U.S. patent application number 11/019402 was filed with the patent office on 2005-08-04 for drilling fluid for casing drilling.
This patent application is currently assigned to SCHLUMBERGER TECHNOLOGY CORPORATION. Invention is credited to Bailey, Louise, Meeten, Gerald, Way, Paul.
Application Number | 20050167159 11/019402 |
Document ID | / |
Family ID | 31503334 |
Filed Date | 2005-08-04 |
United States Patent
Application |
20050167159 |
Kind Code |
A1 |
Bailey, Louise ; et
al. |
August 4, 2005 |
Drilling fluid for casing drilling
Abstract
The present invention provides a method of drilling a
hydrocarbon well using a drillstring adapted to provide a
continuous or quasi-continuous contact with the wall of the well
such that at least of section the well a compacting force is
exerted on filter cake deposited thereon; circulating a drilling
mud through the borehole during the drilling operation such that a
filter cake is deposited on the borehole wall by the drilling mud,
the filter cake being compacted by contact with the drillstring,
including, before the drilling mud enters the borehole a
conditioning additive in the drilling mud, the additive
conditioning the filter cake upon the contact with the drillstring
to increase the yield strength of the filter cake.
Inventors: |
Bailey, Louise; (St. Neots,
GB) ; Meeten, Gerald; (Ware, GB) ; Way,
Paul; (Hauxton, GB) |
Correspondence
Address: |
SCHLUMBERGER-DOLL RESEARCH
36 OLD QUARRY ROAD
RIDGEFIELD
CT
06877-4108
US
|
Assignee: |
SCHLUMBERGER TECHNOLOGY
CORPORATION
Ridgefield
CT
|
Family ID: |
31503334 |
Appl. No.: |
11/019402 |
Filed: |
December 22, 2004 |
Current U.S.
Class: |
175/72 |
Current CPC
Class: |
C09K 8/03 20130101; E21B
41/00 20130101; E21B 17/00 20130101 |
Class at
Publication: |
175/072 |
International
Class: |
E21B 007/18 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 31, 2003 |
GB |
0330234.6 |
Claims
1. A method of drilling a hydrocarbon well using a drill string
adapted to provide a continuous or quasi-continuous contact with
the wall of the well such that at least along a section of the well
a compacting force is exerted on filter cake deposited thereon
circulating a drilling mud through the borehole during the drilling
operation such that a filter cake is deposited on the borehole wall
by the drilling mud, the filter cake being compacted by contact
with the drill string, the method further comprising: including,
before the drilling mud enters the borehole, a conditioning
additive in the drilling mud, the additive conditioning the filter
cake upon said contact with the drill string to increase the yield
strength of the filter cake.
2. A method according to claim 1 wherein the additive is
particulate.
3. A method according to claim 2 wherein the particles are
non-spherical.
4. A method according to claim 3 wherein the particles are
lamellar.
5. A method according to claim 1, wherein the additive is mica
flakes.
6. A method according to claim 1, wherein the additive is rubber
particulates.
7. A method according to claim 1, wherein the drilling mud contains
at least 5 volume % of the additive.
8. A method according to claim 1, wherein the drilling mud contains
up to 20 volume % of the additive.
9. A method according to claim 1, wherein the drill string is
assembled from casing tubes.
10. A method according to claim 1, wherein the drill string
includes one or more subparts with enlarged diameter to emulate
casing drilling.
11. A method according to claim 1, wherein the drill string is
adapted to engage a wall of an open uncased borehole with a low
angle of attack.
12. A drilling mud containing at least 5 volume % of mica
flakes.
13. A drilling mud containing at least 5 volume % of rubber
particulates.
Description
[0001] The present invention relates to methods to enhance the
performance of the filter or mud cake layer on the wall of the
wellbore as protective and isolating layer.
BACKGROUND OF THE INVENTION
[0002] To obtain fluids, such as oil and gas, from a subterranean
reservoir boreholes or wells are drilled from the surface into the
reservoir. The most commonly applied method to drill a well uses a
derrick or mast structure, in which a drill string is assembled and
continuously extended into the borehole as the drilling progresses.
Drilling is performed by rotating a drill bit attached to the end
of the drill string. During the drilling process pressurized
drilling fluid (commonly known as "mud" or "drilling mud") is
pumped from the surface into the hollow drill string to provide
lubrication to various members of the drill string including the
drill bit. On its way back to the surface through the annulus
between drill string and the wall of the borehole, the drilling
fluid removes the cuttings produced by the drill bit.
[0003] In most cases the pressure exerted by the drilling fluid is
above the formation or pore pressure to prevent the entry of
formation fluids into the wellbore during the drilling process. As
a beneficial side effect, a small amount of pressurized mud enters
into porous sections of the formation as it flow across those, thus
leaving behind a layer of larger particles on the borehole wall.
This layer is referred to as filter or mud cake. The mud cake layer
prevents further fluid loss, which can be harmful, damaging
formation permeability and lubricating fractures.
[0004] The barrier provided by the mud cake can potentially
increase the so-called "mud window". The mud window is a pressure
range in which the driller maintains the mud pressure. The mud
pressure should be sufficiently high to prevent influx from the
formation whilst being low enough to prevent a fracturing of the
formation and lost circulation. A wider mud window has the
advantage of effectively increasing the distance that can be
drilled before the open borehole requires a casing. With an
increased distance between subsequent casing shoes or points, the
drilling operation can be completed in a shorter time period and at
reduced costs.
[0005] Considerable efforts have therefore been made to optimize
the filter cake as a protective layer--mostly by adding suitable
chemical compositions to the base drilling fluid in order to
increase the stability of the mud cake and the adjacent formation
or to increase its capability of the mud cake layer to isolate the
borehole from the surrounding formation.
[0006] In a specific branch of drilling techniques normal oil field
casing is used as the drill string so that the well is
simultaneously drilled and cased. This method is commonly referred
to as "casing drilling".
[0007] Under certain circumstances, casing drilling has been shown
to reduce the in-hole trouble time significantly below that
obtained by conventional drilling, hence reducing overall drilling
costs (Fontenot et al. (2003)).
[0008] Casing drilling has been identified as a technology which is
capable of reducing or minimizing the problems associated with
conventional drilling such as stuck pipe, lost circulation, well
control, and failure to run casing. Shepard et al. (2002) showed
that the incidence of wellbore instability, lost circulation,
influx and drag while tripping out were significantly reduced when
using casing drilling compared to conventional drilling methods. It
has been suggested that the success of casing drilling is at least
partly attributable to wellbore plastering. Shepard et al. (2002)
suggested that the process of casing drilling mechanically
strengthens the wellbore by building and maintaining an impermeable
layer on the wellbore. Likewise, Fontenot et al. (2002) suggested
that casing drilling provides a wellbore that is more stable and
less permeable than when drilling with a conventional drill pipe
and collars, and further hypothesised that the casing rotation
mechanically conditions the wellbore wall to create a strong
impermeable surface finish, possibly accomplished by mechanically
plastering the wellbore wall with solids from the drilled cuttings
and the mud
[0009] In the light of the above, it is an object of the present
invention to advantageously condition the interface layer between
an open uncased wellbore and the surrounding formation during
drilling operations.
SUMMARY OF THE INVENTION
[0010] The present invention is at least partly based on a
realization that in casing drilling, the interaction between the
drill string (i.e. the casing) and the filter cake differs from
that which occurs during drilling with conventional drillpipe. For
example, the drill string is in much closer proximity to the filter
cake than a conventional drill pipe would be. This significantly
increases the number and extent of drill string-filter cake
contacts and provides a quasi-continuous or continuous interaction,
which could be described as compacting or, in analogy, as
plastering interaction.
[0011] During each contact, the drill string is also less likely to
deeply penetrate the filter cake than a conventional drill pipe,
because the larger radius of the casing compared to conventional
drill pipe reduces the pressure exerted on the filter cake.
[0012] It is an aspect of the present invention to make use of
these conditions for transferring selected additional material from
the drilling mud into the filter cake to condition the filter cake,
and hence provide a more stable well bore. Thus, in general terms,
the present invention relates to drilling muds containing additives
for conditioning the filter cake during casing drilling.
[0013] Casing drilling is understood to include casing drilling as
such. Also included are methods that rely on the introduction of
one or more large diameter tools or sub into a drilling of normal
diameter. In these methods the compacting sub has a diameter that
ensures a quasi-continuous or continuous contact with the wall of
the borehole and the filter cake.
[0014] The present invention provides a method of drilling a
hydrocarbon well using a drill string adapted to provide a
continuous or quasi-continuous contact with the wall of said well
such that at least on a section of the well a compacting force is
exerted on filter cake deposited thereon
[0015] circulating a drilling mud through the borehole during the
drilling operation such that a filter cake is deposited on the
borehole wall by the drilling mud, the filter cake being compacted
by contact with the drill string,
[0016] the method further comprising:
[0017] including, before the drilling mud enters the borehole a
conditioning additive in the drilling mud, the additive
conditioning the filter cake upon said contact with the drill
string to increase the yield strength of said filter cake.
[0018] By introducing such a conditioning additive, it is possible
to influence the properties of the filter cake in a selective and
optimal manner. For example, preferably, the additive is selected
to increase the strength of the filter cake. This is expected to
improve the quality of the following cement job.
[0019] A typical drilling fluid includes further additives which
vary widely depending on the wellbore and drilling conditions. Such
known additives include any combination of weight materials such as
barite, hematite or calcium, viscosifiers, such as bentonite,
xanthan, guar, hydroxyethyl cellulose or mixed-metal hydroxide,
dispersants (lignite), shale stabilizers, such as polyacrylamide,
glycols, potassium acetate, quaternary ammonium compound, various
other salts and lost circulation material as known in the art.
[0020] Typically, the additive is particulate. Preferably, the
particles are non-spherical, preferably with a ratio of 1:5 or less
between thickness and diameter or width. For example, the particles
may be lamellar. The highly anisometric particles can have a
substantial filter cake strengthening effect.
[0021] In some embodiments, the additive is mica flakes. These are
suitable when the drilling mud is water-based or oil-based. In
other embodiments, the additive is rubber particulates. These are
particularly suitable when the drilling mud is oil-based. Both
additives have been used as additives for different purposes in
known drilling fluids. However, in the present invention, these
additives are used to increase the (yield) strength of a filter
cake in a casing drilling type operation.
[0022] The drilling mud may contain at least 5 volume % of the
additive, and more preferably at least 10 volume %. Experience
suggests that the proportion by volume of additive in the filter
cake will be approximately double that of additive in the mud. If
less than 5 volume % additive is included, the additive can be too
diluted in the filter cake to have a significant conditioning
effect. The drilling mud may contain up to 20 volume % of the
additive, and more preferably up to 15 volume %. If more than 20
volume % additive is included, the mud will tend to become too
viscous.
[0023] A further aspect of the invention provides a drilling mud
suitable for performing the method of the previous aspect. One
example of such a drilling mud may contain at least 5 volume % of
mica flakes, and preferably up to 20 volume % of mica flakes.
[0024] Another example of such a drilling mud may contain at least
5 volume % of rubber particles, and preferably up to 20 volume % of
rubber particles.
[0025] Several subparts in accordance with the above embodiment are
advantageously distributed along the length of the bottom section
of the drill string, which section is to enter the newly drilled
open (uncased) borehole. Thus the action of the first subpart is
reinforced by other subparts passing through the same section of
the well at a later time. One or more subparts may therefore be
located in the drill string above the BHA and/or the drill collar
section.
[0026] These and other aspects of the invention will be apparent
from the following detailed description of non-limitative examples
and drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0027] FIG. 1A shows a known drilling system;
[0028] FIG. 1B shows a detail of the well of FIG. 1A;
[0029] FIG. 2A illustrates a casing drilling operations;
[0030] FIG. 2B shows a cross-section of a casing drilling
arrangement;
[0031] FIG. 2C shows a cross-section of a casing drilling
arrangement in which the casing is off-centre;
[0032] FIG. 3 shows the effect of various particle types on the
yield stress of simulated water-based drilling fluid filter
cake;
[0033] FIG. 4 shows the effect of various particle types on the
yield stress of simulated oil-based drilling fluid filter cake;
and
[0034] FIG. 5 illustrates a subpart of a drill string adapted to
extend the casing drilling method to conventional drilling
operations.
EXAMPLES
[0035] In FIG. 1, there is shown a known well drilling system for
rotary drilling operations. A drill string 111 is shown within a
borehole 102. The borehole 102 is located in the earth 101. The
borehole 102 is being cut by the action of the drill bit 110. The
drill bit 110 is disposed at the far end of a bottom hole assembly
(BHA) 113 that is attached to and forms the lower portion of the
drill string 111. The bottom hole assembly 113 contains a number of
devices including several drill collars 113-1 to increase the
weight on the bit 110.
[0036] The drilling surface system includes a derrick 121 and a
hoisting system, a rotating system, and a mud circulation system
130. The hoisting system which suspends the drill string 111,
includes the draw works 122, a hook 123 and a swivel 124. The
rotating system includes a kelly 125, a rotary table 126, and
engines (not shown). The rotating system imparts a rotational force
on the drill string 111 during a rotational drilling operation in a
manner well known in the art.
[0037] A mud circulation system 130 pumps drilling fluid down the
central opening in the drill string 111. The drilling fluid is
often called mud, and it is typically a mixture of water or diesel
fuel, special clays, and other chemicals. The drilling mud is
stored in a mud pit 131. The drilling mud is drawn into mud pumps
132 which pump the mud though the surface pipe system 133, the
stand pipe 134, the kelly hose 135, and the swivel 124, which
contains a rotating seal, into the kelly 125 and finally through
the drill string 111 and the drill bit 110.
[0038] As the teeth of the drill bit grind and gouges the earth
formation into cuttings the mud is ejected out of openings or
nozzles in the bit 110 with great speed and pressure. These jets of
mud lift the cuttings off the bottom of the hole and away from the
bit, and up towards the surface in the annular space between drill
string 111 and the wall of borehole 102. At the surface the mud and
cuttings leave the well through a side outlet in a blowout
preventer 114 and through the mud return line 115. The blowout
preventer 114 comprises a pressure control device and a rotary
seal. From a cuttings separator (not shown) the mud is returned to
mud pit 131 for storage and re-use.
[0039] Although a system with jointed drill string 111, a kelly 125
and rotary table 126 is shown in FIG. 1, the invention is
applicable to other drilling systems such as in top drive drilling
derricks or coiled tubing. Although the drilling system is shown as
being on land, it is applicable to marine and transitions zone
environments.
[0040] In FIG. 1B there is shown a part of an open hole section of
the borehole 102. The section shown in FIG. 1B includes a section
of the drill string 111 with a tool joint 112 in the center of the
open, i.e. uncased, borehole 102. The borehole traverses a porous
formation layer 103 embedded within layers of impermeable rock 104.
The drilling fluid is circulated through the drill pipe 111 and
returns loaded with cuttings through the annulus between the wall
of the borehole 102 and the pipe 111 as indicated by arrows.
[0041] During the drilling operations, a small amount of the liquid
components of the drilling fluid are absorbed by the formation
leaving behind a layer of solid particles 105. As indicated in FIG.
1B, the mud cake layer 105 is thicker across the porous formation
layers 103 than across impermeable layers 104. The mud cake layer
105 is believed to enhance the stability of the well.
[0042] In order to preserve and possibly enhance the stability of
the mud cake layer 105, the invention proposes the use of casing
drilling or drilling subs that exert force or pressure in a
continuous or quasi-continuous manner on the wall of the borehole
as the drilling operation progresses. Rather than cutting through
the mud cake, casing drilling or subs are designed to slide on the
filter cake gently compressing or compacting it, thus forcing more
fluid or particles into the surrounding formation and/or
solidifying the mud cake layer 105 not unlike wall plastering. The
compacting force is exerted in a radial direction, perpendicular to
the wall of the borehole.
[0043] In FIG. 2A, the drill string 111 of FIG. 1 is replaced by a
casing string 211. The larger diameter of the casing narrows the
gap between the casing 211 and the wall of the well 102.
[0044] As a result the casing 211 exerts at many contact areas a
force on the filter cake 105. The following schematic FIGS. 2B and
2C illustrate the effect of this interaction maintaining the
numerals as above.
[0045] FIG. 2B shows the casing 211 of outer radius OA, coaxially
located inside a wellbore 102 of radius OC (=R), the inside of
which is coated with a filter cake 105 of radius OB. Drilling mud
flows down the well inside the casing 211, and returns in the
annulus 102 of width g between the outer radius of the casing 211
and the inside of the filter cake 105.
[0046] FIG. 2C illustrates the effect of a lateral force F (per
unit length of the bore) causing the casing 211 to penetrate a
distance e into the filter cake 105. This force may arise due to
gravity in a deviated section, or in a curved section from the
axial tension or compression in the casing 211. The force will
compress the filter cake 105 between the casing 211 and the inside
face of the wellbore 102 away from the region of closest approach
of the casing 211 to the face of the wellbore 102. For cake
penetrations which are small, we can ignore the viscous force and
consider the penetration to be determined mainly by the cake's
yield stress .tau..sub.0. If the penetration depth e is small
compared with the thickness H of the cake, and compared to the
annular gap g, cylindrical squeeze flow theory gives: 1 e = FgH 4 R
2 0 , [ 1 ]
[0047] hence showing that for a given force F, the penetration e is
least for:
[0048] 1. a small annular gap g;
[0049] 2. a small filter cake thickness H; and
[0050] 3. a large yield stress .tau..sub.0, i.e. a strong filter
cake.
[0051] The above model assumes that the filter cake has a uniform
yield stress throughout its thickness. However, this is an
oversimplification as real filter cakes on a wellbore wall are
strongest where the matrix stress is greatest, i.e. closest to the
wall However, Equation [1] above is believed to be qualitatively
correct.
[0052] In casing drilling however, the rotating casing and the
filter cake are in closer proximity than in conventional drilling
using drillpipe, and according to well known principles of dynamic
filter cake formation, the azimuthal shear stress of the mud
arising from this proximity will inhibit the deposition of the less
compacted part of the filter cake (i.e. that closest to the
casing).
[0053] Thus, compared to conventional drilling, casing drilling is
likely to result in the following differences in filter cake
properties:
[0054] a) a more uniform yield stress over its thickness;
[0055] b) a smaller thickness; and
[0056] c) a greater mean yield stress .tau..sub.0.
[0057] Property a) above means that the approximations in Equation
[1] will be less significant. Filter cake penetration is believed
to be associated with high torque, drag and the risk of sticking,
whereby some advantages of casing drilling may be attributed to the
small annular gap g in casing drilling and properties b) and c)
above.
[0058] Thus, in embodiments of the present invention, additives to
the drilling mud augment the mean yield stress .tau..sub.0 of the
filter cake. Such augmentation is shown by Equation [1] above to
decrease the lateral casing penetration, and therefore to decrease
torque and drag whilst drilling. A strong filter cake which lines
the wellbore is also expected to increase the stability of the
wellbore.
[0059] In the examples below, we show that granular materials have
a moderate strengthening effect when incorporated into filter cake,
but that other particulate materials, e.g. those which are highly
anisometric in shape or which are deformable, have a much greater
strengthening effect. Such materials may be added as additives to
standard drilling fluid, or may be deliberately incorporated in the
drilling fluid from the start.
[0060] Methods which result in increasing the strength and
decreasing the thickness of the filter cake are also expected to
improve the quality of the cement job.
[0061] In the experiments below, the strengthening effect of
incorporating particulate materials into simulated filter cake was
investigated.
[0062] One set of particulate materials used were of granular shape
in order to simulate ground cuttings which might result from
drilling operations.
[0063] Further sets of particulate materials had lamellar and
spherical shapes. Deformable particulate materials were also used.
These materials would not arise naturally during drilling, but they
can be added to the drilling fluid as additives in order to
advantageously change the condition of the filter cake.
[0064] A filter cake of a water-based drilling fluid was simulated
by adding tap water to cuttings of Oxford shale and moulding the
stiff mixture by hand until it resembled the consistency of a
typical water-based drilling fluid filter cake, similar to that of
potter's clay. The shale contained swelling clays such as
montmorillonite as well as non-swelling clays and sands, and hence
the simulated filter cake approximately resembled the mineral
composition of water-based drilling fluid filter cake. Comparative
measurements of the weight of the simulated filter cake before and
after drying overnight at 105.degree. C. showed the water content
to be 25% by weight.
[0065] Various particulate materials were moulded into this filter
cake simulant, and the resulting strength, expressed as shear yield
stress, was measured by an extrusion method, as described in Benbow
et al. 1991. All the added particles had a size of less than about
0.3 mm.
[0066] FIG. 3 shows the yield stress plotted against the volume
fraction of added particles. All particle types are shown to
strengthen the filter cake, but mica flake had a much greater
effect for a given volume fraction than the rigid granular sand or
the granular rubber.
[0067] A filter cake of an oil-based drilling fluid was simulated
by the modelling clay Plasticine.TM. (manufactured by Humbrol),
which is understood to be a concentrated paste of organophilic clay
dispersed in an oil, and therefore similar to oil-based drilling
fluid filter cake.
[0068] Various particulate materials were moulded into this filter
cake simulant and the resulting strength, expressed as the shear
yield stress, was measured as described above in relation to the
water-based drilling fluid examples. All the added particles had a
size of less than about 0.3 mm.
[0069] FIG. 4 shows the yield stress plotted against the volume
fraction of added particles.
[0070] All particles are shown to strengthen the filter cake, but
mica flake and granular tyre-rubber had a much greater effect at a
given volume fraction than the rigid particles of granular sand or
those of near spherical polystyrene.
[0071] FIGS. 3 and 4 both show that the yield stress of the filter
cake was increased by all the particulate additives used. For a
given volume fraction, mica flake had a disproportionately large
effect on both types of filter cake simulant, compared to sand and
polystyrene. This is believed to be due to the efficient
space-filling properties of highly non-spherical particles.
[0072] For the oil-based filter cake simulant, tyre-rubber
particles also provided a significant yield stress increase. This
is believed to result from absorption by the rubber particles of
some of the oil from the simulant in proximity to the surface of
the particles.
[0073] For both water-based and oil-based filter cake simulants,
the yield stress data .tau..sub.Y(P) can be expressed by the
relationship:
.tau..sub.Y(.phi.)=.tau..sub.Y(0)+b(exp(c.phi.)-1) [2]
[0074] in which .tau..sub.Y(0) is the yield stress of the filter
cake without added particulates and the parameters b and c are
independent of .phi.. Table 1 gives data from the fits of Equation
(2) to the experimental results shown in FIGS. 3 and 4. It shows
that the magnitude of b and c depend strongly on the filter cake
type and on the added particle type.
1 TABLE 1 Added particles .tau..sub.Y(0)/MPa b/MPa c Water-based
Sand 0.122 0.046 5.93 filter-cake Tyre-rubber 0.127 0.144 2.30 Mica
flake 0.117 0.084 25.1 Oil-based Sand 0.104 0.006 6.96 filter-cake
Polystyrene 0.100 0.012 6.89 Tyre-rubber 0.110 0.118 4.97 Mica
flake 0.112 0.027 21.1
[0075] A suitable subpart to extend the advantages of known casing
drilling to conventional drillstring drilling is shown in FIG. 5.
The subpart 530 includes a bottom and upper section 531, 532,
respectively, providing box and pin connection to the remainder of
the drill string (not shown). A main body 533 of the subpart
comprises two frustro-conical sections with a cylindrical middle
section similar to a bobbin. The conical sections include the
bearings for four hinges 534. Mounted onto each of the hinges is a
steel vane or pad element 535 having a flat arcuate shape with
rounded edges to reduce forces against any lateral movement of the
subpart.
[0076] The hinges 534 are spring-loaded to force the four pads to
fold tightly around the main section in the absence of hydraulic
pressure. The drilling fluid provides the hydraulic pressure as it
is pumped from a surface location through the drill string. The
pressurized drilling fluid activates internal cylinders (not shown)
that rotate the vanes 535 around the hinges thus bringing their
distal ends closer to the wall of the borehole. While the drill
string remains in a centered position within the borehole, the
rollers are designed to provide the first area of contact between
the subpart 530 and the formation wall. The hinge-mounted vanes or
pads 535 are configured to bend or flex as the radial distance
between the drill string and the wall varies during the drilling
operations, so as to remain in permanent contact with the wall.
[0077] During the drilling process, the drill string including the
subpart 530 are rotated from the surface, and the subpart
continuously exerts pressure on the formation wall and any mud cake
layer on its surface. When the drilling terminates and the pressure
inside the drill string drops, the vanes 535 fold back around the
main body 533 to facilitate a subsequent tripping operation.
[0078] While the invention has been described in conjunction with
the exemplary embodiments described above, many equivalent
modifications and variations will be apparent to those skilled in
the art when given this disclosure. Accordingly, the exemplary
embodiments of the invention set forth above are considered to be
illustrative and not limiting. Various changes to the described
embodiments may be made without departing from the spirit and scope
of the invention.
REFERENCES
[0079] The references mentioned herein are all incorporated by
reference.
[0080] J J Benbow, S H Jazayeri, J Bridgwater (1991) The flow of
pastes through dies of complicated geometry. Powder Technology
65:393-401.
[0081] K Fontenot, T M Warren, B Houtchens (2002) Casing drilling
proves successful in South Texas. IADC World Drilling 2002, Madrid,
Spain, June 5-6.
[0082] K Fontenot, J Highnote, T Warren (2003) Casing drilling
activity expands in South Texas. SPE/IADC 79862. SPE/IADC Drilling
Conference, Amsterdam, The Netherlands, 19-21 February, 2003.
[0083] S F Shepard, R H Reiley, T M Warren (2002) Casing drilling:
and emerging technology. SPE Drilling & Completion March 2002,
4-14.
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