Washing oily solids

Abstract

Oil residues are removed from contaminated solids, in particular from cuttings produced from drilling a borehole using an oil-based drilling fluid, by contacting the solids with a washing fluid which comprises carbon dioxide and cosolvent under conditions at which carbon dioxide is a supercritical fluid and the cosolvent is in solution in the supercritical carbon dioxide and then separating washed solids from the washing fluid; wherein the washing fluid comprises at least 5% by volume of cosolvent which is one or more organic compounds with a Hildebrand solubility parameter in a range from 16 to 21 MPa 1/2 . The washing process may be applied to drilling cuttings produced offshore.

1 . A method for removing oil residues from solids contaminated therewith comprising
 contacting the solids with a washing fluid which comprises carbon dioxide and cosolvent under conditions at which carbon dioxide is a supercritical fluid and the cosolvent is in solution in the supercritical carbon dioxide and separating washed solids from the washing fluid;   wherein the washing fluid comprises at least 5% by volume of co-solvent which is one or more organic compounds with a Hildebrand solubility parameter in a range from 16 to 21 MPa 1/2 .   
     
     
         2 . A method for removing oil residues from solids contaminated therewith comprising
 contacting the solids with a washing fluid which comprises carbon dioxide and cosolvent under conditions at which carbon dioxide is a supercritical fluid and the cosolvent is in solution in the supercritical carbon dioxide and separating washed solids from the washing fluid;   
       wherein the co-solvent comprises at least 5% by volume of co-solvent which is one or more aliphatic organic compounds, each of which includes at least one of the following:
 a cycloaliphatic ring 
 an olefinic unsaturation 
 an ester group 
 an ether group. 
 
     
     
         3 . A method according to  claim 1  further comprising separating washed solids from used washing fluid, subsequently altering the temperature and/or pressure of the separated used washing fluid so that the carbon dioxide therein becomes gaseous and then separating the gaseous carbon dioxide from liquid or solid residue. 
     
     
         4 . A method according to  claim 1  preceded by drilling a borehole within an oil reservoir, while circulating an oil-based drilling fluid from the surface to a downhole cutting tool and then back to the surface, and separating the cuttings from the drilling fluid returned to the surface, prior to washing the separated cuttings. 
     
     
         5 . A method according to  claim 1  preceded by excavating an oil sand and extracting oil therefrom prior to washing the inorganic solids. 
     
     
         6 . A method according to  claim 1  wherein the co-solvent consists of carbon, hydrogen and oxygen atoms only. 
     
     
         7 . A method according to  claim 1  wherein the co-solvent comprises at least one aliphatic compound containing 5 to 20 carbon atoms and having at least one cycloaliphatic ring and/or at least one olefinic unsaturation. 
     
     
         8 . A method according to  claim 1  wherein the co-solvent comprises at least one aliphatic ester containing at least one a saturated or unsaturated aliphatic chain of 6 to 22 carbon atoms. 
     
     
         9 . A method according to  claim 8  wherein the said co-solvent comprises at least one ester of the general formula
   R 1 —COO—R 2  
 
 where R 1  and R 2  are straight or branched aliphatic hydrocarbon chains optionally including olefinic unsaturation and having a length of 1 to 22 carbon atoms and where R 1  and R 2  together contain 12 to 44 carbon atoms. 
 
     
     
         10 . A method according to  claim 9  wherein R 1  comprises a straight or branched aliphatic hydrocarbon chain optionally including olefinic unsaturation and having a length of 11 to 18 carbon atoms and where R 2  comprises methyl, ethyl, propyl and/or butyl. 
     
     
         11 . A method according to  claim 8  wherein the said co-solvent comprises diesters of formula
   R 1 —Z 1 —R 3 —Z 2 —R 2  
 
 where Z 1  and Z 2  each represent COO or OCO, R 1 , R 2  and R 3  are straight or branched aliphatic hydrocarbon chains optionally including olefinic unsaturation and each having a length of 1 to 22 carbon atoms, and R 1 , R 2  and R 3  together contain from 12 to 66 carbon atoms. 
 
     
     
         12 . A method according to  claim 8  wherein the said co-solvent comprises triglycerides of formula
   R 1 COO—CH 2 —CH(OCOR 4) —CH 2 —OCOR 2  
 
 where R 1 , R 2  and R 4  are straight or branched aliphatic hydrocarbon chains optionally including olefinic unsaturation and each having a length of 1 to 22 carbon atoms, and R 1 , R 2  and R 4  together contain from 12 to 66 carbon atoms. 
 
     
     
         13 . A method according to  claim 12  wherein R 1 , R 2  and R 4  each contain from 11 to 21 carbon atoms. 
     
     
         14 . A method according to  claim 1  wherein the co solvent has Hansen solubility parameters in the ranges:
 δ d  14.5-19.6 MPa 1/2    
 δ p  0-8.2 MPa 1/2    
 δ h  0-6.8 MPa 1/2 . 
 
     
     
         15 . A method according to  claim 1  wherein contacting the solids with the washing fluid is carried out with conditions of temperature and pressure, and with an amount and composition of co-solvent such that the Hildebrand solubility parameter of the washing fluid is at least 16 MPa 1/2