Patent Publication Number: US-6991047-B2

Title: Wellbore sealing system and method

Description:
TECHNICAL FIELD OF THE INVENTION 
   The present invention relates generally to systems and methods for the recovery of subterranean resources and, more particularly, to a wellbore sealing system and method. 
   BACKGROUND OF THE INVENTION 
   Subterranean deposits of coal (typically referred to as “coal seams”) often contain substantial quantities of entrained methane gas. Limited production and use of methane gas from coal seams has occurred for many years because substantial obstacles have frustrated extensive development and use of methane gas deposits in coal seams. 
   In recent years, various methods have been used to retrieve methane gas deposits from coal seams. One such method is the use of underbalanced drilling using a dual-string technique. As an example of this method, a fluid such as drilling fluid is circulated down a drill string, while another relatively light fluid such as air or nitrogen is circulated down an annulus formed between an outside surface of a drill string and an inside surface of a casing string. A mixture of these fluids is retrieved from an annulus formed between an outer surface of the casing string and an inside surface of the wellbore after mixing with a gas or other fluid obtained from a lateral wellbore being drilled. The purpose of the lighter fluid is to lighten the weight of the drilling fluid such that the hydrostatic head of the drilling fluid does not force the drilling fluid into the subterranean formation and create detrimental effects. 
   SUMMARY OF THE INVENTION 
   The present invention provides a wellbore sealing system and method 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 method for drilling wellbores includes drilling a main wellbore and disposing a casing string in the main wellbore. The casing string has a deflecting member and a sealing member coupled thereto. The method further includes disposing a drill string having a drill bit coupled at a lower end thereof in the casing string and drilling, from the main wellbore, a first lateral wellbore at a first depth with the drill bit. The method further includes removing the drill bit from the first lateral wellbore, transferring the casing string and the drill bit to a second depth that is higher than the first depth, drilling, from the main wellbore, a second lateral wellbore at the second depth with the drill bit, and preventing, using the sealing member, a fluid from the first lateral wellbore from flowing above approximately the second depth while drilling the second lateral wellbore. 
   According to another embodiment of the present invention, a system for drilling wellbores includes a casing string, a deflecting member coupled to the casing string, and a sealing member coupled to the deflecting member. The sealing member is adapted to seal a wellbore into which the casing string is inserted such that a fluid existing in the wellbore below the sealing member is prevented from flowing upward past the sealing member. 
   Some embodiments of the present invention may provide one or more technical advantages. These technical advantages may include more efficient drilling and production of methane gas and greater reduction in costs and problems associated with other drilling systems and methods. For example, there may be less damage to lateral wellbores because of mud or other fluids entering a lateral wellbore from the drilling of another lateral wellbore. In addition, cuttings are prevented from dropping into lower lateral wellbores while an upper lateral wellbore is being drilled. Another technical advantage includes providing a method for killing a lateral wellbore, while still being able to drill another lateral wellbore. An additional technical advantage is that underbalanced drilling may be performed along with the teachings of one embodiment of the present invention. 
   Other technical advantages of the present invention are readily apparent to one skilled in the art from the figures, descriptions, and claims included herein. 

   
     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 view illustrating an example slant well system for production of resources from one or more subterranean zones via one or more lateral wellbores; 
       FIG. 2  illustrates an example system for drilling lateral wellbores according to one embodiment of the present invention; 
       FIG. 3  illustrates an example system for drilling lateral wellbores according to another embodiment of the present invention; and 
       FIG. 4  is a flowchart demonstrating an example method for drilling lateral wellbores according to one embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Embodiments of the present invention and their advantages are best understood by referring now to  FIGS. 1 through 4  of the drawings, in which like numerals refer to like parts. 
     FIG. 1  is a cross-sectional view illustrating an example well system  100  for production of resources from one or more subterranean zones  102  via one or more lateral wellbores  104 . In various embodiments described herein, subterranean zone  102  is a coal seam; however, other subterranean formations may be similarly accessed using well system  100  of the present invention to remove and/or produce water, gas, or other fluids. System  100  may also be used for other suitable operations, such as to treat minerals in subterranean zone  102  prior to mining operations, or to inject or introduce fluids, gasses, or other substances into subterranean zone  102 . 
   Referring to  FIG. 1 , well system  100  includes an entry wellbore  105 , two main wellbores  106 , a plurality of lateral wellbores  104 , a cavity  108  associated with each main wellbore  106 , and a rat hole  110  associated with each main wellbore  106 . Entry wellbore  105  extends from a surface  12  towards subterranean zones  102 . Entry wellbore  105  is illustrated in  FIG. 1  as being substantially vertical; however, entry wellbore  105  may be formed at any suitable angle relative to surface  12  to accommodate, for example, surface  12  geometries and/or subterranean zone  102  geometries. 
   Main wellbores  106  extend from the terminus of entry wellbore  105  toward subterranean zones  102 , although main wellbores may alternatively extend from any other suitable portion of entry wellbore  105 . Where there are multiple subterranean zones  102  at varying depths, as illustrated in  FIG. 1 , main wellbores  106  extend through the subterranean zones  102  closest to surface  12  into and through the deepest subterranean zones  102 . There may be one or any number of main wellbores  106 . As illustrated, main wellbores  106  are slant wells and, as such, are formed to angle away from entry wellbore  105  at an angle designated α, which may be any suitable angle to accommodate surface topologies and other factors similar to those affecting entry wellbore  105 . Main wellbores  106  are formed in relation to each other at an angular separation of β degrees, which may be any suitable angle, such as 60 degrees. However, main wellbores  106  may be separated by other angles depending likewise on the topology and geography of the area and location of a targeted subterranean zone  102 . Main wellbores  106  may also include cavity  108  and/or rat hole  110  located at a terminus of each wellbore  106 . Main wellbore  106  may include one, both, or neither cavity  108  and rat hole  110 . 
   Lateral wellbores  104  extend from each main wellbore  106  into an associated subterranean zone  102 . Lateral wellbores  104  are shown in  FIG. 1  to be substantially horizontal; however, lateral wellbores  104  may be formed in other suitable directions off of main wellbores  106  and may have a curvature associated therewith. Any suitable systems and/or methods may be used to drill lateral wellbores  104 ; however, a particular system for drilling lateral wellbores  104  according to one embodiment of the present invention is described below in conjunction with  FIGS. 2 through 4 . 
     FIG. 2  illustrates an example system  200  for drilling lateral wellbores  104  according to one embodiment of the present invention. As illustrated, system  200  includes a drill string  201  having a drill bit  202 , a casing string  204 , a deflecting member  206  having a deflecting surface  208  coupled to a lower end of casing string  204 , and a sealing member  210  coupled to a lower end of deflecting member  206 . 
   Drill string  201  may be any suitable drill string having any suitable length and diameter and any suitable drill bit  202  for the purpose of drilling lateral wellbores  104 . Drill string  201  is typically a hollow conduit for allowing drilling fluids to flow therethrough. Drill bit  202  may be driven through the use of any suitable motor powered by the drilling fluid and may have any suitable configuration. To direct drill string  201  and drill bit  202  for the purpose of drilling lateral wellbore  104 , deflecting surface  208  of deflecting member  206  is utilized. 
   Casing string  204  may be any suitable casing string having any suitable diameter that is to be inserted into main wellbore  106 . Casing string  204  is adapted to rotate within main wellbore  106  as illustrated by arrow  216 . An inner annulus  212  is formed between the inner surface of casing string  204  and the outer surface of drill string  201 . An outer annulus  214  is also formed between an outside surface of casing string  204  and the surface of main wellbore  106 . Inner annulus  212 , outer annulus  214 , and drill string  201  may be used to perform underbalanced drilling. As one example of underbalanced drilling, a first fluid may be circulated down drill string  201 , such as drilling mud or other suitable drilling fluids. A second fluid is circulated down inner annulus  212 , such as air, nitrogen, or other relatively light fluid. Both first and second fluids may be retrieved from outer annulus  214  after mixing with a gas or other fluid produced from lateral wellbore  104 . The purpose of the second fluid is to lighten the weight of the first fluid such that the hydrostatic head of the first fluid does not force first fluid into the subterranean formation. As a variation, the second fluid may be circulated down outer annulus  214  and the mixture of the first and second fluids along with the gas from lateral wellbore  104  may be retrieved via inner annulus  212 . 
   According to the teachings of the present invention, sealing member  210  is adapted to seal main wellbore  106  such that a fluid existing in main wellbore  106  below sealing member  210  is prevented from flowing upward past sealing member  210 . In one embodiment of the invention, this allows the drilling of a lateral wellbore  104   a  in a subterranean zone  102   a  at a first depth  218  and then the drilling of a lateral wellbore  104   b  in a subterranean zone  102   b  at a second depth  220 , while ensuring that any gas or other fluid obtained from lateral wellbore  104   a  at first depth  218  does not flow past sealing member  210  and interfere with the drilling of lateral wellbore  104   b  in subterranean zone  102   b  at second depth  220 . In addition, any cuttings resulting from the drilling of lateral wellbore  104   b  are prevented from dropping into lateral wellbore  104   a.  An example sealing member  210  is illustrated in FIG.  2 . 
   As illustrated in  FIG. 2 , example sealing member  210  includes a bolt  222 , a nut  224 , a plug  226 , a washer  228 , and a resilient member  230 . Bolt  222  is coupled to a lower end  223  of deflecting member  206  in any suitable manner. Nut  224  is threaded on bolt  222 , while washer  228  surrounds bolt  222  and is rigidly coupled to nut  224 . Plug  226  surrounds bolt  222  and is disposed between washer  228  and lower end  223  of deflecting member  206 . 
   Plug  226  is formed from any suitable material, such as an elastomer, resilient enough to be circumferentially expanded or circumferentially retracted but stiff enough to be able to prevent any gas or other fluid existing in main wellbore  106  below sealing member  210  to leak past plug  226 . The circumferential expansion or retraction of plug  226  via the rotation of casing string  204  is described in more detail below. In other embodiments, plug  226  is an air-filled diaphragm formed from any suitable material. 
   Resilient member  230  is coupled to washer  228  in any suitable manner. Resilient member  230 , which may be any suitable resilient member, such as a bow spring, is adapted to engage the wall of main wellbore  106  and apply enough force to the wall of main wellbore  106  to prevent nut  224  and washer  228  from turning while casing string  204  is rotated within main wellbore  106 . Washer  228  and nut  224  are fixed to one another such that, when casing string  204  is rotated, nut  224  and washer  228  do not rotate. In this way, bolt  222  may longitudinally compress plug  226  to circumferentially expand plug  226  so that it may press against the wall of main wellbore  106  to prevent gas or other fluid from flowing upward past plug  226 . Conversely, when casing string  204  is rotated in an opposite direction, then bolt  222  acts to longitudinally decompress plug  226 , thereby circumferentially retracting plug  226  so that gas or other fluid may bypass plug  226 . 
   In operation of one embodiment of system  200  of  FIG. 2 , main wellbore  106  is drilled via any suitable method. Casing string  204  having deflecting member  206  and sealing member  210  attached thereto is inserted into main wellbore  106 . While lowering casing string  204  down main wellbore  106 , plug  226  is in a circumferentially retracted position so that any air or other fluid existing at a depth below sealing member  210  may leak past plug  226 . Once at a desired depth, such as first depth  218 , drill string  201  is inserted within casing string  204  so that lateral wellbore  104   a  may be drilled at first depth  218 . After drilling lateral wellbore  104   a  drill string  201  is retracted from lateral wellbore  104   a.  At this time, casing string  204  is rotated in a desired direction so that plug  226  may be longitudinally compressed and circumferentially expanded to press against the wall of main wellbore  106 . As described above, this prevents any gas or other fluid produced from lateral wellbore  104   a  from traveling up past plug  226 . Casing string  204  may then be raised to second depth  220  so that lateral wellbore  104   b  may be drilled. Lateral wellbore  104   b  may then be drilled with drill bit  202  with the assurance that sealing member  210  will prevent any gas or fluid from passing upward and causing detrimental effects. Other lateral wellbores  104  may be drilled successively at shallower depths according to a similar procedure. Many different types of sealing members  210  are contemplated by the present invention. Another example sealing member is shown below in conjunction with FIG.  3 . 
     FIG. 3  illustrates another example sealing member  310 . In one embodiment, sealing member  310  is a resilient plunger  300  formed from a suitable elastomer; however, other suitable resilient materials may be utilized. As illustrated, plunger  300  includes a plurality of ridges  302  that have an inherent stiffness to prevent gas or other fluid from a depth in main wellbore  106  below plunger  300  from leaking past plunger  300  to a higher depth (or vice versa) while a lateral wellbore  104  is being drilled. In addition, plunger  300 , via ridges  302 , possesses enough resiliency to allow gas or other fluid existing at a depth below plunger  300  to flow past plunger  300  to relieve any potential increasing pressure below plunger  300  when plunger  300  is inserted into main wellbore  106 . Plunger  300  may have other suitable configurations and may be coupled to deflecting member  206  in any suitable manner. In other embodiments, plunger  300  is a hollow plunger having any suitable fluid therein. 
   Plunger  300  may also include a relief valve (not shown) that is operable to allow gas or other fluid at a depth below plunger  300  to flow to a depth above plunger  300  when a predetermined pressure is reached. Any suitable relief valve may be utilized and the relief valve may be coupled to plunger  300  in any suitable manner. The relief valve may be set to open or close at a predetermined pressure depending on the pressure expected to be encountered in main wellbore  106  below sealing member  310 . A relief valve may also be utilized with sealing member  210  of  FIG. 2  in a similar manner. 
     FIG. 4  is a flow chart demonstrating an example method of drilling lateral wellbores  104  according to one embodiment of the present invention. The method begins at step  400  where main wellbore  106  is drilled. Casing string  204  having deflecting member  206  at a lower end thereof is disposed in main wellbore  106  at step  402 . Deflecting member  206  has any suitable sealing member coupled at a lower end thereof. Although example sealing members  210  and  310  are described above, any suitable sealing member may be used within the scope of the present invention. 
   As described above, the sealing member prevents a gas or other fluid from a lower lateral wellbore from flowing up to a higher lateral wellbore at a higher depth while drill string  201  is drilling the higher lateral wellbore. At step  404 , drill string  201  having drill bit  202  is disposed in casing string  204 . At step  406 , a first lateral wellbore  104   a  is drilled from main wellbore  106  at first depth  218 . Deflecting surface  208  of deflecting member  206  is utilized to direct drill string  201  in the desired drilling direction. 
   After first lateral wellbore  104   a  is drilled, drill bit  202  is removed from first lateral wellbore  104   a  at step  408 . At step  410 , casing string  204  and drill bit  202  are transferred to second depth  220  that is less than first depth  218 . Any gas or other fluid produced from first lateral wellbore  104   a  is prevented, as denoted by step  412 , from flowing up to second depth  220  by the sealing member. At step  414 , second lateral wellbore  104   b  is drilled from main wellbore  106  at second depth  220  with drill bit  202 . Successive lateral wellbores  104  may be drilled at successively higher depths per the above method. In lieu of a slant well system, the described example method may be used with other suitable well systems. 
   Although the present invention is described with several embodiments, various changes and modifications may be suggested to one skilled in the art. The present invention intends to encompass such changes and modifications as they fall within the scope of the appended claims.