Abstract:
Methods and apparatus are disclosed for recovering magnetically attractable wellbore casing fragments from drilling fluid used in hydrocarbon-producing formations.

Description:
FIELD OF THE INVENTION 
   The present invention relates to an apparatus and methods for recovering magnetically attractable articles from fluid, and more particularly to an apparatus and methods for recovering magnetically attractable fragments from fluid that has passed through oil and gas well casings to determine the metal loss from the well casings. 
   BACKGROUND OF THE INVENTION 
   Casings used to line wells in oil- and gas-producing formations typically suffer damage from erosion, perforation (such as for the purpose of running additional lines into such a formation), and ordinary wear and tear from the operation of the wells. Since the integrity of well casing is important to the integrity of the well, monitoring the condition of well casing is an important part of well maintenance. Drilling fluid is circulated in well casing for purposes including removing drill cuttings from the casing and from the face of the bit, so one way to monitor the condition of the casing is to collect and analyze the casing fragments released into the drilling fluid. The quantity of casing fragments collected from the drilling fluid is indicative of the quantity of fragments being generated down hole. 
   Solids and cuttings are generally removed from drilling fluids at the surface by solids control equipment such as shale shakers and hydrocyclones, which dump solids into collection bins. It is known to place a “ditch magnet” into the drilling fluid system to collect casing fragments from the drilling fluids. The shale shaker is a device in an oil well drilling process used to collect oversize drill cuttings, etc. from drilling fluid. The shale shaker is monitored for metal filings to assess metal wear such as for example, casing wear. For monitoring the metal wear, a shale shaker magnet is often used to magnetically attract and collect thereon at least a portion of metal filings that enter the shale shaker. The magnets are periodically removed from the shale shaker and the metal filings collected therefrom and weighed in order to quantify the filings that have been collected in the time period. The quantity of filings that are collected are indicative of the amount of metal filings passing into the shale shaker and, therefore, also indicative of the amount of metal filings being generated down hole. 
   The typical ditch magnet is heavy, and requires at least two persons to lower it into the drilling fluid stream. As metal fragments adhere to the ditch magnet, the device becomes even heavier and difficult for personnel to remove. Removal of the metal particles from the ditch magnet is difficult because of the strong magnetic field, which can also result in the magnetization of handles or other features of the device. Drilling personnel usually run their hands over the surface of the ditch magnet in an effort to strip the magnetic materials from the magnet. In prior art devices, the handle often complicates the collection of the magnetic materials attracted about it. The collection process becomes slow and laborious, and the completeness of the collection process can vary from person to person and from time to time because of the added complexity of removing the collected materials about the handle. Thus, the amount of metal fragments retrieved and therefore the accuracy of the calculation of total metal loss in the casing depends on the skill and thoroughness of the personnel removing the fragments from the ditch magnets. 
   Another known method of fragment removal employs shrouded or sheathed magnets in a non-magnetic housing which includes a lid connectable to the housing so that the magnets are removable from the housing. By removing the magnets from the housing, the housing can be demagnetized to facilitate collection of the metal filings from the exterior surface of the housing. However, the connection between the lid and the housing can become fouled by drilling mud and metal filings so that the reconnection of the lid to the housing becomes difficult. There is a need for an apparatus and method for inexpensive removal of casing fragments from drilling fluids without the disadvantages of the known devices and methods. 
   SUMMARY OF THE INVENTION 
   The present invention is directed to methods and apparatus for removing casing fragments from fluids circulated in hydrocarbon-producing wells. 
   In one aspect, the invention is directed to a method for monitoring the condition of well casing by recovering magnetically attractable casing fragments from fluid in a vessel having an upper end, including placing a reusable magnetic separator in the fluid in the vessel, wherein the separator includes a magnetic body, at least one nonmagnetic end contiguous to the body, an exterior surface spanning the body and nonmagnetic end, and a hanger; retaining the separator in the fluid for a selected period of time; removing the separator from the vessel; and urging the casing fragments along the exterior surface of the separator to the nonmagnetic end and collecting them. In another aspect, the invention is directed to a magnetic separator, having a bare magnet body, at least one nonmagnetic end contiguous to the body, and an exterior surface spanning the body and nonmagnetic end. 
   It is to be understood that other aspects of the present invention will become readily apparent to those skilled in the art from the following detailed description, wherein various embodiments of the invention are shown and described by way of illustration. As will be realized, the invention is capable for other and different embodiments and its several details are capable of modification in various other respects, all without departing from the spirit and scope of the present invention. Accordingly the drawings and detailed description are to be regarded as illustrative in nature and not as restrictive. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Referring to the drawings wherein like reference numerals indicate similar parts throughout the several views, several aspects of the present invention are illustrated by way of example, and not by way of limitation, in detail in the figures, wherein: 
       FIG. 1A  is a side elevation of an embodiment of an apparatus according to the present invention. 
       FIG. 1B  is a perspective view of another embodiment of an apparatus according to the disclosed invention. 
       FIG. 2  is a schematic view of a device and a method according to the disclosed invention. 
       FIG. 3  shows an exploded isometric view of an embodiment the disclosed invention. 
   

   DETAILED DESCRIPTION OF THE EMBODIMENTS 
   The detailed description set forth below in connection with the appended drawings is intended as a description of various embodiments of the present invention and is not intended to represent the only embodiments contemplated by the inventor. The detailed description includes specific details for the purpose of providing a comprehensive understanding of the present invention. However, it will be apparent to those skilled in the art that the present invention may be practiced without these specific details. 
   Referring to  FIG. 1A , one apparatus according to the invention is a reusable magnetic separator  10  for retrieving metal fragments from hydrocarbon well fluids including a magnet body  12  contiguous to at least one nonmagnetic end  14 , and an exterior surface  16 . 
   In some embodiments of the invention, the separator may include more than one nonmagnetic end. In other embodiment, the separator may be connectable to one or more hangers, for suspension thereof in use. The hanger may include a cable, a rope, a chain, or other conventional materials. Where more than one hanger is used, the points of connection of the hanger may be spaced apart and furthermore the points of connection of the hangers may each be disposed at a nonmagnetic end. 
   Referring to  FIG. 1B , another reusable magnetic separator  10   a  is shown. Reusable magnetic separator  10   a  is formed as an elongate member including a magnetically attractant body  12   a , a first nonmagnetic end  14   a ′ and an opposite nonmagnetic end  14   a ″. A first connector  15   a ′ is positioned at first nonmagnetic end  14   a ″ for accepting connection of a hanger (not shown) and a second connector  15   a ′ is positioned at the opposite nonmagnetic end for connection of a second hanger (not shown). The first and the second connectors may be in the form of eyebolts, as shown. Body  12   a  and ends  14   a ′ and  14   a ″ are contiguous and formed by a housing  17   a  that extends about the separator. Housing  17   a  contains therein one or more magnetic sources, illustrated herein as bar magnets  22   a , forming the magnetic body  12   a . The magnets  22   a  do not extend into the housing at its ends forming nonmagnetic ends  14   a ′,  14   a ″. Housing  17   a  may have a surface that is substantially smooth and substantially free of protrusions along its sides. 
   Referring to  FIG. 2 , a method of the invention includes placing a reusable magnetic separator  10   b  into fluid  28  in a vessel  20 , such as a shale shaker, and retaining the separator  10   b  in the fluid  28  for a selected period of time; the magnetic field separates and magnetically collects the casing fragments  30  and other magnetically attractable materials from the fluid  28 . After a suitable selected period of time, the separator  10   b  is removed from the vessel  20  and the collected materials are collected from the separator. To release the casing fragments  30  from the separator  10   b , the casing fragments  30  are urged along the exterior surface  16   b  to the nonmagnetic end  14   b , when they are no longer attracted to, and will fall away from, the separator. If the separator includes more than one nonmagnetic end, the magnetically attractable casing fragments may be collected by urging them to either or both nonmagnetic ends. The recovered casing fragments  30  may be analyzed (qualitatively and/or quantitatively) to assess the condition of the well casing. 
   As shown in  FIG. 2 , in some embodiments, the separator  10   b  may be suspended in the fluid  28  with one or more hangers  18   a . In various embodiments of the invention, the length of the hanger or hangers may be selected to maintain the separator above the bottom of the vessel. Since a shale shaker may accumulate settled materials, suspending the separator may facilitate collection of materials thereon as the separator is held up out of the accumulated materials and open in the flow of the fluid moving therepast. The selected length of the hanger may be fixed in some embodiments of the inventive methods so that when the separator is removed and repositioned within the vessel, it is suspended at the same position within the vessel each time. 
   Another aspect of the invention is a method for monitoring the condition of well casing by recovering magnetically attractable casing fragments from drilling fluid returning from the well, wherein the casing fragments may be generated by use or modification of the well casing. In this method, a reusable magnetic separator having a magnetic body and a nonmagnetic end contiguous to the body is placed in drilling fluid contained in a vessel, such as a shale shaker, whereby magnetically attractable casing fragments are separated from the fluid by the magnetic field created by the magnetic body. After a suitable selected period of time, the separator is removed from the fluid, and the casing fragments are urged along the exterior surface of the separator to the nonmagnetic end where they can be removed easily. The magnetic separator used in some embodiments may include a housing substantially free of protrusions along its sides and containing bar magnets, at least one nonmagnetic end, an eye bolt on the at least one nonmagnetic end attaching such nonmagnetic end to a hanger (such as a chain or other hanger type). In some embodiments, the collected casing fragments may be weighed after each of a number of similar time periods such that the amounts collected per time period may be compared over time. In another embodiment, weight of the recovered casing fragments may calculated and compared to a total weight of the casing originally installed in the well, which may be known or calculated, so that the percent of metal lost from the casing is obtainable for example by dividing the weight of the casing fragments recovered from the well by the total weight of the casing originally installed in the well. The casing fragments may also be subjected to qualitative assessment, such as by visual inspection. 
   Yet another aspect of the invention is a method for collecting magnetically attractable particles from fluid including placing a reusable magnetic separator in fluid, wherein the separator includes a magnetic body which in turn may have bare magnet, at least one nonmagnetic end contiguous to the body, and an exterior surface spanning the body and the nonmagnetic end; retaining the separator in the fluid for a selected period of time; removing the separator from the fluid; and, urging the particles along the exterior surface of the separator to the nonmagnetic end and collecting them. 
   Referring to  FIG. 3 , in some embodiments of the invention the body  12   c  may include at least one magnet  22 , and each magnet  22  may have a bore  26  such that the bores  26  of adjacent magnets  22  are aligned along an axis and a retainer  24  can be inserted through the bore  26  of each magnet  22 . At least one end of the retainer  24  may be attached to a nonmagnetic end  14   c , which nonmagnetic end is further attached by a connector to a hanger  18 . 
   The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to those embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein, but is to be accorded the full scope as defined in the claims, wherein reference to an element in the singular, such as by use of the article “a” or “an” is not intended to mean “one and only one” unless specifically so stated, but rather “one or more”. All structural and functional equivalents to the elements of the various embodiments described throughout the disclosure that are know or later come to be known to those of ordinary skill in the art are intended to be encompassed by the elements of the claims. Moreover, nothing disclosed herein is intended to be dedicated to the public regardless of whether such disclosure is explicitly recited in the claims. No claim element is to be construed under the provisions of 35 USC 112, sixth paragraph, unless the element is expressly recited using the phrase “means for” or “step for”.