Viscosity control and filtration of well fluids

Abstract

Circulating completion, workover and drilling fluids used in hydrocarbon recovery are filtered after monitoring for viscosity, which frequently causes plugging of filters. A viscometer generates a signal representative of viscosity in the fluid; the signal is used by a programmable controller to divert viscous fluid from the filter, or to take other action to prevent damage to the filter. The viscometer can be used in various positions in the system. Fluids deemed too viscous for the filter can be sent to a viscosity-reducing device, which may be a heating, shear-thinning, or cavitation device, to reduce its viscosity, enabling the fluid to pass through a filter without fouling. After filtering and a return to a lower temperature, the fluid may be treated if necessary to become viscous again for a useful purpose. A temperature monitor can be deployed on the fluid emerging or downstream from the cavitation or other device to assist in correlating temperatures to viscosities of various fluids. The cavitation device can also be used to increase the concentration of a dilute polymer-containing fluid to a usefully viscous value.

1 - 20 . (canceled) 
     
     
         21 . Method of treating a used well fluid containing a viscosity-enhancing agent, comprising passing said fluid through a filter capable of shear-thinning said fluid, thereby reducing its viscosity while also removing solids from said fluid. 
     
     
         22 . Method of  claim 21  followed by reusing said fluid in a well. 
     
     
         23 . Method of  claim 21  wherein said viscosity-enhancing agent is a xanthan derivative. 
     
     
         24 . Method of  claim 23  followed by adjusting the hydrolysis of said xanthan derivative after it passes through said filter, whereby the viscosity of said fluid is enhanced. 
     
     
         25 . Method of  claim 24  followed by reusing said fluid in a well. 
     
     
         26 . Method of  claim 21  wherein said viscosity-enhancing agent is a guar or guar derivative. 
     
     
         27 . Method of  claim 26  wherein said guar or guar derivative is crosslinked. 
     
     
         28 . Method of  claim 21  including adding viscosity-enhancing agent to said fluid after said fluid passes through said filter. 
     
     
         29 . Method of  claim 21  wherein said filter comprises sintered particles. 
     
     
         30 . Method of treating a used well fluid deemed too viscous to pass through a filter without a risk of plugging said filter because of its viscosity, comprising heating said used well fluid, thereby reducing its viscosity, and passing said fluid having a reduced viscosity through said filter. 
     
     
         31 . Method of  claim 30  wherein said heating is performed at least partly by passing said fluid between two surfaces, at least one of which is moving relative to the other. 
     
     
         32 . Method of  claim 30  followed by passing said filtered fluid through a heat exchanger to preheat said used well fluid, followed by treating said preheated used well fluid by the method of  claim 30 . 
     
     
         33 . Method of treating a used well fluid deemed too viscous to pass through a filter without a risk of plugging said filter because of its viscosity, comprising shear-thinning said used well fluid, thereby reducing its viscosity, and passing said fluid having a reduced viscosity through said filter. 
     
     
         34 . Method of  claim 33  wherein said shear-thinning is performed at least partly by passing said fluid between two surfaces, at least one of which is moving relative to the other. 
     
     
         35 . Method of  claim 33  followed by adding viscosity-enhancing agent to said filtered, reduced viscosity fluid to increase its viscosity for reuse in a well. 
     
     
         36 . Method of processing a dirty well fluid comprising optionally measuring the viscosity of said well fluid, passing said well fluid through a cavitation device if said fluid is deemed too viscous to be filtered, thereby reducing the viscosity of said fluid, and filtering the fluid thereby obtained. 
     
     
         37 . Method of  claim 36  wherein said reduced viscosity is obtained primarily by heating in said cavitation device. 
     
     
         38 . Method of  claim 36  wherein said reduced viscosity is obtained primarily by shear-thinning in said cavitation device. 
     
     
         39 . Method of  claim 36  including recycling at least a portion of said reduced viscosity fluid through said cavitation device. 
     
     
         40 . Method of  claim 36  including substantially continuously controlling the operation of said cavitation device to maintain a viscosity in said fluid emerging from said cavitation device such that said fluid is not deemed too viscous to be filtered. 
     
     
         41 . Method of  claim 40  including monitoring the temperature of said fluid emerging from said cavitation device and wherein the viscosity of said fluid is maintained by controlling the operation of said cavitation device to control the temperature of said fluid emerging from said cavitation device. 
     
     
         42 - 57 . (canceled)