Methods for drilling and producing from coal bed formations and associated apparatus

Abstract

A method of drilling a formation, comprising drilling at least one wellbore in a coal bed methane formation using a drill string having an inner string and an outer string, the inner string and outer string defining a passageway therebetween; providing a drilling medium to drill apparatus for use in drilling the formation, the drilling medium provided through one of the inner or outer strings; and returning a combined medium comprising drilling medium, drilling cuttings, produced water and/or gas from the formation to surface via the other of the inner and outer string. Subsequent to drilling the formation, there are also described methods and apparatus for producing from coal bed methane formations. In some examples, this includes producing a first fluid, or fluid product from a first flow passage within a wellbore; and also producing a second fluid, or fluid product, from a second flow passage within the wellbore.

1 . A method of drilling coal bed methane formations, comprising:
 drilling at least one wellbore in a coal bed methane formation using a drill string having an inner string and an outer string, the inner string and outer string defining a passageway therebetween;   providing a drilling medium to drill apparatus for use in drilling the formation, the drilling medium provided through one of the inner or outer strings; and   returning a combined medium comprising drilling medium, drilling cuttings, produced water and/or gas from the formation to surface via the other of the inner and outer string.   
     
     
         2 . The method according to  claim 1 , wherein the combined medium comprises at least drilling medium and drilling cuttings. 
     
     
         3 . The method according to  claim 1 , wherein the method comprises providing air as the drilling fluid. 
     
     
         4 . The method according to  claim 1  comprising separating the combined medium in order to retrieve produced gas from the combined medium. 
     
     
         5 . The method according to  claim 1 , wherein providing a drilling medium to drill apparatus is achieved such that that drilling medium, when returned to surface, will have been in contact only with the formation at a specific location. 
     
     
         6 . The method according to  claim 1 , comprising isolating, while drilling, one or more waterzones or acquirers from the wellbore. 
     
     
         7 . The method according to  claim 1 , wherein the drilling provides a primary wellbore, and the method then comprising drilling one or more secondary wellbores from the primary wellbore. 
     
     
         8 . The method according to  claim 7 , wherein each secondary wellbore is drilled in a deviated relationship with respect to the primary wellbore. 
     
     
         9 . The method according to  claim 7 , wherein secondary wellbore is drilled in the same manner as the primary wellbore. 
     
     
         10 . The method according to  claim 1 , wherein the method comprises drilling the well bore such that water and gas can be produced from tubing provided in the wellbore, after completion, and that gas can be produced to surface from an annulus provided between casing the tubing. 
     
     
         11 . A method of producing from coal bed methane formations, comprising:
 producing a first fluid, or fluid product, from a first flow passage within a wellbore; and   producing a second fluid, or fluid product, from a second flow passage within the wellbore.   
     
     
         12 . The method according to  claim 11 , wherein the first fluid passage is provided by a through bore or tubing and the second fluid passage is provided by an annulus between the through bore, or tubing, and a second bore. 
     
     
         13 . The method of  claim 12 , wherein the second bore is provided by completion and/or open wellbore. 
     
     
         14 . The method according to  claim 11 , wherein the first fluid contains comparatively more water than the second fluid. 
     
     
         15 . The method according to  claims 11 , wherein the second fluid contains comparatively more methane than the first fluid. 
     
     
         16 . A coal bed method formation comprising one or more wellbores obtainable according to  claim 1 .