Method and apparatus for reducing a skin effect in a downhole environment

Abstract

A method for reducing a skin effect in a downhole environment is provided, including the step of radiating vibrational waves at a wellbore wall such that the vibrational waves have at least one direction of greatest vibrational energy transfer directed toward the wall, thereby reducing the skin effect. An apparatus for reducing a skin effect in a downhole environment is also provided. The apparatus includes at least one vibrational wave source having at least one direction of greatest vibrational energy transfer, and a means for positioning the vibrational wave source proximate a wellbore wall.

1 . A method of reducing a skin effect in a downhole environment, comprising the step of radiating vibrational waves at a wellbore wall such that the vibrational waves have at least one direction of greatest vibrational energy transfer directed toward the wellbore wall, thereby reducing the skin effect.  
   
   
       2 . The method of  claim 1  wherein the radiating step comprises the step of positioning at least one vibrational wave source proximate the wellbore wall, wherein the at least one vibrational wave source has at least one direction of greatest energy transfer.  
   
   
       3 . The method of  claim 2  wherein the radiating step further comprises the steps of: 
 radiating vibrational waves from at least one vibrational wave source at the wellbore wall; and    flushing away any particles from the wellbore wall and from any structures or materials present at the wellbore wall with fluid flow.    
   
   
       4 . The method of  claim 3  wherein the step of radiating vibrational waves from at least one vibrational wave source and the step of flushing away any particles occur simultaneously.  
   
   
       5 . The method of  claim 2  wherein the radiating step further comprises the steps of: 
 radiating vibrational waves from a plurality of vibrational wave sources at the wellbore wall; and    flushing away any particles from the wellbore wall and from any structures or materials present at the wellbore wall with fluid flow.    
   
   
       6 . The method of  claim 5  wherein the step of radiating vibrational waves from a plurality of vibrational wave sources comprises the step of radiating vibrational waves in succession from each vibrational wave source.  
   
   
       7 . The method of  claim 5  wherein the step of radiating vibrational waves from a plurality of vibrational wave sources comprises the step of radiating vibrational waves simultaneously.  
   
   
       8 . The method of  claim 5  wherein the step of radiating vibrational waves from a plurality of vibrational wave sources comprises the step of radiating vibrational waves simultaneously and substantially continuously.  
   
   
       9 . The method of  claim 5  wherein the step of radiating vibrational waves from a plurality of vibrational wave sources comprises the step of radiating vibrational waves having at least two different frequencies from the plurality of vibrational wave sources.  
   
   
       10 . The method of  claim 5  wherein the step of radiating vibrational waves from a plurality of vibrational wave sources comprises selecting an order of activation and one or more periods of activation time for the plurality of vibrational wave sources to optimize usage of available power.  
   
   
       11 . The method of  claim 2  wherein the at least one vibrational wave source is an acoustic wave source having at least one direction of greatest energy transfer.  
   
   
       12 . The method of  claim 11  wherein the acoustic wave source is an oval-mode acoustic wave source having a plurality of directions of greatest energy transfer.  
   
   
       13 . The method of  claim 2  further comprising the step of placing the at least one vibrational wave source in the well.  
   
   
       14 . The method of  claim 2  further comprising the step of orienting the at least one vibrational wave source such that at least one direction of greatest vibrational energy transfer is directed toward the wellbore wall.  
   
   
       15 . The method of  claim 2  further comprising the step of maintaining a standoff distance between the vibrational wave source and the wellbore wall.  
   
   
       16 . The method of  claim 2  further comprising the step of optimizing reduction of the skin effect by creating a standing wave pattern between the vibrational wave source and the wellbore wall.  
   
   
       17 . The method of  claim 2  further comprising the steps of: 
 detecting accretions of particles between the wellbore wall and the at least one vibrational wave source;    moving the at least one vibrational wave source away from the wellbore wall when a threshold level of accreted particles between the wellbore wall and the at least one vibrational wave source is detected;    radiating vibrational waves at the accreted particles; and    repositioning the at least one vibrational wave source proximate the wellbore wall.    
   
   
       18 . The method of  claim 2  further comprising the steps of: 
 monitoring whether the vibrational wave source transfers sufficient vibrational energy to the wellbore wall to reduce the skin effect; and    repositioning the vibrational wave source to optimally decrease the skin effect.    
   
   
       19 . The method of  claim 2  further comprising the steps of: 
 monitoring whether the vibrational wave source transfers sufficient vibrational energy to the wellbore wall to reduce the skin effect; and    altering the vibrational waves radiated by the vibrational wave source to optimally decrease the skin effect.    
   
   
       20 . The method of  claim 2  further comprising the step of determining how much the skin effect in the downhole environment has been reduced.  
   
   
       21 . The method of  claim 20  wherein the determining step comprises the steps of: 
 measuring a speed of sound for the downhole environment; and    comparing the measured speed of sound to a control speed of sound for a previously-cleaned wellbore wall.    
   
   
       22 . The method of  claim 20  wherein the determining step comprises the steps of: 
 measuring a speed of sound for the downhole environment; and    comparing the measured speed of sound to a control speed of sound measured before the vibrational waves were radiated at the wellbore wall.    
   
   
       23 . The method of  claim 20  wherein the determining step comprises the steps of: 
 measuring an acoustic attenuation value for the downhole environment; and    comparing the acoustic attenuation value to a control acoustic attenuation value for a previously-cleaned wellbore wall.    
   
   
       24 . An apparatus for reducing a skin effect in a downhole environment, comprising: 
 at least one vibrational wave source having at least one direction of greatest vibrational energy transfer; and    a means for positioning the vibrational wave source proximate a wellbore wall.    
   
   
       25 . The apparatus of  claim 24  wherein the vibrational wave source comprises an oval-mode acoustic wave source  
   
   
       26 . The apparatus of  claim 24  further comprising a tool body, wherein the tool body houses a control for the vibrational wave source.  
   
   
       27 . The apparatus of  claim 24  further comprising a means for placing the vibrational wave source in a well.  
   
   
       28 . The apparatus of  claim 27  wherein the means for placing the vibrational wave source in the well comprises a wireline.  
   
   
       29 . The apparatus of  claim 27  wherein the means for placing the vibrational wave source in the well comprises coiled tubing.  
   
   
       30 . The apparatus of  claim 27  wherein the means for placing the vibrational wave source in the well comprises a well tractor.  
   
   
       31 . The apparatus of  claim 24  wherein the means for positioning the vibrational wave source proximate the wellbore wall is a decentralizer.  
   
   
       32 . The apparatus of  claim 31  wherein the decentralizer comprises a bowed spring member that pushes against a first side of the wellbore wall to position the vibrational wave source proximate a second, opposing side of the wellbore wall.  
   
   
       33 . The apparatus of  claim 31  further comprising a means for orienting the vibrational wave source such that at least one direction of greatest vibrational energy transfer is directed toward the wellbore wall.  
   
   
       34 . The apparatus of  claim 33  wherein the means for orienting the vibrational wave source comprises a rotator-resolver, wherein the rotator-resolver orients the vibrational wave source such that the at least one direction of greatest energy transfer is directed toward the wellbore wall.  
   
   
       35 . The apparatus of  claim 34  wherein the decentralizer comprises: 
 at least two articulated joints connecting the vibrational wave source to the rotator-resolver; and    at least one retractable arm, wherein the at least one retractable arm positions the vibrational wave source proximate the wellbore wall.    
   
   
       36 . The apparatus of  claim 34  wherein the decentralizer comprises: 
 a vibrational wave source pad attached to the rotator-resolver; and    at least one retractable arm, wherein the at least one retractable arm positions the vibrational wave source proximate the wellbore wall.    
   
   
       37 . The apparatus of  claim 24  further comprising at least one standoff contactor, wherein the at least one standoff contactor maintains a standoff distance between the vibrational wave source and the wellbore wall.  
   
   
       38 . The apparatus of  claim 37  wherein the at least one standoff contactor maintains a standoff distance chosen to enable creation of a standing wave pattern between the vibrational wave source and the wellbore wall.  
   
   
       39 . The apparatus of  claim 37  wherein the at least one standoff contactor includes contact points that contact the wellbore wall.  
   
   
       40 . The apparatus of  claim 39  further comprising an actuator that moves the vibrational wave source relative to the contact points to adjust the standoff distance.  
   
   
       41 . The apparatus of  claim 24  further comprising a means for detecting accretions of particles between the vibrational wave source and the wellbore wall.  
   
   
       42 . The apparatus of  claim 41  wherein the means for detecting accretions of particles comprises: 
 an accelerometer coupled to the vibrational wave source, wherein the accelerometer produces an electrical signal proportional to vibrations experienced by the vibrational wave source; and    a processing unit that monitors the electrical signal, wherein the processing unit can detect a signature vibration pattern indicating that particles have accreted.    
   
   
       43 . The apparatus of  claim 24  further comprising a means for monitoring energy transfer from the vibrational wave source to the wellbore wall.  
   
   
       44 . The apparatus of  claim 43  wherein the means for monitoring energy transfer comprises: 
 a hydrophone suitable for use in downhole environments, wherein the hydrophone converts vibrational energy traveling through a fluid present near the wellbore wall into an electrical signal; and    a processing unit, which monitors the electrical signal.    
   
   
       45 . The apparatus of  claim 43  wherein the means for monitoring energy transfer comprises: 
 an accelerometer connected to the vibrational wave source, wherein the accelerometer produces an electrical signal proportional to vibrations experienced by the vibrational wave source; and    a processing unit, which monitors the electrical signal.    
   
   
       46 . The apparatus of  claim 43  wherein the means for monitoring energy transfer from the vibrational wave source to the wellbore wall comprises: 
 an accelerometer that produces an electrical signal proportional to vibrations experienced by the wellbore wall, wherein the accelerometer is acoustically isolated from the vibrational wave source; and    a processing unit that measures the electrical signal.    
   
   
       47 . The apparatus of  claim 24  wherein the apparatus for reducing a skin effect in a downhole environment comprises a plurality of vibrational wave sources.  
   
   
       48 . The apparatus of  claim 47  wherein the plurality of vibrational wave sources are displaced axially with an axial gap between each vibrational wave source.  
   
   
       49 . The apparatus of  claim 47  wherein the plurality of vibrational wave sources are displaced circumferentially with a circumferential gap between each vibrational wave source.  
   
   
       50 . The apparatus of  claim 24  further comprising a means for determining how much the skin effect in the downhole environment has been reduced.  
   
   
       51 . The apparatus of  claim 50  wherein the means for determining how much the skin effect in the downhole environment has been reduced comprises: 
 an accelerometer contacting the wellbore wall, wherein the accelerometer is acoustically isolated from the vibrational wave source; and    a processing unit coupled to the accelerometer.    
   
   
       52 . An apparatus for reducing a skin effect in a downhole environment, comprising: 
 a vibrational wave source having at least one direction of greatest vibrational energy transfer;    at least one standoff contactor, wherein the at least one standoff contactor maintains a standoff distance between the vibrational wave source and a wellbore wall;    a decentralizer, wherein the decentralizer positions the vibrational wave source proximate a wellbore wall; and    a wireline, wherein the wireline may be used to place the vibrational wave source in the well.    
   
   
       53 . The apparatus of  claim 52  further comprising a hydrophone.  
   
   
       54 . The apparatus of  claim 52  further comprising an accelerometer.  
   
   
       55 . An apparatus for reducing a skin effect in a downhole environment, comprising: 
 a vibrational wave source having at least one direction of greatest vibrational energy transfer;    at least one standoff contactor, wherein the at least one standoff contactor maintains a standoff distance between the vibrational wave source and a wellbore wall;    a rotator-resolver, wherein the rotator-resolver orients the vibrational wave source such that the at least one direction of greatest vibrational energy transfer is directed toward the wellbore wall;    at least two articulated joints connecting the vibrational wave source to the rotator-resolver; and    at least one retractable arm, wherein the at least one retractable arm positions the vibrational wave source proximate the wellbore wall.    
   
   
       56 . The apparatus of  claim 55  further comprising a hydrophone.  
   
   
       57 . The apparatus of  claim 55  further comprising an accelerometer.  
   
   
       58 . An apparatus for reducing a skin effect in a downhole environment, comprising: 
 a vibrational wave source having at least one direction of greatest vibrational energy transfer;    at least one standoff contactor, wherein the at least one standoff contactor maintains a standoff distance between the vibrational wave source and a wellbore wall;    a rotator-resolver, wherein the rotator-resolver orients the vibrational wave source such that the at least one direction of greatest vibrational energy transfer is directed toward the wellbore wall;    a vibrational wave source pad attached to the rotator-resolver; and    at least one retractable arm, wherein the at least one retractable arm positions the vibrational wave source proximate the wellbore wall.    
   
   
       59 . The apparatus of  claim 58  further comprising a hydrophone.  
   
   
       60 . The apparatus of  claim 58  further comprising an accelerometer.  
   
   
       61 . An apparatus for reducing a skin effect in a downhole environment, comprising: 
 a plurality of vibrational wave sources wherein each vibrational wave source has at least one direction of greatest vibrational energy transfer;    at least one standoff contactor, wherein the at least one standoff contactor maintains a standoff distance between the plurality of vibrational wave sources and a wellbore wall;    a rotator-resolver, wherein the rotator-resolver orients the plurality of vibrational wave sources such that the at least one direction of greatest vibrational energy transfer is directed toward the wellbore wall;    a vibrational wave source pad attached to the rotator-resolver; and    at least one retractable arm, wherein the at least one retractable arm positions the plurality of vibrational wave sources proximate the wellbore wall.    
   
   
       62 . The apparatus of  claim 61  further comprising a hydrophone.  
   
   
       63 . The apparatus of  claim 61  further comprising an accelerometer.