EP0178709A1 - Stabilizer - Google Patents

Abstract

1. A method for modifying the trajectory of a cutting tool for a deep directional drilling well, driven either by a hanging motor or a hanging turbine with a rate of at least 700 rot/min or by a rotary table from the surface at a rate of at least 100 rot/min, by means of a stabilizing device having helicoïdal lateral ribs (8) separated by passageways (14) of drilling fluid and provided with a hardfacing material affording good erosion and abrasion resistance, characterized in that at least one substantially circumferential groove is defined in the ribs and located in a plane which is perpendicular to the axis of rotation, so as to interconnected the passageways (14) of drilling fluid.

Description

The present invention relates to a device for stabilizing a drill string, consisting of a steel cylinder having laterally helical projections provided with a coating offering good resistance to erosion and abrasion.

The stabilization devices are mainly intended to control the direction and quality of drilling in deep vertical or directional wells.

As is known from US Pat. No. 4,245,709, a stabilizing sleeve usually used for directional turbine or rotary drilling, consists of a cylindrical steel casing fixed to the end of a drill string, in the vicinity of a diamond-tipped bit or a crown, in alignment with the latter, by means of a cylindrical end piece of determined length, provided with a standardized fixing thread.

Helical projections provided on the outer side wall of the aforementioned envelope determine a cylinder of diameter substantially equal to the diameter of the drilled hole. The diameter of the envelope is generally a few tens of millimeters less than the diameter of the cylinder determined by the helical projections.

The helical projections are covered with a coating, having excellent resistance to erosion and abrasion.

The recesses formed between the projections allow the rock waste entrained by the drilling fluid to rise.

The stabilizing sleeve makes it possible to distribute this contact along with a larger surface, the forces that the diamond drilling tool on the side wall of the drilled well, thus reducing the capacity of lateral destruction of the rock by the tool under the 'effect of its own weight and limiting the pendulum effect of the entire drilling rig as well as spiraling in drilling with a turbine.

Spiraling is a deformation of the corkscrew hole. It has the effect of increasing the risk of the drill string getting stuck in the hole.

The pendulum effect meanwhile brings the profile of the well closer to the vertical. However, this goal is not sought in deviated drilling. The use of a stabilizing sleeve makes it possible to achieve adequate stabilization of the entire drill string. We thus manage to maintain or even increase the inclination of the deviated wells.

It has been found that the stabilizing sleeves used in deviated deep boreholes for the reasons mentioned above have an important influence on the azimuthal deviation of the drill string.

• - dans le cas du forage rotary, une déviation azimutale orientée vers la droite, lorsqu'on prend la direction instantanée de forage comme référence,
• - dans le cas du forage à la turbine, une déviation azimutale vers la gauche, lorsqu'on prend la direction instantanée de forage comme référence.

From the numerous data collected on various sites, we can generally characterize the behavior of the drill string. We observe that :

• - in the case of rotary drilling, an azimuth deviation oriented to the right, when the instantaneous direction of drilling is taken as a reference,
• - in the case of turbine drilling, an azimuth deviation to the left, when the instantaneous direction of drilling is taken as a reference.

Numerous tests have shown that the intensity of azimuthal deflection to the left in turbine drilling is strongly influenced by the length of the stabilizing sleeve. The deviation intensity is defined as the increase in the deviation from an initial direction of drilling per unit of length drilled.

On average observed in wells inclined at about 45 °, a deviation intensity of 0.5 to 1.80 degrees per hundred feet for lengths of stabilization devices between 9 and 18 inches (22.86 to 45.72 cm).

The present invention aims to reduce the amplitude of unwanted deviations and proposes a device for this stabilization, comprising with respect to conventional devices, modifications which will make it possible to keep with the rock, a length and therefore a sufficient contact surface only to limit the lateral aggressiveness of the drilling tool and at the same time controlling the azimuthal deflection angle to the left of the gasket during drilling with the turbine.

It relates to a device for stabilizing a drill string, consisting of a cylindrical steel body having laterally helical projections provided with a coating offering good resistance to erosion and abrasion, essentially characterized in that it comprises at least one substantially circumferential groove formed in the above-mentioned projections, so as to connect the recesses between them these; according to a feature of the invention, the aforementioned grooves are formed over part of the height of the projections.

The grooves are advantageously provided, preferably by milling, at regular intervals along the helical projections.

In a particular embodiment, a single groove has a helical shape with a short pitch.

A different embodiment includes at least two portions of sleeves of the same diameter arranged in the same alignment behind the drilling tool.

Other features and details of the invention will appear during the following detailed description of a particular embodiment of the invention given by way of non-limiting example with reference to the accompanying drawings.

• - la figure 1 est une vue en élévation latérale d'un trépan de forage à pointes diamantées muni d'une première forme de réalisation d'un dispositif de stabilisation suivant l'invention ;
• - la figure 2 est une vue en perspective de la jupe de stabilisation illustrée à la figure 1 ;
• - la figure 3, est une vue semblable à la figure 1, d'une deuxième forme de réalisation d'un dispositif de stabilisation ;
• - la figure 4 montre une coupe transversale perpendiculaire à l'axe de forage d'un palier radial en fonctionnement hydrodynamique ;
• - la figure 5 montre une coupe transversale, perpendiculaire à l'axe de forage, d'un palier radial en fonctionnement par contact direct ;
• -la figure 6 est un diagramme illustrant une première relation existant entre l'intensité de la déviation à gauche d'un puits de forage à la turbine en fonction de la longueur du dispositif de stabilisation;
• - la figure 7 est un diagramme illustrant une seconde relation existant entre la charge statique correspondant à un comportement hydrodynamique équivalent, en fonction de 1₂ longueur du dispositif de stabilisation; et
• - la figure ε montre la corrélation existant entre l'intensité de le déviation a gauche d'un puits de forage à la turbine et la charge statique correspondant à un comportement hydrodynamique équivalent.

In these drawings:

• - Figure 1 is a side elevational view of a drill bit with diamond points provided with a first embodiment of a stabilization device according to the invention;
• - Figure 2 is a perspective view of the stabilization skirt illustrated in Figure 1;
• - Figure 3, is a view similar to Figure 1, of a second embodiment of a stabilization device;
• - Figure 4 shows a cross section perpendicular to the drilling axis of a radial bearing in hydrodynamic operation;
• - Figure 5 shows a cross section, perpendicular to the drilling axis, of a radial bearing in operation by direct contact;
• FIG. 6 is a diagram illustrating a first relationship existing between the intensity of the deviation to the left of a wellbore to the turbine as a function of the length of the stabilization device;
• - Figure 7 is a diagram illustrating a second relationship between the static load corresponding to an equivalent hydrodynamic behavior, as a function of 1 ₂ length of the stabilization device; and
• - Figure ε shows the correlation between the intensity of the deviation to the left of a wellbore to the turbine and the static load corresponding to an equivalent hydrodynamic behavior.

In the above drawings, the same reference notations designate identical or analogous elements.

As illustrated in FIG. 1, a drilling tool designated as a whole by the reference notation 1, usually used for deep directional drilling with a turbine or rotary, consists of a drilling head 2 proper, produced either made of composite material shaped by powder metallurgy techniques, either steel or cast metal. The head 2 is a drill bit or a drilling crown provided over its entire surface in contact with the bottom of the well, with cutting elements 3 placed so as to make effective both the destruction of the rock and the evacuation of shavings.

This drilling head 2 is fixed to the end of a drill string, not shown, by means of a frustoconical end piece 4 of variable length between 15 and 100 cm and have a fixing thread 5 meeting the standards in force.

A stabilization device, consisting of a cylindrical body 6 of steel, having laterally helical projections 7 provided with a coating 8 having sufficient resistance to erosion and abrasion and generally designated by the reference notation 9, is mounted in alignment with the drilling head 2, behind the latter, on the cylindrical end piece 4.

The coating 8 of the helical projections 7 may consist of a hard metal or of a composite material, possibly diamond-coated.

These known tools have, as explained above, a tendency to deviate to the left or to the right depending on whether it is a turbine drilling or a rotary drilling.

The phenomena of deviation of drilling tools in deep deviated wells are explained when we apply the Sommerfeld theory of bearings with hydrodynamic functioning.

It is indeed permissible to assimilate a stabilization device 9 rotated in m deep well deviated to a conventional smooth bearing 10 consisting of a shaft 11 rotating inside a bearing 12 (Figures 4 and 5).

• 1. lubrification hydrodynamique, ou
• 2. contact direct.

According to Sommerfeld's theory, the plain bearings 10 can operate in two distinct ways, under the following conditions:

• 1. hydrodynamic lubrication, or
• 2. direct contact.

In hydrodynamic lubrication, an oil film 13 is established permanently between the two surfaces in relative movement, namely the shaft 11 and the bearing 12. The oil film under pressure is generated by the very movement of the 'shaft 11 provided that the speed of rotation is sufficient.

In the second case, the surfaces 10 and 11 in relative movement are in direct contact. This case is encountered in mechanics at the start of hydrodynamic bearings and in some civil engineering machines, where the relative speeds are low.

Sommerfeld's theory which makes it possible to predict the behavior of plain bearings subjected to hydrodynamic lubrication is described in the review entitled "Engineering technique", volume B, in chapter 6,71 devoted to Hydrodynamic bearings.

• - son diamètre ;
• - le rapport sans dimension de la longueur du palier sur son diamètre.

From Sommerfeld's theory, we can deduce that a smooth bearing is characterized geometrically by:

• - its diameter;
• - the dimensionless ratio of the length of the bearing to its diameter.

The choice of operating mode; namely the hydrodynamic lubrication or the direct contact depends on the speed of rotation of the bearing, the dynamic viscosity of the lubricating fluid, the length of the bearing, the diameter of the link, the load applied to the rotor and the relative radial clearance, relative to the radius, relative radial clearance between 0.8. 10 ^-3 and 4.10 ^-3 .

The setting angle is one of the parameters that characterize the average position of the rotor in the stator. It is indicated by the reference notation ø in FIG. 4. Sommerfeld's theory also demonstrates that the setting angle, the resisting torque, the dissipated power and the axial flow of lubricant depend only for a given length / diameter ratio, of the relative eccentricity ε, equal to e / c, that is to say to the ratio of absolute eccentricity, expressed in millimeters, on absolute radial clearance also expressed in millimeters.

In the simple case where the bearing 10 is completely smooth and the applied load strictly constant, the limit of the hydrodynamic operation is reached when the difference between the absolute radial clearance c and the absolute eccentricity e is equal to the sum of the roughness of the machined surfaces , it then follows a direct contact and a radical modification of the behavior of the bearing.

• - la paroi rocheuse est géométriquement irrégulière;
• - le fluide "lubrifiant" est en réalité de la boue de forage chargée des débris de roche ;
• - l'arbre 11 constitué par le dispositif stabilisateur 9 n'est pas lisse mais comprend des saillies 8 délimitant des évidements 14 pour le passage du fluide de forage et des déblais.

In the case of a stabilization device 9 driven in rotation in a well being drilled, the problem is obviously more complex:

• - the rock wall is geometrically irregular;
• - the "lubricating" fluid is actually drilling mud loaded with rock debris;
• - The shaft 11 formed by the stabilizing device 9 is not smooth but includes projections 8 delimiting recesses 14 for the passage of drilling fluid and cuttings.

Despite these imperfections, one can imagine extrapolating Sommerfeld's theory to the stabilization device 9 in rotation in a deviated well.

Given the imperfection of the conditions at the bottom of the hole vis-à-vis the ideal case of the plain bearing, one must expect that for a number of Sommerfeld S defined conventionally, the relative eccentricity will be closer to 1 than for a plain bearing of the same length, same diameter and same speed of rotation.

There are therefore drilling conditions for which a transition is observed between a hydrodynamic behavior and a behavior in direct contact.

When using tools equipped with stabilizing sleeves driven in rotation by a turbine reaching high speeds of the order of about 700 revolutions per minute, it can be assumed that the minimum Sommerfeld number is reached. Due to the special conditions already mentioned above, the operation in hydrodynamic lubrication is however never fully established. It is getting closer and closer as the Sommerfeld number increases, that is to say, all other conditions remaining identical, as the length of the stabilizing sleeve 9 increases.

Figure 6 shows, in fact, the relationship observed for a turbine drill tilted at about 45 ° C between the intensity of deviation to the left and the length of the stabilization device. We can assimilate this relation to a function of the first degree, when all the other parameters remain identical.

FIG. 7 shows how the static load Pst corresponding to an equivalent hydrodynamic behavior varies, as a function of the length of the stabilization device. When the measurement points of the deviation intensity on the left and of the aforementioned static load corresponding to an equivalent hydrodynamic behavior are plotted on a diagram shown in FIG. 8, it can be seen that said points show a tendency towards alignment.

There is therefore an undeniable correlation between the above variables when implementing high rotational speeds.

On the other hand, for rotary drilling without a stabilizing device or with a relatively short sleeve, at a rotation speed of between 100 and 200 revolutions per minute only, the Sommerfeld number and therefore the admissible load at given relative eccentricity is much lower; we can therefore admit that the conditions? of hydrodynamic operation are never fulfilled and the tool guard 1 alone or the tool guard 1 extended by a short stabilizing device 9 operates in direct contact.

From the arguments developed above, it is deduced that the variation in the intensity of deviation to the left when drilling with a turbine is linked to a more or less hydrodynamic behavior of the system. This explanation is confirmed by the observation of a deviation to the left at the turbine and to the right at the rotary.

Indeed, by examining FIGS. 4 and 5, it is noted that the fundamental difference existing between the hydrodynamic operation and that with direct contact is in the average position of the rotor bearing in the stator housing.

• - une charge verticale agissant de haut en bas sur le palier rotorique,
• - une rotation ω du palier rotorique dans le sens horlogique semblable à celle de l'outil de forage vu de l'arrière.

Suppose, as shown in Figures 4 and 5:

• - a vertical load acting from top to bottom on the rotor bearing,
• - a rotation ω of the rotor bearing in a clockwise direction similar to that of the drilling tool seen from the rear.

• - à gauche de la verticale passant par le centre du palier rotori^que dans le ces du fonctionnement hydrodynamique ;
• - à droite de la verticale passant par le centre du palier rotori^que dans le cas du fonctionnement en contact direct.

Note that the contact point or the minimum point of separation of the rotor bearing from the stator bearing is located:

• - to the left of the vertical passing through the center of the rotori ^q ue bearing in the hydrodynamic operation;
• - to the right of the vertical passing through the center of the rotori ^q ue bearing in the case of direct contact operation.

However, the hole drilled in the turbine, for which we assumed a more or less hydrodynamic operation of the skirt, deviates precisely to the left and the hole drilled in rotary, for which it has been shown that the skirt or the guard of the tool alone must have a behavior in direct contact, deviates precisely to the right.

The invention consists in bringing to a known stabilizing device an improvement with a view to controlling accidental deviations without, however, modifying the total length of the above-mentioned device 9, which is essential to avoid spiraling.

This improvement consists in providing, perpendicular to the longitudinal axis of the stabilizing device 9, at least one groove 15, substantially circumferential formed in the projections 8 above, so as to interconnect, the recesses 14 included therebetween.

As illustrated in FIGS. 1 and 2, the grooves 15 can be made in the above-mentioned projections, by milling, over part of their height. These grooves 15 have the effect of bringing into communication an area in which the lubricant is subjected to a high pressure, with an area in which the lubricant is at a lower pressure. Such a groove 15 reduces the bearing capacity of the bearing and therefore the deviation to the left due to the hydrodynamic operation.

Figure 3 shows a second possible embodiment in which the groove 15, of helical shape is formed in a direction different from that of the helical projections 8 above. A double spiral sleeve is thus obtained.

EXAMPLE 1

To give an order of magnitude of the influence of these modifications, let us take a numerical example: either a stabilizing skirt whose behavior is assumed to be similar to that of a plain bearing of the same diameter and same length. We consider a reference skirt whose ratio L / D = 1, and whose bearing capacity is set equal to 1.

A skirt of double length, therefore having a ratio L / D = 2 will have a bearing capacity of 3.35 whereas if we practice two grooves perpendicular to the axis of the tool cutting the bearing surface into three equal parts, the same skirt of double length will only have a bearing capacity of 1.05, that is to say almost identical to that of the reference skirt.

It is obvious that the invention is not limited to the embodiments described above and that numerous modifications can be made to said forms without thereby withdrawing them from the scope of the following claims.

Claims (5)

1. Stabilizing device consisting of a cylindrical steel casing having laterally helical projections (8) provided with a coating offering good resistance to erosion and abrasion, characterized in that it comprises at least one groove (15) substantially circumferential formed in the aforesaid projections (8) so as to connect the recesses (14) lying between them. 2. Stabilizing device according to claim 1, characterized in that the said grooves (15) are provided over part of the height of the projections (8). 3. Stabilizing device according to any one of claims 1 and 2, characterized in that the grooves (15) are formed at possibly regular intervals along the helical projections (8). 4. Stabilizing device according to any one of claims 1 to 3, characterized in that a single groove (15) has a helical shape with short pitch. 5. Stabilizing device according to any one of claims 1 to 4, characterized in that it consists of at least two portions of sleeves of the same diameter arranged in the same alignment behind the drilling tool (1).

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