Measurements of rock parameters

Abstract

Methods and apparatus to measure physical parameters such as density and porosity of the rock matrix in a near wellbore area are provided. A borehole tool having a number of transducer elements in a transducer array is placed at an outermost surface of the borehole tool and is capable of emitting focused high frequency ultrasound beams into the rock matrix in the near wellbore area. The transducer array may be placed on the ribs or stabilizers of the borehole tool, and/or on a sleeve with a lower rotational speed, and may include a fronting material with similar acoustic impedance as the rock matrix. A method for measuring physical parameters of the rock matrix in a near wellbore area is also provided where a focused high frequency ultrasound beam is emitted into the rock matrix in the near wellbore area from one or more transducer arrays on a borehole tool.

1 . A borehole tool for performing measurements in a wellbore comprising a number of transducer elements in at least one transducer array placed at an outermost surface of the borehole tool for emitting at least one focused beam of high frequency ultrasound into the rock matrix in the near wellbore area when in use. 
   
   
       2 . A borehole tool according to  claim 1 , where said at least one transducer array is arranged for close contact with the formation. 
   
   
       3 . A borehole tool according to  claim 1 , where said at least one transducer array is placed on the ribs or stabilizers of the borehole tool. 
   
   
       4 . A borehole tool according to  claim 1 , where said at least one transducer array is placed approximately along the axis of length of the wellbore. 
   
   
       5 . A borehole tool according to  claim 1 , where said at least one transducer array is placed approximately along the periphery of the tool. 
   
   
       6 . A borehole tool according to  claim 1 ,where said at least one transducer array is placed on a sleeve of the borehole tool with a lower rotational speed. 
   
   
       7 . A borehole tool according to  claim 1 , where said at least one transducer array comprises a fronting material at least partly with similar acoustic impedance as the rock matrix. 
   
   
       8 . A borehole tool according to  claim 1 , where said at least one transducer array comprises a fronting material at least partly of a ceramic. 
   
   
       9 . A borehole tool according to  claim 1 , where said at least one transducer array comprises a fronting material at least partly of a crystalline structure based on CaCO 3 . 
   
   
       10 . A borehole tool according to  claim 1  further comprising memory and one or more processors for processing data measured by said at least one transducer array. 
   
   
       11 . A borehole tool according to  claim 1  further comprising a processor for influencing at least one of the functional parameters of the at least one transducer array selected from the group consisting of: frequency, amplitude and focal point position of the emitted focused beam. 
   
   
       12 . A method for measuring physical parameters of the rock matrix in a near wellbore area comprising the steps of
 from one or more transducer arrays comprising a number of transducer elements and placed on a borehole tool, emitting at least one focused beam of high frequency ultrasound into the rock matrix in the near wellbore area, the beam given a focal point position, frequency and amplitude,   measuring the amplitude of the reflected signal,   measuring the time of the largest amplitude in the reflected signal.   
   
   
       13 . A method according to  claim 12  further comprising determining the density of the rock matrix using the laws of reflection. 
   
   
       14 . A method according to  claim 12  further comprising generating 2D and/or 3D pictures of the formation in the near wellbore area. 
   
   
       15 . A method according to  claim 14  further comprising determining the porosity of the rock matrix in the near wellbore area from said pictures. 
   
   
       16 . A method according to  claim 12  further comprising emitting series of beams of different focal point positions. 
   
   
       17 . A method according to  claim 12  further comprising emitting series of beams of different frequencies. 
   
   
       18 . A method according to  claim 12  further comprising applying one or more correction filters to generate near perfect focus of the emitted beam. 
   
   
       19 . A method according to  claim 12  further comprising applying Fourier analysis on harmonic frequencies to determine the type of fluid in a porous volume in the near wellbore area.