Abstract:
A guide tube bundle includes two or more guide tubes. Each guide tube includes a first aperture at a first end and a second aperture at a second end. The longitudinal axis of the first aperture of each guide tube is offset from the longitudinal axis of the second aperture of the guide tube Furthermore, the guide tubes are configured longitudinally adjacent to each other and are twisted around one another.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]    This application is a divisional application of U.S. application Ser. No. 10/004,316 filed Oct. 30, 2001 and entitled “Slant Entry Well System and Method”. 
     
    
     
       TECHNICAL FIELD OF THE INVENTION  
         [0002]    The present invention relates generally to systems and methods for the recovery of subterranean resources and, more particularly, to a slant entry well system and method.  
         BACKGROUND OF THE INVENTION  
         [0003]    Subterranean deposits of coal contain substantial quantities of entrained methane gas. Limited production and use of methane gas from coal deposits has occurred for many years. Substantial obstacles, however, have frustrated more extensive development and use of methane gas deposits in coal seams. The foremost problem in producing methane gas from coal seams is that while coal seams may extend over large areas of up to several thousand acres, the coal seams are fairly shallow in depth, varying from a few inches to several meters. Thus, while the coal seams are often relatively near the surface, vertical wells drilled into the coal deposits for obtaining methane gas can only drain a fairly small radius around the coal deposits. Further, coal deposits are not amenable to pressure fracturing and other methods often used for increasing methane gas production from rock formations. As a result, once the gas easily drained from a vertical well bore in a coal seam is produced, further production is limited in volume. Additionally, coal seams are often associated with subterranean water, which must be drained from the coal seam in order to produce the methane.  
           [0004]    Horizontal drilling patterns have been tried in order to extend the amount of coal seams exposed to a drill bore for gas extraction. Such horizontal drilling techniques, however, require the use of a radiused well bore which presents difficulties in removing the entrained water from the coal seam. The most efficient method for pumping water from a subterranean well, a sucker rod pump, does not work well in horizontal or radiused bores.  
           [0005]    As a result of these difficulties in surface production of methane gas from coal deposits, which must be removed from a coal seam prior to mining, subterranean methods have been employed. While the use of subterranean methods allows water to be easily removed from a coal seam and eliminates under-balanced drilling conditions, they can only access a limited amount of the coal seams exposed by current mining operations. Where longwall mining is practiced, for example, underground drilling rigs are used to drill horizontal holes from a panel currently being mined into an adjacent panel that will later be mined. The limitations of underground rigs limits the reach of such horizontal holes and thus the area that can be effectively drained. In addition, the degasification of a next panel during mining of a current panel limits the time for degasification. As a result, many horizontal bores must be drilled to remove the gas in a limited period of time. Furthermore, in conditions of high gas content or migration of gas through a coal seam, mining may need to be halted or delayed until a next panel can be adequately degasified. These production delays add to the expense associated with degasifying a coal seam.  
         SUMMARY OF THE INVENTION  
         [0006]    The present invention provides a slant entry well system and method for accessing a subterranean zone from the surface that substantially eliminates or reduces the disadvantages and problems associated with previous systems and methods. In particular, certain embodiments of the present invention provide a slant entry well system and method for efficiently producing and removing entrained methane gas and water from a coal seam without requiring excessive use of radiused or articulated well bores or large surface area in which to conduct drilling operations.  
           [0007]    In accordance with one embodiment of the present invention, a guide tube bundle includes two or more guide tubes. Each guide tube includes a first aperture at a first end and a second aperture at a second end. The longitudinal axis of the first aperture of each guide tube is offset from the longitudinal axis of the second aperture of the guide tube Furthermore, the guide tubes are configured longitudinally adjacent to each other and are twisted around one another.  
           [0008]    Embodiments of the present invention may provide one or more technical advantages. These technical advantages may include the formation of a plurality of slanted well bores and drainage patterns to optimize the area of a subsurface formation which may be drained of gas and liquid resources. This allows for more efficient drilling and production and greatly reduces costs and problems associated with other systems and methods.  
           [0009]    Another technical advantage includes providing a method for orienting well bores using a guide tube bundle inserted into an entry well bore. The guide tube bundle allows for the simple orientation of the slant well bores in relation to one another and optimizes the production of resources from subterranean zones by optimizing the spacing between the slanted well bores.  
           [0010]    Other technical advantages of the present invention will be readily apparent to one skilled in the art from the following figures, descriptions, and claims.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]    For a more complete understanding of the present invention and its advantages, reference is now made to the following description taken in conjunction with the accompanying drawings, wherein like numerals represent like parts, in which:  
         [0012]    [0012]FIG. 1 illustrates an example slant well system for production of resources from a subterranean zone;  
         [0013]    [0013]FIG. 2A illustrates a vertical well system for production of resources from a subterranean zone;  
         [0014]    [0014]FIG. 2B illustrates a portion of An example slant entry well system in further detail;  
         [0015]    [0015]FIG. 3 illustrates an example method for producing water and gas from a subsurface formation;  
         [0016]    FIGS.  4 A- 4 C illustrate construction of an example guide tube bundle;  
         [0017]    [0017]FIG. 5 illustrates an example entry well bore with an installed guide tube bundle;  
         [0018]    [0018]FIG. 6 illustrates the use of an example guide tube bundle in an entry well bore;  
         [0019]    [0019]FIG. 7 illustrates an example system of slanted well bores;  
         [0020]    [0020]FIG. 8 illustrates an example system of an entry well bore and a slanted well bore;  
         [0021]    [0021]FIG. 9 illustrates an example system of a slanted well bore and an articulated well bore;  
         [0022]    [0022]FIG. 10 illustrates production of water and gas in an example slant well system;  
         [0023]    [0023]FIG. 11 illustrates an example drainage pattern for use with a slant well system; and  
         [0024]    [0024]FIG. 12 illustrates an example alignment of drainage patterns for use with a slant well system.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0025]    [0025]FIG. 1 illustrates an example slant well system for accessing a subterranean zone from the surface. In the embodiment described below, the subterranean zone is a coal seam. It will be understood that other subterranean formations and/or low pressure, ultra-low pressure, and low porosity subterranean zones can be similarly accessed using the slant well system of the present invention to remove and/or produce water, hydrocarbons and other fluids in the zone, to treat minerals in the zone prior to mining operations, or to inject or introduce fluids, gases, or other substances into the zone.  
         [0026]    Referring to FIG. 1, a slant well system  10  includes an entry well bore  15 , slant wells  20 , articulated well bores  24 , cavities  26 , and rat holes  27 . Entry well bore  15  extends from the surface  11  towards the subterranean zone  22 . Slant wells  20  extend from the terminus of entry well bore  15  to the subterranean zone  22 , although slant wells  20  may alternatively extend from any other suitable portion of entry well bore  15 . Where there are multiple subterranean zones  22  at varying depths, as in the illustrated example, slant wells  20  extend through the subterranean zones  22  closest to the surface into and through the deepest subterranean zone  22 . Articulated well bores  24  may extend from each slant well  20  into each subterranean zone  22 . Cavity  26  and rat hole  27  are located at the terminus of each slant well  20 .  
         [0027]    In FIGS.  1 , and,  5 - 8 , entry well bore  15  is illustrated as being substantially vertical; however, it should be understood that entry well bore  15  may be formed at any suitable angle relative to the surface  11  to accommodate, for example, surface  11  geometries and attitudes and/or the geometric configuration or attitude of a subterranean resource. In the illustrated embodiment, slant well  20  is formed to angle away from entry well bore  15  at an angle designated alpha, which in the illustrated embodiment is approximately 20 degrees. It will be understood that slant well  20  may be formed at other angles to accommodate surface topologies and other factors similar to those affecting entry well bore  15 . Slant wells  20  are formed in relation to each other at an angular separation of beta degrees, which in the illustrated embodiment is approximately sixty degrees. It will be understood that slant wells  20  may be separated by other angles depending likewise on the topology and geography of the area and location of the target coal seam  22 .  
         [0028]    Slant well  20  may also include a cavity  26  and/or a rat hole  27  located at the terminus of each slant well  20 . Slant wells  20  may include one, both, or neither of cavity  26  and rat hole  27 .  
         [0029]    [0029]FIGS. 2A and 2B illustrate by comparison the advantage of forming slant wells  20  at an angle. Referring to FIG. 2A, a vertical well bore  30  is shown with an articulated well bore  32  extending into a coal seam  22 . As shown by the illustration, fluids drained from coal seam  22  into articulated well bore  32  must travel along articulated well bore  32  upwards towards vertical well bore  30 , a distance of approximately W feet before they may be collected in vertical well bore  30 . This distance of W feet is known as the hydrostatic head and must be overcome before the fluids may be collected from vertical well bore  30 . Referring now to FIG. 2B, a slant entry well  34  is shown with an articulated well bore  36  extending into coal seam  22 . Slant entry well  34  is shown at an angle alpha away from the vertical. As illustrated, fluids collected from coal seam  22  must travel along articulated well bore  36  up to slant entry well  34 , a distance of W′ feet. Thus, the hydrostatic head of a slant entry well system is reduced as compared to a substantially vertical system. Furthermore, by forming slant entry well  34  at angle alpha, the articulated well bore  36  drilled from tangent or kick off point  38  has a greater radius of curvature than articulated well bore  32  associated with vertical well bore  30 . This allows for articulated well bore  36  to be longer than articulated well bore  32  (since the friction of a drill string against the radius portion is reduced), thereby penetrating further into coal seam  22  and draining more of the subterranean zone.  
         [0030]    [0030]FIG. 3 illustrates an example method of forming a slant entry well. The steps of FIG. 3 will be further illustrated in subsequent FIGS.  4 - 11 . The method begins at step  100  where the entry well bore is formed. At step  105 , a fresh water casing or other suitable casing with an attached guide tube bundle is installed into the entry well bore formed at step  100 . At step  110 , the fresh water casing is cemented in place inside the entry well bore of step  100 .  
         [0031]    At step  115 , a drill string is inserted through the entry well bore and one of the guide tubes in the guide tube bundle. At step  120 , the drill string is used to drill approximately fifty feet past the casing. At step  125 , the drill is oriented to the desired angle of the slant well and, at step  130 , a slant well bore is drilled down into and through the target subterranean zone.  
         [0032]    At decisional step  135 , a determination is made whether additional slant wells are required. If additional slant wells are required, the process returns to step  115  and repeats through step  135 . Various means may be employed to guide the drill string into a different guide tube on subsequent runs through steps  115 - 135 , which should be apparent to those skilled in the art.  
         [0033]    If no additional slant wells are required, the process continues to step  140 . At step  140  the slant well casing is installed. Next, at step  145 , a short radius curve is drilled into the target coal seam. Next, at step  150 , a substantially horizontal well bore is drilled into and along the coal seam. It will be understood that the substantially horizontal well bore may depart from a horizontal orientation to account for changes in the orientation of the coal seam. Next, at step  155 , a drainage pattern is drilled into the coal seam through the substantially horizontal well. At decisional step  157 , a determination is made whether additional subterranean zones are to be drained as, for example, when multiple subterranean zones are present at varying depths below the surface. If additional subterranean zones are to be drained, the process repeats steps  145  through  155  for each additional subterranean zone. If no further subterranean zones are to be drained, the process continues to step  160 .  
         [0034]    At step  160 , production equipment is installed into the slant well and at step  165  the process ends with the production of water and gas from the subterranean zone.  
         [0035]    Although the steps have been described in a certain order, it will be understood that they may be performed in any other appropriate order. Furthermore, one or more steps may be omitted, or additional steps performed, as appropriate.  
         [0036]    [0036]FIGS. 4A, 4B, and  4 C illustrate formation of a casing with associated guide tube bundle as described in step  105  of FIG. 3. Referring to FIG. 4A, three guide tubes  40  are shown in side view and end view. The guide tubes  40  are arranged so that they are parallel to one another. In the illustrated embodiment, guide tubes  40  are 9⅝″ joint casings. It will be understood that other suitable materials may be employed.  
         [0037]    [0037]FIG. 4B illustrates a twist incorporated into guide tubes  40 . The guide tubes  40  are twisted gamma degrees in relation to one another while maintaining the lateral arrangement to gamma degrees. Guide tubes  40  are then welded or otherwise stabilized in place. In an example embodiment, gamma is equal to 10 degrees.  
         [0038]    [0038]FIG. 4C illustrates guide tubes  40 , incorporating the twist, in communication and attached to a casing collar  42 . The guide tubes  40  and casing collar  42  together make up the guide tube bundle  43 , which may be attached to a fresh water or other casing sized to fit the length of entry well bore  15  of FIG. 1 or otherwise suitably configured.  
         [0039]    [0039]FIG. 5 illustrates entry well bore  15  with guide tube bundle  43  and casing  44  installed in entry well bore  15 . Entry well bore  15  is formed from the surface  11  to a target depth of approximately three hundred and ninety feet. Entry well bore  15 , as illustrated, has a diameter of approximately twenty-four inches. Forming entry well bore  15  corresponds with step  100  of FIG. 3. Guide tube bundle  43  (consisting of joint casings  40  and casing collar  42 ) is shown attached to a casing  44 . Casing  44  may be any fresh water casing or other casing suitable for use in down-hole operations. Inserting casing  44  and guide tube bundle  43  into entry well bore  15  corresponds with step  105  of FIG. 3.  
         [0040]    Corresponding with step  110  of FIG. 3, a cement retainer  46  is poured or otherwise installed around the casing inside entry well bore  15 . The cement casing may be any mixture or substance otherwise suitable to maintain casing  44  in the desired position with respect to entry well bore  15 .  
         [0041]    [0041]FIG. 6 illustrates entry well bore  15  and casing  44  with guide tube  43  in its operative mode as slant wells  20  are about to be drilled. A drill string  50  is positioned to enter one of the guide tubes  40  of guide tube bundle  43 . In order to keep drill string  50  relatively centered in casing  44 , a stabilizer  52  may be employed. Stabilizer  52  may be a ring and fin type stabilizer or any other stabilizer suitable to keep drill string  50  relatively centered. To keep stabilizer  52  at a desired depth in well bore  15 , stop ring  53  may be employed. Stop ring  53  may be constructed of rubber or metal or any other foreign down-hole environment material suitable. Drill string  50  may be inserted randomly into any of a plurality of guide tubes  40  of guide tube bundle  43 , or drill string  50  may be directed into a selected joint casing  40 . This corresponds to step  115  of FIG. 3.  
         [0042]    [0042]FIG. 7 illustrates an example system of slant wells  20 . Corresponding with step  120  of FIG. 3, tangent well bore  60  is drilled approximately fifty feet past the end of entry well bore  15  (although any other appropriate distance may be drilled). Tangent well bore  60  is drilled away from casing  44  in order to minimize magnetic interference and improve the ability of the drilling crew to guide the drill bit in the desired direction. Corresponding with step  125  of FIG. 3, a radiused well bore  62  is drilled to orient the drill bit in preparation for drilling the slant entry well bore  64 . In a particular embodiment, radiused well bore  62  is curved approximately twelve degrees per one hundred feet (although any other appropriate curvature may be employed).  
         [0043]    Corresponding with step  130  of FIG. 3, a slant entry well bore  64  is drilled from the end of the radius well bore  62  into and through the subterranean zone  22 . Alternatively, slant well  20  may be drilled directly from guide tube  40 , without including tangent well bore  60  or radiused well bore  62 . An articulated well bore  65  is shown in its prospective position but is drilled later in time than rat hole  66 , which is an extension of slant well  64 . Rat hole  66  may also be an enlarged diameter cavity or other suitable structure. After slant entry well bore  64  and rat hole  66  are drilled, any additional desired slant wells are then drilled before proceeding to installing casing in the slant well.  
         [0044]    [0044]FIG. 8 is an illustration of the casing of a slant well  64 . For ease of illustration, only one slant well  64  is shown. Corresponding with step  140  of FIG. 3, a whip stock casing  70  is installed into the slant entry well bore  64 . In the illustrated embodiment, whip stock casing  70  includes a whip stock  72  which is used to mechanically direct a drill string into a desired orientation. It will be understood that other suitable casings may be employed and the use of a whip stock  72  is not necessary when other suitable methods of orienting a drill bit through slant well  64  into the subterranean zone  22  are used.  
         [0045]    Casing  70  is inserted into the entry well bore  15  through guide tube bundle  43  and into slant entry well bore  64 . Whip stock casing  70  is oriented such that whip stock  72  is positioned so that a subsequent drill bit is aligned to drill into the subterranean zone  22  at the desired depth.  
         [0046]    [0046]FIG. 9 illustrates whip stock casing  70  and slant entry well bore  64 . As discussed in conjunction with FIG. 8, whip stock casing  70  is positioned within slant entry well bore  64  such that a drill string  50  will be oriented to pass through slant entry well bore  64  at a desired tangent or kick off point  38 . This corresponds with step  145  of FIG. 3. Drill string  50  is used to drill through slant entry well bore  64  at tangent or kick off point  38  to form articulated well bore  36 . In a particular embodiment, articulated well bore  36  has a radius of approximately seventy-one feet and a curvature of approximately eighty degrees per one hundred feet. In the same embodiment, slant entry well  64  is angled away from the vertical at approximately ten degrees. In this embodiment, the hydrostatic head generated in conjunction with production is roughly thirty feet. However, it should be understood that any other appropriate radius, curvature, and slant angle may be used.  
         [0047]    [0047]FIG. 10 illustrates a slant entry well  64  and articulated well bore  36  after drill string  50  has been used to form articulated well bore  36 . In a particular embodiment, a horizontal well and drainage pattern may then be formed in subterranean zone  22 , as represented by step  150  and step  155  of FIG. 3.  
         [0048]    Referring to FIG. 10, whip stock casing  70  is set on the bottom of rat hole  66  to prepare for production of oil and gas. A sealer ring  74  may be used around the whip stock casing  70  to prevent gas produced from articulated well bore  36  from escaping outside whip stock casing  70 . Gas ports  76  allow escaping gas to enter into and up through whip stock casing  70  for collection at the surface.  
         [0049]    A pump string  78  and submersible pump  80  is used to remove water and other liquids that are collected from the subterranean zone through articulated well bore  36 . As shown in FIG. 10, the liquids, under the power of gravity and the pressure in subterranean zone  22 , pass through articulated well bore  36  and down slant entry well bore  64  into rat hole  66 . From there the liquids travel into the opening in the whip stock  72  of whip stock casing  70  where they come in contact with the installed pump string  78  and submersible pump  80 . Submersible pump  80  may be a variety of submersible pumps suitable for use in a down-hole environment to remove liquids and pump them to the surface through pump string  78 . Installation of pump string  78  and submersible pump  80  corresponds with step  160  of FIG. 3. Production of liquid and gas corresponds with step  165  of FIG. 3.  
         [0050]    [0050]FIG. 11 illustrates an example drainage pattern  90  that may be drilled from articulated well bores  36 . At the center of drainage pattern  90  is entry well bore  15 . Connecting to entry well bore  15  are slant wells  20 . At the terminus of slant well  20 , as described above, are substantially horizontal well bores  92  roughly forming a “crow&#39;s foot” pattern off of each of the slant wells  20 . As used throughout this application, “each” means all of a particular subset. In a particular embodiment, the horizontal reach of each substantially horizontal well bore  92  is approximately fifteen hundred feet. Additionally, the lateral spacing between the parallel substantially horizontal well bores  92  is approximately eight hundred feet. In this particular embodiment, a drainage area of approximately two hundred and ninety acres would result. In an alternative embodiment where the horizontal reach of the substantially horizontal well bore  92  is approximately two thousand four hundred and forty feet, the drainage area would expand to approximately six hundred and forty acres. However, any other suitable configurations may be used. Furthermore, any other suitable drainage patterns may be used.  
         [0051]    [0051]FIG. 13 illustrates a plurality of drainage patterns  90  in relationship to one another to maximize the drainage area of a subsurface formation covered by the drainage patterns  90 . Each drainage pattern  90  forms a roughly hexagonal drainage pattern. Accordingly, drainage patterns  90  may be aligned, as illustrated, so that the drainage patterns  90  form a roughly honeycomb-type alignment.  
         [0052]    Although the present invention has been described with several embodiments, various changes and modifications may be suggested to one skilled in the art. It is intended that the present invention encompass such changes and modifications as fall within the scope of the appended claims.