Note: Descriptions are shown in the official language in which they were submitted.
WO 2013/133720
PCT/N02013/050046
METHOD FOR ZONE ISOLATION IN A SUBTERRANEAN WELL
The invention relates to a method for zone isolation in a subterranean well.
More spe-
cifically, the invention relates to a method in which a balanced plug over a
longitudinal
section is established in the entire cross section of the well to prevent
undesired pro-
s duction from a reservoir.
Isolation between zones in different production intervals is essential to be
able to con-
trol and optimize the production from a subterranean well such as a petroleum
well or
a geothermal well. As a reservoir is being emptied and/or existing barriers
for isolation
between different zones are becoming weaker, the fluid flows within the
reservoir may
io change so that the production decreases or, at worst, comes to a halt.
For example,
when a production interval is emptied of oil, the interface between water and
oil may
gradually be draw upwards and enter the producing zone, so-called coning, so
that a
flow of water completely or partially replaces the flow of hydrocarbons into
the pro-
duction string of the well. Gas coning may also occur. Barriers intended to
prevent
15 undesired fluid flows between different zones of a reservoir are
subjected to great
strains, in the form of powerful pressures and temperature differences among
other
things, hence intense tension and stress forces. It is known that this may
result in
damage to a cement barrier so that the integrity of the barrier is ruined.
This may
result in undesired fluid production behind casing and casing liners, among
other
20 things, and could further reduce or, at worst, make further production
from the well
impossible.
The invention has for its object to remedy or reduce at least one of the
drawbacks of
the prior art or at least provide a useful alternative to the prior art.
A method for zone isolation in a subterranean well, the well being provided
with a pipe
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body, at least in a portion, characterized by the method including
(A) providing a plug over a longitudinal section in the well, the plug
covering substan-
tially the entire cross section of the well at least in a portion of the
longitudinal sec-
tion, so that the plug fills the inside of the pipe body and an annulus
between the out-
side of the pipe body and a surrounding well body.
The pipe body may be, for example, a casing or a casing liner of types known
per se
and the pipe body may be part of a longer pipe string.
The surrounding well body may be another pipe body, or it may be the formation
it-
self.
It is also known that a well plug may be established by means of a method and
devic-
es as proposed in the Norwegian patent application 20111641 entitled "Method
for
combined cleaning and plugging in a well, washing tool for directional washing
in a
well, and use of the washing tool" and by the Norwegian patent application
20120099
entitled "Apparatus and metthod for positioning of a fluidized plugging
material in an
oil well or gas well", both filed in the name of the present applicant.
In a first embodiment, step (A) of the method may include the substeps of:
(Al) lowering a perforation tool into the pipe body to the longitudinal
section where
the plug is to be set; and
(A2) forming perforations in the pipe body along the longitudinal section by
means of
the perforation tool.
The perforation tool may be a perforation gun of a type known per se.
This may be appropriate in order to ensure good circulation of a plugging
material
from the inside of the pipe body out into the annulus on the outside of the
pipe body.
The perforation may be carried out in an undamaged/unperforated portion of the
pipe
25 body or in an already perforated portion of the pipe body if the number,
distribution
and design of the perforations are not sufficient to ensure god circulation
for subse-
quent washing and plugging. A preferred distribution of the perforations in
the pipe
body may be in the order of 12 per foot in a 135/45 degrees' phase within said
longi-
tudinal section.
3C In a first embodiment of the method, the plug may remain set in the
entire cross sec-
tion of the well. This may be advantageous in, for example, a case in which a
barrier
element set earlier has lost its integrity and there is undesired fluid
production behind
a casing or a casing liner from a part of the formation below. Thus, a plug
covering the
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entire cross section could isolate the formation, from which the undesired
fluid produc-
tion is coming, from the rest of the well.
In addition, or as an alternative, step (A) of the method may include the
following
substeps:
s (A3) by means of a washing tool which is attached to a string allowing
through-flow
and which is lowered to the longitudinal section, pumping a washing fluid down
the
string and out into the pipe body via the washing tool;
(A4) by means of a directional-control means connected to the washing tool,
directing
the washing fluid into the annulus between the outside of the pipe body and
the sur-
is rounding formation; and
(A5) pumping a fluidized plugging material down the string and out into the
pipe body,
and thereby also into the annulus via the perforations in the pipe body.
Further details about the substeps A1-A5 and also about said washing tool can
be
found in the above-mentioned Norwegian patent application 20111641.
15 It may be an advantage if a displacement member in the form of a
pressure apparatus
as described in the Norwegian patent application 20120099 mentioned is used to
fur-
ther displace and distribute the fluidized plugging material in the casing and
further
out into the annulus.
In one embodiment of the method, the steps of perforation (A2) and washing
(A3, A4)
.25 may be carried out in separate trips down the well.
In another embodiment of the method, the steps of perforation (A2) and washing
(A3,
A4) may be carried out in one and the same trip into the well. A combined
perforation
and washing apparatus is described in the Norwegian patent application
20111641
mentioned. The perforation tool and the washing tool may be releasable in
combina-
25 tion or individually from the string.
In one embodiment, the method may further include leaving the perforation tool
in the
well. This may be practical to save operation time if the perforation tool can
be "hid-
den" in the well and/or if the perforation tool is a drillable one.
As an alternative, or in addition, the method may further include leaving the
washing
3C tool in the well. This may be advantageous in order to save operation
time and/or to
use the washing tool as a base for the plug that is to be established. It may
be advan-
tageous if the washing tool is a drillable one.
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In a second embodiment, after step (A), the method may include the step of:
(B) drilling out a centrally through-going portion of the plug, so that at
least a cross-
sectional portion of the plug on the outside of the pipe body remains. This
may be de-
sirable in a case in which there is to be production from a part of the well
lying below
,E the plug and the well path therefore has to be opened up again.
As an addition to said first or second embodiment, the method may include
providing
one or more perforations in a portion of the pipe body outside the
longitudinal section
in which the plug has been set. This may be necessary if existing production
perfora-
tions have been blocked or closed off from the rest of the well in connection
with the
is isolating.
The fluidized plugging material may be, for example, cement slurry,
unconsolidated
mass or a combination thereof.
In what follows, examples of preferred embodiments are described, which are
visual-
ized in the accompanying drawings, in which:
15 Figures 1-8 show, in side views, simplified schematic sections of a well
in different
stages in accordance with a first embodiment of the method of the pre-
sent invention; and
Figures 9-10 show, in side views, simplified schematic sections of a well in
different
stages in accordance with a second embodiment of the method of the
present invention.
In what follows, the reference numeral 1 indicates a subterranean well as used
in the
method of the present invention. The well 1 has been drawn in a schematic and
great-
ly simplified manner, and well elements which are not central to the invention
may
have been left out of the drawings. Well fluids and cement barriers already
esta b-
25 lished, which will be known to a person skilled in the art, are not
shown in the figures.
A casing 21 extends down the well 1, forming a radial boundary between a well
path 2
and a surrounding formation 7. A pipe body 211 in the form of a casing liner
is hung
from the lower portion of the casing 21, extending down into a producing part
of the
well 1. The casing liner 211 is formed with perforations 212, through which
fluids may
30 flow from the formation 7 into the well 1. A connection pipe 210 and the
casing liner
211 together form a pipe string which extends throughout the length of the
well 1. In
the exemplary embodiment shown, the pipe string is formed with one and the
same
inner diameter. The purpose of the method of the present invention is to
isolate for-
mation zones, from which undesired fluids are entering the well 1, from the
rest of the
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well 1, whether it be undesired fluid flow through producing perforations 212
as shown
in the figures 1-8, or undesired fluid flow behind casing 21 or casing liners
211 as
shown in the figures 9-10.
In figure 1, a producing well 1 is shown. An interface between water and oil
has been
s drawn upwards and into the producing zone of the formation 7, so that an
undesired
flow of water, indicated by arrows in towards the perforations 212, has
completely or
partially replaced the flow of hydrocarbons into the well 1. To remove or at
least re-
duce the undesired water flow into the well 1, there is a wish to isolate the
zone, from
which the undesired production is coming, from the rest of the well 1. The
reference
is numeral 221 indicates a safety/production valve of a type known per se.
Figure 2 shows the well 1 after a perforation tool 33 has been lowered into
the casing
liner 211 and placed along a longitudinal section 1Li opposite the
perforations 212. The
perforation tool 33 may be a perforation gun of a type known per se. The
perforation
tool 33 is used to form new perforations 213 in the casing liner 211 which is
to be
19 used in subsequent washing and plugging as shown in figure 3. In a case
in which the
existing perforations 212 satisfy the requirements for design, position and
density as
required in the subsequent washing and plugging operations as described above,
it will
not be necessary to form new perforations 213. Figure 3 shows the well 1 after
the
string 3 with the perforation tool 33 has been pulled out and new perforations
213
zo have been formed in the casing liner 211.
A combined washing and plugging tool 35 is then lowered into the well 1 within
the
casing liner 211 as shown in figure 4. Perforation and cleaning and plugging
may be
carried out in the same trip or in separate trips down the well 1. A washing
fluid not
shown is carried through the string 3, into the casing liner 211 and further
out into an
25 annulus 5 via the perforations 213. It may be an advantage if the
washing fluid is di-
rected substantially radially into the annulus 5 by means of a directional-
control
means 351, as described in the Norwegian patent application 20111641. A
washing
fluid at great velocity may remove various particles, deposits and remains
from earlier
downhole operations, so that a fluidized plugging material which is
subsequently to be
3C carried into the annulus 5 may flow freely and be adhered in a better
way. Then the
fluidized plugging material is pumped through the string 3 and out into the
casing liner
211 and thereby also into the annulus 5 via the perforations 213 in the casing
liner
211, so that a plug 25 is formed over the longitudinal section 1_1, as shown
in figure 5.
At least in a portion within the longitudinal section Li, the plug 25 of cured
plugging
35 material extends over the entire cross section Ti of the well 1. It may
be an ad-
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vantage if an apparatus as described in the Norwegian patent application
20120099 is
used in order to further displace and distribute the fluidized plugging
material in the
casing liner 211 and out into the annulus 5. The latter apparatus is not shown
in the
figures connected to the present document.
s In figure 6, the well 1 is shown after a central through-going portion of
the plug 25
has been drilled away by means of a drilling tool 31. A cross-sectional
section T3 of
the plug 25 outside the casing liner 211 is left inside the longitudinal
section L1. The
remaining cross-sectional section T3 of the plug 25 outside the casing liner
211 forms
a barrier 51 in the annulus 5 between the casing liner 211 and the formation
7, there-
is by isolating the well 1 from the reservoir zone from which the undesired
water produc-
tion was coming.
Figure 7 shows the well 1 after it has been fully isolated for the above-
mentioned pur-
poses, whereas figure 8 shows the well 1 after new perforations 214 have been
formed in the casing liner 211 at a distance from the longitudinal section Li
so that
19 there may be production from another zone without undesired water drive.
The dis-
tance between the longitudinal section L1 and the new perforations 214 may be
very
large, maybe in the order of kilometres.
Figure 9 shows a well 1 in which an undesired water flow, indicated by arrows,
is com-
ing from a formation zone below the production zone and is flowing in behind
the cas-
20 ing liner 211. This may quite possibly be a result of an earlier poor
and/or difficult ce-
mentation job. There is therefore a need for new zone isolation. A plug is set
in the
entire cross section of the well, as shown in figure 10, in a portion below
perforations
212 already producing, by means of steps indicated in the figures 2-5. The
plug 25
isolates the well 1 from the zone from which the undesired water production
was corn-
25 ing and the production may be resumed via the perforations 212 existing
already.
