Note: Descriptions are shown in the official language in which they were submitted.
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METHOD FOR DRILLING AND COMPLETING A HYDROCARBON
PRODUCTION WELL
Background of the Invention
The invention relates to a method for drilling and
completing a hydrocarbon production well, such as a well
for the production of oil and/or gas.
Traditionally hydrocarbon production wells are
created by first drilling a large borehole section in
which a large diameter casing is inserted and cemented in
place to stabilize the borehole wall. Subsequently a
borehole extension of a smaller diameter is drilled and a
casing is inserted into said extension such that said
further casing extends from the bottom of said extension
to the top of the borehole whereupon said further casing
is cemented in place inside the borehole extension and
also inside the previously set casing.
This process is repeated until the borehole reaches
the vicinity of the hydrocarbon bearing formation. If
that formation is unstable the casing is extended into
that formation and subsequently perforated to enable
inflow of hydrocarbons. If the hydrocarbon bearing
formation is stable an essentially open hole is created
in which a permeable production liner is inserted and
surrounded by for example a gravel pack.
The production liner is normally connected to the
lower end of a production tubing which is lowered through
the casing string such that it spans the length of the
borehole from the wellhead until the vicinity of the
hydrocarbon bearing formation, where the tubing is
sealingly secured to the casing by means of a production
packer.
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Since the borehole wall and the inner surface of a
previously installed casing may be irregular and the
borehole may be curved significant clearances are
required between the various casings and production
tubing which results in a significant amount of
unproductive annular space and redundant drilling work to
be done.
Typically in a hydrocarbon production well the
diameter of the upper part of the borehole near the earth
surface and internal diameter of the upper casing part
may well exceed half a metre, whereas the internal
diameter of the production tubing through which
hydrocarbons are produced is between 10 and
25 centimetres.
Numerous attempts have been made to reduce the amount
of unproductive annular space in wells. US patent
specifications Nos. 3,162,245; 3,203,483 and 5,014,779
disclose the use of originally corrugated tubulars which
are expanded into a cylindrical shape against the inside
of a casing by an expansion mandrel or sphere. A
disadvantage of the use of corrugated tubulars is that
they are difficult to manufacture and that the wall of
the expanded tubulars may have non-uniformity of strength
around their circumference which reduce their
reliability.
International patent application, publication
No. WO 93/25799 discloses the use of an essentially
cylindrically shaped casing which is expanded against the
borehole wall by an expansion mandrel so as to induce
compressive force between the casing and surrounding
formation.
This known expandable casing may be located between a
surface casing arranged in an upper part of the wellbore
and a production casing arranged in a lower part of the
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wellbore. Since the surface and production casings are not
expanded downhole this known well casing technique still
either involves the use of conventional casing parts that
require the drilling of an oversized borehole or the
expansion of a casing string which is inserted and expanded
after the full length of the borehole has been drilled,
which is not always possible.
French patent application No. 2,741,907 discloses
a well lining method in which a flexible hose is used, which
after insertion into the well is inflated by injection of a
heavy liquid and subsequently hardened by polymerization. A
difficulty with the known method is that a two-step
inflation and chemical curing process is time consuming and
generates a fragile tubular which may have an irregular
strength and shape.
U.S. Patent No. 5,348,095 discloses a well lining
method in which casing sections which are made of a ductile
material are expanded using an expansion cone which defines
a semi-top angle which is between 30 and 45 such that also
the wellbore and surrounding formation are expanded. The
use of such a relatively blunt expansion cone and
deformation of the surrounding formation creates high
bending forces during the expansion process, which may
easily cause irregular expansion and even rupture of the
casing.
It is an object of the present invention to
provide a method for drilling and completion of a
hydrocarbon production well in which a casing can be
installed or extended to protect the borehole wall against
caving in during various phases of the drilling process and
where installation of both the casing and production tubing
can be achieved in such a way that along at least a
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substantial part of the length of the borehole the
accumulated width of the annular spaces between the tubing,
casing or casings and the surrounding formation is kept to a
minimum.
It is a further object of the present invention to
provide a method for creating a well in which the amount of
steelwork required for casing and completing the well is
kept to a minimum.
Summary of the Invention
The present invention provides a method for
drilling and completing a hydrocarbon production well, the
method comprising the steps of: A) drilling a section of a
borehole into an underground formation; inserting a casing
into the drilled borehole section and radially expanding and
securing the casing within said borehole section;
B) lowering a drill bit through the expanded casing and
drilling a subsequent section of the borehole; inserting a
next casing into said subsequent section of the borehole and
radially expanding and securing said next casing within said
\/20 subsequent borehole section; and C) repeatingy step B a
number of times until the borehole has reached the vicinity
of a hydrocarbon bearing formation, characterised in that
said next casing is installed so as to co-axially overlap
with the previously installed casing, and in that said next
casing is expanded against the previously installed casing
so as to further expand the previously installed casing.
Preferably only the first casing extends from the
earth surface into the borehole and any subsequent casing
only partly overlaps a previously set casing.
In such case it is preferred that the length along
which subsequent casing sections overlap each other is less
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than 10% of the length of each casing itself and also that
along at least a substantial part of the length of the
borehole from the earth surface to the vicinity of the
hydrocarbon bearing formation the variation in diameter of
the borehole is less than 10%.
In that case a slim borehole of an almost uniform
diameter along its entire length is created, which is
drilled with a minimal amount of drilling effort and
steelwork installed within the well.
In some circumstances, however, it may still be
required that at least two casings that are subsequently
inserted into the borehole each extend to the wellhead.
Furthermore, it is preferred that after installing
said casings a production tubing is inserted into the
borehole such that the production tubing extends from the
earth surface to the vicinity of the hydrocarbon formation;
and the tubing is radially expanded inside the string of
expanded casings.
Suitably the casings and optionally the tubing are
plastically expanded in radial direction by moving an
expansion mandrel therethrough in a longitudinal direction
and they are made of a formable steel grade which is subject
to strain hardening without incurring any necking and
ductile fracturing as a result of the expansion process and
wherein an expansion mandrel is used which has along part of
its length a tapering non-
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metallic surface.
In such case it is preferred that the expansion
mandrel has a tapering ceramic surface and that the
tubing and casings are made of a formable steel grade
having a yield strength-tensile strength ratio which is
lower than 0.8 and a yield strength of at least 275 MPa.
It is also preferred that the production tubing and
at least one of the casings consists of a tubular which
is inserted into the borehole by reeling the tubular from
a reeling drum.
Alternatively, the production tubing and/or at least
one of the casings may be made up of a series of pipe
sections that are interconnected at the wellhead by screw
joints, welding or bonding to form an elongate pipe of a
substantially cylindrical shape that can be expanded and
installed downhole in accordance with the method
according to the invention.
Brief Description of the Drawings
The invention will be described in more detail with
reference to the accompanying drawings, in which
Fig. 1 is a longitudinal sectional view of a well
comprising a series of radially expanded casings of
substantially uniform diameter that have been installed
using the method according to the present invention;
Fig. 2 shows the well of Fig. 1 in which a production
tubing has been expanded within the series of casings;
Fig. 3 is a longitudinal sectional view of a series
of telescoping expanded casings and of a production
tubing that have been installed in accordance with the
method according to the invention; and
Fig. 4 is a longitudinal sectional view of a
production tubing which is expanded downhole by an
expansion mandrel.
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Detailed description of the Invention
Referring now to Fig. 1 there is shown a borehole 1
that extends from the earth surface 2 through a number of
underground formation layers 3, 4, 5 and 6 into an oil
and/or gas bearing formation layer 7.
In the example shown it is assumed that a casing 8,
9, 10 or 11 needs to be inserted to protect the
borehole 1 against caving in each time when the
borehole 1 has passed an interface 12, 13, 14 or 15
between different formation layers 3, 4, 5, 6 or 7.
Accordingly, initially the first and upper section 1A
of the borehole 1 is drilled and after the interface 12
has been reached the upper casing 8 is inserted into the
upper borehole section 1A and radially expanded by means
of an expansion mandrel 16. The expanded casing 8 may be
secured to the borehole wall by means of an annular body
(not shown) of cement or a bonding agent. Alternatively,
the expanded casing 8 may be secured to the borehole wall
by friction. Such friction may be generated by providing
the outer surface of the casing 8 with spikes (not shown)
and/or by radially pressing the casing into the
formation 3.
Subsequently, the drill bit is lowered through the
upper casing 8 to the bottom of the first borehole
section 1A and the second section 1B of the borehole 1 is
drilled. After the next interface 13 has been reached,
the second casing 9 is lowered through the first casing 8
to the bottom of the second borehole section 1B and
radially expanded by means of the expansion mandrel 16.
When the expansion mandrel 16 reaches the area where
the casings 8 and 9 co-axially overlap each other the
second casing 9 will further expand the first casing 8
which generates a strong bond and seal generated by
frictional and compressive forces. In order to alleviate
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the increased expansion forces at the area of overlap the
length over which the casings 8 and 9 overlap each other
is relatively small, preferably less than 10% of the
length of the shortest casing 8 and 9 and the bottom of
the upper casing 8 may be pre-expanded and/or provided
with slits or grooves (not shown) which widen up or break
open during the expansion process.
The second casing 9 is secured to the borehole wall
in the same way as the first casing 8. Furthermore the
second and any further borehole sections 1B, 1C and 1D
are drilled by means of an underreamer bit which is able
to drill the whole length of the borehole 1 at
substantially the same diameter.
Subsequently, the third and fourth borehole sections
1C and 1D are each drilled and cased in the same manner
as described with reference to the second borehole
section 1B.
At the bottom of section 1D there is shown the
expansion mandrel 16 which is moved downwardly in
longitudinal direction through the lowermost casing 11,
thereby radially expanding the casing 11 in a manner
which is described in more detail with reference to
Fig. 4.
Referring now to Fig. 2 there is shown the borehole 1
of Fig. 1 in which a production tubing 17 is being
installed by longitudinally moving an expansion
mandrel 18 therethrough.
The tubing 17 is expanded to an outer diameter which
is substantially equal to the inner diameter of the
expanded casings so that the production tubing 17 forms
an internal cladding to the casings 8, 9, 10 and 11 and
the walls of the tubing 17 and casings 8, 9, 10 and 11
mutually reinforce each other. The lower end of the
production tubing that extends beyond the lower end of
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the lowermost casing 11 into the oil and/or gas bearing
formation 7 may be provided with staggered axial slots
(not shown) which open up to a diamond shape as a result
of the pipe expansion process in order to permit inflow
of oil and/or gas from the formation 7 into the
borehole 1, which fluids then flow up through the
interior of the tubing 17 to the earth surface 2.
Instead of providing the inflow section at the lower
end of the production tubing 17 with axial slots, it may
be provided with non-slotted apertures as well. These
apertures may be circular, oval or square holes that are
punched into, or cut away from, the tubing wall and which
are arranged in an overlapping or non-overlapping pattern
which may be staggered or not.
The presence of such non-slotted apertures creates a
tubing which will, after expansion thereof, generally
have a higher strength than an expandable tubing with
overlapping staggered axial slots.
Also the expandable casings 8, 9, 10 and 11 may be
provided with at least some slotted or non-slotted
apertures in order to alleviate the forces required to
expand these casings, in particular in the areas where
the casings 8, 9, 10 and 11 overlap each other and in
other areas, such as curved sections of the borehole 1,
where expansion forces are high.
It will be understood that in such case the
production tubing 17 is not perforated in the areas where
any of the casings 8, 9, 10 and 11 is perforated so as to
retain a fluid tight seal between the interior of the
tubing 17 and the surrounding formation layers 3, 4, 5
and 6.
Referring now to Fig. 3 there is shown a borehole 20
that has been drilled into an underground formation 21.
In the upper part of the borehole 20A a first
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casing 22 is installed and expanded. In the example shown
the upper part of the borehole 20A has an internal
diameter of about 25.4 cm. The unexpanded first casing 22
has an outer diameter of about 18.8 cm when it is lowered
into the borehole. The expanded first casing 22 has an
outer diameter of about 23.4 cm so that a small annulus
is left around the expanded first casing 22 which is
filled with cement 23.
Subsequently the second part of the borehole 20B is
drilled to an internal diameter of about 21 cm and a
second casing 24 is inserted in unexpanded form into the
borehole such that it extends from the top of the
borehole 20 to the bottom of the second part 20B thereof.
The unexpanded second casing 24 has an outer diameter of
15.7 cm and is expanded inside the borehole 20 to an
outer diameter of 19.5 cm.
The second casing 24 is cemented inside the second
part of the borehole 20B and inside the first casing by
an annular body of cement 23.
Then a third borehole section 20C having an internal
diameter of 17.8 cm is drilled from the bottom of the
second borehole section 20B into the formation 21,
whereupon a third casing section 25 is inserted into the
borehole 20 and expanded. The unexpanded third casing 25
has an outer diameter of about 13 cm and is expanded to
an outer diameter of about 16.3 cm.
Thereafter a fourth borehole section 20D having an
internal diameter of about 14.2 cm is drilled and a
fourth casing 26 is inserted into the borehole 20 and
subsequently expanded from an outer diameter of 10.1 cm
to an outer diameter of about 13 cm.
Inside the fourth casing 26 a production tubing 27 is
inserted and expanded against the inner surface of said
casing 26 to form a clad tubing 27.
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To facilitate injection of service and/or kill fluids
into the well and to permit installation of conduits for
measuring or other equipment a coiled service conduit 28
is inserted into the production tubing 27 and sealingly
connected near the bottom of the tubing 27 by a
production packer 29.
The service conduit 28 contains perforations 30 just
above the production packer so that oil and/or gas can be
produced from the inflow region.of the well, the bottom
of the service conduit 28 and the perforations 30 into
the production tubing 27.
As a result of the expansion of the casings 22, 24,
25 and 26 and of the production tubing 27 it is possible
that a production tubing having an internal diameter of
more than 10 cm is installed in a borehole 20 of which
the upper section 20A has an internal diameter of about
cm. It will be understood by those skilled in the art
of drilling of oil and/or gas production wells that the
method according to the invention facilitates the use of
20 a larger diameter production tubing 27 inside a smaller
diameter borehole 20 than conventional well drilling and
completion techniques.
It will also be understood that instead of using only
expanded casings inside the borehole one or more casings
25 may still be an unexpandable conventional casing. For
example the upper casing may be a conventional casing, in
which one or more telescoping expandable casing sections,
as shown in Fig. 3, are inserted and the lower part of
the borehole may be equipped with monobore casings as
shown in Fig. 1 and 2.
Now referring to Fig. 4, there is shown a borehole
traversing an underground formation 41 and a casing 42
that is fixed within the borehole by means of an annular
body of cement 43.
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A production tubing 44 which is made of a dual phase,
high-strength low-alloy (HSLA) steel or other formable
high-strength steel is suspended within the casing 42.
An expansion mandrel 45 is moved in longitudinal
direction through the tubing 44 thereby expanding the
tubing 44 such that the outer diameter of the expanded
tubing is slightly smaller than, or is about equal to,
the internal diameter of the casing 42.
The expansion mandrel 45 is equipped with a series of
ceramic surfaces 46 which restrict frictional forces
between the pig and tubing 44 during the expansion
process. In the example shown the semi top angle A of the
conical ceramic surface that actually expands the tubing
is about 25 . It has been found that zirconium oxide is a
:15 suitable ceramic material which can be formed as a smooth
conical ring. Experiments and simulations have shown that
if the semi cone top angle A is between 20 and 30 the
pipe deforms such that it obtains an S-shape and touches
the tapering part of the ceramic surface 46 essentially
at the outer tip or rim of said conical part and
optionally also about halfway the conical part.
The experiments also showed that it is beneficial
that the expanding tubing 44 obtains an S-shape since
this reduces the length of the contact surface between
the tapering part of the ceramic surface 46 and the
tubing 44 and thereby also reduces the amount of friction
between the expansion mandrel 45 and the tubing 44.
. Experiments have also shown that if said semi top
angle A is smaller than 15 this results in relatively
high frictional forces between the tube and pig, whereas
is said top angle is larger than 30 this will involve
redundant plastic work due to plastic bending of the
tubing 44 which also leads to higher heat dissipation and
to disruptions of the forward movement of the pig 45
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through the tubing 44. Hence said semi top angle A is
preferably selected between 15 and 30 and should always
be between 5 and 45 .
Experiments have also shown that the tapering part of
the expansion mandrel 45 should have a non-metallic outer
surface to avoid galling of the tubing during the
expansion process. The use of a ceramic surface for the
tapering part of the expansion mandrel furthermore caused
the average roughness of the inner surface of the
tubing 44 to decrease as a result of the expansion
process. The experiments have also shown that the
expansion mandrel 45 provided with a ceramic tapering
surface 46 could expand a tubing 45 made of a formable
steel such that the outer tubing diameter D2 after
expansion was at least 20% larger than the outer diameter
Dl of the unexpended tubing and that suitable formable
steels are dual phase (DP) high-strength low alloy (HSLA)
steels known as*DP55 and*DP60; ASTM A106 HSLA seamless
pipe, ASTM A312 austenitic stainless steel pipes, grades
TP 304 L and TP 316 L and a high-retained austenite high-
strength hot rolled steel, known as*TRIP steel manu-
factured by the Nippon Steel Corporation.
The mandrel 45 is provided with a pair of sealing
rings 47 which are located at such a distance from the
conical ceramic surface 46 that the rings 47 face the
plastically expanded section of the tubing 44. The
sealing rings serve to avoid that fluid at high hydraulic
pressure would be present between the conical ceramic
surface 46 of the mandrel 45 and the expanding tubing 44
which might lead to an irregularly large expansion of the
tubing 44.
The expansion mandrel 45 is provided with a central
vent passage 47 which is in communication with a coiled
vent line 48 through which fluid may be vented to the
*Trade-mark
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surface. After completion of the expansion process the
pig 45 may be pulled up to surface by the vent line and a
coiled kill and/or service line (not shown) may be
lowered into the expanded tubing 44 to facilitate
injection of kill and/or treatment fluids towards the
hydrocarbon fluid inflow zone which is normally be done
via the annulus between the production tubing and the
well casing. However, if the tubing 44 is expanded to a
smaller diameter then the residual annular space between
the casing 42 and expanded tubing 44 can be used for
venting of fluids during the expansion process and for
injection of fluids during the production process, in
which case there is no need for using a vent line 48 and
kill and/or service lines.
In conventional wells it is often necessary to use a
production tubing having an outer diameter which is less
than 50% of the inner diameter of the innermost well
casing to enable a smooth insertion of the tubing even if
the well is deviated and the casing has an irregular
inner surface. Therefore it is apparent that the in-situ
tubing expansion method according to the present
invention enhances an efficient use of the wellbore.
It will be understood that instead of moving the
expansion mandrel 45 through the tubing 44 by means of
hydraulic pressure, the mandrel can also be pulled
through the tubing by means of a cable or pushed through
the tubing by means of pipe string or rod.
It will also be understood that the casing 42 and the
casings 8, 9, 10, 11, 22, 24, 25 and 26 that are shown in
Fig. 1, 2 and 3 can be expanded using a similar expansion
process as described for the expansion of the tubing 44
with reference to Fig. 4, if these casings are also made
of a formable steel grade.
Preferably the expandable production tubing and
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expandable casings are made of a formable steel grade
having a yield strength-tensile strength ratio which is
lower than 0.8 and a yield strength which is at least 275
MPa.
The invention will now be further described on the
basis of the following comparative experiments.
Experiment 1
An expansion mandrel having a conical ceramic surface
(semi top angle A of cone = 20 ) was moved through a
10' conventional oil field tubular, known as casing grade L80
13% Cr, which is a widely used casing type, having an
initial outer diameter of 101.6 mm (4"), an initial wall
thickness of 5.75 mm, a burst pressure of 850 bar and a
strain hardening exponent n = 0.075. The expansion
mandrel was designed such that the outer diameter of the
expanded tubular would be 127 mm, so that the increase in
diameter would be 20%. The tubular burst during the
expansion process. Analysis showed that the ductility
limit of the material had been exceeded so that ductile
fracturing occurred.
Experiment 2
An experiment was carried out with a coiled tubing of
*
the type QT-800 which is increasingly used as a pro-
duction tubing in oil or gas wells. The tubing had an
initial outer diameter of 60.3 mm, a wall thickness of
5.15 mm, a burst pressure of 800 bar and a strain
hardening exponent n = 0.14. An expansion mandrel was
moved through the tubing which mandrel comprised a
conical ceramic surface such that the semi top angle A of
a cone enveloping the conical surface was 5 and which
was designed such that the outer diameter of the expanded
tubing would be 73 mm (increase of about 21%). This
tubing burst during the expansion process. Analysis
revealed that due to high friction forces the expansion
*Trade-mark
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pressure had exceeded the burst pressure of the pipe
during the expansion process.
Experiment 3
An experiment was carried out with a seamless pipe
made of a formable steel grade known as ASTM
A 106 Grade B. The pipe had an initial outer diameter of
101.6 mm (4"), an initial wall thickness of 5.75 mm and a
strain hardening exponent n = 0.175.
An expansion mandrel was pumped through the pipe,
which mandrel comprised a ceramic conical surface such
that the semi top angle A of a cone enveloping the
conical surface was 20 and such that the outer diameter
of the expanded pipe was 127 mm (5") and the outer
diameter increased by 21%.
The pipe was expanded successfully and the hydraulic
pressure exerted to the mandrel to move the mandrel
through the pipe was between 275 and 300 bar. The burst
pressure of the expanded pipe was between 520 and
530 bar.
