Electromagnetic Probe

Abstract

An electromagnetic probe 1 measures the electromagnetic properties of a sub surface formation GF in a limited zone surrounding a well-bore hole WBH. The well-bore hole is filled with a well-bore fluid DM. The probe comprises a pad 2 having a first face defining a first area arranged to be positioned in contact with a well-bore wall WBW. The probe 1 further comprises: at least two transmitting antennas 4 A, 4 B defining a central point CP between them, each antenna being spaced from a distance do from the central point, and at least a first 5 A, 5 B and a second set 5 C, 5 D of receiving antennas, each set comprising a first receiving antenna 5 A; 5 C and a second receiving antenna 5 B; 5 D, the first receiving antenna being positioned on one side of the transmitting antennas and the second receiving antenna being positioned on other side of the transmitting antennas so that each set encompass the transmitting antennas 4 A, 4 B.

1 . An electromagnetic probe ( 1 ) for measuring the electromagnetic properties of a subsurface formation (GF) in a limited zone surrounding a well-bore hole (WBH), the well-bore hole being filled with a well-bore fluid (DM), the probe comprises:
 a pad ( 2 ) having a first face defining a first area arranged to be positioned in contact with a well-bore wall (WBW),   
     wherein the probe ( 1 ) further comprises:
 at least two transmitting antennas ( 4 A,  4 B) defining a central point (CP) between them, each antenna being spaced from a distance (d 0 ) from the central point, 
 at least a first ( 5 A,  5 B) and a second set ( 5 C,  5 D) of receiving antennas, each set comprising a first receiving antenna ( 5 A;  5 C) and a second receiving antenna ( 5 B;  5 D), the first receiving antenna being positioned on one side of the transmitting antennas and the second receiving antenna being positioned on other side of the transmitting antennas so that each set encompass the transmitting antennas ( 4 A,  4 B). 
 the first set of receiving antennas ( 5 A,  5 B) is spaced from a first distance (d 1 ) from the central point (CP), the second set of receiving antennas ( 5 C,  5 D) is spaced from a second distance (d 2 ) from the central point (CP), the second distance (d 2 ) being greater than the first distance (d 1 ), 
 the transmitting ( 4 A,  4 B) and receiving ( 5 A,  5 B,  5 C,  5 D) antennas are positioned along a line (AA′) in the first face, and 
 an electronic arrangement ( 3 ) comprising at least one transmitter module ( 3 ′) arranged to excite the transmitting antennas ( 4 A,  4 B) by applying an excitation signal according to at least a first and a second frequency, and at least one receiver module ( 3 ″) coupled to at least one receiving antenna ( 5 A;  5 B;  5 C;  5 D) and arranged to determine an attenuation and a phase shift of each reception signal provided by each receiving antenna ( 5 A;  5 B;  5 C;  5 D) relatively to the excitation signal. 
 
   
   
       2 . A probe for measuring the electromagnetic properties of a subsurface formation according to  claim 1  wherein the transmitting antennas ( 4 A,  4 B) are sensibly identical, each antenna ( 4 A;  4 B) comprising two perpendicular dipoles ( 44 ,  46 ) embedded in a cavity ( 42 ) and arranged to transmit electromagnetic energy according to a broadside mode (BSM) and an endfire mode (EFM). 
   
   
       3 . A probe for measuring the electromagnetic properties of a subsurface formation according to  claim 1 , wherein the receiving antennas ( 5 A,  5 B,  5 C,  5 D) are sensibly identical, each antenna ( 5 A;  5 B;  5 C;  5 D) comprising two perpendicular dipoles ( 44 ,  46 ) embedded in a cavity ( 42 ) and arranged to receive electromagnetic energy according to a broadside mode (BSM) and an endfire mode (EFM). 
   
   
       4 . A probe for measuring the electromagnetic properties of a subsurface formation according to  claims 1 , wherein the probe further comprises a first open-ended coaxial wire ( 6 A) arranged in the first side and positioned sensibly perpendicularly to the first area between a transmitting antenna ( 4 A) and a receiving antenna ( 5 B). 
   
   
       5 . A probe for measuring the electromagnetic properties of a subsurface formation according to  claim 4 , wherein the electronic arrangement ( 3 ) further comprises a first open ended coaxial wire controlling circuit ( 3 ′″), said circuit comprising:
 a transmitting module (T 3 ′″) for sending a high-frequency input signal (IS) into the first open ended coaxial wire ( 6 A), and   a receiving module (R 3 ′″) for determining a first reflection coefficient based on a high frequency output signal (OS) reflected by the first open-ended coaxial wire and a propagation coefficient based on a high frequency output signal (OS) received by tile first open-ended coaxial Wire following an excitation of the transmitting antennas ( 4 A,  4 B).   
   
   
       6 . A probe for measuring the electromagnetic properties of a subsurface formation according to  claim 1 , wherein the pad ( 2 ) further comprises a second face arranged to be in contact with the well-bore fluid (DM), and the probe ( 1 ) further comprises a second open-ended coaxial wire ( 6 B) arranged in the second face. 
   
   
       7 . A probe for measuring the electromagnetic properties of a subsurface formation according to  claim 6 , wherein the electronic arrangement further comprises a second open ended coaxial wire controlling circuit ( 3 ′″), said circuit comprising:
 a transmitting module (T 3 ″′) for sending a high-frequency input signal (IS) into the second open ended coaxial wire ( 6 B), and   a receiving module (R 3 ″′) for determining a second reflection coefficient based on a high frequency output signal (OS) reflected by the second open-ended coaxial wire ( 6 B).   
   
   
       8 . A probe for measuring the electromagnetic properties of a subsurface formation according to  claim 1 , wherein the electronic arrangement ( 3 ) has a homodyne architecture comprising a variable high frequency source (LOS) providing a high frequency signal to:
 the at least one transmitter module ( 3 ′) arranged to excite the transmitting antennas ( 4 A,  4 B),   the at least one receiver module ( 3 ″) coupled to the at least one receiving antenna ( 5 A;  5 B;  5 C;  5 D), and   the transmitting, module (T 3 ″′) and tile receiving module (R 3 ″′) of the first and second open ended coaxial wire controlling circuits ( 3 ′″).   
   
   
       9 . A logging tool (TL) arranged to be deployed in a well-bore hole (WBH), wherein the logging, tool (TL) comprises a probe ( 1 ) according to  claim 1  and a positioning arrangement (AR) for positioning the probe in contact with a well-bore wall (WBW) at a determined depth in the well bore hole (WBH). 
   
   
       10 . A method for measuring the electromagnetic properties of a subsurface formation (GF) in a limited zone surrounding a well-bore hole (WBH), the well-bore hole being filled with a well-bore fluid (DM), the method comprises the steps of:
 a) positioning a probe ( 1 ) for measuring the electromagnetic properties of the subsurface formation in contact with a well-bore wall (WBW) at a first depth, the probe comprising at least two transmitting antenna ( 4 A,  4 B) and at least a first ( 5 A,  5 B) and a second ( 5 C,  5 D) set of receiving antennas,   
     wherein the method further comprises the steps of:
 b) transmitting an excitation electromagnetic energy around a central point (CP) into the limited zone by energizing at first transmitting antenna ( 4 A,  4 B) with an excitation signal (ES) according to a broadside mode (BSM) and according to a first frequency, 
 c) measuring a broadside/broadside reception signal (RS) at the receiving antennas ( 5 A.  5 B,  5 C,  5 D) according to a broadside mode (BSM) and measuring simultaneously a broadside/endfire reception signal (RS) at the receiving antennas ( 5 A,  5 B,  5 C,  5 D) according to an endfire mode (EFM), at least at a first distance (d 1 ) and at a second distance (d 2 ) from the central point (CP), 
 d) repeating the transmitting step b) and the measuring steps c) by energizing a second transmitting antenna ( 4 B;  4 A) with an excitation signal (ES) according to a broadside mode (BSM) and according to a first frequency, 
 e) transmitting an excitation electromagnetic energy around a central point (CP) into the limited zone by energizing the first transmitting antenna ( 4 A;  4 B) with an excitation signal (ES) according to an endfire mode (EFM) and according to the first frequency. 
 f) measuring an endfire/broadside reception signal (RS) at the receiving antennas ( 5 A,  5 B,  5 C  5 D) according to the broadside mode (BSM) and measuring simultaneously a broadside/endfire reception signal at the receiving antennas ( 5 A,  5 B,  5 C  5 D) according to the endfire mode (EFM) at least at the first distance (d 1 ) and at a second distance (d 2 ) from the central point (CP), 
 g) repeating the transmitting step e) and the measuring steps f) by energizing the second transmitting antenna ( 4 B;  4 A) with an excitation signal (ES) according to a endfire mode (EFM) and according to a first frequency and 
 h) repeating the transmitting and measuring steps b) to g) at least at a second frequency. 
 
   
   
       11 . A method for measuring the electromagnetic properties of a subsurface formation according to  claim 10 , wherein the transmitting steps b), d), e) and g) are performed simultaneously, the excitation electromagnetic energy transmitted by the first transmitting antennas being signed by a first low frequency, the excitation electromagnetic energy transmitted by the second transmitting antennas being signed by a second low frequency. 
   
   
       12 . A method for measuring the electromagnetic properties of a subsurface formation according to  claim 10 , wherein the transmitting steps b) to h) are performed simultaneously, the excitation signal (ES) comprising a plurality of frequencies at least the first and the second frequencies. 
   
   
       13 . A method for measuring the electromagnetic properties of a subsurface formation according to any one of the  claim 10 , wherein the method further comprises the steps of:
 determining an attenuation and a phase shift of each reception signal (RS) provided by each receiving antenna ( 5 A,  5 B,  5 C,  5 D) relatively to the excitation signal (ES),   estimating the electromagnetic properties of the subsurface formation at different frequencies in the limited zone surrounding the well-bore hole (WBH) for at least a first radial investigation depth (RD 1 ) correlated to the first distance (d 1 ) and a second radial investigation depth (RD 2 ) correlated to the second distance (d 2 ).   
   
   
       14 . A method for measuring the electromagnetic properties of a subsurface formation according to  claim 10 , wherein the method further comprises the steps of:
 measuring a high frequency output signal (OS) received by a first open-ended coaxial wire ( 6 A) following an excitation of the transmitting antennas ( 4 A,  4 B),   determining, an attenuation and a phase shift of the high frequency output signal (OS) relatively to the excitation signal (ES), and   estimating a thickness of a mudcake (MC) on the well-bore wall (WBW) by determining a transmission coefficient based on the attenuation and phase shift.   
   
   
       15 . A method for measuring the electromagnetic properties of a subsurface formation according to  claim 10 , wherein the method further comprises the steps of:
 measuring a high frequency output signal (OS) received by the receiving antennas ( 5 B,  5 D) following an excitation of a first open-ended coaxial wire ( 6 A),   determining an attenuation and a phase shift of the high frequency output signal (OS) relative to the excitation signal (ES), and   estimating a thickness of a mudcake (MC) on the well-bore wall (WBW) by determining a propagation coefficient based on the attenuation.   
   
   
       16 . A method for measuring the electromagnetic properties of a subsurface formation according to  claim 10 , wherein the method further comprises the steps of:
 sending a high-frequency input signal (IS) into a first open ended coaxial wire ( 6 A) in contact with the well-bore wall (WBW),   measuring a high frequency output signal (OS) reflected by the first open-ended coaxial wire   estimating the electromagnetic properties of the mudcake (MC) on the well-bore wall (WBW) by determining a mudcake reflection coefficient based on the high frequency output signal (OS).   
   
   
       17 . A method for measuring the electromagnetic properties of a subsurface formation according to  claim 10 , wherein the method further comprises the steps of:
 sending a high-frequency input signal (IS) into a second open ended coaxial wire ( 6 B) in contact with a well-bore fluid (DM),   measuring a high frequency output signal (OS) reflected by the second open-ended coaxial wire ( 6 B), and   estimating the electromagnetic properties of the well-bore fluid by determining a well-bore fluid reflection coefficient based on the high frequency output signal (OS).   
   
   
       18 . A method for measuring the electromagnetic properties of a subsurface formation according to  claim 10 , wherein the method further comprises the step of correcting the calculated electromagnetic properties of the subsurface formation (GF) in the limited zone surrounding the well-bore hole (WBH) based on the estimated electromagnetic properties and the thickness of the mudcake (MC). 
   
   
       19 . A method for measuring the electromagnetic properties of a subsurface formation according to  claim 10 , wherein the method further comprises the step of comparing the signals provided by the first open ended coaxial wire and the second open ended coaxial wire for estimating the quality of the pad ( 2 ) application against the bore-hole wall (WBW).