Drilling normally to sub-normally pressured formations

Abstract

A system and method for drilling a substantially horizontal well bore in a normally to sub-normally pressured formation. The normally to sub-normally pressured formation is an unconventional reservoir. The well bore is drilled over-balanced with a drilling fluid including a fluid loss agent. The fluid loss agent is operable to form a filter cake on the well bore during drilling.

1 . A method for drilling a well bore, comprising: 
 drilling a substantially horizontal well bore in a coal seam; and    drilling the well bore over-balanced with a drilling fluid comprising at least one of aphrons and micelles to form a filter cake on a wall of the well bore during drilling.    
   
   
       2 . The method of  claim 1 , wherein the drilling fluid comprises a density at or greater than 9.5 pounds per gallon.  
   
   
       3 . The method of  claim 1 , wherein the drilling fluid comprises a density at or greater than 10 pounds per gallon.  
   
   
       4 . The method of  claim 1 , wherein the drilling fluid comprises a density substantially the same as that of the coal seam cuttings produced by drilling the well bore.  
   
   
       5 . The method of  claim 1 , wherein the drilling fluid comprises a viscosity agent.  
   
   
       6 . The method of  claim 1 , wherein the filter cake invasion into the formation comprises a depth of less than 5 centimeters.  
   
   
       7 . The method of  claim 1 , wherein the coal seam comprises at least one of naturally occurring fractures and cleats.  
   
   
       8 . The method of  claim 1 , wherein the drilling fluid further comprises starch.  
   
   
       9 . The method of  claim 1 , further comprising adjusting at least one of a flow rate and a property of the drilling fluid based at least in part on a difference between an actual amount of debris recovered per unit time and an expected amount of cuttings recovery per unit time.  
   
   
       10 . A system for drilling a well bore, comprising: 
 a drill bit coupled by a drill string to a rig at a surface, the drill bit operable to drill a well bore in a coal seam; and    a drilling fluid pumped through the drill string to the drill bit, the drilling fluid comprising at least one of aphrons and micelles to form a filter cake on the wall of the well bore during drilling.    
   
   
       11 . The system of  claim 10 , wherein the drilling fluid comprises a density at or greater than 9.5 pounds per gallon.  
   
   
       12 . The system of  claim 10 , wherein the drilling fluid comprises a density at or greater than 10 pounds per gallon.  
   
   
       13 . The system of  claim 10 , wherein the drilling fluid comprises a density substantially the same as that of the coal seam cuttings produced by drilling the well bore.  
   
   
       14 . The system of  claim 10 , wherein the drilling fluid comprises a viscosity agent.  
   
   
       15 . The system of  claim 10 , wherein the filter cake invasion into the formation comprises a depth of less than 5 centimeters.  
   
   
       16 . The system of  claim 10 , wherein the coal seam comprises at least one of naturally occurring fractures and cleats.  
   
   
       17 . The system of  claim 10 , wherein the drilling fluid further comprises starch.  
   
   
       18 . The system of  claim 10 , wherein the drilling fluid comprises FLC 2000.  
   
   
       19 . The method of  claim 1 , wherein the drilling fluid comprises FLC 2000.