Patent Publication Number: US-6659178-B2

Title: Apparatus and method for sealing well bores and bore holes

Description:
BACKGROUND OF THE INVENTION 
     The present invention generally relates to devices and methods for sealing well bores and bore holes, and more specifically to a method and apparatus which effectuates the sealing of well bores and bore holes through the use of mineral substances formed into compressed plates, where the compressed plates have the property of swelling into an expanded state upon contact with, and absorption of, a liquid. Among other applications, the disclosed method and apparatus may be used to seal off well bores and bore holes associated with the production, injection and/or disposal of water, hydrocarbons, and other fluids. The disclosed method and apparatus may also be utilized in the sealing of bore holes associated with the storage and/or disposal of nuclear materials. The terms well bore and bore hole are hereinafter used interchangeably and are intended to refer to any excavation which is deeper than the measurement across its opening. 
     Sealing or plugging a well bore may be required for a number of reasons, with each situation presenting different operational constraints. One common application of sealing or plugging a well bore occurs when a well is to be abandoned. Proper well abandonment is required to protect freshwater aquifers from fluid migration from other zones penetrated by the well bore. For example, in oil and gas wells, proper abandonment is necessary to prevent migration of fluids from a hydrocarbon zone to an adjacent freshwater zone. Proper abandonment is necessary to protect the freshwater aquifer and to confine hydrocarbons. Agencies which regulate oil and gas production typically require a cement plug, or plugs of other substances with adequate physical properties, to be placed across specified intervals for abandonment purposes. According to the usual regulatory requirements, the plug must extend from the total depth of the well or from at least one hundred feet below the bottom of each oil and gas zone to at least one hundred feet above the top of each oil or gas zone. In a cased well, all perforations are to be plugged and the plug is to extend at least 100 feet above the top of a landed liner, the uppermost perforations, the casing cementing point, the water shut-off holes, or the oil or gas zone, whichever is highest. An additional plug is required across fresh-saltwater interfaces. Fluids having the proper weight and consistency to prevent movement of other fluids into the well bore are placed across all intervals not otherwise plugged. 
     The most common method of sealing or plugging a well bore is pumping in a cement slurry to the zone of interest. However, depending upon the situation, design of an appropriate cement slurry can be complicated, requiring a number of different and expensive additives. Moreover, in the usual situation, a number of expensive resources must be assembled for the operation. Equipment such as a drilling rig, work-over unit, portable mast, pumping and blending works, bulk trucks, etc., and the personnel to operate the equipment, may be required to stand by during the course of the operation. The equipment and personnel may continue to stand by even after application of the cement slurry has concluded, waiting for the cement to harden to an acceptable strength. 
     Another known disadvantage of cement is that it can degrade over time, such that it might contract or crack, thereby providing channels through which fluid migration might take place. Even without such degradation, cement is known to have some permeability, potentially allowing fluid flow through a cement plug. 
     As an alternative to using cement as a plugging or sealing material, it is known to use high quality course ground chemically unaltered sodium bentonite (hereinafter referred to as sodium bentonite). Sodium bentonite is the name given to clay containing over 90% sodium montmorillonite, one of several minerals within the smectite group. These substances exhibit pronounced swelling tendencies when exposed to a hydrating liquid. Sodium bentonite has long been identified as a material with excellent plugging ability. Dry sodium bentonite will swell to a size ten to twenty-five times its dry state when hydrated. Hydrated sodium bentonite has extremely low permeability, a much-desired characteristic for an isolation plug. It has long been identified as a suitable material for plugging monitoring wells, seismic shot holes, mining shafts, exploratory holes, water wells, and oil and gas wells. Sodium bentonite has also been identified as an excellent plugging material for high-level nuclear waste repositories because of its ability to confine waste migration and resist alteration over time. 
     A simple method is known for using sodium bentonite to create a plug in a well bore. This method comprises simply pouring a small granular form of dry sodium bentonite into the well bore from the surface, filling the hole from the bottom upward. However, sodium bentonite in granular form (having a diameter of no greater than ⅜ inches) will swell quickly upon encountering water or other liquids. As sodium bentonite hydrates and expands, its density decreases, resulting in a reduced falling velocity and increased exposure to well bore liquids before reaching the desired depth. This characteristic of the granular form of sodium bentonite creates a risk that the material will bridge and plug off the well before a plug is achieved at the desired depth. Therefore, the use of finely ground sodium bentonite is generally limited to shallow well bores up to 100 feet in depth. This material might also be used in a deeper well bore containing very little liquid. 
     Because of the risk of bridging off, alternative placement methods for sodium bentonite have been proposed. In one method, bentonite is poured from the surface while rotating an auger drill within the well to force the bentonite downward into the well. In another method, bentonite chips are encapsulated and poured into the well from the surface. It is also known to use chemically unaltered compressed sodium bentonite nodules, which are poured from the surface and, ideally, fall to the intended plugging zone where they accumulate until the desired plug height is reached. The nodules are typically manufactured from roll type briquetting and compacting machines. Compression of the nodule reduces the hydration and expansion rates typical of uncompressed sodium bentonite, allowing use of this material in deeper applications. However, all of these methods continue to rely upon surface pouring the sodium bentonite into the well. Notwithstanding improvements offered by these methods, there remains a potential for the material to bridge off above the desired depth of the plug, particularly where there is an excessive pour rate. Well bore irregularities, obstructions, extreme directional changes, fluid interfaces, viscous emulsions, and other common well bore occurrences may cause the initially poured grains, capsules or nodules to decelerate. Subsequently poured sodium bentonite may catch up with the initial material, causing the grains, capsules or nodules to congregate, and ultimately to bridge. 
     Nodules may present a further disadvantage. Depending upon how the nodules are packaged and delivered to the well site, sodium bentonite residue may accumulate from nodule-to-nodule contact. If this residue is included in the surface pour, the residue will begin to hydrate almost immediately upon contact with well liquids, thereby increasing the liquid viscosity and decreasing the velocity of the surrounding nodules. It is also possible for nodule-to-nodule contact to take place during the surface pour or as the nodules are falling into place within the well bore, which once again can generate sodium bentonite residue resulting in an increase in the liquid viscosity. 
     Another disadvantage of surface pouring sodium bentonite grains, capsules or nodules is that forming a plug by surface pouring these materials is limited to generally vertical wells. These materials will tend to collect or bridge in highly deviated and/or horizontal well bores, rendering it unlikely that the lateral portion of the well bore can be effectively plugged. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to an apparatus and method for sealing well bores and bore holes which meets the needs identified above. The apparatus comprises a first plate having a top surface, a bottom surface, and a peripheral edge surface bound by the top surface and the bottom surface. The peripheral edge surface has a maximum width defined by the linear distance between a first point on the peripheral edge surface to an opposite second point on the peripheral edge surface. The plate has a first compressed state wherein the maximum width is smaller than the diameter of the well bore or the bore hole to be sealed. The plate is formed from a mineral substance. This mineral substance has the property of swelling into a second expanded state upon contact with a liquid and absorption of that liquid. The apparatus requires means for placing the plate within the well bore or bore hole. Among the mineral substances which may be utilized for forming the plate are members of the group of clay minerals known as smectites, including sodium montmorillonite, calcium montmorillonite, sodium bentonite and calcium bentonite. 
     In one embodiment the plate may be round. For this embodiment, the plate has a first compressed state wherein the plate has a diameter smaller than the diameter of the well bore. 
     A method of sealing well bores and bore holes is also disclosed. The method comprises the steps of first disposing a mineral substance into a mold, where the substance has the property of swelling upon contact with a liquid and absorption of the liquid. The mineral substance is then molded into a plate, where the plate has a top surface, a bottom surface, and a peripheral edge surface bound by the top surface and the bottom surface. The peripheral edge surface has a maximum width defined by the linear distance between a first point on the peripheral edge surface to an opposite second point on the peripheral edge surface. The plate is compressed into a first compressed state where the maximum width is smaller than the diameter of the well bore. The plate is thereafter placed into the well bore with placement means. The plate is thereafter exposed to liquid such that the mineral substance swells into a second expanded state upon contact with the liquid and absorption of the liquid. 
     These and other features, aspects, and advantages of the present invention will become better understood with regard to the following description, appended claims, and accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic showing down-hole zones producing into a well bore. 
     FIG. 2 shows the setting of one embodiment of the disclosed apparatus and method. 
     FIG. 3 shows the configuration of the well bore after placement of one embodiment of the disclosed apparatus. 
     FIG. 4 shows the setting of one embodiment of the disclosed apparatus and method in a well bore having a deviated section. 
     FIG. 5A shows a top view of a plate used in the disclosed method and apparatus. 
     FIG. 5B shows a side view of a plate used in the disclosed method and apparatus. 
     FIG. 5C shows a side view of a stack of plates used in the disclosed method and apparatus. 
     FIG. 6A shows a top view of an alternative embodiment of a plate used in the disclosed method and apparatus, the plate having grooves in the peripheral edge surface. 
     FIG. 6B shows a side view of an alternative embodiment of a plate used in the disclosed method and apparatus. 
     FIG. 6C shows a side view of an alternative embodiment of a stack of plates used in the disclosed method and apparatus. 
     FIG. 7A shows a top view of an alternative embodiment of a plate used in the disclosed method and apparatus, the plate having ridges and grooves in the top surface and bottom surface. 
     FIG. 7B shows a side view of an alternative embodiment of a plate used in the disclosed method and apparatus, the plate having ridges and grooves in the top surface and bottom surface. 
     FIG. 7C shows a side view of an alternative embodiment of a stack of plates used in the disclosed method and apparatus, the plates having ridges and grooves in the top surface and bottom surface. 
     FIG. 8A shows a top view of an alternative embodiment of a plate used in the disclosed method and apparatus, the plate having a convex top surface and a concave bottom surface. 
     FIG. 8B shows a side view of an alternative embodiment of a plate used in the disclosed method and apparatus, the plate having a convex top surface and a concave bottom surface. 
     FIG. 8C shows a side view of an alternative embodiment of a stack of plates used in the disclosed method and apparatus, the plates having convex top surfaces and concave bottom surfaces. 
     FIG. 9A shows a top view of an alternative embodiment of a plate used in the disclosed method and apparatus, the plate having ridges and grooves in the top surface and bottom surface. 
     FIG. 9B shows a side view of an alternative embodiment of a plate used in the disclosed method and apparatus, the plate having ridges and grooves in the top surface and bottom surface. 
     FIG. 9C shows a side view of an alternative embodiment of a stack of plates used in the disclosed method and apparatus, the plates having ridges and grooves in the top surface and bottom surface. 
     FIG. 10A shows a top view of an alternative embodiment of a plate used in the disclosed method and apparatus, the plate having ridges and grooves in the top surface and bottom surface. 
     FIG. 10B shows a side view of an alternative embodiment of a plate used in the disclosed method and apparatus, the plate having ridges and grooves in the top surface and bottom surface. 
     FIG. 10C shows a side view of an alternative embodiment of a stack of plates used in the disclosed method and apparatus, the plates having ridges and grooves in the top surface and bottom surface. 
     FIG. 11 shows alternative means for placement of a stack of plates. 
     FIG. 12 shows alternative means for placement of a stack of plates. 
     FIG. 13 shows alternative means for placement of a stack of plates. 
     FIG. 14 shows alternative means for placement of a stack of plates. 
     FIG. 15 shows alternative means for placement of a stack of plates. 
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Referring now specifically to the drawings, FIG. 1 shows well bore  10  into which fluids are flowing from a producing zone  12 . Within the same well bore  10 , there may exist cap rock zones  14  which have such low permeability that the cap rock zone  14  effectively contains fluids within the producing zone  12  except for fluids which flow from the producing zone  12  into the well bore  10 . Shale, claystone, and other fine-grained sediments are typical cap rocks. However, once well bore  10  has been drilled or excavated, a conduit has been created by which fluids from the producing zone  12  may flow around the cap rock zone  14  and flow into other permeable zones, including fresh water zone  16 . If producing zone  12  contains hydrocarbons, salt water, or other mineral substances, it is obvious that well bore  10  might provide a conduit for flow of those substances into a fresh water zone  16 , resulting in the contamination of the fresh water. The well bore  10  must be designed to prevent such flow from adjacent zones into fresh water zones, and various governmental agencies oversee the design, operation, and abandonment of well bores to insure reasonable precautions are taken to prevent the flow of contaminants into fresh water zones. In the case of hydrocarbon wells, the well bore  10  is typically lined with steel casing, and a cement sheath is installed around the casing in the annular space between the rock face and the casing. The casing and cement sheath are thereafter perforated to provide flow channels from the producing zone  12  into the well bore  10 . Ideally, the cement sheath forms an effective seal between the casing and the cap rock zone  14 , thereby preventing fluids to flow up through the casing-open hole annulus from the producing zone  12  into the fresh water zone  16 . In addition, regulatory agencies usually require the operators of hydrocarbon wells to demonstrate the existence of an effective “water shut-off” directly below known fresh water zones, to show that the fresh water zone has been safely isolated from fluids produced from lower zones. 
     For a number of different operational reasons, including abandonment of a producing zone  12 , it is often necessary to seal or plug off the producing zone  12 . In the past, the plugs have generally been composed of cement. However, for the reasons described above, it is advantageous to use other substances for plug materials, including mineral substances which swell upon contact with and adsorption of liquids, such as members of the group of clay minerals known as smectites, including sodium montmorillonite, calcium montmorillonite, sodium bentonite and calcium bentonite. 
     The disclosed method and apparatus utilize plates made from these substances. As shown in FIG. 2, compressed plates  18  made from these materials are inserted into the well bore  10  with means for placing the plate  18  within the well bore  10 , such as wireline, tubing strings, coiled tubing or sucker rod strings. FIG. 3 depicts the well bore  10  when compressed plates  18  have been set adjacent to each producing zone  12 , and fresh water zone  16 . FIG. 3 also depicts compressed plates  18  being set adjacent to the cap rock zone  14 . Once the compressed plates  18  are in place within the well bore  10 , the liquids within the well bore will begin to hydrate the compressed plates, such that the plates  18  swell into a second expanded state. If necessary, liquid may be introduced into the well bore to initially hydrate the compressed plates  18 . The plates  18  should hydrate within  24  hours. Referring once again to FIG. 3, it is to be appreciated that once the pressure plates hydrate and expand within the well bore  10 , the fresh water zone  16  will effectively be isolated from the producing zone  12 . 
     FIG. 4 depicts a well bore  10 ′ which has a segment  24  which deviates substantially from vertical. Deviated and horizontal wells present a situation where a surface pour of any material, including sodium bentonite, is not an appropriate method of creating a plug because materials can not be effectively placed within the deviated segment  24 , and will not effectively seal off the deviated segment because the materials will gravitate to the bottom of the well bore  10 ′. However, the disclosed apparatus may be successfully applied in these situations, because the plates  18  conform to the orientation of the deviated segment  24 . As shown in FIG. 4, compressed plates  18  are installed with means for placing the plates within the well bore  10 ′. Where the plates  18  are to be installed in a deviated segment  24  of a well bore  10 ′, the placement means must be a tubing string, sucker rod string, coiled tubing, or some other device capable of being placed into compression to push the stack of plates  18  into the deviated segment. It is to be appreciated that wireline is not an acceptable placement means for installing plates  18  into the deviated segment  24 . 
     In addition to the compressed plates  18 , spacers  22  made from filler material may be installed adjacent to the compressed plates  18 . While the spacers  22  may be made out of the same materials used to fabricate the compressed plates  18 , the spacers  22  may also be made from fuller&#39;s earth, Portland cement, silica sand, mica, diatomaceous earth, and different combinations thereof. The spacers  22  may be installed in the well bore  10  adjacent to the compressed plates  18 . As depicted in FIG.  2  and FIG. 3, the spacers  22  may be run ahead of the compressed plates  18  to form a base for the compressed plates to rest upon. The spacers  22  may also lend additional lateral support to the well bore  10 , but still allow liquids to flow around the spacers so that the plates  18  remain hydrated. If the plates  18  become dehydrated, they may no longer form an effective seal. 
     As shown in FIGS.  5 (A-C) through  10 (A-C), compressed plate  18  has a top surface  26 , a bottom surface  28 , and a peripheral edge surface  30 . The peripheral edge surface  30  has a maximum width  32  defined by the linear distance between a first point  34  on the peripheral edge surface  30  to an opposite second point  36  on the peripheral edge surface. The compressed plate  18  has a first compressed state in which the maximum width  32  is smaller than the diameter of the well bore  10 . The compressed plate  18  is formed from a mineral substance which has the property of swelling into a second expanded state upon contact with and absorption of a liquid  38  within the well bore  10 . Mineral substances which have been found to include these properties include the group of clay minerals known as smectites. Among these clay minerals are sodium montmorillonite and calcium montmorillonite. Sodium bentonite, which is the trade name given to clay containing over 90% sodium montmorillonite, exhibits distinct swelling tendencies and is an appropriate mineral substance for the fabrication of the plates. When sodium bentonite is used as the mineral substance for fabrication of the compressed plate  18 , the sodium bentonite should be finely ground and chemically unaltered. The sodium bentonite will have a moisture content of approximately 6 percent to 10 percent. Calcium bentonite also exhibits some swelling tendencies, but these tendencies are not as pronounced as with sodium bentonite. Therefore, application of the apparatus with plates  18  fabricated from calcium bentonite may be more limited than plates  18  made with sodium bentonite. 
     The mineral substance is then press molded into a plate form such as those depicted in FIGS.  5 (A-C) through  10 (A-C). A dry pressing method may be used for forming the compressed plates  18 . This process is used for forming many types of ceramic products, including tiles. However, the term “dry pressing” is not strictly accurate because the materials being pressed may contain from 3% to 15% water. Pressures used in dry pressing vary from a few hundred psi to 100,000 psi depending upon the material being compacted, the shape of the plate, and the quality necessary for the particular design requirements for the compressed plates  18 . Pressing is usually accomplished in steel dies using either hydraulic or mechanical means of producing the desired pressures. 
     One acceptable process for forming the compressed plates is through a method called high pressure jolt squeeze technology. In this process, the mineral substance is placed, in dry form, within a mold, such as that used for pressing tiles. The material is subjected to high pressure compression through the process, which acts to consolidate and bind the dry material together into the desired shape. 
     The plate  18  may be fabricated such that top surface  26  and bottom surface  28  are centered relative to a vertical axis  40 . A bore  42  may be placed in the plate  18  such that the bore  42  extends from the top surface  26  to the bottom surface  28 , with the bore  42  centered relative to the vertical axis  40 . A mandrel  44 , fabricated from tubing, rods or other round stock, may then be inserted through the bore  42 , such that the plate  18  may be placed within the well bore  10  by connecting the mandrel to a tubing and/or rod string  46  as depicted in FIG.  12 . Using this means of placing the plate  18  into the well bore  10 , a plate retainer assembly  48  equipped with shear pin  50  may be attached to the mandrel  44  as shown in FIG.  13 . Jars  52  may also be used for breaking shear pin  50  so that the tubing or rod string  46  is released from the plate  18 . FIG. 14 shows an alternative assembly for inserting plate  18  into the well bore, which also includes centralizers  54  and scratchers  56 , which may be reciprocated within the well bore to remove oil or other debris from the well bore  10  before the plates  18  are hydrated. 
     Alternatively, the mandrel  44  may be connected to a wireline  58  as depicted in FIG. 15 for placing the plate  18  within the well bore  10 . A wireline plate retainer assembly  60  equipped with a shear pin  62  may be attached to the mandrel  44 . Wireline jars  64  may be used for breaking shear pin  62  so that the wireline  58  is released from the plate  18 . 
     The plate  18  may be round, as shown in FIG.  5 A. Where round plates are used, the plate must have a first compressed state where the diameter  32  of the plate is smaller than the diameter of the well bore. 
     The disclosed method and apparatus may use a compressed plate  18  or multiple compressed plates. As shown in FIGS.  5 (A-C) through  10 (A-C) when multiple compressed plates  18  are applied to a well bore  10 , the plates may be arranged such that there is a first plate  18 A, a second plate  18 B, and a plurality of intermediate plates  18 C. As with a single plate installation, in the multiple plate installation each plate has a top surface  26 , a bottom surface  28 , and a peripheral edge surface  30  bound by the top surface  26  and the bottom surface  28 . The peripheral edge surface  30  continues to have a maximum width  32  defined by the linear distance between a first point  34  on the peripheral edge surface to an opposite second point  36  on the peripheral edge surface. The first plate  18 A is at a top position, the second plate  18 B is at a bottom position, and the intermediate plates  18 C are stacked between the first plate  18 A and the second plate  18 B. 
     As shown in FIGS.  5 (A-C) through  10 (A-C), the top surface  26  of each intermediate plate  18 C is configured to mate with the bottom surface  28  of the adjacent plate. It is to be appreciated that the combinations of mating surfaces which might be used is practically limitless. The mating surfaces may assist the plates  18  in forming a more consolidated plug. As shown in FIGS.  7 (A-C),  9 (A-C) and  10 (A-C), the mating surfaces may include a ridge  66  on the top surface  26  with a corresponding groove  68  on the bottom surface  28  convex adapted to receive the ridge  66  of an underlying plate. The top surface  26  might also be concave and the bottom surface  28 , where the bottom surface  28  is adapted to receive the top surface of an underlying plate. Likewise, as shown in FIG. 8, the top surface  26  might be convex and the bottom surface  28  concave, where the bottom surface is adapted to receive the top surface of an underlying plate. 
     The peripheral edge surface  30  may also have slots  64 , which allow liquid bypass as the plate  18  is lowered into the well bore  10 . 
     While the above is a description of various embodiments of the present invention, further modifications may be employed without departing from the spirit and scope of the present invention. For example, the size, shape, position and/or material of the various components may be changed as desired. Thus the scope of the invention should not be limited by the specific structures disclosed. Instead the true scope of the invention should be determined by the following claims.