Method for cleaning an oil field capillary tube

Abstract

A method and apparatus for removing deposits formed within a capillary tube that has been used to deliver treatment chemicals into a well. The method includes pumping a cleaning solution through the capillary tube coil, preferably after the capillary tube has been removed from the well and formed as a coil. The cleaning solution comprises at least 20 weight percent of a surfactant or dispersant, at least 5 weight percent of a coupling agent, and at least 10 weight percent solvent. A preferred surfactant or dispersant is selected from the group consisting of an alkyl-aryl sulphonate and a phosphate ester. An example of a cleaning solution includes dodecylbenzeneylsulphonic (DDBSA) acid, ethylene glycol monobutyl ether and toluene.

1 . A method for removing deposits formed within a capillary tube that has been used to deliver treatment chemicals into a well, comprising:
 pumping a cleaning solution through the capillary tube coil, wherein the cleaning solution comprises at least 20 weight percent of a surfactant or dispersant, at least 5 weight percent of a coupling agent, and at least 10 weight percent solvent.   
     
     
         2 . The method of  claim 1 , wherein the surfactant or dispersant is selected from the group consisting of an alkyl aryl sulphonate and a phosphate ester. 
     
     
         3 . The method of  claim 1 , wherein the surfactant or dispersant is a sulphonic acid. 
     
     
         4 . The method of  claim 3 , wherein the sulphonic acid is dodecylbenzenesulphonic acid. 
     
     
         5 . The method of  claim 4 , wherein the cleaning solution comprises between 30 and 70 percent of a surfactant. 
     
     
         6 . The method of  claim 4 , wherein the coupling agent is a non-ionic coupling agent such as ethylene glycol monobutyl ether. 
     
     
         7 . The method of  claim 4 , wherein the coupling agent is a glycol ether. 
     
     
         8 . The method of  claim 1 , wherein the solvent is toluene. 
     
     
         9 . The method of  claim 1 , further comprising:
 measuring the pressure drop and flow rate of the cleaning solution pumped through the capillary tube coil; and   continuing to pump the cleaning solution through the capillary tube coil until the capillary tube coil is determined to be clean.   
     
     
         10 . The method of  claim 9 , wherein the capillary tube coil is determined to be clean if the measured pressure drop and flow rate are within 15 percent of a pressure drop and flow rate measured on a new capillary tube coil having the same nominal length and diameter under the same nominal pressure and other conditions. 
     
     
         11 . The method of  claim 1 , further comprising:
 pumping the cleaning solution into the capillary tube string at a constant supply pressure;   measuring a flow rate of the cleaning solution being pumped through the capillary tube coil; and   continuing to pump the cleaning solution through the capillary tube coil until the measured flow rate is within 15 percent of a flow rate that would be expected through a new capillary tube coil having the same nominal length and diameter under the same nominal pressure and other conditions.   
     
     
         12 . The method of  claim 1 , further comprising:
 pumping the cleaning solution through the capillary tube coil at a constant flow rate;   measuring the pressure drop of the cleaning solution between the ends of the capillary tube coil; and   continuing to pump the cleaning solution through the capillary tube coil until the measured pressure drop is within 15 percent of a pressure drop that would be expected through a new capillary tube coil having the same nominal length and diameter under the same pressure and other conditions.   
     
     
         13 . The method of  claim 1 , further comprising:
 reversing the flow direction of cleaning solution being pumped through the capillary tube coil.   
     
     
         14 . The method of  claim 1 , further comprising:
 allowing the cleaning solution to remain in the capillary tube coil for a period greater than one hour before resuming the pumping.   
     
     
         15 . The method of  claim 1 , further comprising:
 changing the orientation of the capillary tube coil as the cleaning solution is pumped through the capillary tube coil.   
     
     
         16 . The method of  claim 1 , further comprising:
 heating the capillary tube coil or the cleaning solution so that the capillary tube coil or the cleaning solution have a temperature greater than ambient temperature as the cleaning solution is pumped through the capillary tube coil.   
     
     
         17 . The method of  claim 1 , wherein the capillary tube has a diameter between one-eighth inch and two inches. 
     
     
         18 . The method of  claim 1 , wherein the step of removing water from the tube includes passing an alcohol through the tube. 
     
     
         19 . The method of  claim 18 , wherein the alcohol is isopropyl alcohol. 
     
     
         20 . A method for removing deposits formed within a capillary tube that has been used to deliver treatment chemicals into a well, comprising:
 flowing a cleaning solution through the capillary tube and into the well, wherein the cleaning solution comprises a sulphonic acid.   
     
     
         21 . The method of  claim 20 , further comprising:
 producing hydrocarbons from the well while the cleaning solution flows through the capillary tube.