Patent Publication Number: US-7222670-B2

Title: System and method for multiple wells from a common surface location

Description:
TECHNICAL FIELD 
   The present invention relates generally to the field of subterranean exploration and drilling and, more particularly, to a system and method for multiple wells from a common surface location. 
   BACKGROUND 
   Subterranean deposits of coal contain substantial quantities of entrained methane gas. Limited production in use of methane gas from coal deposits has occurred for many years. Substantial obstacles, however, have frustrated more extensive development in 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 drilling 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. 
   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 seams. The most efficient method for pumping water from a subterranean well, a sucker rod pump, does not work well in horizontal or radiused bores. 
   SUMMARY 
   The present invention provides a system and method using multiple articulated and drainage wells from a common surface well that substantially eliminates, reduces, or minimizes the disadvantages and problems associated with previous systems and methods. In particular, certain embodiments of the present invention provide a system and method using multiple articulated and drainage wells from a single surface well for efficiently producing and removing entrained methane gas and water from a coal seam without requiring that multiple wells be drilled from the surface. 
   In accordance with one embodiment of the present invention, a system for accessing a subterranean zone from an entry well including an entry well extending from the surface. The entry well has a substantially vertical portion. One or more drainage wells extend from the entry well to a subterranean zone. One or more articulated wells extend from the entry well to the subterranean zone. At least one of the articulated wells intersects at least one of the one or more drainage wells at a junction proximate the subterranean zone. A drainage pattern is formed coupled to the junction and operable to conduct fluids from the subterranean zone to the junction. 
   The technical advantage of the present invention include providing a method and system for using multiple articulated and drainage wells from a common surface well. In particular, a technical advantage may include the formation of an entry well, a plurality of drainage wells, a plurality of articulated wells, and drainage patterns from a single surface location to minimize the number of surface wells needed to access a subterranean zone for draining 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. 
   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 through multiple wells drilled from a common surface well; 
       FIG. 2  is a cross-sectional diagram illustrating production of fluids from a subterranean zone through a well bore system in accordance with one embodiment of the present invention; 
       FIG. 3  illustrates one embodiment of subterranean drainage patterns of the well system of  FIG. 2 ; 
       FIG. 4  illustrates an example method for producing fluids from a subterranean zone using the well bore system of  FIG. 1 ; 
       FIG. 5A  illustrates construction of an example guide tube bundle for insertion into entry well of  FIG. 1 ; and 
       FIG. 5B  illustrates an example entry well with an installed guide tube bundle. 
   

   DETAILED DESCRIPTION OF THE DRAWINGS 
     FIG. 1  is a diagram illustrating a system  10  for accessing a subterranean zone using multiple articulated and drainage wells from a common surface well in accordance with an embodiment of the present invention. In particular embodiments, the subterranean zone is a coal seam. However, it should be understood that other subterranean zones can be similarly accessed using system  10  of the present invention to remove and/or produce water, hydrocarbons and other fluids from the zone, to treat minerals in the zone prior to mining operations, or to inject, introduce, or store a fluid or other substance into the zone. 
   Referring to  FIG. 1 , system  10  includes an entry well  12 , drainage wells  14 , articulated wells  16 , cavities  18 , and sumps  20 . Entry well  12  extends from surface  22  towards subterranean zone  24 . Drainage wells  14  extend from the terminus of entry well  12  to subterranean zone  24 , although drainage wells  14  may alternatively extend from any other suitable portion of entry well  12 . Articulated wells  16  also may extend from the terminus of entry well  12  to subterranean zone  24  and may each intersect a corresponding drainage well  14 . Cavity  18  and sump  20  may be located at the intersection of an articulated well  16  and a corresponding drainage well  14 . 
   Entry well  12  is illustrated as being substantially vertical; however, it should be understood that entry well  12  may be formed at any suitable angle relative to surface  22  to accommodate, for example, surface geometries and attitudes and/or the geometric configuration or attitude of a subterranean resource. In the illustrated embodiment, drainage wells  14  are formed as slant wells that angle away from entry well  12  at an angle designated α. The angle α depends, in part, on the depth of subterranean zone  24 . It will be understood that drainage wells  14  may be formed at other angles to accommodate surface topologies and other factors similar to those affecting entry well  12 . Furthermore, although drainage wells  14  are illustrated as having the same angle of slant over their entire length (below entry well  12 ), drainage wells  14  may have two or more portions below entry well  12  that are at different angles. For example, the portion of drainage wells  14  from which cavity  18  is formed and/or which is intersected by the corresponding articulated well  16  may be substantially vertical. In the illustrated embodiment, drainage wells  14  are formed in relation to each other at an angular separation of β degrees. In one embodiment, the angle β equals twice the angle α. It will be understood that drainage wells  14  may be separated by other angles depending likewise on the topology and geography of the area and location of subterranean zone  24 . 
   In particular embodiments, an enlarged cavity  18  may be formed from each drainage well  14  at the level of subterranean zone  24 . As described in more detail below, cavity  18  provides a junction for the intersection of drainage well  14  by a corresponding articulated well  16  used to form a subterranean drainage bore pattern in subterranean zone  24 . Cavity  18  also provides a collection point for fluids drained from subterranean zone  24  during production operations. In one embodiment, cavity  18  has a radius of approximately eight feet; however, any appropriate diameter cavity may be used. Cavity  18  may be formed using suitable under-reaming techniques and equipment. A portion of drainage well  14  may continue below cavity  18  to form a sump  20  for cavity  18 . Although cavities  18  and sumps  20  are illustrated, it should be understood that particular embodiments do not include a cavity and/or a sump. 
   Each articulated well  16  extends from the terminus of entry well  12  to cavity  18  of a corresponding drainage well  14  (or to the drainage well  14  if no cavity is formed). Each articulated well  16  includes a first portion  34 , a second portion  38 , and a curved or radiused portion  36  interconnecting portions  34  and  38 . In  FIG. 1 , portion  34  is illustrated substantially vertical; however, it should be understood that portion  34  may be formed at any suitable angle relative to surface  22  to accommodate surface  22  geometric characteristics and attitudes and/or the geometric configuration or attitude of subterranean zone  24 . Portion  38  lies substantially in the plane of subterranean zone  24  and intersects the large diameter cavity  18  of a corresponding drainage well  14 . In  FIG. 1 , the plane of subterranean zone  24  is illustrated substantially horizontal, thereby resulting in a substantially horizontal portion  38 ; however, it should be understood that portion  38  may be formed at any suitable angle relative to surface  22  to accommodate the geometric characteristics of subterranean zone  24 . Each articulated well  16  may be drilled using an articulated drill string  26  that includes a suitable down-hole motor and a drill bit  28 . A measurement while drilling (MWD) device  30  may be included in articulated drill string  26  for controlling the orientation and direction of a well bore drilled by the motor and bit  28 . Any suitable portion of articulated well  16  may be lined with a suitable casing. 
   In the illustrated embodiment, drainage well  14  is sufficiently angled away from a corresponding articulated well  16  to permit the large radiused curved portion  36  and any desired portion  38  to be drilled before intersecting cavity  18 . In particular embodiments, curved portion  36  may have a radius of one hundred to one hundred fifty feet; however, any suitable radius may be used. This angle α may be chosen to minimize the angle of curved portion  36  to reduce friction in articulated well  16  during drilling operations. As a result, the length of articulated well  16  is maximized. 
   After cavity  18  has been successfully intersected by articulated well  16 , drilling is continued through cavity  18  using articulated well string  26  to provide a drainage bore pattern  32  in subterranean zone  24 . In  FIG. 1 , drainage bore pattern  32  is illustrated substantially horizontal corresponding to a substantially horizontally illustrated subterranean zone  24 ; however, it should be understood that drainage bore pattern  32  may be formed at any suitable angle corresponding to the geometric characteristics of subterranean zone  24 . During this operation, gamma ray logging tools and conventional MWD devices may be employed to control and direct the orientation of drill bit  28  to retain drainage bore pattern  32  within the confines of subterranean zone  24  and to provide substantially uniform coverage of a desired area within subterranean zone  24 . Drainage bore pattern  32  may comprise a single drainage bore extending into subterranean zone  24  or it may comprise a plurality of drainage bores. Further information regarding an example drainage bore pattern  32  is described in more detail below. In addition, although pattern  32  is illustrated as extending from cavity  18 , portion  38  of articulated wells  16  may be extended appropriately so that portion  38  serves the function of draining fluids from the subterranean zone  24 . 
   During the process of drilling drainage bore pattern  32  in a coal seam or other appropriate formations, drilling fluid or “mud” may be pumped down articulated drill string  26  and circulated out of drill string  26  in the vicinity of a bit  28 , 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 drill string  26  and the walls of articulated well  16  until it reaches surface  22 , 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 articulated well  16  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 subterranean zone  24 . Accordingly, if the full hydrostatic pressure is allowed to act on subterranean zone  24 , the result may be loss of drilling fluid in entrained cuttings into the formation. Such a circumstance is referred to as an “over-balanced” drilling operation in which they hydrostatic fluid pressured 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 also tends to plug the pores in subterranean zone  24 , which are needed to drain the coal seam of gas and water. 
   To prevent over-balanced drilling conditions during formation of drainage bore pattern  32 , air compressors or other suitable pumps may be provided to circulate compressed air or other suitable fluids down drainage wells  14  and back up through corresponding articulated wells  16 . The circulated air or other fluid will mix with the drilling fluid in the annulus around the articulated drill string  26  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 significantly 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. Alternatively, tubing may be inserted into drainage well  14  such that air pumped down through the tubing forces the fluid back through the annulus between the tubing and drainage well  14 . 
   In yet another embodiment, a down-hole pumping unit  40  may be installed in cavity  18 , as illustrated in  FIG. 1 , to pump drilling fluid and cuttings to surface  22  through drainage well  14 . This eliminates the friction of air and fluid returning through articulated well  16  and may reduce down-hole pressure to nearly zero. 
   Foam, which may be compressed air mixed with water, may also be circulated down through the articulated drill string  26  along with the drilling mud in order to aerate the drilling fluid in the annulus as articulated well  16  is being drilled and, if desired, as drainage bore pattern  32  is being drilled. Drilling of drainage bore pattern  32  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  28  exits articulated drill string  26  in the vicinity of drill bit  28 . However, the larger volume of air which can be circulated down drainage wells  14  permits greater aeration of the drilling fluid than generally is possible by air supplied through articulated drill string  26 . 
     FIG. 2  illustrates production of fluids from drainage bore pattern  32   a  and  32   b  in subterranean zone  24  in accordance with one embodiment of the present invention. In this embodiment, after wells  14  and  16 , respectively, as well as desired drainage bore patterns  32 , have been drilled, articulated drill string  26  is removed from articulated wells  16 . In particular embodiments, articulate wells may be suitably plugged to prevent gas from flowing through articulate wells  16  to the surface  22 . 
   Referring to  FIG. 2 , the inlets for down-hole pumps  40  or other suitable pumping mechanisms are disposed in drainage wells  14  in their respective cavities  18 . Each cavity  18  provides a reservoir for accumulated fluids allowing intermittent pumping without adverse effects of a hydrostatic head caused by accumulated fluids in the well bore. Each cavity  18  also provides a chamber for gas/water separation for fluids accumulated from drainage bore patterns  32 . 
   Each down-hole pump  40  is connected to surface  22  via a respective tubing string  42  and may be powered by sucker rods extending down through wells  14  of tubing strings  42 . Sucker rods are reciprocated by a suitable surface mounted apparatus, such as a powered walking beam  46  to operate each down-hole pump  40 . Each down-hole pump  40  is used to remove water and entrained coal finds from subterranean zone  24  via drainage bore patterns  32 . In the case of a coal seam, once the water is removed to the surface, it may be treated for separation of methane which may be dissolved in the water and for removal of entrained finds. After sufficient water has been removed from subterranean zone  24 , pure coal seam gas may be allowed to flow to surface  22  through the annulus of wells  14  around tubing strings  42  and removed via piping attached to a well head apparatus. At surface  22 , the methane is treated, compressed and pumped through a pipeline for use as fuel in a conventional manner. Each down-hole pump  40  may be operated continuously or as needed to remove water drained from subterranean zone  24  into cavities  18 . 
     FIG. 3  illustrates one embodiment of the subterranean patterns  32   a  and  32   b  for accessing subterranean zone  24  or other subterranean zone. The patterns  32   a  and  32   b  may be used to remove or inject water, gas or other fluids. The subterranean patterns  32   a  and  32   b  each comprise a multi-lateral pattern that has a main bore with generally symmetrically arranged and appropriately spaced laterals extending from each side of the main bore. As used herein, the term each means every one of at least a subset of the identified items. It will be understood that other suitable multi-branching or other patterns including or connected to a surface production bore may be used. For example, the patterns  32   a  and  32   b  may each comprise a single main bore. Referring to  FIG. 3 , patterns  32   a  and  32   b  each include a main bore  150  extending from a corresponding cavity  18   a  or  18   b , respectively, or intersecting wells  14  or  16  along a center of a coverage area to a distal end of the coverage area. The main bore  150  includes one or more primary lateral bores  152  extending from the main bore  150  to at least approximately to the periphery of the coverage area. The primary lateral bores  152  may extend from opposite sides of the main bore  150 . The primary lateral bores  152  may mirror each other on opposite sides of the main bore  150  or may be offset from each other along the main bore  150 . Each of the primary lateral bores  152  may include a radiused curving portion extending from the main bore  150  and a straight portion formed after the curved portion has reached a desired orientation. For uniform coverage, the primary lateral bores  152  may be substantially evenly spaced on each side of the main bore  150  and extend from the main bore  150  at an angle of approximately forty-five degrees. The primary lateral bores  152  may be shortened in length based on progression away from the corresponding cavity  18   a  or  18   b . Accordingly, the distance between the cavity or intersecting well bore and the distal end of each primary lateral bore  152  through the pattern may be substantially equally for each primary lateral  152 . 
   One or more secondary lateral bores  152  may be formed off one or more of the primary lateral bores  152 . In a particular embodiment, a set of secondary laterals  154  may be formed off the primary lateral bores  152  of each pattern  32   a  and  32   b  closest to the corresponding cavity  18   a  and  18   b . The secondary laterals  154  may provide coverage in the area between the primary lateral bores  152  of patterns  32   a  and  32   b . In a particular embodiment, a first primary lateral  154  may include a reversed radius section to provide more uniform coverage of subterranean zone  24 . 
   The subterranean patterns  32   a  and  32   b  with their central bore and generally symmetrically arranged and appropriately spaced auxiliary bores on each side may provide a substantial uniform pattern for draining fluids from subterranean zone  24  or other subterranean zone. The number and spacing of the lateral bores may be adjusted depending on the absolute, relative and/or effective permeability of the coal seam and the size of the area covered by the pattern. The area covered by the pattern may be the area drained by the pattern, the area of a spacing unit that the pattern is designed to drain, the area within the distal points or periphery of the pattern and/or the area within the periphery of the pattern as well as surrounding area out to a periphery intermediate to adjacent or neighboring patterns. The coverage area may also include the depth, or thickness of the coal seam or, for thick coal seams, a portion of the thickness of the seam. Thus, the pattern may include upward or downward extending branches in addition to horizontal branches. The coverage area may be a square, other quadrilateral, or other polygon, circular, oval or other ellipsoid or grid area and may be nested with other patterns of the same or similar type. It will be understood that other suitable drainage bore patterns may be used. 
   As previously described, the well bore  150  and the lateral bores  152  and  154  of patterns  32   a  and  32   b  are formed by drilling through the corresponding cavity  18   a  or  18   b  using the drill string  26  in appropriate drilling apparatus. During this operation, gamma ray logging tools and conventional MWD technologies may be employed to control the direction and orientation of drill bit  28  so as to retain the drainage bore pattern within the confines of subterranean zone  24  and to maintain proper spacing and orientation of wells  150  and  152 . In a particular embodiment, the main well bore  150  of each pattern  32   a  and  32   b  is drilled with an incline at each of the plurality of lateral branch points  156 . After the main well bore  150  is complete, the drill string  26  is backed up to each successive lateral point  156  from which a primary lateral bore  152  is drilled on each side of the well bore  150 . The secondary laterals  154  may be similarly formed. It will be understood that the subterranean patterns  32   a  and  32   b  may be otherwise suitably formed. Furthermore, as described above, a pattern (as illustrated in  FIG. 3 ) or otherwise may be formed off of portion  38  of articulated well  16  (which would function as well bore  150 ) such that cavities  18  are located at the end of portion  38 /well bore  150 . 
     FIG. 4  is a flow diagram illustrating a method for preparing subterranean zone  24  for mining operations in accordance with particular embodiments of the present invention. The example method begins at step  400  in which entry well  12  is drilled substantially vertically from the surface. At step  402 , a casing with guide tubes is installed into the entry well  12 . At step  404 , the casing is cemented in place inside entry well  12 . 
   At step  406 , drill string  26  is inserted through entry well  12  and one of the guide tubes in the guide tube bundle. At step  408 , drill string  26  is used to drill approximately fifty feet past the casing. At step  410 , the drill is oriented to the desired angle of the drainage well  14  and, at step  412 , drainage well bore  14  is drilled down into and through target subterranean zone  24 . 
   At step  414 , down-hole logging equipment may be utilized to identify the location of the subterranean zone  24 . At step  416 , cavity  18   a  is formed in first drainage well  14  at the location of subterranean zone  24 . As previously discussed, cavity  18  may be formed by underreaming and other conventional techniques. At decisional step  418 , if additional drainage wells are to be drilled, the method returns to step  406 . If no additional drainage wells  14  are to be drilled, then the method proceeds to step  420 . 
   At step  420 , articulated well  16  is drilled to intersect cavity  18 . At step  422 , drainage bore pattern  32  is drilled into subterranean zone  24 . At step  424 , production equipment is installed into drainage wells  14  and at step  426  the process ends with the production of fluids (such as water and gas) from the subterranean zone  24 . 
   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. 
     FIG. 5A  illustrates formation of a casing with associated guide tube bundle as described in step  402  of  FIG. 4 . Three guide tubes  48  are shown in side view and end view. The guide tubes  48  are arranged so that they are parallel to one another. In the illustrated embodiment, guide tubes  48  are 9⅝″ joint casings. It will be understood that other suitable materials may be employed. As an example, guide tubes  48   a  and  48   b  serve as the tubes through which drainage wells  14   a  and  14   b  are drilled, respectively. In this example, guide tube  48   c  serves as the tube through which both articulated wells  16   a  and  16   b  are drilled. It will be understood that other suitable arrangements may be employed. In another embodiment, guide tubes  48  may be attached to a casing collar such that the guide tubes  48  and casing collar make up the guide tube bundle. 
     FIG. 5B  illustrates entry well  12  with guide tubes  48  and a casing collar  50  cemented in entry well  12 . Entry well  12  is formed from the surface  22  to a target depth (in particular embodiments, approximately three hundred feet). In a particular embodiment, entry well  12  has a diameter of approximately twenty-four inches. Forming entry well  12  corresponds with step  400  of  FIG. 4 . Guide tubes  48  are shown attached to a casing collar  50 . Casing collar  50  may be any casing suitable for use in down-hole operations. Inserting casing collar  50  and guide tubes  48  into entry well  12  corresponds with step  402  of  FIG. 4 . 
   Corresponding with step  404  of  FIG. 4 , a cement retainer  52  is poured or otherwise installed around the casing inside entry well  12 . The cement casing may be any mixture or substance otherwise suitable to maintain casing  50  in the desired position with respect to entry well  12 . 
   In operation, drill string  26  is positioned to enter one of the guide tubes  48 . In order to keep drill string  26  relatively centered in casing  50 , a stabilizer  54  may be employed. Stabilizer  54  may be a ring and fin type stabilizer or any other stabilizer suitable to keep drill string  26  relatively centered. To keep stabilizer  54  at a desired depth in well bore  12 , stop ring  56  may be employed. Stop ring  56  may be constructed of rubber or metal or any other foreign down-hole environment material suitable. Drill string  26  may be inserted randomly into any of a plurality of guide tubes  48 , or drill string  26  may be directed into a selected guide tube  48   a . This corresponds to step  406  of  FIG. 4 . 
   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.