Note: Descriptions are shown in the official language in which they were submitted.
CA 02396282 2002-07-04
WO 01/53655 PCT/EP00/13370
IMPROVED METHOD FOR THE DRILLING OF OIL WELLS
The present invention relates to an improved
method for the drilling of oil wells which allows
the positioning of lining columns, operating with
an almost constant clearance for the whole of the
desired well depth and which substantially consists
in effecting the drilling, guaranteeing the elimi-
nation of any geometrical curvature and irregulari-
ties of the hole, whether it be vertical or devi-
ated.
During the drilling of oil wells, lining op-
erations of the hole (pipe-laying) are effected
which comprise the positioning of appropriate cas-
ings at pre-established intervals in relation to
the depth reached and characteristics of the forma-
dons penetrated.
During the pipe-laying, in order to guarantee
easy descent of the lining columns into the well,
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., ,
it is generally necessary to ensure that the dif-
ference between the external casing diameter and
the hole diameter (clearance) is maintained at suf-
ficiently high values.
During conventional technological drilling,
the clearance between casing and hole can vary from
values of about 6-7 inches ( I5-16 cm) for the sur-
face and/or intermediate phases, to values of al-
i ~~
mostYCn inch for the deeper phases (for example:
~4crw~,, 50, gGw. ~S ~ 3'S,~3~cw~
Y 6" hole forr~20" conductor pipe,~7 1/2" hole for Y
~) ) )
3r , ~Zc~, .14~45c.~, ,~I, S'Sc~.,r~
13 3/8", Y I2 1/4", hole forY~9 5/8" casing,YC8 1/2')
hole fo~C7" casing) .
The necessity of adopting high clearance va'_-
ues is linked to the high rigidity of pipes with a
larger diameter/thickness and the impossibility of
drilling perfectly vertical wells and/or with a
controlled curvature. In fact, the poor flexibility
of pipes together with a certain degree of hole ir-
regularity (deviations, curving and/or narrowing)
can make the lowering of columns into the well dif-
ficult especially during the surface .and/or inter-
mediate phases.
The necessity, according to the conventional
technologies, of producing holes with a considera-
bly larger diameter with respect to that of the
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casing to guarantee descent to the well bottom dur
ing the surface and intermediate phases, causes the
formation of a.large quantity of waste products and
a long duration of the plant on the territory with
consequent long times and high drilling costs.
The drilling method according to the present
invention allows, with the same diameter of the
production column, the dimensions of the upper well
part (surface and intermediate columns) to be re-
duced. This enables a significant reduction in the
consumption of materials (mud, cement and steel)
and consequently the production of waste products.
This technique also avoids the necessity of produc-
ing holes with a diameter which is too large with
respect to the diameter of the columns to be low-
eyed, which generally implies the possibility of
effecting holes with a smaller diameter compared to
the conventional technique. All of this positively
influences the advancement rate of the bit there-
fore allowing the production times of the holes to
be reduced, with a consequent decrease in the
costs. The technique according to the present in-
vention also enables a significant reduction in the
operating costs, as the verticality and/or regular
curvature of the well facilitates all workover and
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25-01-2002 CA 02396282 2002-07-04 EP0013370
well intervention operations.
This method comprises a drilling and pipe-
laying technique which allows the positioning of
the lining columns operating with an almost 3c~i~
stant clearance with values of more or less~C~lS. S
inches (3-4 cm) for the whole well depth (from the
top to the bottom), or in any case for the whole of
the desired well depth. The fact that a reduced
clearance is adopted, allows. with the same number
i0 of columns and final diameter of the production
casing, the dimensions of the upper part of the
well to be greatly reduced.
This solution is mainly suitable for applica
tions in deep. vertical or deviated wells, also in
I5 the presence of formations with a low drilling ca
pacity and/or difficulty in controlling the trajec-
tort'. In these cases the use of the technique ac-
cording to the invention allows considerable time
saving and reduction in the drilling costs.
20 ' An object of the present invention therefore
relates to an improved method for the drilling of
oil wells and for the contemporaneous positioning
of appropriate casings, characterized in that the
clearance is kept almost constant for the whole of
25 the desired well depth, consisting in drilling the
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well section of interest, maintaining a high degree
of hole regularity by the use of automatic verti-
cality and/or curvature control equipment.
In particular, the method according to the
following invention comprises effecting the drill
ing phase according to the following procedures:
- automatic control of the verticality and/or
curvature of the well;
use of bits equipped with adequate distribu-
torn and roller reamers, in order to guarantee
hole regularity and calibration;
use of drilling mud with chemical and
rheological characteristics which are such as
to minimize any possible problems of hole in
stability;
- constant control of all the drilling parame-
ters in order to maintain a curvature (BUR/DO)
of 0.7 degrees every 30 m, with a maximum
slope of 1.5 degrees in the vertical sections.
For the automatic control of the well verti-
cality, the use of the device called "Straight Hole
Drilling Device (SDD)", a drilling instrument pro-
duced by the Applicant in collaboration with Baker
Hughes, has proved to be particularly advantageous.
This device, contrary to the conventional systems,
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automatically effects a continuous correction of
the verticality and is based on a retro-activated
control which .ensures the absolute verticality of
holes, even in formations which have a strong ten-
dency to cause the bit trajectory to deviate from
the vertical.
The use of a device called Autotrak, a drill-
ing instrument produced by the Applicant, again in
collaboration with Baker Hughes, has proved to be
advantageous for the automatic control of the cur-
vature. This device effects a continuous correction
of the curvature which guarantees an optimum geome-
try in the deviated sections.
A preview of both apparatuses produced in col-
laboration with Baker was provided in the paper SPE
50379 of November 1998.
Various alternatives are available on the mar-
ket both for the automatic verticality control and
curvature control, such as:
- RDS of Camco;
- AGS of Cambridge Automation
- Well Director of Well Done
As an illustrative but non-limiting example of
the method according to the present invention, the
pipe-laying procedure is effected as follows.
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After producing a perfectly vertical and well
calibrated hole the lining columns can be lowered
into the well.. In order to facilitate the passage
of the casing into the hole calibrated with a re-
duced clearance, the following precautions should
be observed:
~ Use threaded connections of the flush or near-
flush type. The integral connection called "A-
SFC" (Agip Semi Flush Connection) described in
patent application 5934 filed on 19/02/1999 by
the same Applicant, can be advantageously
used. This connection has a limited clearance
(external diameter 2.5o higher than the exter-
nal pipe diameter) and is characterized by a
significant improvement in the compression and
torque strength/efficiency, with respect to
existing connections of the same category. The
joint is also equipped with a double metal to
metal seal which makes it suitable for appli-
cations in deep wells and/or in the presence
of high pressures.
~ Check the perfect rectilinearity of the pipes.
The tolerances admitted by the API regulation
in terms of residual manufacturing deforma-
dons are not acceptable in effecting the Lean
25-01-2002 CA 02396282 2002-07-04 EP0013370
technique. The rectilinearity must therefore
be accurately checked before beginning the
piping operations.
~ Limit the use of centralizers (if necessary
use an Integral Hlade Centralizer).
~ During the pipe laying, limit the descent rate
of the column to avoid forcing and the crea-
tion of dangerous ramming linked to the re-
duced ring dimensions.
~ Use cementation shoes of the centralized type
(Stabilizer Shoe) equipped with an auto fill-
up device.
~ During the cementation special malts with a
high fluidity and mechanical resistance are
used.
In the case of possible deviated sections, in
addition to the following precautions, curvature
should be planned in relation to the flexibility of
the casings to be used.
Operating as described above, it was possible
to lower a casing with an external diameter
3,81 cue,
slightly less than that of the hole (aboutYCl.S
inched) into the well, creating a narrower pipe-
laying profile (Lean), with the advantages de-
scribed above and without jeopardizing the diameter
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of the production column.
Figure 1 compares the conventional pipe-laying
program with the "Lean" program. The data in said
figure were obtained in the Monte Enoc 9 well ef-
fected in the Field of Val D'Agri in Basilicata. It
is evident how with the "Lean" solution, starting
from a lower diameter of the surface and intermedi-
ate columns, a production column is obtained with
the same diameter as that produced with the conven-
tional solution.
Figure 2 describes a further two examples of
Lean pipe-laying, which can provide a valid alter-
native to the previous scheme, above all in contin-
gency situations.
Figure 3 schematically represents a comparison
between the hole sections.
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