Patent Publication Number: US-6655462-B1

Title: Magnetic well cleaning apparatus

Description:
This invention relates to well cleaning equipment and more specifically, apparatus and method for cleaning out the inside of a liner or casing in an oil or gas well. 
     BACKGROUND OF THE INVENTION 
     It is common practice after drilling a borehole for the purpose of oil extraction, to line the borehole with a well casing and a liner. After installation of the liner, it is generally necessary to clean out the inside thereof in order to wash away any debris or other contaminants. 
     Various types of cleaning apparatus are known and available. One such type of cleaning apparatus is generically referred to as a casing scraper. This type of tool typically incorporates steel casing scraper blades that scrape the inside of the casing or tubing in the well. Scraper blades are particularly suitable for removing relatively large particles or debris from the surface of the casing or liner. A considerable amount of debris found within the well bore and on the surface of the casing or liner comprises of rust particles and/or metal chips or scrapings originating from equipment used in the well and the casing or liner itself. 
     Usually, the scraper blades are biased in an outward or radial direction by springs which are designed to maintain the blades in firm contact with the casing wall or other tubing in the well. In the present invention, it is recognised that while this is desirable for the purposes of cleaning the casing and removing debris therefrom, there are other times when the pressure of the casing blades against the tubing or casing is disadvantageous. For example, when a casing scraper is removed from the well, the outwardly biased scraper blades can dislodge further debris causing same to become loose in the circulation fluid and negate the effect of the cleaning work that has already been performed. 
     SUMMARY OF THE INVENTION 
     Similar difficulties can be encountered with other types of well clean-up tools, including brushes, circulation tools and the like. 
     An object of the present invention is to obviate or at least mitigate the disadvantage described above and, more particularly, the disadvantage of debris having been removed from the casing wall or liner becoming loose in the circulation fluid, thereby remaining in the well. 
     In our co-pending British Patent Application Number 9806274.8, there is described apparatus for catching such debris and this is one proposed method and apparatus for dealing with the aforementioned problem. The present invention provides an alternative solution in the form of apparatus and method for collecting loose debris and particles in a well casing or liner. The present invention also provides apparatus which can remove ferrous materials suspended in viscous fluid within a well. 
     According to the present invention, there is provided apparatus for collecting loose debris or particles in a well casing or liner, the apparatus comprising a body having or supporting one or more magnets. 
     The apparatus may be a casing scraper having scraper blades, wherein the scraper blades are magnetic. 
     The apparatus may alternatively be a catcher for catching loose debris particularly during the extraction of the catcher from the well. 
     The body is preferably adapted for attachment to a work string. 
     Typically, the magnets are permanent magnets. 
     The apparatus may comprise a magnetic sub. 
     In a preferred embodiment the apparatus is comprised of an upper and lower stabiliser wherein a magnetic sub is located between the stabilisers. 
     The apparatus may also comprise a protective sleeve, positioned over the magnets which preferably can rotate relative to the upper and lower stabilisers. Typically the protective sleeve is made of stainless steel. 
     The apparatus may be changeable between an inactivated mode wherein the magnetic field which attracts loose debris or particles is off, and an activated mode where the magnetic field is on. 
     In one embodiment the apparatus comprises a split sleeve having a first and second row of magnets. 
     Preferably the magnets are selectively activated or deactivated by virtue of moving one of the first or second row of magnets relative to the other of the first or second row of magnets. 
     According to a second aspect of the present invention, there is a method of trapping or retaining debris or particles in a well casing or liner, the method comprising the steps of: 
     a) running a magnetic tool or sub in the liner or casing with the magnets inactivated; 
     b) activating the magnetic tool to create a magnetic force to attract and retain said debris or particles; and; 
     c) removing the magnetic tool or sub from the well in order to remove the debris or particles. 
     Preferably, the magnetic tool is located below a well clean-up tool in a work string. The well clean-up tool may be a casing scraper, brushing tool or the like. 
     Alternatively, the well clean-up tool may comprise a magnetised portion or area, suitably below the cleaning members located on the same tool. The cleaning members may, for example, be casing scrapers, brushes or the like. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING FIGURES 
     Various embodiments of the invention will now be described by way of example only with reference to the accompanying figures, in which: 
     FIG. 1 shows a magnetic well cleaning apparatus, 
     FIG. 2 illustrates a magnet activation mechanism, 
     FIG. 3 shows a casing scraper incorporating a magnetic portion; and 
     FIGS. 4 and 5 show a work string including a magnetic sub. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring firstly to FIG. 1, one embodiment of a magnetic cleaning tool is generally depicted at  1  and is comprised of a body  2  having an upper  3  and lower  4  stabiliser sleeve which can be mounted on a work string (not shown). The stabiliser sleeves  3  and  4  are typically non-rotating spiral stabilisers. The main tool body  2  rotates through and relative to the stabiliser sleeves  3  and  4  and thus prevents wear and damage of the casing or liner which lines the well bore during pipe rotation. A plurality of magnets  5  are integrally located in the body  2 . The magnets  5  are mounted on a split sleeve  6  in a first inner  9  and second outer  10  row. A protective sleeve of stainless steel  7  is located over the split sleeve  6 , the protective sleeve  7  also being free to rotate relative to the stabilisers  3  and  4 . Ferrous metal debris which is present in the well is attracted to the magnets  5  and held onto the stainless steel sleeve  7  until the tool  1  is retrieved from the well. Stabiliser sleeves  3  and  4  prevent the captured debris from being brushed or wiped off the tool  1  by the movement of the work string. 
     Typically the tool  1  would be run into a well with other conventional well clean-up tools (not shown) in an inactive mode, that is without a magnetic field to attract any ferrous debris which may be in the well. After the cleaning process is complete, the magnets are activated and the tool is removed or “tripped” from the well. As the tool  1  is raised from the well, ferrous debris and particles will be attracted to the magnets  5  and retained on stainless steel sleeve  7  until the tool is retrieved. 
     FIG. 2 illustrates the magnet activation means of the apparatus. It can be seen that sleeve  8  has a split configuration having two rows of magnets  9  and  10 . When the split sleeve  8  is in the configuration shown at (a) the magnets  9  and  10  are aligned such that the magnetic fields act in addition to attract any ferrous debris and particles  11  which are present. It can be seen from (a) that as a result, ferrous debris  11  will attach to the stainless steel sleeve  7 . To covert the magnets to the inactivated mode as shown at (b), movement of, in this case the lower half of the split sleeve  8 , displaces the magnets  9  in the lower row, so that the orientation of the magnetic field is changed such that it does not attract the ferrous debris  11 . 
     Turning now to FIG. 3 an alternative embodiment of a magnetic tool  12  is designed as a casing scraper and includes scraper blades  13  that are biased in an outward or radial direction by biasing means such as springs (not shown). In use, the blades  13  are maintained in contact with a casing wall  14  in a downhole well or environment. 
     The blades  13  are made of steel that has been pre-magnetised during manufacture. The scraper blades  1  therefore act as permanent magnets suitable for collecting and trapping debris susceptible to magnetic attraction. 
     In use, debris is held most typically to the upper edge  13   a  of the magnetic scraper blades and, to a lesser extent, to the lower edge  13   b  thereof. 
     In an alternative embodiment, permanent magnets may be incorporated as separate elements in otherwise non-magnetic scraper blades. 
     In FIG. 4, a work string generally depicted at  15  is illustrated which includes a well clean-up tool in the form of a brush tool  16 . Below the brush tool  16  is a separate sub  17  provided with an enlarged outside diameter having close contact with the casing wall  18 . Grooves  19  are provided near the outer circumference of the sub  17  to enhance bypass area. 
     The sub  17  comprises largely of a permanent magnet adapted to attract and retain debris or particles susceptible to magnetic attraction. In a preferred embodiment shown in FIG. 5 the magnetic sub  19  is rotatable through an upper  20  and lower  21  spiral stabiliser which are mounted on a work string  22 . 
     The clean-up tool  16  is appropriately positioned above the sub  17  so that any particles or debris dislodged by the bristles  16  are likely to fall into the small annular area between the casing wall  18  and the outer circumference of the sub  17 , whereat they are attracted to the walls of the sub  17  and retained in contact therewith. 
     In the situation where the work string is being extracted from the well bore, the sub  17 , being placed below the clean-up tool  16 , will follow the clean-up tool out of the well and thus move into the position at which the clean-up tool had been immediately prior, thereby improving the efficiency of collecting metallic particles and other debris suitable for magnetic attraction. 
     Notably, that any cleanup or other function tool could replace the brush tool  16  depicted in FIG. 4 without departing from the invention. 
     In a preferable embodiment, there may be provided a magnetic sub, similar to that depicted in FIG. 4, but also designed to catch and retain other particles or debris which are not susceptible to magnetic attraction. 
     Thus, it may be seen that the present invention relates to the collection and retention of debris and other particles partially or wholly by magnetic means. The invention provides a welcome improvement to collecting debris that has been dislodged by the cleaning action of known well clean-up tools. This accords with the desire not only to clean casing and other tubing in a well, but also clean the interior of the well itself. The apparatus can be run in conjunction with other wellbore clean-up tools to collect ferrous metal debris during clean-up and remove it from the well. 
     While the invention finds an obvious application in wells used for the production of oil or gas, it may also have alternative utility in the cleaning of pipelines or other tubing. 
     Further modifications and improvements may be incorporated without departing from the scope of the invention herein intended.