Abstract:
A roller arm centralizer to center a drill string in a well pipe. The arms of the roller arm centralizer include shoulders to limit movement of the arms in the direction of the centralizer body which prevents the arms from being locked in a straight line adjacent to the centralizer body. The shoulders also prevent the arms from being forced into an undesired configuration; wherein one arm is parallel to the body and the other two arms form a &#34;V&#34;, by an abrupt decrease in the bore diameter. The roller arm centralizer remains operative when passing through relatively narrow sections of well pipe or through well pipe having abrupt changes in diameter.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a roller arm centralizer to center a tool in a well pipe. 
     DESCRIPTION OF THE PRIOR ART 
     In drilling and testing operations in a well bore or well pipe, it is desirable to center the drill string in the well pipe. 
     U.S. Pat. No. 2,490,350 taught the use of a centering device that used a plurality of two segment arms that were normally in a retracted position along the device and centered the drill string within the bore when activated from the surface. U.S. Pat. No. 4,243,099 taught a device for centering a tool in a well bore wherein a plurality of arm members were extended to contact the well bore, and thereby center the device, by means of a reversable electric motor controlled from the surface. U.S. Pat. No. 3,555,689 taught a centralizing device wherein a plurality of arched springs contacted the well bore to center the drill string and a plurality of interconnected arms prevented singular movement of one spring. U.S. Pat. No. 3,977,468 taught a well bore centering device that used a number of interconnected sensing arms with springs to center the apparatus as well as measure and record changes in the well bore diameter. U.S. Pat. No. 3,978,924 taught a drill string centralizer that used bow springs attached to mechanical arms to maintain contact with the bore hole wall. 
     The centralizers of the prior art are limited in the usefulness in that the use of bow springs to contact the bore hole wall or the tubing results in a dangerous wear condition. As a bow spring wears out, it makes for a very sharp edge that creates handling problems for the operators when they try to remove it from the hole. If a bow spring should wear out and break in the hole, it will almost certainly stick itself in the hole and cause considerable problems during the removal process. 
     The centralizers that use a rigid arm with a wheel on the end are limited in that sudden, short recesses, such as tubing collars and tools in a tubing string, cause their small contact points to hang up and either stick the tool string in the hole or create a jerking action which can violently shake the tool string and ruin the accuracy of a caliper survey. For these reasons, in the prior art, a surface controlled motor has often been used to retract the arms or to reduce the arm centralizing pressure when the tool must travel through tubing. 
     The centralizer that uses a bow spring as in U.S. Pat. Nos. 3,978,924 and 3,977,468 are limited in several ways. To have a hidden spring flexible enough to allow the 30° to 35° mentioned in U.S. Pat. No. 3,978,924, the spring will also have to be quite thin and therefore provide only a small force. The weaker the force provided by this hidden spring, the more danger there is of the arms being locked against the body of the tool. Also, with the arm design shown in FIGS. 2 and 3 of U.S. Pat. No. 3,978,924, there is a danger of the linkage forming a locked condition upon re-entering the tubing string or otherwise engaging any other sharp restriction. 
     The centralizers of the prior art are limited in their usefulness in that when they are run through a narrower portion of a pipe, the spring means may become deformed or the mechanical arms may become locked in a position essentially adjacent to the apparatus body. In such case, the centering arms might no longer be forced out into contact with the pipe wall and the desired centering of the string would not be accomplished. 
     SUMMARY OF THE INVENTION 
     The present invention relates to a new and improved roller arm centralizer apparatus in which a tool is centered in a well pipe even when the pipe diameter varies widely. 
     It is an object of the present invention to provide a well pipe centering device that will not catch or hang up in sudden or sharp restrictions in the pipe, or upon re-entering the pipe from open hole below the pipe. 
     It is also an object to provide a centering device which is shorter by virtue of having an increased arm angle capability. 
     The apparatus comprises an elongated body with provision at one end to attach to a wire line and provision at the other end to attach to a well tool such as a caliper tool. Attached to the body are two stationary collars. Equally spaced around the body and attached to the body by movable collars are three centering arms. Each centering arm is made up of a center roller arm segment and two connector segments. At the pivot point where the end segments are attached to the center roller arm segment is a means to limit movement of the segments in the direction of the body. Such means also prevents the segments from becoming forced from the desired &#34;open U&#34; configuration into an undesired configuration, wherein one end segment is parallel to the body and the center and other end segments form a &#34;V&#34;, by an abrupt decrease in the bore diameter. 
     The centering arms are forced laterally outwardly by coil springs mounted between the stationary and movable collars. Mounted on each end segment is an arch spring to further urge each centering arm outwardly to prevent locking of the centering arms in alignment with the body. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a plan view of the present invention. 
     FIG. 1a is a plan view of the present invention showing a wireline attachment. 
     FIG. 2 is a cross-sectional view of the roller arm centralizer along line 2--2 of FIG. 1. 
     FIG. 3 is a cross-sectional view along line 3--3 of FIG. 2. 
     FIG. 4 is a cross-sectional view of a roller arm segment. 
     FIG. 5 is a cross-sectional view of a roller arm segment along line 5--5 of FIG. 4. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The apparatus A consists of a rigid body 10 having an upper end 10a to which is attached a connector 12 by a locking pin 14. The connector 12 has a conventional fishing neck 12a. The upper end of the connector 12 has a slot 12b and shoulders 12c to interlock with an adapter 111 which is threadably connected to a wire line socket member 11 which has a wireline 13 secured thereto in any known manner (FIG. 1A). The lower end 10b of the body 10 is threaded to receive a caliper adapter 15. The lower end 10b of body 10 has two slots 17, at right angles, so that a locking pin 19 may be inserted through one of the slots 17 and a collar 151 on the adapter 15 to prevent unthreading of the caliper adapter 15. 
     The caliper adapter 15 preferably has a swivel caliper adapter, commonly called a universal joint, which includes collar 151 having a threaded bore to receive threads on the lower end 10b of the body 10 and an open lower end 151a of a &#34;U&#34; configuration. A second swivel part 152 has an open upper end 152a of a &#34;U&#34; configuration. A third swivel part 153 is pivotally mounted within the open &#34;U&#34; of the collar 151 by pivot pin 154. Pivot pin 154 is locked in place by locking pin 155. The open &#34;U&#34; of the second swivel part 152 is pivotally mounted to the lower part of the center part 153 by pivot pin 156, such that the &#34;U&#34; of the collar 151 is at right angles and interconnects with the &#34;U&#34; of the second part 152. Pivot pin 156 is locked in place by locking pin 157. The upper end of a caliper tool 18 (partially shown) is connected to the lower end of the caliper adapter part 152. The upper surface 151b of collar 151 is at the lower end of body 10 for a purpose to be hereinafter described. 
     A stationary collar 24 is threadably attached to the upper end 10a of the body 10. The stationary collar 24 is locked in position by locking collar 25 which is also threadably mounted on body 10 such that it can abut collar 24 thereby locking collar 24 in position. Around the body 10 between the stationary collars 24 and 151 are two movable collars 26. The movable collars 26 serve to space three centering arms 28 around the body. Each of the centering arms 28 is made up of a center roller bar segment 30 and two end segments 32. The end segments 32 are pivotably connected by pivot pins 29 to the movable collars 26 and the roller bar segments 30. 
     The roller bar segments comprise a pair of bars 34 and a plurality of rollers 38 and 39. End rollers 39, which protect the pivot point as the well pipe diameter changes, are mounted on clevis pins 40 retained by cotter pins 41 at the pivot points between the roller arm segment 30 and the end segments 32. End segments 32 have a clevis configuration 32c and rollers 39 are mounted in the center of the clevis with bars 34 pivotally mounted to the outside of the clevis. Rollers 38 are mounted on hardened dowel pins 36 retained between bars 34. Dowel pins 36 are pinned by lock pin 37 so that the dowel pins do not rotate. 
     The roller bar segments 30 are pivotally connected to the end segments 32 by clevis pins 40 retained by cotter pin 41. Each arm 32 has a shoulder 32b which is adapted to engage a shoulder 34b on bar 34 to limit movement of the roller arm segments 30 toward the body 10. As will be more evident hereinafter, such shoulders 32b and 34b  permit the arms 32 and 34 to assume a substantially parallel position relative to the body 10, but prevent it from going further inwardly. Mounted on each end segment 32 in a slot 41 is an arch spring 42 that biases the end segment 32 laterally away from the body 10. Thus, if the arms 32 and 34 are collapsed to a substantially parallel position relative to body 10 by reason of passage through a narrower section of well pipe, upon further passage to a larger diameter portion of the well pipe, the springs 42 urge the arms 32 and 34 out. 
     The roller bar segments 30 are biased laterally away from the body 10 by a pair of coil springs 44 around the body 10 between the movable collars 26 and the fixed collars 22 and 24. The coil springs 44 bias the movable collars 26 away from the stationary collars 151 and 24 thereby forcing the attached ends 32a of the end segments 32 together for biasing the roller bar segment 30 laterally away from the body 10. The travel of the movable collars away from fixed collars 151 and 24 is limited by two longitudinally spaced stops 46 mounted on the body 10. The stops 46 are horseshoe shaped and slide into grooves 49 in the body 10 and are held in place by set screws 51. The tension of the coil springs 44 is adjustable by threading the threaded collar 24 upwardly and downwardly on the threads at the upper end 10a of the body 10. The threaded collar 24 is locked in its desired position by abutment of locking collar 25 against collar 24. 
     In the preferred form of the invention, the stops 46 are positioned so as to permit the bar segments 30 to move outwardly from the tool body 10 so that the angle between the segments 30 and the arms 32 is about 45°. This angle could be increased but as the angle gets greater there is a risk that the centralizer would be difficult to collapse back down by restrictions in the well bore or pipe. By reason of such relatively large angle, the length of the tool is shorter than those in the prior art. 
     In the use of the centralizer A of this invention, it is mounted at the upper end 18 (FIG. 2) of a caliper tool (not shown) or any other tool and to a wire line 13 at its upper end (FIG. 1A) to center the calipering tool in a well pipe. As the centralizer A is lowered into a well pipe, the rollers 38 and 39 mounted on the roller bar segment 30 are forced laterally into contact with the internal wall of the well pipe by coil springs 44, thereby centering the apparatus A and the caliper or other tool connected therebelow. As the well pipe diameter varies, coil springs 44 bias the centering arms 28 to maintain the drill string at the center of the bore. When the roller arm centralizer encounters a narrower length of pipe or an abrupt change in pipe diameter, the engagement of the shoulders 32b and 34b prevents the roller bar segments 30 and the two attached end segments 32 from aligning along the body 10 in a position such that coil springs 44 would not be able to force the centralizer arms 28 laterally outwardly. For example, if such shoulders 32b and 34b were not provided, inward pivoting could occur at either the upper roller 39 or the lower roller 39 so that one of such rollers 39 moved inwardly towards the body 10 while the other roller 39 stayed in contact with the internal wall of the well pipe, resulting in a collapsed condition which could not be overcome by the springs 44 or 42. In such a situation, the tool would become unable to perform its centralizing function. The present invention avoids such a problem. 
     Arch springs 42 urge the spacers laterally away from the body 10 by augmenting the coil springs 44 outward biasing action as the centering arms 28 approach a position in alignment along the body 10. 
     Although the invention is described for centering a calipering tool mounted on a wire line for use in a well pipe, the invention is adaptable for use in centering other apparatus in a pipe, casing or open bore without departing from the spirit and scope of the invention. 
     It should be understood that the foregoing description and drawings of the invention are not intended to be limiting, but are only exemplary of the inventive features which are defined in the claims.