrack into which two secondary sidetracks
debouch.
Detailed Description of preferred Embodiments
Referring now to Fig. 1 there is shown a well system
1 according to the present invention which comprises a
vertical main wellbore 2 which extends from a wellhead 3
at or near the earth surface 4 into a subsurface
formation 5. Three primary sidetracks 6 debouch into the
main wellbore 2. A secondary sidetrack 7 debouches into
each primary sidetrack 6 through an opening 8 in the wall
of an expanded expandable steel liner 9, of which only
the secti-^ 4_n the region of each opening 8 is shown.
The use of expanded liners 9 maximizes the internal
width of the liners 9. Thus, it the wellbore of each
sidetrack has a width of about 10 cm, the expanded liner
may have an internal width of about seven to
eight centimetres.
Such an internal width is a minimal requirement to
allow a drilling assembly to be inserted into the primary
sidetracks 6 which can be used to drill secondary
sidetracks 7 of a sufficient width which is necessary to
allow hydrocarbon fluids to flow in sufficient quantities
through the secondary sidetracks 7 into the primary
sidetracks.
Preferably also the main wellbore 2 is cased with an
expandable steel casing which is cladded against the
wellbore during the expansion process in a similar manner
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as the expandable liners 9 have been cladded against the
wellbore of the primary sidetracks 6.
This allows a further increase in the internal width
of the liners 9 and of the secondary sidetracks 7.
The primary and secondary sidetracks 6 and 7 each
extend into hydrocarbon fluid bearing formations 10 which
are shown as shaded areas in the drawing.
It will be understood that the illustrated well
system provides a root-like well configuration which
provides an optimum drainage of hydrocarbon fluids from
the hydrocarbon fluid bearing formations 10.
Referring now to Fig. 2 there is shown a vertical
primary wellbore 20 from which a primary sidetrack 21 has
been drilled away in a horizontal direction.
The primary sidetrack 21 is lined with an expandable
steel liner 22. Preferably the liner 22 is formed by a
coiled tubing which has been used during drilling to feed
drilling fluid to a drill bit (not shown) and to a
hydraulic downhole mud motor (not shown) which is used to
rotate the drill bit.
After completion of drilling the coiled tubing is
expanded such that it is cladded against the weilbore and
subsequently serves as a steel lining of the wellbore of
the primary sidetrack 21.
Subsequently a 4.5 inch (= about 12 cm) shoe 22 and a
plug 23 are installed near the toe 24 of the primary
sidetrack 21 inside the liner 22.
Then a whipstock 25 is inserted and anchored within
the liner 22 and a hanger 26 having an internal width of
about 7 cm is inserted into the expanded liner 22 which
has an internal width of about 10 cm. Then a drilling
assembly (not shown) is inserted through the hanger 26
and is induced by the whipstock 25 to mill an opening
into the liner 22 and to subsequently drill the secondary
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sidetrack 30 into a hydrocarbon fluid bearing
formation 31.
In the example shown a conventional steel liner 31
has been inserted into the secondary sidetrack 30 which
has an outer diameter of about 7 cm and which is
perforated in the well inflow zone by means of a
perforating gun (not shown).
After completion of the first secondary sidetrack 30
another whipstock 32 is inserted and anchored inside the
expanded liner 22 close to the heel of the lateral
primary sidetrack 21 whereupon yet another secondary
sidetrack 33 is drilled and completed in the same manner
as described with reference to the first secondary
sidetrack 30.
After insertion of a steel liner 34 in the second
secondary sidetrack either an opening (not shown) is
drilled through the wall of the liner 34 and through the
whipstock 34 or an already existing fluid passage in the
whipstock and a fluid passage in the hanger 35 are used
to allow hydrocarbon fluid to flow from the first
secondary sidetrack 30 and through the primary
sidetrack 21 into the main wellbore 20.
