Drilling fluid, apparatus, and method

Abstract

Disclosed are drilling fluids suitable for use in connection with oil well drilling. The drilling fluids of the invention include in one embodiment a liquid base, an alkyl glucoside, such as methyl glucoside, and a borehole stability promoter that includes a maltodextrin, a carboxyalkyl starch, a hemicellulose-containing material, or a mixture of the foregoing. In another embodiment, the drilling fluid includes a liquid base and molasses solids, preferably in combination with an alkyl glucoside and more preferably in further combination with one of the aforementioned borehole stability promoters. In another embodiment, the drilling fluid includes sorbitol, preferably in conjunction with a borehole stability promoter. The drilling fluids of the invention surprisingly have a reduced tendency to swell shale as compared with known drilling fluids. Also disclosed are a drilling apparatus and process. The drilling apparatus includes a drill string, which may be conventional, that is fluidically coupled to a source of drilling fluid, the source of drilling fluid including the drilling fluid of the invention. The process of the invention includes the step of circulating the drilling fluid of the invention through a drill string during borehole drilling.

What is claimed is:  
     
         1 . A drilling fluid comprising: 
 a liquid base selected from the group consisting of water, water-miscible liquids, and mixtures thereof;    sorbitol, said sorbitol being present in at least an amount effective to inhibit shale swelling; and    a borehole stability promoter selected from the group consisting of a maltodextrin, a carboxyalkyl starch, hemicellulose, and mixtures thereof, said borehole stability promoter being present in at least an amount effective to inhibit shale swelling.    
     
     
         2 . A composition according to  claim 1 , wherein said liquid base comprises water.  
     
     
         3 . A composition according to  claim 1 , wherein said liquid base includes polyglycerine.  
     
     
         4 . A composition according to  claim 3 , wherein said liquid base includes polyglycerine and water.  
     
     
         5 . A composition according to  claim 1 , said borehole stability promoter comprising hemicellulose.  
     
     
         6 . A composition according to  claim 5 , wherein hemicellulose is present in said drilling fluid in an amount ranging from about 0.002 to about 0.2 lbs./gallon by dry basis weight.  
     
     
         7 . A composition according to  claim 5 , wherein said hemicellulose comprises a hemicellulose fraction obtained via alkaline hydrolysis of corn hulls.  
     
     
         8 . A composition according to  claim 1 , said borehole stability promoter comprising a maltodextrin.  
     
     
         9 . A composition according to  claim 8 , wherein said maltodextrin is present in an amount ranging from about 0.002 to about 0.2 lbs./gallon by dry basis weight.  
     
     
         10 . A composition according to  claim 1 , said borehole stability promoter comprising a mixture of maltodextrin and hemicellulose.  
     
     
         11 . A composition according to  claim 10 , wherein said borehole stability promoter is present in a total amount ranging from about 0.002 to about 0.2 lbs./gallon by dry basis weight.  
     
     
         12 . A composition according to  claim 1 , said borehole stability promoter comprising a carboxymethyl starch.  
     
     
         13 . A composition according to  claim 12 , said carboxymethyl starch having a DS of about 0.2.  
     
     
         14 . A composition according to  claim 12 , said borehole stability promoter comprising a mixture of carboxymethyl starch and maltodextrin.  
     
     
         15 . A composition according to  claim 12 , said borehole stability promoter comprising a mixture of carboxymethyl starch and hemicellulose  
     
     
         16 . A drilling apparatus comprising: 
 a drill string;    at least one pump for circulating a drilling fluid through at least a portion of said drill string, said pump being fluidically connected to a source of drilling fluid, said drilling fluid comprising:    a liquid base selected from the group consisting of water, water-miscible liquids, and mixtures thereof;    sorbitol; and    a borehole stability promoter selected from the group consisting of a maltodextrin, a carboxyalkyl starch, hemicellulose, and mixtures thereof, said borehole stability promoter being present in at least an amount effective to inhibit shale swelling.    
     
     
         17 . A drilling process comprising the steps of: 
 cutting a borehole into the earth using a drill string; and    circulating a drilling fluid through at least a portion of said drill string, said drilling fluid comprising:    a liquid base selected from the group consisting of water, water-miscible liquids, and mixtures thereof;    sorbitol; and    a borehole stability promoter selected from the group consisting of a maltodextrin, a carboxyalkyl starch, hemicellulose, and mixtures thereof, said borehole stability promoter being present in at least an amount effective to inhibit shale swelling.    
     
     
         18 . A composition comprising: 
 sorbitol; and    a borehole stability promoter, said borehole stability promoter being selected from the group consisting of a maltodextrin, a carboxyalkyl starch, hemicellulose, and mixtures thereof, said borehole stability promoter being present in an amount ranging from about 0.1% to about 5% by dry basis weight of said alkyl glucoside.    
     
     
         19 . A composition comprising: 
 sorbitol; and    an alkyl glycoside, said alkyl glycoside being selected from among the α-form, the β-form, and mixtures thereof, said alkyl glycoside selected from among the methyl, ethyl, propyl, and butyl glucosides of glucose, maltose, maltotriose, and maltotetraose.    
     
     
         20 . A composition comprising: 
 sorbitol; and    molasses solids, said molasses solids being present in at least an amount effective to inhibit shale swelling.