OA12135A - Improved method for the drilling of oil wells. - Google Patents

Abstract

Method for the drilling of oil wells and for the positioning of the appropriate casings, consisting in drilling the well section of interest and, during the drilling, in maintaining a high degree of hole regularity by the use of automatic verticality and/or curvature control equipment. This method allows the positioning of casings with an almost constant clearance with values of +/- 1.5 inches for the whole well depth (lean profile).

Description

12135

IMPROVED METHOD FOR THE DRILLING OF OIL WELLS

The présent invention relates to an improvedmethod for the drilling of oil wells which allowsthe positioning of lining columns, operating with an almost constant clearance for the whole of the desired well depth and which substantially consistsin effecting the drilling, guaranteeing the élimi-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 effectedwhich comprise the positioning of appropriate' cas-ings at pre-established intervals in relation tothe depth reached and characteristics of the forma-tions penetrated.

During the pipe-laying, in order to guaranteeeasy descent of the lining columns into the well, 2 12135 it is generally necessary to ensure that the différence between the external casing diameter and the hole diameter (clearance) is maintained at sufficiently high values.

During conventional techonology drilling, the clearance 5 between casing and hole can vary from values of about 6-7 inches (15-16 cm) for the surface and/or intermediate phases, to values of almost 2,54 cm (an inch) for the deeper phases (for example : 66, 04 cm (26") hole for 50,8 cm (20") conductor pipe, 44,45 cm (17 *s") 10 hole for 39,97 cm (13 3/8"), 31,12 cm (12 ^") hole for 24,45 cm (9 5/8") casing, 21,59 cm (8 *s") hole for 17,78 cm (7") casing.

The necessity of adopting high clearance values is linked to the high rigidity of pipes with a larger 15 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 irregularity(déviations, curving and/or narrowing) can make the 20 lowering of columns into the well difficult especiallyduring the surface and/or intermediate phases.

The necessity, according to conventional technologies,of producing holes with a considerably larger diameterwith respect to that of the 12135 casing to guarantee descent to the well bottom dur-ing the surface and intermediate phases, causes theformation of a .large quantity of waste products anda long duration of the plant on the territory withconséquent long times and high drilling costs.

The drilling method according to the présent invention allows, with the same diameter of the production column, the dimensions of the upper wellpart (surface and intermediate columns) to be re-duced. This enables a significant réduction in theconsumption of materials (mud, cernent 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 withrespect to the diameter of the columns to be low-ered, which generally implies the possibility ofeffecting holes with a smaller diameter compared tothe conventional technique. Ail of this positively influences the advancement rate of the bit there- fore allowing the production times of the holes tobe reduced, with a conséquent decrease in thecosts. The technique according to the présent in-vention also enables a significant réduction in theoperating costs, as the verticality and/or regular curvature of the well facilitâtes ail workover and 4 12135 well intervention operations.

This method comprises a drilling and pipe-laying technique which allows the positioning ofthe lining columns operating with an almost con-stant clearance with values of more or less 3,81 cm Çl.5inches )(3-4 cm) for the whole well depth (from thetop to the bottom), or in any case for the whole ofthe desired well depth. The fact that a reducedclearance is adopted, allows, with the same numberof columns and final diameter of the productioncasing, the dimensions of the upper part of thewell to be greatly reduced.

This solution is mainly suitable for applica-tions in deep, vertical or deviated wells, also inthe presence of formations with a low drilling ca-pacity and/or difficulty in controlling the trajec-tory. In these cases the use of the technique ac-cording to the invention allows considérable timesaving and réduction in the drilling costs.

An object of the présent invention thereforerelates to an improved method for the drilling ofoil wells and for the contemporaneous positioningof appropriate casings, characterired in that theclearance is kept almost constant for the whole ofthe desired well depth, consisting in drilling the 5 12135 well section of interest, maintaining a high degreeof hole regularity by the use of automatic verti-cality and/or curvature control equipment.

In particular, the method according to thefollowing invention comprises effecting the drill-ing phase according to the following procedures: automatic control of the verticality and/orcurvature of the well; use · of bits equipped with adéquate distribu-tors and roller reamers, in order to guaranteehole regularity and calibration; use of drilling mud with Chemical andrheological characteristics which are such asto minimize any possible problems of hole in-stability; constant control of ail the drilling parame-ters in order to maintain a curvature (BÜR/DO)of 0.7 degrees every 30 m, with a maximumslope of 1.5 degrees in the vertical sections.

For the automatic control of the well verti-cality, the use of the device called "Straight HoleDrilling Device (SDD)", a drilling instrument pro-duced by the Applicant in collaboration with BakerHughes, has proved to be particularly advantageous.This device, contrary to the conventional Systems, 12135 automatically effects a continuous correction ofthe verticality and is based on a retro-activatedcontrol which ensures the absolute verticality ofholes, even in formations which hâve 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 incollaboration 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 ofthe method according to the présent invention, thepipe-laying procedure is effected as follows. 7 12135

After producing a perfectly vertical and wellcalibrated hole the lining columns can be loweredinto the well.. In order to facilitate the passageof the casing into the hole calibrated with a re-duced clearance, the following précautions should be observed: * Use threaded connections of the flush or near-flush type. The intégral connection called "A-SFC" (Agip Semi Flush Connection) described in patent application 5934 filed on 19/02/1999 bythe same Applicant, can be advantageously used. This connection has a limited clearance (external diameter 2.5% higher than the exter-nal pipe diameter) and is characterized by asignificant improvement in the compression andtorque strength/efficiency, with respect toexisting connections of the same category. Thejoint is also equipped with a double métal tométal seal which makes it suitable for appli-cations in deep wells and/or in the presenceof high pressures. • Check the perfect rectilinearity of the pipes.

The tolérances admitted by the API régulationin terms of residual manufacturing deforma-tions are not acceptable in effecting the Lean 8 12135 technique. The rectilinearity must thereforebe accurately checked before beginning thepiping operations. • Limit the use of centralizers (if necessaryuse an Intégral Blade Centralizer). • During the pipe laying, limit the descent rateof the column to avoid forcing and the créa-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 spécial malts with ahigh fluidity and mechanical résistance are used.

In the case of possible deviated sections, inaddition to the following précautions, curvatureshould be planned in relation to the flexibility ofthe casings to be used.

Operating as described above, it was possibleto lower a casing with an external diameterslightly less than that of the hole (about 3,81cm (1.5inches) into the well, creating a narrower pipe-laying profile (Lean), with the advantages de-scribed above and without jeopardizing the diameter 12135 of the production column.

Figure 1 compares the conventional pipe-layingprogram with the "Lear." program. The data in saidfigure were obtained in the Monte Enoc 9 well ef-fected in the Field of Val D’Agri in Basilicata. Itis évident how with the "Lean" solution, starting from a lower diameter of the surface and intermedi- ate columns, a production column is obtained withthe sanie' diameter as that produced with the conven-tional solution.

Figure 2 describes a further two examples ofLean pipe-laying, which can provide a valid alter-native to the previous scheme, above ail in contin-gency situations.

Figure 3 schematically represents a comparison between the hole sections.

Claims (2)

10 12135 CLAIMS

1. A method for the drilling of oil wells and positioning of the appropriate casings, consisting in drilling the well section of interest and, 5 during the drilling, in maintaining a high degree of hole regularity by the use of automatic verticality and/or curvature control equipment, said method being characterized in that the drilling phase is carried out observing the following précautions: 10 · Automatic control of the verticality and/or curvature of the well using the device called "Straight Hole Drilling Device"(SDD); • Use of bits equipped with adeguate distributors and roller reamers 15 · Use of drilling mud with Chemical and rheological characteristics which are such as to minimize any possible well instability problems • Constant control of ail the drilling parameters in order to maintain a curvature (BUR/DO) of 0,7 20 degrees of every 30m, with a maximum slope of 1,5 degrees in the vertical sections.