a. Field of Invention
This invention relates to a casing scraper, that is a tool for use in a wellbore to scrape debris from the interior of the wellbore casing.
b. Description of Related Art
In wellbore clean-up and mud displacement operations it is well known to use a casing scraper to remove debris from the interior surface of the casing. Casing scrapers may be non-rotating (that is there is substantially no rotation of the casing scraper relative to the casing) or may be rotating (in which case the scraper is forcibly rotated relative to the casing to increase the scraping action). In many clean-up operations, particularly on newly cased wells, non-rotating scrapers are preferred because of their relatively less aggressive scraping action. However, in other clean-up operations a more aggressive action produced by rotating the scraper at, for example 40-120 rpm is preferred.
Scrapers are available from a number of commercial sources, and the present invention provides an improved design in this type of tool.
According to a first aspect of the present invention a casing scraper comprises at least one blade module, the blade module comprising a tubular housing having a plurality of windows formed therein; a respective scraper block mounted in each window, each scraper block having retaining projections which prevent the scraper block moving completely through its associated window, and spring means acting on the scraper blocks to bias them radially outwardly of the housing.
The combination of scraper blocks with retaining projections which prevent them moving completely through the windows and spring means which bias the scraper blocks radially outwardly means that, within limits determined by the design, the scraper blocks can float radially as they encounter variations in the inside diameter of the casing being scraped. Contact of the scraper blocks with the casing will be under the influence of the springs, and if an area of reduced casing ID is encountered the springs will be compressed to allow the scraper blocks to move radially inwardly. Each block module is accordingly able to accommodate variations in casing ID.
In the preferred embodiment of the present invention a plurality of modules are provided along the length of the tool. Preferably, the modules are identical and are interconnected to prevent relative rotation therebetween.
Preferably, the or each module is rotatably mounted on a mandrel to enable the scraper to function as a non-rotating scraper. In the preferred embodiment of the invention means are additionally provided for rotationally locking the or each module to the associated mandrel so that the tool may function as a rotating scraper. Preferably, the change from non-rotating to rotating operation may be effected on site by manipulation of a locking member provided on the tool assembly.
Preferably, the spring means are coil springs and in the preferred embodiment of the invention are die springs. Preferably, the springs react between the scraper blocks and a base plate which is itself secured to the housing by screws which are inserted from the interior of the tubular housing, that is the heads of the screws are located facing radially inwardly. Preferably, backing off of the screws to an extent which will disengage the screws from the housing is prevented by the presence of the mandrel. Accordingly, when the various components have been assembled there is no possibility of the screws backing off to such an extent that the connection between the spring base plate and the housing is lost.
The invention will be better understood from the following description of a preferred embodiment thereof given by way of example only, reference being had to the accompanying drawings wherein:
Referring firstly to
The mandrel 2 has a box connector 8 at the upper end thereof and a pin connector 9 at the lower end thereof to enable the scraper 1 to be connected with other tools to form a bottom hole assembly. The mandrel includes a threaded region which is covered by a thread protector 10. The thread protector 10 is a steel sleeve which is internally threaded to mate with the threads on the mandrel. When the tool is operating in a non-rotating mode the thread protector 10 is maintained in the position illustrated in
Each of the components 3, 4, 5, 6, 7 is connected to its adjacent component or components by means which prevent relative rotation therebetween. In particular, the lower end of the upper stabiliser 3 is formed with castellations 13 which mate with complementary castellations 14 provided on the upper end of the blade module 5, the lower end of the blade module 5 is provided with castellations 15 which mate with complementary castellations provided on the upper end of a coupler 16, and castellations on the lower end of the coupler 16 mate with castellations 17 on the upper end of the blade module 6. The blade modules 6 and 7 are likewise interconnected by a coupler 18 whilst the lower end of the blade module 7 has castellations 19 which mate with complementary castellations on the upper end of the stabiliser 4. Thus, the two stabilisers and the three blade modules form an interconnected assembly 20 all the components of which are rotationally interlocked with each other.
Referring now to
It will be noted that the lower end of the mandrel includes a shoulder 24 which will retain all the components of the assembly 20 on the mandrel in the event of failure of the ball bearings.
If the tool 1 is required to operate in a rotating mode, that is with the assembly 20 rotationally fast with the mandrel, this can be effected on site by removing the circlip 12 and rotating the thread protector 10 relative to the mandrel 2 to engage castellations 25 provided on the lower end of the thread protector 10 with complementary castellations 26 provided on the upper end of the stabiliser 3. When the thread protector 10 has been torqued down to the required value it is locked in place by suitable means, for example a circlip located in a groove provided for the purpose in the mandrel. With the castellations 25, 26 inter-engaged with each other and the thread protector 10 locked in position the entire assembly 20 will rotate with the mandrel and accordingly the tool can operate at a rotating scraper.
Details of the mounting arrangements for the scraper blades are illustrated in
The scraper blocks are retained in position by respective base plates 37 which are secured to the body 30 by screws 38. The heads of the screws faced radially inwardly, i.e. the screws are inserted form the interior of the body 30. Accordingly, each blade module can be pre-assembled as a complete unit before being mounted on the mandrel 2. A small working clearance is provided between the head of each screw 38 and the mandrel 2 with the result that the degree to which each screw 38 can back off in use is limited by the presence of the mandrel itself. After assembly the screw 38 will, in general, be locked in place by suitable means, for example a thread locking compound. However, the arrangement described ensures integrity of the assembly in use even if the primary screw locking arrangements fail. The screws 38 preferably have a socket formation on the radially outer end thereof as well as on the radially inner end. The formation on the outer end will be accessible via the through holes provided for the screws in the tubular body and accordingly the screws may be tightened either during assembly or on site by means of a tool inserted radially inwardly through the screw holes.
Springs 39 are provided to act between each base plate 37 and its associated scraper block 32 so that the scraper blocks are biassed radially outwardly relative to the longitudinal axis of the tool. The maximum external diameter of the scraper blades is determined by the inter-engagement of the shoulders 34 and the projections 35. However, if a tool is run in a casing having a diameter less than this maximum, this reduced diameter can be accommodated by compression of the springs 39. For example, in a typical design intended for a nominal 9⅝ casing the overall diameter defined by the blades may vary from 8.469 inch to 9.175 inch. The spring load may be adjusted either by adjusting the strength of the springs or the number of the springs. In the preferred embodiment of the invention a total of eleven spring positions are provided under each block. Some or all of these locations may be furnished with springs according to the spring strength required.
Preferably, the springs 39 are high strength die springs.
As illustrated, each of the stabilizers has right hand helical blades. It will be appreciated, however, that other blade configurations are possible and in particular in certain applications straight blades may be desirable.
The castellation arrangements for rotationally interlocking the components allow the respective blade modules to be circumferentially offset from each other as illustrated in
It will be noted that each of the blade modules 5,6,7 is located radially by the components at either end thereof. To this end, each of the adjacent components includes a spigot portion which extends into the end region of each housing to provide radial support for the housing. The effect of this arrangement is that the blade modules are located radially relative to the mandrel by the components on either side of the module. Accordingly, a small running clearance can be provided between the components of the modules and the underlying mandrel so that the modules do not rub on the mandrel when the tool is operating in its non-rotating mode. It will also be noted that although in the preferred arrangement the stabilisers are mounted by means of ballbearings and axial load imposed by the thread protector 10 is reacted on the mandrel via the ballbearings, alternative arrangements are possible and in particular a plane thrust bearing may be provided for reacting the axial loading imposed by the thread protector.
It will be noted from
Number | Date | Country | Kind |
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0405524.0 | Mar 2004 | GB | national |
0423855.6 | Oct 2004 | GB | national |
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2811210 | Guillot | Oct 1957 | A |
4798246 | Best | Jan 1989 | A |
5819353 | Armell et al. | Oct 1998 | A |
6152220 | Carmichael et al. | Nov 2000 | A |
6408945 | Telfer | Jun 2002 | B1 |
6851472 | Hern et al. | Feb 2005 | B2 |
Number | Date | Country | |
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20050205252 A1 | Sep 2005 | US |