Well bore cleaning

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 having a density at least about the density of the cuttings produced by drilling the well bore.

1 . A method for drilling a well bore, comprising: 
 drilling a substantially horizontal well bore in a normally to sub-normally pressured formation, the normally to sub-normally pressured formation comprising an unconventional reservoir; and    drilling the well bore over-balanced with a drilling fluid comprising a density greater than 9.5 pounds per gallon.    
   
   
       2 . The method of  claim 1 , wherein the drilling fluid comprises a density at or greater than 10 pounds per gallon.  
   
   
       3 . The method of  claim 1 , the drilling fluid comprising a density substantially at that of the cuttings produced by drilling the well bore.  
   
   
       4 . The method of  claim 3 , wherein drilling the substantially horizontal well bore is performed at a rate that is greater than if the drilling fluid had a density substantially less than that of the cuttings produced by drilling the well bore.  
   
   
       5 . The method of  claim 1 , further comprising adjusting at least one of the flow rate and the properties of the drilling fluid based at least in part on a difference between an actual amount of cuttings recovery per unit time and an expected amount of cuttings recovery per unit time.  
   
   
       6 . The method of  claim 1 , wherein the unconventional reservoir comprises a coal bed.  
   
   
       7 . The method of  claim 1 , wherein the unconventional reservoir comprises a shale.  
   
   
       8 . The method of  claim 1 , wherein the unconventional reservoir comprises at least one of naturally occurring fractures and cleats.  
   
   
       9 . 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 horizontal well bore in a normally to sub-normally pressured formation, the normally to sub-normally pressured formation comprising an unconventional reservoir; and    a drilling fluid pumped through the drill string to the drill bit and recirculated to the surface through the well bore, the drilling fluid comprising a density greater than 9.5 pounds per gallon.    
   
   
       10 . The system of  claim 9 , wherein the drilling fluid comprises a density at least  10  pounds per gallon.  
   
   
       11 . The system of  claim 9 , wherein the drilling fluid comprises a density substantially at that of the cuttings produced by drilling the well bore.  
   
   
       12 . The system of  claim 9 , wherein the drilling fluid further comprises a viscosity agent.  
   
   
       13 . The system of  claim 9 , wherein the drilling fluid further comprises at least one of micelles and aphrons.  
   
   
       14 . The system of  claim 9 , wherein the unconventional reservoir comprises a coal seam.  
   
   
       15 . The system of  claim 9 , wherein the unconventional reservoir comprises a shale.  
   
   
       16 . The system of  claim 9 , wherein the unconventional reservoir comprises at least one of naturally occurring fractures and cleats.  
   
   
       17 . The system of  claim 9 , wherein the drilling fluid comprises FLC 2000.  
   
   
       18 . The system of  claim 17 , wherein the drilling fluid further comprises starch.  
   
   
       19 . The system of  claim 9 , wherein the drilling fluid is adapted to form a filter cake to seal the well bore in the normally to sub-normally pressured formation during drilling.  
   
   
       20 . A method for drilling a well bore, comprising: 
 drilling a substantially horizontal well bore in a normally to sub-normally pressured formation, the normally to sub-normally pressured formation comprising an unconventional reservoir; and    drilling the well bore over-balanced with a drilling fluid comprising a density at least about the density of the cuttings produced by drilling the well bore.    
   
   
       21 . The method of  claim 20 , wherein the drilling fluid comprises a density greater than 9.5 pounds per gallon.  
   
   
       22 . The method of  claim 20 , wherein the drilling fluid comprises a density at or greater than 10 pounds per gallon.  
   
   
       23 . The method of  claim 20 , wherein the reservoir comprises a coal seam.  
   
   
       24 . The method of  claim 20 , wherein drilling the substantially horizontal well bore is performed at a rate that is greater than if the drilling fluid had a density substantially less than that of the cuttings produced by drilling the well bore.  
   
   
       25 . The method of  claim 20 , further comprising adjusting at least one of the flow rate and the properties of the drilling fluid based at least in part on a difference between an actual amount of cuttings recovery per unit time and an expected amount of cuttings recovery per unit time.  
   
   
       26 . The method of  claim 20 , wherein the unconventional reservoir comprises at least one of naturally occurring fractures and cleats.  
   
   
       27 . The method of  claim 20 , wherein the drilling fluid comprises FLC 2000.  
   
   
       28 . The method of  claim 1 , wherein the drilling fluid comprises FLC 2000.