Patent Publication Number: US-6986388-B2

Title: Method and system for accessing a subterranean zone from a limited surface area

Description:
RELATED APPLICATION 
   This application is a continuation of U.S. application Ser. No. 09/774,996 filed Jan. 30, 2001 and entitled “Method and System for Accessing a Subterranean Zone from a Limited Surface Area” by Joseph A. Zupanick et al, now U.S. Pat. No. 6,662,870. 

   TECHNICAL FIELD OF THE INVENTION 
   The present invention relates generally to the field of subterranean exploration and drilling and, more particularly, to a method and system for accessing a subterranean zone from a limited surface area. 
   BACKGROUND OF THE INVENTION 
   Subterranean deposits of coal, whether of “hard” coal such as anthracite or “soft” coal such as lignite or bituminous 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 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, 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. 
   Prior systems and methods generally require a fairly level surface area from which to work. As a result, prior systems and methods generally cannot be used in Appalachia or other hilly terrains. For example, in some areas the largest area of flat land may be a wide roadway. Thus, less effective methods must be used, leading to production delays that add to the expense associated with degasifying a coal seam. Additionally, prior systems and methods generally require fairly large working surface area. Thus, many subterranean resources are inaccessible because of current mining techniques and the geographic limitations surrounding the resource. Additionally, potential disruption or devastation to the environment surrounding the subterranean resources often prevents the mining of many subterranean resources. 
   SUMMARY OF THE INVENTION 
   The present invention provides a method and system for accessing subterranean deposits from a limited surface area that substantially eliminates or reduces the disadvantages and problems associated with previous systems and methods. 
   In accordance with one embodiment of the present invention, a system for accessing a subsurface formation from a limited surface area includes a first well bore extending from the surface to a target zone. The first well bore includes an angled portion disposed between the target zone and the surface. The system also includes a second well bore extending from the surface to the target zone. The second well bore is offset from the first well bore at the surface and intersects the first well bore at a junction proximate the target zone. The system further includes a well bore pattern extending from the junction into the target zone. 
   In accordance with another embodiment of the present invention, a method for accessing a subsurface formation from a limited surface area includes forming a first well bore extending from the surface to a target zone. The first well bore includes an angled portion disposed between the target zone and the surface. The method also includes forming a second well bore extending from the surface to the target zone. 
   The second well bore is offset from the first well bore at the surface and intersects the first well bore at a junction proximate the target zone. The method further includes forming a well bore pattern extending from the junction into the target zone. 
   Technical advantages of the present invention include providing an improved method and system for accessing subterranean deposits from a limited area on the surface. In particular, a well bore pattern is drilled in a target zone from an articulated surface well at least in close proximity to another or second surface well. The second surface well includes an angled portion to accommodate location of the second surface well in close proximity to the articulated well while providing an adequate distance at the target zone between the second surface well and the articulated well to accommodate the radius of the articulated well. The well bore pattern is interconnected to the second surface well through which entrained water, hydrocarbons, and other fluids drained from the target zone can be efficiently removed and/or produced. The well bore pattern may also be used to inject or introduce a fluid or substance into the subterranean formation. As a result, gas, oil, and other fluids from a large, low pressure or low porosity formation can be efficiently produced at a limited area on the surface. Thus, gas may be recovered from formations underlying rough topology. In addition, environmental impact is minimized as the area to be cleared and used is minimized. 
   Yet another technical advantage of the present invention includes providing an improved method and system for preparing a coal seam or other subterranean deposit for mining and for collecting gas from the seam after mining operations. In particular, a surface well, with a vertical portion, an articulated portion, and a cavity, is used to degasify a coal seam prior to mining operations. This reduces both needed surface area and underground equipment and activities. This also reduces the time needed to degasify the seam, which minimizes shutdowns due to high gas content. In addition, water and additives may be pumped into the de-gasified coal seam through the combined well prior to mining operations to minimize dust and other hazardous conditions, to improve efficiency of the mining process, and to improve the quality of the coal product. After mining, the combined well is used to collect gob gas. As a result, costs associated with the collection of gob gas are minimized to facilitate or make feasible the collection of gob gas from previously mined seams. 
   Other technical advantages of the present invention will be readily apparent to one skilled in the art from the following figures, description, and claims. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     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: 
       FIG. 1  is a cross-sectional diagram illustrating a system for accessing a subterranean zone from a limited surface area in accordance with an embodiment of the present invention; 
       FIG. 2  is a cross-sectional diagram illustrating a system for accessing a subterranean zone from a limited surface area in accordance with another embodiment of the present invention; 
       FIG. 3  is a cross-sectional diagram illustrating a system for accessing a subterranean zone from a limited surface area in accordance with another embodiment of the present invention; 
       FIG. 4  is a diagram illustrating a top plan view of a pinnate well bore pattern for accessing a subterranean zone in accordance with an embodiment of the present invention; 
       FIG. 5  is a diagram illustrating a top plan view of a pinnate well bore pattern for accessing a subterranean zone in accordance with another embodiment of the present invention; 
       FIG. 6  is a diagram illustrating a top plan view of a pinnate well bore pattern for accessing a subterranean zone in accordance with another embodiment of the present invention; 
       FIG. 7  is a diagram illustrating a top plan view of multiple well bore patterns in a subterranean zone through an articulated surface well intersecting multiple surface cavity wells in accordance with an embodiment of the present invention; 
       FIG. 8  is a diagram illustrating a top plan view of multiple well bore patterns in a subterranean zone through an articulated surface well intersecting multiple cavity wells in accordance with another embodiment of the present invention; 
       FIG. 9  is a flow diagram illustrating a method for accessing a subterranean zone from a limited surface area in accordance with an embodiment of the present invention; 
       FIG. 10  is a flow diagram illustrating a method for accessing a subterranean zone from a limited surface area in accordance with another embodiment of the present invention; 
       FIG. 11  is a flow diagram illustrating a method for accessing a subterranean zone from a limited surface area in accordance with another embodiment of the present invention; 
       FIG. 12  is a flow diagram illustrating a method for accessing a subterranean zone from a limited surface area in accordance with another embodiment of the present invention; and 
       FIG. 13  is a diagram illustrating a system for accessing a subterranean zone in accordance with an embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1  is a diagram illustrating a system  10  for accessing a subterranean zone from a limited surface area in accordance with an embodiment of the present invention. In this embodiment, the subterranean zone is a coal seam. However, it should be understood that other subterranean formations and/or other low pressure, ultra-low pressure, and low porosity subterranean zones can be similarly accessed using the system  10  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, introduce, or store a gas, fluid or other substance into the zone. 
   Referring to  FIG. 1 , a well bore  12  extends from the surface  14  to a target coal seam  16 . The well bore  12  intersects, penetrates and continues below the coal seam  16 . In the embodiment illustrated in  FIG. 1 , the well bore  12  includes a portion  18 , an angled portion  20 , and a portion  22  disposed between the surface  14  and the coal seam  16 . IN  FIG. 1 , portions  18  and  22  are illustrated substantially vertical; however, it should be understood that portions  18  and  22  may be formed at other suitable angles and orientations to accommodate surface  14  and/or coal seam  16  variations. 
   In this embodiment, the portion  18  extends downwardly in a substantially vertical direction from the surface  14  a predetermined distance to accommodate formation of radiused portions  24  and  26 , angled portion  20 , and portion  22  to intersect the coal seam  16  at a desired location. Angled portion  20  extends from an end of the portion  18  and extends downwardly at a predetermined angle relative to the portion  18  to accommodate intersection of the coal seam  16  at the desired location. Angled portion  20  may be formed having a generally uniform or straight directional configuration or may include various undulations or radiused portions as required to intersect portion  22  and/or to accommodate various subterranean obstacles, drilling requirements or characteristics. Portion  22  extends downwardly in a substantially vertical direction from an end of the angled portion  20  to intersect, penetrate and continue below the coal seam  16 . 
   In one embodiment, to intersect a coal seam  16  located at a depth of approximately 1200 feet below the surface  14 , the portion  18  may be drilled to a depth of approximately 300 feet. Radiused portions  24  and  26  may be formed having a radius of approximately 400 feet, and angled portion  20  may be tangentially formed between radiused portions  24  and  26  at an angle relative to the portion  18  to accommodate approximately a 250 foot offset between portions  18  and  22  at a depth of approximately 200 feet above the target coal seam  16 . The portion  22  may be formed extending downwardly the remaining 200 feet to the coal seam  16 . However, other suitable drilling depths, drilling radii, angular orientations, and offset distances may be used to form well bore  12 . The well bore  12  may also be lined with a suitable well casing  28  that terminates at or above the upper level of the coal seam  16 . 
   The well bore  12  is logged either during or after drilling in order to locate the exact vertical depth of the coal seam  16 . As a result, the coal seam  16  is not missed in subsequent drilling operations, and techniques used to locate the coal seam  16  while drilling need not be employed. An enlarged cavity  30  is formed in the well bore  12  at the level of the coal seam  16 . As described in more detail below, the enlarged cavity  30  provides a junction for intersection of the well bore  12  by an articulated well bore used to form a subterranean well bore pattern in the coal seam  16 . The enlarged cavity  30  also provides a collection point for fluids drained from the coal seam  16  during production operations. In one embodiment, the enlarged cavity  30  has a radius of approximately eight feet and a vertical dimension which equals or exceeds the vertical dimension of the coal seam  16 . The enlarged cavity  30  is formed using suitable under-reaming techniques and equipment. Portion  22  of the well bore  12  continues below the enlarged cavity  30  to form a sump  32  for the cavity  30 . 
   An articulated well bore  40  extends from the surface  14  to the enlarged cavity  30 . In this embodiment, the articulated well bore  40  includes a portion  42 , a portion  44 , and a curved or radiused portion  46  interconnecting the portions  42  and  44 . The portion  44  lies substantially in the plane of the coal seam  16  and intersects the enlarged cavity  30 . In  FIG. 1 , portion  42  is illustrated substantially vertical, and portion  44  is illustrated substantially horizontal; however, it should be understood that portions  42  and  44  may be formed having other suitable orientations to accommodate surface  14  and/or coal seam  16  characteristics. 
   In the illustrated embodiment, the articulated well bore  40  is offset a sufficient distance from the well bore  12  at the surface  14  to permit the large radius curved portion  46  and any desired distance of portion  44  to be drilled before intersecting the enlarged cavity  30 . In one embodiment, to provide the curved portion  46  with a radius of 100-150 feet, the articulated well bore  40  is offset a distance of approximately 300 feet from the well bore  12  at the surface  14 . This spacing minimizes the angle of the curved portion  46  to reduce friction in the articulated well bore  40  during drilling operations. As a result, reach of the articulated drill string drilled through the articulated well bore  40  is maximized. However, other suitable offset distances and radii may be used for forming the articulated well bore  40 . The portion  42  of the articulated well bore  40  is lined with a suitable casing  48 . 
   The articulated well bore  40  is drilled using an articulated drill string  50  that includes a suitable down-hole motor and bit  52 . A measurement while drilling (MWD) device  54  is included in the articulated drill string  50  for controlling the orientation and direction of the well bore drilled by the motor and bit  52 . 
   After the enlarged cavity  30  has been successfully intersected by the articulated well bore  40 , drilling is continued through the cavity  30  using the articulated drill string  50  and appropriate drilling apparatus to provide a subterranean well bore pattern  60  in the coal seam  16 . The well bore pattern  60  and other such well bores include sloped, undulating, or other inclinations of the coal seam  16  or other subterranean zone. During this operation, gamma ray logging tools and conventional measurement while drilling devices may be employed to control and direct the orientation of the drill bit  52  to retain the well bore pattern  60  within the confines of the coal seam  16  and to provide substantially uniform coverage of a desired area within the coal seam  16 . 
   During the process of drilling the well bore pattern  60 , drilling fluid or “mud” is pumped down the articulated drill string  50  and circulated out of the drill string  50  in the vicinity of the bit  52 , where it is used to scour the formation and to remove formation cuttings. The cuttings are then entrained in the drilling fluid which circulates up through the annulus between the drill string  50  and the walls of the articulated well bore  40  until it reaches the surface  14 , where the cuttings are removed from the drilling fluid and the fluid is then recirculated. This conventional drilling operation produces a standard column of drilling fluid having a vertical height equal to the depth of the articulated well bore  40  and produces a hydrostatic pressure on the well bore corresponding to the well bore depth. Because coal seams tend to be porous and fractured, they may be unable to sustain such hydrostatic pressure, even if formation water is also present in the coal seam  16 . Accordingly, if the full hydrostatic pressure is allowed to act on the coal seam  16 , the result may be loss of drilling fluid and entrained cuttings into the formation. Such a circumstance is referred to as an “over-balanced” drilling operation in which the hydrostatic fluid pressure in the well bore exceeds the ability of the formation to withstand the pressure. Loss of drilling fluids and cuttings into the formation not only is expensive in terms of the lost drilling fluids, which must be made up, but it also tends to plug the pores in the coal seam  16 , which are needed to drain the coal seam of gas and water. 
   To prevent over-balance drilling conditions during formation of the well bore pattern  60 , air compressors  62  are provided to circulate compressed air down the well bore  12  and back up through the articulated well bore  40 . The circulated air will admix with the drilling fluids in the annulus around the articulated drill string  50  and create bubbles throughout the column of drilling fluid. This has the effect of lightening the hydrostatic pressure of the drilling fluid and reducing the down-hole pressure sufficiently that drilling conditions do not become over-balanced. Aeration of the drilling fluid reduces down-hole pressure to approximately 150-200 pounds per square inch (psi). Accordingly, low pressure coal seams and other subterranean zones can be drilled without substantial loss of drilling fluid and contamination of the zone by the drilling fluid. 
   Foam, which may be compressed air mixed with water, may also be circulated down through the articulated drill string  50  along with the drilling mud in order to aerate the drilling fluid in the annulus as the articulated well bore  40  is being drilled and, if desired, as the well bore pattern  60  is being drilled. Drilling of the well bore pattern  60  with the use of an air hammer bit or an air-powered down-hole motor will also supply compressed air or foam to the drilling fluid. In this case, the compressed air or foam which is used to power the down-hole motor and bit  52  exits the articulated drill string  50  in the vicinity of the drill bit  52 . However, the larger volume of air which can be circulated down the well bore  12  permits greater aeration of the drilling fluid than generally is possible by air supplied through the articulated drill string  50 . 
     FIG. 2  is a diagram illustrating system  10  for accessing a subterranean zone from a limited surface area in accordance with another embodiment of the present invention. In this embodiment, the articulated well bore  40  is formed as previously described in connection with FIG.  1 . The well bore  12 , in this embodiment, includes a portion  70  and an angled portion  72  disposed between the surface  14  and the coal seam  16 . The portion  70  extends downwardly from the surface  14  a predetermined distance to accommodate formation of a radiused portion  74  and angled portion  72  to intersect the coal seam  16  at a desired location. In this embodiment, portion  70  is illustrated substantially vertical; however, it should be understood that portion  70  may be formed at other suitable orientations to accommodate surface  14  and/or coal seam  16  characteristics. Angled portion  72  extends from an end of the portion  70  and extends downwardly at a predetermined angle relative to portion  70  to accommodate intersection of the coal seam  16  at the desired location. Angled portion  72  may be formed having a generally uniform or straight directional configuration or may include various undulations or radiused portions as required to intersect the coal seam  16  at a desired location and/or to accommodate various subterranean obstacles, drilling requirements or characteristics. 
   In one embodiment, to intersect a coal seam  16  located at a depth of approximately 1200 feet below the surface  14 , the portion  70  may be drilled to a depth of approximately 300 feet. Radiused portion  74  may be formed having a radius of approximately 400 feet, and angled portion  72  may be tangentially formed in communication with the radiused portion  74  at an angle relative to the portion  70  to accommodate approximately a 300 foot offset between the portion  70  and the intersection of the angled portion  72  at the target coal seam  16 . However, other suitable drilling depths, drilling radii, angular orientations, and offset distances may be used to form well bore  12 . The well bore  12  may also be lined with a suitable well casing  76  that terminates at or above the upper level of the coal seam  16 . 
   The well bore  12  is logged either during or after drilling in order to locate the exact depth of the coal seam  16 . As a result, the coal seam  16  is not missed in subsequent drilling operations, and techniques used to locate the coal seam  16  while drilling need not be employed. The enlarged cavity  30  is formed in the well bore  12  at the level of the coal seam  16  as previously described in connection with FIG.  1 . However, as illustrated in  FIG. 2 , because of the angled portion  72  of the well bore  12 , the enlarged cavity  30  may be disposed at an angle relative to the coal seam  16 . As described above, the enlarged cavity  30  provides a junction for intersection of the well bore  12  and the articulated well bore  40  to provide a collection point for fluids drained from the coal seam  16  during production operations. Thus, depending on the angular orientation of the angled portion  72 , the radius and/or vertical dimension of the enlarged cavity  30  may be modified such that portions of the enlarged cavity  30  equal or exceed the vertical dimension of the coal seam  16 . Angled portion  72  of the well bore  12  continues below the enlarged cavity  30  to form a sump  32  for the cavity  30 . 
   After intersection of the enlarged cavity  30  by the articulated well bore  40 , a pumping unit  78  is installed in the enlarged cavity  30  to pump drilling fluid and cuttings to the surface  14  through the well bore  12 . This eliminates the friction of air and fluid returning up the articulated well bore  40  and reduces down-hole pressure to nearly zero. Pumping unit  78  may include a sucker rod pump, a submersible pump, a progressing cavity pump, or other suitable pumping device for removing drilling fluid and cuttings to the surface  14 . Accordingly, coal seams and other subterranean zones having ultra low pressures, such as below 150 psi, can be accessed from the surface. Additionally, the risk of combining air and methane in the well is substantially eliminated. 
     FIG. 3  is a diagram illustrating system  10  for accessing a subterranean zone from a limited surface area in accordance with another embodiment of the present invention. In this embodiment, the articulated well bore  40  is formed as previously described in connection with FIG.  1 . The well bore  12 , in this embodiment, includes an angled portion  80  disposed between the surface  14  and the coal seam  16 . For example, in this embodiment, the angled portion  80  extends downwardly from the surface  14  at a predetermined angular orientation to intersect the coal seam  16  at a desired location. Angled portion  80  may be formed having a generally uniform or straight directional configuration or may include various undulations or radiused portions as required to intersect the coal seam  16  at a desired location and/or to accommodate various subterranean obstacles, drilling requirements or characteristics. 
   In one embodiment, to intersect a coal seam  16  located at a depth of approximately 1200 feet below the surface  14 , the angled portion  80  may be drilled at an angle of approximately 20 degrees from vertical to accommodate approximately a 440 foot offset between the surface  14  location of the angled portion  80  and the intersection of the angled portion  80  at the target coal seam  16 . However, other suitable angular orientations and offset distances may be used to form angled portion  80  of well bore  12 . The well bore  12  may also be lined with a suitable well casing  82  that terminates at or above the upper level of the coal seam  16 . 
   The well bore  12  is logged either during or after drilling in order to locate the exact depth of the coal seam  16 . As a result, the coal seam  16  is not missed in subsequent drilling operations, and techniques used to locate the coal seam  16  while drilling need not be employed. The enlarged cavity  30  is formed in the well bore  12  at the level of the coal seam  16  as previously described in connection with FIG.  1 . However, as illustrated in  FIG. 2 , because of the angled portion  80  of the well bore  12 , the enlarged cavity  30  may be disposed at an angle relative to the coal seam  16 . As described above, the enlarged cavity  30  provides a junction for intersection of the well bore  12  and the articulated well bore  40  to provide a collection point for fluids drained from the coal seam  16  during production operations. Thus, depending on the angular orientation of the angled portion  80 , the radius and/or vertical dimension of the enlarged cavity  30  may be modified such that portions of the enlarged cavity  30  equal or exceed the vertical dimension of the coal seam  16 . Angled portion  80  of the well bore  12  continues below the enlarged cavity  30  to form a sump  32  for the cavity  30 . 
   After the well bore  12 , articulated well bore  40 , enlarged cavity  30  and the desired well bore pattern  60  have been formed, the articulated drill string  50  is removed from the articulated well bore  40  and the articulated well bore  40  is capped. A down hole production or pumping unit  84  is disposed in the well bore  12  in the enlarged cavity  30 . The enlarged cavity  30  provides a reservoir for accumulated fluids allowing intermittent pumping without adverse effects of a hydrostatic head caused by accumulated fluids in the well bore. Pumping unit  84  may include a sucker rod pump, a submersible pump, a progressing cavity pump, or other suitable pumping device for removing accumulated fluids to the surface. 
   The down hole pumping unit  84  is connected to the surface  14  via a tubing string  86 . The down hole pumping unit  84  is used to remove water and entrained coal fines from the coal seam  16  via the well bore pattern  60 . Once the water is removed to the surface  14 , it may be treated for separation of methane which may be dissolved in the water and for removal of entrained fines. After sufficient water has been removed from the coal seam  16 , pure coal seam gas may be allowed to flow to the surface  14  through the annulus of the well bore  12  around the tubing string  86  and removed via piping attached to a wellhead apparatus. At the surface  14 , the methane is treated, compressed and pumped through a pipeline for use as a fuel in a conventional manner. The down hole pumping unit  84  may be operated continuously or as needed to remove water drained from the coal seam  16  into the enlarged diameter cavity  30 . 
     FIGS. 4-6  are diagrams illustrating top plan views of subterranean well bore patterns  60  for accessing the coal seam  16  or other subterranean zone in accordance with embodiments of the present invention. In these embodiments, the well bore patterns  60  comprise pinnate well bore patterns that have a central or main well bore with generally symmetrically arranged and appropriately spaced lateral well bores extending from each side of the main well bore. The pinnate well bore pattern approximates the pattern of veins in a leaf or the design of a feather in that it has similar, substantially parallel, auxiliary well bores arranged in substantially equal and parallel spacing on opposite sides of an axis. The pinnate well bore pattern with its central bore and generally symmetrically arranged and appropriately spaced auxiliary well bores on each side provides a uniform pattern for accessing a subterranean formation. As described in more detail below, the pinnate well bore pattern provides substantially uniform coverage of a square, other quadrilateral, or grid area and may be aligned with longwall mining panels for preparing the coal seam  16  for mining operations. A plurality of well bore patterns may also be nested adjacent each other to provide uniform coverage of a subterranean region. It will be understood that other suitable well bore patterns may be used in accordance with the present invention. 
   The pinnate and other suitable well bore patterns  60  drilled from the surface  14  provide surface access to subterranean formations. The well bore pattern  60  may be used to uniformly remove and/or insert fluids or otherwise manipulate a subterranean deposit. In non-coal applications, the well bore pattern  60  may be used initiating in-situ burns, “huff-puff” steam operations for heavy crude oil, and the removal of hydrocarbons from low porosity reservoirs. 
     FIG. 4  is a diagram illustrating a pinnate well bore pattern  100  in accordance with one embodiment of the present invention. In this embodiment, the pinnate well bore pattern  100  provides access to a substantially square area  102  of a subterranean zone. A number of the pinnate patterns  100  may be used together to provide uniform access to a large subterranean region. 
   Referring to  FIG. 4 , the enlarged cavity  30  defines a first corner of the area  102 . The pinnate well bore pattern  100  includes a main well bore  104  extending diagonally across the area  102  to a distant corner  106  of the area  102 . Preferably, the well bore  12  and articulated well bore  40  are positioned over the area  102  such that the well bore  104  is drilled up the slope of the coal seam  16 . This will facilitate collection of water, gas, and other fluids from the area  102 . The well bore  104  is drilled using the articulated drill string  50  and extends from the enlarged cavity  30  in alignment with the articulated well bore  40 . 
   A set of lateral well bores  110  extend from opposites sides of well bore  104  to a periphery  112  of the area  102 . The lateral well bores  110  may mirror each other on opposite sides of the well bore  104  or may be offset from each other along the well bore  104 . Each of the lateral well bores  110  includes a radius curving portion  114  extending from the well bore  104  and an elongated portion  116  formed after the curved portion  114  has reached a desired orientation. For uniform coverage of the square area  102 , pairs of lateral well bores  110  are substantially evenly spaced on each side of the well bore  104  and extend from the well bore  104  at an angle of approximately 45 degrees. However, the lateral well bores  110  may be form at other suitable angular orientations relative to well bore  104 . The lateral well bores  110  shorten in length based on progression away from the enlarged diameter cavity  30  in order to facilitate drilling of the lateral well bores  110 . Additionally, as illustrated in  FIG. 4 , a distance to the periphery  112  of the area  102  to cavity  30  or well bores  30  or  40  measured along the lateral well bores  110  is substantially equal for each lateral well bore  110 , thereby facilitating the formation of the lateral well bores  110 . 
   The pinnate well bore pattern  100  using a single well bore  104  and five pairs of lateral bores  110  may drain a coal seam area of approximately 150 acres in size. Where a smaller area is to be drained, or where the coal seam has a different shape, such as a long, narrow shape, or due to surface or subterranean topography, alternate pinnate well bore patterns may be employed by varying the angle of the lateral well bores  110  to the well bore  104  and the orientation of the lateral well bores  110 . Alternatively, lateral well bores  110  can be drilled from only one side of the well bore  104  to form a one-half pinnate well bore pattern. 
   The well bore  104  and the lateral well bores  110  are formed by drilling through the enlarged cavity  30  using the articulated drill string  50  and an appropriate drilling apparatus. During this operation, gamma ray logging tools and conventional measurement while drilling (MWD) technologies may be employed to control the direction and orientation of the drill bit so as to retain the well bore pattern  100  within the confines of the coal seam  16  and to maintain proper spacing and orientation of the well bore  104  and lateral well bores  110 . 
   In a particular embodiment, the well bore  104  is drilled with an incline at each of a plurality of lateral kick-off points  108 . After the well bore  104  is complete, the articulated drill string  50  is backed up to each successive lateral point  108  from which a lateral well bore  110  is drilled on each side of the well bore  104 . It will be understood that the pinnate well bore pattern  100  may be otherwise suitably formed in accordance with the present invention. 
   In the embodiment illustrated in  FIG. 4 , well bore pattern  100  also includes a set of lateral well bores  120  extending from lateral well bores  110 . The lateral well bores  120  may mirror each other on opposite sides of the lateral well bore  110  or may be offset from each other along the lateral well bore  110 . Each of the lateral well bores  120  includes a radius curving portion  122  extending from the lateral well bore  110  and an elongated portion  124  formed after the curved portion  122  has reached a desired orientation. For uniform coverage of the area  102 , pairs of lateral well bores  120  may be disposed substantially equally spaced on each side of the lateral well bore  110 . Additionally, lateral well bores  120  extending from one lateral well bore  110  may be disposed to extend between lateral well bores  120  extending from an adjacent lateral well bore  110  to provide uniform coverage of the area  102 . However, the quantity, spacing, and angular orientation of lateral well bores  120  may be varied to accommodate a variety of resource areas, sizes and drainage requirements. 
     FIG. 5  illustrates a pinnate well bore pattern  130  in accordance with another embodiment of the present invention. In this embodiment, the pinnate well bore pattern  130  provides access to a substantially rectangular area  132 . The pinnate well bore pattern  130  includes a well bore  124  extending substantially diagonally from each corner of the area  132  and a plurality of lateral well bores  136  that are formed as described in connection with well bore  104  and lateral bores  110  of FIG.  4 . For the substantially rectangular area  132 , however, the lateral well bores  136  on a first side of the well bore  134  include a shallow angle while the lateral well bores  136  on the opposite side of the well bore  134  include a steeper angle to together provide uniform coverage of the area  132 . 
     FIG. 6  illustrates a pinnate well bore pattern  140  in accordance with another embodiment of the present invention. In this embodiment, the enlarged cavity  30  defines a first corner of an area  142  of the zone. The pinnate well bore pattern  140  includes a well bore  144  extending diagonally across the area  142  to a distant corner  146  of the area  142 . Preferably, the well bore  12  and the articulated well bore  40  are positioned over the area  142  such that the well bore  144  is drilled up the slope of the coal seam  16 . This will facilitate collection of water, gas, and other fluids from the area  142 . The well bore  144  is drilled using the articulated drill string  50  and extends from the enlarged cavity  30  in alignment with the articulated well bore  40 . 
   A plurality of lateral well bores  148  extend from the opposites sides of well bore  144  to a periphery  150  of the area  142  as described above in connection with well bores  104  and  110  of FIG.  4 . The lateral well bores  148  may mirror each other on opposite sides of the well bore  144  or may be offset from each other along the well bore  144 . Each of the lateral well bores  148  includes a radius curving portion  150  extending from the well bore  144  and an elongated portion  152  extending from the radius curving portion  150 . The elongated portion  152  is formed after the curving portion  150  has reached a desired orientation. The first set of lateral well bores  148  located proximate to the cavity  30  may also include a radius curving portion  154  formed after the curving portion  150  has reached a desired orientation. In this set, the elongated portion  152  is formed after the curving portion  154  has reached a desired orientation. Thus, the first set of lateral well bores  148  kicks or turns back towards the enlarged cavity  30  before extending outward through the formation, thereby extending the drainage area back towards the cavity  30  to provide uniform coverage of the area  142 . For uniform coverage of the area  142 , pairs of lateral well bores  148  are substantially evenly spaced on each side of the well bore  144  and extend from the well bore  144  at an angle of approximately 45 degrees. However, lateral well bores  148  may be formed at other angular orientations relative to the well bore  144 . The lateral well bores  148  shorten in length based on progression away from the enlarged cavity  30  in order to facilitate drilling of the lateral well bores  148 . Additionally, as illustrated in  FIG. 6 , a distance to the periphery  150  of the area  142  from the cavity  30  measured along each lateral well bore  148  is substantially equal for each lateral well bore  148 , thereby facilitating the formation of lateral well bores  148 . 
   The well bore  144  and the lateral well bores  148  are formed by drilling through the enlarged cavity  30  using the articulated drill string  50  and an appropriate drilling apparatus. During this operation, gamma ray logging tools and conventional measurement while drilling (MWD) technologies may be employed to control the direction and orientation of the drill bit so as to retain the well bore pattern  140  within the confines of the coal seam  16  and to maintain proper spacing and orientation of the well bore  144  and lateral well bores  148 . In a particular embodiment, the well bore  144  is drilled with an incline at each of a plurality of lateral kick-off points  156 . After the well bore  144  is complete, the articulated drill string  50  is backed up to each successive lateral point  156  from which a lateral well bore  148  is drilled on each side of the well bore  144 . It should be understood that the pinnate well bore pattern  140  may be otherwise suitably formed in accordance with the present invention. 
     FIG. 7  is a diagram illustrating multiple well bore patterns in a subterranean zone through an articulated well bore  40  intersecting multiple well bores  12  in accordance with an embodiment of the present invention. In this embodiment, four well bores  12  are used to access a subterranean zone through well bore patterns  60 . However, it should be understood that a varying number of well bores  12  and well bore patterns  60  may be used depending on the geometry of the underlying subterranean formation, desired access area, production requirements, and other factors. 
   Referring to  FIG. 7 , four well bores  12  are formed disposed in a spaced apart and substantially linear formation relative to each other at the surface  14 . Additionally, the articulated well bore  40 , in this embodiment, is disposed linearly with the well bores  12  having a pair of well bores  12  disposed on each side of the surface location of the articulated well bore  40 . Thus, the well bores  12  and the articulated well bore  40  may be located over a subterranean resource in close proximity to each other and in a suitable formation to minimize the surface area required for accessing the subterranean formation. For example, according to one embodiment, each of the well bores  12  and the articulated well bore  40  may be spaced apart from each other at the surface  14  in a linear formation by approximately twenty-five feet, thereby substantially reducing the surface area required to access the subterranean resource. As a result, the well bores  12  and articulated well bore  40  may be formed on or adjacent to a roadway, steep hillside, or other limited surface area. Accordingly, environmental impact is minimized as less surface area must be cleared. Well bores  12  and  40  may also be disposed in a substantially nonlinear formation in close proximity to each other as described above to minimize the surface area required for accessing the subterranean formation. 
   As described above, well bores  12  are formed extending downwardly from the surface and may be configured as illustrated in  FIGS. 1-3  to accommodate a desired offset distance between the surface location of each well bore  12  and the intersection of the well bore  12  with the coal seam  16  or other subterranean formation. Enlarged cavities  30  are formed proximate the coal seam  16  in each of the well bores  12 , and the articulated well bore  40  is formed intersecting each of the enlarged cavities  30 . In the embodiment illustrated in  FIG. 7 , the bottom hole location or intersection of each of the well bores  12  with the coal seam  16  is located either linearly or at a substantially ninety degree angle to the linear formation of the well bores  12  at the surface. However, the location and angular orientation of the intersection of the well bores  12  with the coal seam  16  relative to the linear formation of the well bores  12  at the surface  14  may be varied to accommodate a desired access formation or subterranean resource configuration. 
   Well bore patterns  60  are drilled within the target subterranean zone from the articulated well bore  40  extending from each of the enlarged cavities  30 . In resource removal applications, resources from the target subterranean zone drain into each of the well bore patterns  60 , where the resources are collected in the enlarged cavities  30 . Once the resources have been collected in the enlarged cavities  30 , the resources may be removed to the surface through the well bores  12  by the methods described above. 
     FIG. 8  is a diagram illustrating multiple horizontal well bore patterns in a subterranean zone through an articulated well bore  40  intersecting multiple well bores  12  in accordance with another embodiment of the present invention. In this embodiment, four well bores  12  are used to collect and remove to the surface  14  resources collected from well bore patterns  60 . However, it should be understood that a varying number of well bores  12  and well bore patterns  60  may be used depending on the geometry of the underlying subterranean formation, desired access area, production requirements, and other factors. 
   Referring to  FIG. 8 , four well bores  12  are formed disposed in a spaced apart and substantially linear formation relative to each other at the surface  14 . In this embodiment, the articulated well bore  40  is offset from and disposed adjacent to the linear formation of the well bores  12 . As illustrated in  FIG. 8 , the articulated well bore  40  is located such that a pair of well bores  12  are disposed on each side of the articulated well bore  40  in a direction substantially orthogonal to the linear formation of well bores  12 . Thus, the well bores  12  and the articulated well bore  40  may be located over a subterranean resource in close proximity to each other and in a suitable formation to minimize the surface area required for gas production and coal seam  16  treatment. For example, according to one embodiment, each of the well bores  12  may be spaced apart from each other at the surface  14  in a linear formation by approximately twenty-five feet, and the articulated well bore  40  may be spaced apart from each of the two medially-located well bores  12  by approximately twenty-five feet, thereby substantially reducing the surface area required to access the subterranean resource and for production and drilling. As a result, the well bores  12  and articulated well bore  40  may be formed on or adjacent to a roadway, steep hillside, or other limited surface area. Accordingly, environmental impact is minimized as less surface area must be cleared. 
   As described above, well bores  12  are formed extending downwardly from the surface and may be configured as illustrated in  FIGS. 1-3  to accommodate a desired offset distance between the surface location of each well bore  12  and the intersection of the well bore  12  with the coal seam  16 . Enlarged cavities  30  are formed proximate the coal seam  16  in each of the well bores  12 , and the articulated well bore  40  is formed intersecting each of the enlarged cavities  30 . In the embodiment illustrated in  FIG. 8 , the bottom hole location or intersection of each of the well bores  12  with the coal seam  16  is located either linearly or at a substantially ninety degree angle to the linear formation of the well bores  12  at the surface. However, the location and angular orientation of the intersection of the well bores  12  with the coal seam  16  relative to the linear formation of the well bores  12  at the surface  14  may be varied to accommodate a desired drainage formation or subterranean resource configuration. 
   Well bore patterns  60  are drilled within the target subterranean zone from the articulated well bore  40  extending from each of the enlarged cavities  30 . In resource collection applications, resources from the target subterranean zone drain into each of the well bore patterns  60 , where the resources are collected in the enlarged cavities  30 . Once the resources have been collected in the enlarged cavities  30 , the resources may be removed to the surface through the well bores  12  by the methods described above. 
     FIG. 9  is a flow diagram illustrating a method for enhanced access to a subterranean resource, such as a coal seam  16 , from a limited surface area in accordance with an embodiment of the present invention. In this embodiment, the method begins at step  500  in which areas to be accessed and well bore patterns for the areas are identified. Pinnate well bore patterns may be used to provide optimized coverage for the region. However, it should be understood that other suitable well bore patterns may also be used. 
   Proceeding to step  502 , a plurality of well bores  12  are drilled from the surface  14  to a predetermined depth through the coal seam  16 . The well bores  12  may be formed having a substantially linear spaced apart relationship relative to each other or may be nonlinearly disposed relative to each other while minimizing the surface area required for accessing the subterranean resource. Next, at step  504 , down hole logging equipment is utilized to exactly identify the location of the coal seam  16  in each of the well bores  12 . At step  506 , the enlarged cavities  30  are formed in each of the well bores  12  at the location of the coal seam  16 . As previously discussed, the enlarged cavities  30  may be formed by under reaming and other conventional techniques. 
   At step  508 , the articulated well bore  40  is drilled to intersect each of the enlarged cavities  30  formed in the well bores  12 . At step  510 , the well bores  104  for the pinnate well bore patterns are drilled through the articulated well bore  40  into the coal seam  16  extending from each of the enlarged cavities  30 . After formation of the well bores  104 , lateral well bores  110  for the pinnate well bore pattern are drilled at step  512 . Lateral well bores  148  for the pinnate well bore pattern are formed at step  514 . 
   At step  516 , the articulated well bore  40  is capped. Next, at step  518 , the enlarged cavities  30  are cleaned in preparation for installation of downhole production equipment. The enlarged cavities  30  may be cleaned by pumping compressed air down the well bores  12  or other suitable techniques. At step  520 , production equipment is installed in the well bores  12 . The production equipment may include pumping units and associated equipment extending down into the cavities  30  for removing water from the coal seam  16 . The removal of water will drop the pressure of the coal seam and allow methane gas to diffuse and be produced up the annulus of the well bores  12 . 
   Proceeding to step  522 , water that drains from the well bore patterns into the cavities  30  is pumped to the surface  14 . Water may be continuously or intermittently pumped as needed to remove it from the cavities  30 . At step  524 , methane gas diffused from the coal seam  16  is continuously collected at the surface  14 . Next, at decisional step  526 , it is determined whether the production of gas from the coal seam  16  is complete. The production of gas may be complete after the cost of the collecting the gas exceeds the revenue generated by the well. Or, gas may continue to be produced from the well until a remaining level of gas in the coal seam  16  is below required levels for mining operations. If production of the gas is not complete, the method returns to steps  522  and  524  in which water and gas continue to be removed from the coal seam  16 . Upon completion of production, the method proceeds from step  526  to step  528  where the production equipment is removed. 
   Next, at decisional step  530 , it is determined whether the coal seam  16  is to be further prepared for mining operations. If the coal seam  16  is to be further prepared for mining operations, the method proceeds to step  532 , where water and other additives may be injected back into the coal seam  16  to rehydrate the coal seam  16  in order to minimize dust, improve the efficiency of mining, and improve the mined product. 
   If additional preparation of the coal seam  16  for mining is not required, the method proceeds from step  530  to step  534 , where the coal seam  16  is mined. The removal of the coal from the coal seam  16  causes the mined roof to cave and fracture into the opening behind the mining process. The collapsed roof creates gob gas which may be collected at step  536  through the well bores  12 . Accordingly, additional drilling operations are not required to recover gob gas from a mined coal seam  16 . Step  536  leads to the end of the process by which a coal seam  16  is efficiently degasified from the surface. The method provides a symbiotic relationship with the mine to remove unwanted gas prior to mining and to rehydrate the coal prior to the mining process. 
   Thus, the present invention provides greater access to subterranean resources from a limited surface area than prior systems and methods by providing decreasing the surface area required for dual well systems. For example, a plurality of well bores  12  may be disposed in close proximity to each other, for example, in a linearly or nonlinearly spaced apart relationship to each other, such that the well bores  12  may be located along a roadside or other generally small surface area. Additionally, the well bores  12  may include angled portions  20 ,  72  or  80  to accommodate formation of the articulated well bore  40  in close proximity to the well bores  12  while providing an offset to the intersection of the articulated well bore  40  with the well bores  12 . 
     FIG. 10  is a flow diagram illustrating a method for enhanced access to a subterranean resource, such as a coal seam  16 , from a limited surface area in accordance with an embodiment of the present invention. In this embodiment, the method begins at step  600  in which areas to be accessed and well bore patterns for the areas are identified. Pinnate well bore patterns may be used to provide optimized coverage for the region. However, it should be understood that other suitable well bore patterns may also be used. 
   Proceeding to step  602 , the portion  18  of the well bore  12  is formed to a predetermined depth. As described above in connection with  FIG. 1 , the depth of the portion  18  may vary depending on the location and desired offset distance between the intersection of the well bore  12  with the coal seam  16  and the surface location of the well bore  12 . The angled portion  20  of the well bore  12  is formed at step  604  extending from the portion  18 , and the portion  22  of the well bore  12  is formed at step  606  extending from the angled portion  20 . As described above in connection with  FIG. 1 , the angular orientation of the angled portion  20  and the depth of the intersection of the angled portion  20  with the portion  22  may vary to accommodate a desired intersection location of the coal seam  16  by the well bore  12 . 
   Next, at step  608 , down hole logging equipment is utilized to exactly identify the location of the coal seam  16  in the well bore  12 . At step  610 , the enlarged cavity  30  is formed in the portion  22  of the well bore  12  at the location of the coal seam  16 . As previously discussed, the enlarged cavity  30  may be formed by under reaming and other conventional techniques. 
   At step  612 , the articulated well bore  40  is drilled to intersect the enlarged cavity  30  formed in the portion  22  of the well bore  12 . At step  614 , the well bore  104  for the pinnate well bore pattern is drilled through the articulated well bore  40  into the coal seam  16  extending from the enlarged cavity  30 . After formation of the well bore  104 , lateral well bores  110  for the pinnate well bore pattern are drilled at step  616 . Lateral well bores  148  for the pinnate well bore pattern are formed at step  618 . 
     FIG. 11  is a flow diagram illustrating a method for enhanced access to a subterranean resource, such as a coal seam  16 , from a limited surface area in accordance with an embodiment of the present invention. In this embodiment, the method begins at step  700  in which areas to be accessed and well bore patterns for the areas are identified. Pinnate well bore patterns may be used to provide optimized coverage for the region. However, it should be understood that other suitable well bore patterns may also be used. 
   Proceeding to step  702 , the portion  70  of the well bore  12  is formed to a predetermined depth. As described above in connection with  FIG. 2 , the depth of the portion  70  may vary depending on the location and desired offset distance between the intersection of the well bore  12  with the coal seam  16  and the surface location of the well bore  12 . The angled portion  72  of the well bore  12  is formed at step  704  extending downwardly from the portion  70 . As described above in connection with  FIG. 2 , the angular orientation of the angled portion  72  may vary to accommodate a desired intersection location of the coal seam  16  by the well bore  12 . 
   Next, at step  706 , down hole logging equipment is utilized to exactly identify the location of the coal seam  16  in the well bore  12 . At step  708 , the enlarged cavity  30  is formed in the angled portion  72  of the well bore  12  at the location of the coal seam  16 . As previously discussed, the enlarged cavity  30  may be formed by under reaming and other conventional techniques. 
   At step  710 , the articulated well bore  40  is drilled to intersect the enlarged cavity  30  formed in the angled portion  72  of the well bore  12 . At step  712 , the well bore  144  for the pinnate well bore pattern is drilled through the articulated well bore  40  into the coal seam  16  extending from the enlarged cavity  30 . After formation of the well bore  144 , a first radius curving portion  150  of a lateral well bore  110  for the pinnate well bore pattern is drilled at step  714  extending from the well bore  144 . A second radius curving portion  152  of the lateral well bore  110  is formed at step  716  extending from the first radius curving portion  150 . The elongated portion  154  of the lateral well bore  110  is formed at step  718  extending from the second radius curving portion  152 . At decisional step  720 , a determination is made whether additional lateral well bores  110  are required. If additional lateral well bores  110  are desired, the method returns to step  714 . If no additional lateral well bores  110  are desired, the method ends. 
     FIG. 12  is a flow diagram illustrating a method for enhanced access to a subterranean resource, such as a coal seam  16 , from a limited surface area in accordance with an embodiment of the present invention. In this embodiment, the method begins at step  800  in which areas to be accessed and well bore patterns for the areas are identified. Pinnate well bore patterns may be used to provide optimized coverage for the region. However, it should be understood that other suitable well bore patterns may also be used. 
   Proceeding to step  802 , the angled portion  80  of the well bore  12  is formed. As described above in connection with  FIG. 3 , angular orientation of the angled portion  80  may vary to accommodate a desired intersection location of the coal seam  16  by the well bore  12 . Next, at step  804 , down hole logging equipment is utilized to exactly identify the location of the coal seam  16  in the well bore  12 . At step  806 , the enlarged cavity  30  is formed in the angled portion  80  of the well bore  12  at the location of the coal seam  16 . As previously discussed, the enlarged cavity  30  may be formed by under reaming and other conventional techniques. 
   At step  808 , the articulated well bore  40  is drilled to intersect the enlarged cavity  30  formed in the angled portion  80  of the well bore  12 . At step  810 , the well bore  104  for the pinnate well bore pattern is drilled through the articulated well bore  40  into the coal seam  16  extending from the enlarged cavity  30 . After formation of the well bore  104 , lateral well bores  110  for the pinnate well bore pattern are drilled at step  812 . Lateral well bores  148  for the pinnate well bore pattern are formed at step  814 . 
   Thus, the present invention provides greater access to subterranean resources from a limited surface area than prior systems and methods by decreasing the surface area required for dual well systems. For example, according to the present invention, the well bore  12  may be formed having an angled portion  20 ,  72  or  80  disposed between the surface  14  and the coal seam  16  to provide an offset between the surface location of the well bore  12  and the intersection of the well bore  12  with the coal seam  16 , thereby accommodating formation of the articulated well bore  40  in close proximity to the surface location of the well bore  12 . 
     FIG. 13  is a diagram illustrating system  10  for accessing a subterranean zone  200  in accordance with an embodiment of the present invention. As illustrated in  FIG. 13 , the well bore  40  is disposed offset relative to a pattern of well bores  12  at the surface  14  and intersects each of the well bores  12  below the surface  14 . In this embodiment, well bores  12  and  40  are disposed in a substantially nonlinear pattern in close proximity to each other to minimize the area required for the well bores  12  and  40  on the surface  14 . In  FIG. 13 , well bores  12  are illustrated having a configuration as illustrated in  FIG. 1 ; however, it should be understood that well bores  12  may be otherwise configured, for example, as illustrated in  FIGS. 2-3 . 
   Referring to  FIG. 13 , well bore patterns  60  are formed within the zone  200  extending from cavities  30  located at the intersecting junctions of the well bores  12  and  40  as described above. Well bore patterns  60  may comprise pinnate patterns, as illustrated in  FIG. 13 , or may include other suitable patterns for accessing the zone  200 . As illustrated in  FIG. 13 , well bores  12  and  40  may be disposed in close proximity to each other at the surface  14  while providing generally uniform access to a generally large zone  200 . For example, as discussed above, well bores  12  and  40  may be disposed within approximately 30 feet from each other at the surface while providing access to at least approximately 1000-1200 acres of the zone  200 . Further, for example, in a nonlinear well bore  12  and  40  surface pattern, the well bores  12  and  40  may be disposed in an area generally less than five hundred square feet, thereby minimizing the footprint required on the surface  14  for system  10 . Thus, the well bores  12  and  40  of system  10  may be located on the surface  14  in close proximity to each other, thereby minimizing disruption to the surface  14  while providing generally uniform access to a relatively large subterranean zone. 
   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.