EP0039278A1 - Apparatus for determining the stuck point of drill pipes in a borehole - Google Patents

Abstract

The device comprises a body lowered inside the rods and having an upper part (26) and a lower part (27) movable with respect to each other with limited displacements. Each part of the body is anchored inside the rods and movements between said parts are detected when stresses are applied to the rods on the surface. A first transformer with radial coils has a primary winding (35) secured to one part of the body and a secondary winding (36, 37) secured to the other part to detect angular displacements. A second axial coil transformer has a primary winding (40) secured to one part of the body and a secondary winding (41, 42) secured to the other part to detect longitudinal movements. The signals supplied by the transformers are linear functions of the respective displacements.

Description

The invention relates to devices used in soundings and more particularly to devices for detecting the point of jamming of a column of rods in a sounding.

When a column of rods such as a drill string is trapped in a borehole, a conventional method for determining the depth of the pinch point is to apply twists and pulls to the column at the surface and determine up to 'to what depth these deformations are transmitted. To detect these deformations, a device is used which is lowered into the column at the end of a cable and placed at successive depths.

A conventional device for detecting the jamming point, described for example in United States patent No. 3,686,943 granted to WD Smith, comprises a body having an upper part and a lower part which are mounted so that they can be moved one by the other. relative to each other according to limited displacements and upper and lower anchoring members mounted respectively on these upper and lower parts to immobilize each of the body parts in two zones longitudinally spaced from the column. Electric motors controlled via the cable serve to move the anchoring members apart and bring them closer to the body and a sensor mounted between the parts of the body detects the relative movements of said parts when the column is elastically deformed by stresses applied on the surface. .

In the American patent n ° 4.105.071 (Y. Nicolas and A. Landaud) is proposed a sensor which includes two detectors, one independent tension and the other independent of the twists applied to the rods. Such a sensor has the advantage of being able to determine whether a torsion applied to the surface rods has been transmitted in depth. In particular, when it is desired to unscrew the free part of the rods, it is necessary to apply a unscrewing torque to a particular joint slightly tensioned, before exploding a charge at this joint. This operation known as "back off" is very commonly performed. In deviated wells with an elbow, the torque applied to the surface rods is poorly transmitted and it is customary to pull and release the rods at the same time as the application of the torque, to overcome friction along the survey. A sensor as described in the above US patent makes it possible to know directly whether the torque has been transmitted in depth. Unfortunately, such a sensor, the detectors of which are strain gauges disposed on elastically deformable parts, has a high stiffness and high forces are necessary to deform it. Under these conditions, it often happens that the anchors of the device are not strong enough to transmit such forces and slide inside the rods without deforming the elastic parts of the sensor.

Other known sensors are described in American patents No. 3,686,943 (W.D. Smith) already mentioned and No. 2,530,309 (P.W. Martin). These sensors use coils which detect the width of an air gap between poles of a magnetic circuit, this width being modified by the longitudinal and angular movements between the parts of the body. These sensors have the disadvantage of being sensitive to both these angular and longitudinal movements. In addition, these sensors must be reset to zero, before measurement, in a position which only allows rotations in one direction. It is however desirable to be able to measure the transmission at the bottom of screwing and unscrewing torques.

The invention relates to a sensor for detecting the point of jamming of the rods in a borehole which has good characteristics of precision and reliability and which makes it possible to separately detect the twists of the pulls with a low stiffness.

According to the invention, a device for detecting the point of jamming of rods in a borehole comprises a body having two parts which are movable with respect to each other and separate detection means for detecting respectively the angular and longitudinal movements between the parts of the body.

The angular detection means comprise: a first transformer having a primary winding secured to a first part of the body and supplies periodic current to induce a first signal in a secondary winding secured to the second part of the body, a first of these windings comprising a radial coil, that is to say an axis perpendicular to said direction and the second winding comprising two coils also radial and arranged on either side of the first winding. In this way the first signal is sensitive to the angular displacements between the parts of the body but is insensitive to the longitudinal displacements between these parts.

The coils of the second winding are mounted with their parallel axes and the first part of the body is mounted angularly movable on either side of a median angular position for which the axis of the coil of the first winding is perpendicular to the axes of the coils of the second winding.

The longitudinal detection means comprise: a second transformer having a primary winding secured to the first part of the body and supplied with periodic current to induce a second signal in a secondary winding secured to the second part of the body, a first of these windings comprising a axial coil, that is to say an axis parallel to said direction and the second winding comprising two axial coils spaced longitudinally and partially surrounding said first winding. In this way the second signal is sensitive to the longitudinal displacements between the parts of the body but is insensitive to the angular displacements between these parts.

Preferably one of the parts of the body forms a sleeve inside which a chamber is formed which contains the transformers. This chamber is filled with oil and means are provided to maintain the internal pressure of the chamber equal to that of the sounding, for example using a floating piston.

The device further comprises elastic means for opposing the weight of the lower part and pushing it upwards so that it can then move downward relative to the upper part after anchoring in the column of rods. In addition, means are provided for bringing the first part of the body substantially to said middle position of the second transformer so that this first part can rotate relative to the second part in one direction or the other.

• - la figure 1 est une vue en cours d'opération d'un dispositif de détection selon l'invention pour trouver le point de coincement d'une colonne de tiges dans un sondage;
• - la figure 2 est une coupe longitudinale d'une partie de l'appareil de fond de la figure 1;
• - la figure 3 est une vue en perspective d'un détail de l'appareil de la figure 2; et
• - la figure 4 est un schéma des circuits utilisés pour obtenir des signaux de détection du dispositif selon l'invention.

The characteristics and advantages of the invention will emerge more clearly from the description which follows, given by way of nonlimiting example with reference to the appended drawings in which:

• - Figure 1 is a view during operation of a detection device according to the invention for finding the point of jamming of a column of rods in a borehole;
• - Figure 2 is a longitudinal section of a portion of the bottom apparatus of Figure 1;
• - Figure 3 is a perspective view of a detail of the apparatus of Figure 2; and
• - Figure 4 is a diagram of the circuits used to obtain detection signals from the device according to the invention.

Referring to Figure 1, a jamming point detection device comprises a bottom device 10 suspended in a column of rods 11 at the end of a cable 12. The rods 11 disposed in a borehole 13 are trapped by the formations at a point 14 whose depth is to be determined. The rods are suspended on the surface in a known manner from a drilling tower (not shown) equipped with mechanisms enabling these rods to be applied tensile and torsional forces. The cable 12 comprises one or more electrical conductors connected to a surface device 15. This device is suitable for sending an electrical supply current and electrical control signals to the downhole device and for receiving the signals coming from this device. to process, display and save them.

The downhole apparatus 10 generally comprises an electronic section 20, an upper anchoring system 21, a sensor 22, a lower anchoring system 23. The electronic section 20 is formed of a waterproof envelope containing electronic circuits. The sensor 22 is formed by a body 25 having an upper part .26 and a lower part 27 mounted movable with respect to one another with limited displacements both longitudinally and angularly. The upper 21 and lower 23 anchoring systems are respectively fixed to the upper 26 and lower 27 parts of the body in order to immobilize these two parts in two zones longitudinally spaced from the column of rods.

Each anchoring system can be of the type described in US Patent No. 3,686,943 already cited, with articulated arms adapted to move away from the body to come into abutment against the internal wall of the rods. These arms, which may be three in number, engage for example on an axial displacement control rod driven by an electric motor which transmits its movement to the rod by means of an endless screw. Each anchoring system includes a motor controlled at will from the surface.

At the bottom of the bottom device, one can consider attaching an explosive support adapted to receive several lengths of detonating cord to carry out an explosion at a selected rod joint located above the jamming point. Beforehand, a couple of loosening is applied from the surface to this selected joint which is slightly tensioned, so that the explosion has the effect of triggering the loosening at this level. If this operation succeeds, a maximum length of free rods is thus removed from the borehole.

The sensor 22 provides signals representative of the relative displacements between the parts of the body when the rods are elastically deformed by stresses of tension or torsion applied to the surface. Following these constraints, the sensor 22 indicates a displacement between the parts of the body, only if the bottom device is anchored above the point of jamming 14. By anchoring the device 10 at various depths, it is therefore possible to find the one below which no more signal is obtained, that is to say the one which corresponds to the depth of the jamming point.

The sensor 22 is shown in more detail in FIG. 2. The upper part 26 of the body is extended downwards by a mandrel 30 which can rotate and move longitudinally in a sleeve 31 v which extends upwards the lower part 27. As will be seen later, the relative movements of the two parts 26 and 27 are limited longitudinally and in rotation. The upper part 26 has a tapping 32 allowing it to be fixed to the upper anchoring system 21, and connectors 33 fixed in isolation on the body to ensure suitable electrical connections with the top of the bottom appliance.

To detect the angular displacements between the two parts 26 and 27, the sensor comprises a first transformer formed by a primary fixed to the mandrel 30 and a secondary fixed to the sleeve 31. The primary consists of a coil 35 whose axis is radial , that is to say perpendicular to the longitudinal direction XX 'of the device (see also Figure 3). The secondary is formed by two coils 36 and 37 whose axes are also radial.

As will be seen below, the two coils of the secondary are connected in series and when the primary is supplied with periodic current, the signal induced in the secondary is representative of the relative angular position of the mandrel 30 and of the sleeve 31.

Ξn middle angular position, that is to say at an equal distance from the stops which limit the rotation of the mandrel 30 in the sleeve 31, the axis of the coil 35 of the primary is perpendicular to the common axis of the coils 36 and 37 high school. In this middle position, the signal induced in the secondary is zero. The coils 35, 36 and 37 are long enough in the direction of the direction XX ′ so that the limited longitudinal displacement of the mandrel 30 relative to the sleeve 31 does not modify the output signal of the angular displacement transformer.

To detect the longitudinal displacements between the two parts 26 and 27, the sensor 22 comprises a second transformer formed by a primary fixed to the mandrel 30 and a secondary fixed to the sleeve 31. The primary consists of an axial coil 40, that is that is to say an axis parallel to the direction XX ′ and the secondary by two other axial coils 41 and 42 connected in opposition. The coil 40 is placed on the mandrel so as to be centered halfway between the coils -41 and 42 when the sleeve 31 is in the high position relative to the mandrel 30 in order to provide a substantially zero signal in this position. This second transformer, symmetrical around the axis XX ′, is insensitive to the relative angular displacements of the two parts of the body.

The lower end of the mandrel 30 comprises a collar 43 on which a spring 44 compressed between this collar and an internal shoulder of the sleeve 31 comes to bear. This spring 44 is suitable for applying to the sleeve 31 an upwardly directed force slightly greater than the weight hanging from the lower part 27 of the device. In this way, when anchoring systems 21 and 23 are anchored in the column of rods, the lower part 27 of the body is in the high position relative to the upper part 26. If one exercises on the column of rods a traction which results, at the depth of the device by an elongation between the anchoring zones, this elongation is then fully transmitted to the parts 21 and 22 of the body which, being then in close position, can move away freely l one of the other.

The lower part 27 of the body ends down at the end by a smaller diameter end on which is rotatably mounted a threaded ring 47 held in place by a stop 48. This end has a housing in which is placed a support 50 for connectors 51 to make the appropriate electrical connections with the lower anchoring system 23.

The space between the mandrel 30 and the sleeve 31 forms a sealed chamber 52 closed upwards by an annular piston 53 mounted to slide on the mandrel. Seals 54 and 55 seal between the piston and the mandrel 30 and between the piston and the sleeve 31. The chamber 52 is filled with hydraulic fluid and the pressure equalization piston 53 maintains the chamber at the pressure of the fluids sounding: In this way the mandrel and the sleeve are not subjected to any longitudinal force due to the pressure of the drilling fluids.

The different coils are connected to the electronic section of the device by conductors such as 58, 59 connected to the connectors 33.

The apparatus further comprises means for substantially bringing the mandrel 30 to the median angular position for which the axis of the primary coil 35 is perpendicular to the common axis of the coils 36, 37. These means comprise a window 56 cut out from the internal face of the sleeve 31. The window 56 has two sides parallel to the longitudinal direction XX ′, a flat lower face and upper ramps converging upwards at a point located in the middle of the two parallel sides. A guide key 57 integral with the mandrel 30 can move inside this window. Normally the key 57 is therefore held in abutment against the underside of the window 56 by the spring 44. The longitudinal sides of the window 56 limit the angular displacement of the mandrel 30 relative to the sleeve 31. To bring the detector transformer to the middle position angular displacement, the lower anchoring system 23 is anchored and the cable is pulled to bring the guide key 57 to the top of the window 56. The mandrel which could have rotated until it was abutted against the sides of the window is thus returned to the median angular position by the key 57 which slides along one of the upper ramps of the window 56. The cable tension is then released and under the action of the spring 44, the key 57 returns to the bottom of window 56 while remaining substantially equidistant from its longitudinal sides. The lower part of the body is, at this instant, in the high position relative to the upper part. The angular displacement transformer is in the middle position and the coil 40 of the longitudinal displacement transformer is substantially centered on the midpoint between the coils 41 and 42 of the secondary. The device is therefore ready to measure the elongation of the rods and their twists in one direction or the other.

Referring to Figure 4, there is shown the circuits of the device which are mostly located in the electronic section 20. A supply circuit 60 supplies a triangular periodic current at the frequency of 1000 Hz to the primary coils 35 and 40 which induce rectangular voltages in the secondary coils. The secondary coils 36 and 37 of the angular displacement detector transformer are connected in series to the input terminals of a differential amplifier 61. The output signal of amplifier 61 is rectified in phase by a synchronous detector 62 having for reference the signal at 1000 Hz from the power supply 60. The output signal from synchronous detector 62 is a DC voltage V _R linear function of the angular displacement of the mandrel 30 in the sleeve 31. This signal V _R whose sign indicates the direction of rotation is transmitted by the cable 12 to the surface apparatus 15 after being converted, if necessary by means of d 'an appropriate transmission system.

The secondary coils 41 and 42 of the longitudinal displacement detector transformer are connected in opposition to the terminals of a differential amplifier 63, the output of which is connected to a synchronous detector 64. The reference of the detector 64 is supplied by the power supply 60. The signal output V _L of the synchronous detector 64 is a DC voltage proportional to the longitudinal displacement of the mandrel 30 relative to the sleeve 31. This signal V _L is transmitted to the surface via the cable 12 like the signal V _R.

In operation, the apparatus is assembled as shown in FIG. 1 and it is lowered inside the column of rods 11 to the depth where it is desired to determine whether these rods are free. At the chosen depth , the lower system 23 is anchored and the cable 12 is pulled to return the angular displacement detector transformer to the midpoint. Then close the lower anchoring system and anchor the device again, starting with the upper anchoring system 21. This ensures that the weight of the top of the device and the cable does not come compress sensor 22.

Torsional and tensile stresses are then applied to the surface of the rod column while displaying and recording the longitudinal and angular displacement signals of the sensor. If these signals indicate that the rods are free at the depth where the device is located, the above operations are repeated at other depths until the jamming point 14 is determined for which the sensor 22 no longer indicates displacements. If one wishes to unscrew the rods above the jamming point, the sensor 22 makes it possible to detect whether a unscrewing torque has indeed been transmitted to the desired depth, thanks to the first transformer which is only sensitive to rotation.

The embodiment which has just been described can be the subject of numerous variants. The primary and secondary of each transformer are interchangeable. The sleeve can be secured to the upper anchor and the mandrel to the lower anchor. The two opposing coils can be fixed to the mandrel. The median focusing system can be achieved by other means Etc. These variants are obviously possible without however departing from the scope of the invention.

Claims (8)

1. Device for detecting the point of jamming of the rods in a borehole, comprising: a body adapted to be suspended in the rods at the end of a cable, said body having a longitudinal direction and comprising two movable parts. one relative to the other longitudinally and angularly, each of the parts being adapted to be anchored inside the rods by a surface control; and first and second means for detecting respectively the angular and longitudinal movements between said parts when the rods are deformed by applying to them surface torsional and tensile stresses, characterized in that the angular detection means comprise: a first transformer having a primary winding secured to a first part of the body and supplied with periodic current to induce a first signal in a secondary winding secured to the second part of the body, a first of said windings comprising a radial coil, that is to say say axis perpendicular to said direction and the second of said windings comprising two coils also radial and arranged on either side of the first winding so that said first signal is sensitive to angular cuts between said parts of the body but is insensitive to movement longitudinal between said parts. 2. Device according to claim 1, characterized in that the longitudinal detection means comprise: a second transformer having a primary winding secured to the first part of the body and supplied with periodic current to induce a second signal in a secondary winding secured to the second part of the body, a first of said windings comprising an axial coil, that is to say with an axis parallel to said direction and the second of said windings comprising two axial coils spaced longitudinally and partially surrounding said first winding so that said second signal is sensitive to longitudinal movements between said parts of the body but is insensitive to angular movements between said parts. 3. Device according to claim 2, characterized in that said first single coil windings are said primary windings and said second windings are said secondary windings of the first and second transformers. 4. Device according to claim 3, characterized in that the coils of the secondary winding of the first transformer are mounted with their parallel axes and in that the first part of the body is mounted movable with limited angular displacement on each side of a median angular position for which the axis of the coil of the primary winding of said first transformer is perpendicular to the axes of the coils of the secondary winding. 5. Device according to claim 4, characterized in that it further comprises means for bringing the first part of the body to an angular position corresponding substantially to the middle position of said second transformer. 6. Device according to one of claims 1 to 5, characterized in that one of the parts of the body comprises a sleeve having a longitudinal axis and inside which is mounted a longitudinally movable and rotating relative to said axis a mandrel extending the other part. 7. Device according to claim 6, characterized in that it comprises: a chamber produced inside said sleeve and in which said first and second detection means are placed, said chamber being filled with a hydraulic fluid; and means for maintaining said chamber at the sounding pressure. 8. Device according to one of the preceding claims, characterized in that it further comprises elastic means for opposing the weight suspended from the lower part of the body and pushing up this lower part so that it can move down from the upper part of the body after anchoring in the column of rods.

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