High stability, high lubricity, low toxicity, high biodegradability drilling fluid

Abstract

A drilling fluid including at least about 2 wt % olefin, at least about 5 wt % n-paraffins, and at least about 2 wt % isoparaffins, wherein the isoparaffins are substantially wholly terminal monomethyl branched is provided. A method for producing the drilling fluid, and a method for drilling a borehole using the drilling fluid are disclosed.

What is claimed is:  
     
         1 . A base fluid comprising: 
 at least about 5 wt % olefins;    at least about 5 wt % n-paraffins; and    between about 2 and 50 wt % branched paraffins wherein substantially all of the branch groups are monomethyl and wherein the ratio of terminal monomethyl branching to internal monomethyl branching is at least about 1:1.5.    
     
     
         2 . The base fluid of  claim 1  wherein the ratio of terminal monomethyl branching to internal monomethyl branching is at least about 1:1.  
     
     
         3 . The base fluid of  claim 1  wherein the n-paraffins are present in an amount of at least about 20 wt % and wherein the ratio of terminal monomethyl branching to internal monomethyl branching is at least about 1.5:1.  
     
     
         4 . The base fluid of  claim 1  wherein the n-paraffins are present in an amount of at least about 40 wt % and wherein the ratio of terminal monomethyl branching to internal monomethyl is at least about 2:1.  
     
     
         5 . The base fluid of  claim 1  wherein the base fluid is a product of a Fischer-Tropsch reaction.  
     
     
         6 . The base fluid of  claim 5  wherein the Fischer-Tropsch reaction incorporates feed syngas having 10-60% N 2 .  
     
     
         7 . A drilling fluid comprising: 
 the base fluid of  claim 1 .    
     
     
         8 . The drilling fluid of  claim 7  further comprising: 
 at least one additive selected from the group of surfactants, viscosifiers, weighting agents, fluid loss control agents and proppants.  
 
     
     
         9 . A drilling fluid comprising: 
 from about 2 to about 90 wt % olefins;    from about 2 to about 50 wt % isoparaffins; wherein the isoparaffins are substantially terminal monomethyl branched.    from about 5 to about 90 wt % n-paraffins; and    from about 0 to about 10 wt % oxygenates.    
     
     
         10 . The drilling fluid of  claim 9  wherein the olefins are present in an amount of from about 7 to about 10 wt %.  
     
     
         11 . The drilling fluid of  claim 9  wherein the isoparaffins are present in an amount of from about 3 to about 15 wt %.  
     
     
         12 . The drilling fluid of  claim 9  wherein the n-paraffins are present in an amount of from about 65 to about 90 wt %.  
     
     
         13 . The drilling fluid of  claim 9  wherein the oxygenates are present in an amount of from about 0 to about 5 wt %.  
     
     
         14 . The drilling fluid of  claim 9  wherein the base fluid is a product of Fischer-Tropsch reaction on a synthesis gas.  
     
     
         15 . The drilling fluid of  claim 14  wherein the Fischer-Tropsch reaction incorporates feed syngas having 10-60% N 2 .  
     
     
         16 . The drilling fluid of clam 14 wherein the synthesis gas is produced by autothermal reformation.  
     
     
         17 . The drilling fluid of  claim 16  wherein the autothermal reformation occurs in the presence of air.  
     
     
         18 . The drilling fluid of  claim 16  wherein the autothermal reformation occurs in the presence of 10-60% N 2 .  
     
     
         19 . The drilling fluid of  claim 9  further comprising: 
 at least one additive selected from the group of surfactants, viscosifiers, weighting agents, fluid loss control agents and proppants.  
 
     
     
         20 . The drilling fluid of  claim 9  wherein the olefins are: 
 from about 7 to about 10 wt %;  
 the isoparaffins are from about 2 to about 15 wt %; wherein the isoparaffins are substantially terminal monomethyl branched.  
 The n-paraffins are from about 65 to about 90 wt %; and  
 the oxygenates are from about 0 to about 5 wt %.  
 
     
     
         21 . The drilling fluid of  claim 20  wherein the drilling fluid is a product of a Fischer-Tropsch reaction.  
     
     
         22 . The drilling fluid of  claim 20  further comprising: 
 at least one additive selected from the group of surfactants, viscosifiers, weighting agents, fluid loss control agents and proppants.  
 
     
     
         23 . The drilling fluid of  claim 20  wherein the base fluid comprises from about 25 to about 85 volume % of the drilling fluid.  
     
     
         24 . The drilling fluid of  claim 23  wherein the base fluid comprises from about 25 to about 85 volume % of the drilling fluid.  
     
     
         25 . The drilling fluid of  claim 22  wherein the Fischer-Tropsch reaction incorporates feed syngas having 10-60% N 2 .  
     
     
         26 . The drilling fluid of  claim 23  wherein the feed syngas is produced by autothermal reformation in the presence of air.  
     
     
         27 . A process for producing a drilling fluid comprising the steps of: 
 (a) producing a light Fischer-Tropsch liquid;    (b) distilling the light Fischer-Tropsch liquid to obtain a C 13 -C 20+  product having C 13 -C 20+  hydrocarbons and oxygenates.    (c) dehydrating all or a part of the alcohols in the C 13 -C 20+  product by passing the C 13 -C 20+  product over an activated alumina catalyst to produce a dehydrated product;    (d) recovering the dehydrated product; and    (e) separating the aqueous and organic phases of the dehydrated product.    
     
     
         28 . The process of  claim 27  further comprising the step of: 
 (f) adding one or more additive selected from the group of surfactants, viscosifiers, weighting agents, fluid loss control agents and proppants to the organic phase of the dehydrated product.  
 
     
     
         29 . The process of  claim 27  further comprising the step of (b 1 ) vaporizing the C 13 -C 20+  product before step (c) and after step (b).  
     
     
         30 . The process of  claim 29  wherein the dehydrated product from step (c) is in the gaseous state and step (d) further includes condensing the dehydrated product.  
     
     
         31 . The process of  claim 30  wherein the heat from condensing the dehydrated product is recycled to at least partially vaporize the C 13 -C 20+  product in step (b 1 ).  
     
     
         32 . The process of  claim 27  wherein the light Fischer-Tropsch liquid is produced from a feed syngas having 10-60% N 2 .  
     
     
         33 . The process of  claim 27  wherein the feed syngas is produced by autothermal reformation in the presence of air.  
     
     
         34 . The process of  claim 27  wherein a C 14 -C 18  product is obtained in step (b) and dehydrated in step (c).  
     
     
         35 . A method of drilling a borehole in a subterranean formation comprising the steps of: 
 (a) rotating a drill bit at the bottom of the borehole;    (b) introducing a drilling fluid into the borehole wherein the drilling fluid comprises a base fluid comprising: 
 from about 5 to about 90 wt % olefins;  
 from about 2 to about 50 wt % isoparaffins; wherein the isoparaffins are substantially terminal monomethyl branched;  
 from about 5 to about 90 wt % n-paraffins; and  
 from about 0 to about 10 wt % oxygenates.  
   
     
     
         36 . The process of  claim 35  wherein the drilling fluid comprises: 
 from about 7 to about 10 wt % olefins;  
 from about 2 to about 15 wt % isoparaffins; wherein the isoparaffins are substantially terminal monomethyl branched;  
 from about 65 to about 90 wt % n-paraffins; and  
 from about 0 to about 5 wt % oxygenates.  
 
     
     
         37 . The process of  claim 35  wherein the base fluid is derived from a Fischer-Tropsch reaction.  
     
     
         38 . The process of  claim 37  wherein the Fischer-Tropsch reaction incorporates feed syngas having 10-60% N 2 .  
     
     
         39 . The process of  claim 37  wherein the feed syngas is produced by autothermal reformation in the presence of air.