Method and devices for determining characteristics of geological formations by transmission of acoustic signals

Claim 1

A method for determining characteristics of a geological formation using data processing means, this method comprising the steps of transmitting acoustic signals through the studied geological formation, this signal travelling through the formation, measuring the attenuation of these signals between two points spaced from each other along the direction Of propagation of these signals, this attenuation being a function delta of the logarithm of the ratio of the squares of the amplitudes of the signals appearing at said two points respectively, expressed by the relationship: delta delta g + Af1/3 + Bf + Cf2 + N1f3 + N2f4 + . . . + Nifi 2 wherein delta g is the geometrical attenuation factor which depends, in particular, on the degree of fracturation of the formation, A is the attenuation coefficient due to the movement of flow of the fluids through the pores of the formation and which depends on characteristic parameters of the porous medium and on the fluids impregnating the same, B is the attenuation coefficient due to the frictions between solids during the propagation of the acoustic signals, C represents the attenuation coefficient due to the frictions between fluids, the series of the terms N1f3, N2f4 . . . Nifi 2 represents all the attenuation factors which are respectively functions of f3, f4 . . . fi 2, f being the frequency of the transmitted signals, the method further comprising the steps of transmitting signals, having at least two frequencies f1, f2 . . . fi 4, the number of the transmission frequencies being at least equal to the number of parameters delta g, A, B, C, N1 . . . Ni to be determined, measuring the attenuation delta 1, delta 2 . . . delta i 4 of the signals between said two points spaced from each other along the direction of propagation of the acoustic signals for each of said transmission frequencies, and determining, through said data processing means, the values of at least the two first of said parameters delta g, A, B and C complying with the relationships: delta 1 delta g+Af11/3+Bf1+Cf12+N1f13+ . . . +Nif1i 2 delta 2 delta g+Af21/3 + Bf2 + Cf22 + N1f23 + . . . + Nif2i 2 delta i 4 delta g+Afi 41/3 +Bfi 4+ N1fi 43 + . . . + Nifi 4i 2 the values of B, C, N1 . . . Ni being considered as equal to zero when only two frequencies are used for the transmission and the values of C, N1 . . . Ni being considered as equal to zero when the number of transmission frequencies is equal to three.

Claim 2

A method for determining characteristics of a geological formation using data processing means, this method comprising the steps of transmitting acoustic signals through the studied geological formation, this signal travelling through the formation, measuring the attenuation of these signals between two points spaced from each other along the direction Of propagation of these signals, this attenuation being a function delta of the logarithm of the ratio of the squares of the amplitudes of the signals appearing at said two points respectively, expressed by the relationship: delta delta g + Af1/3 + Bf + Cf2 + N1f3 + N2f4 + . . . + Nifi 2 wherein delta g is the geometrical attenuation factor which depends, in particular, on the degree of fracturation of the formation, A is the attenuation coefficient due to the movement of flow of the fluids through the pores of the formation and which depends on characteristic parameters of the porous medium and on the fluids impregnating the same, B is the attenuation coefficient due to the frictions between solids during the propagation of the acoustic signals, C represents the attenuation coefficient due to the frictions between fluids, the series of the terms N1f3, N2f4 . . . Nifi 2 represents all the attenuation factors which are respectively functions of f3, f4 . . . fi 2, f being the frequency of the transmitted signals, the method further comprising the steps of transmitting signals, having at least two frequencies f1, f2 . . . fi 4, the number of the transmission frequencies being at least equal to the number of parameters delta g, A, B, C, N1 . . . Ni to be determined, measuring the attenuation delta 1, delta 2 . . . delta i 4 of the signals between said two points spaced from each other along the direction of propagation of the acoustic signals for each of said transmission frequencies, and determining, through said data processing means, the values of at least the two first of said parameters delta g, A, B and C complying with the relationships: delta 1 delta g+Af11/3+Bf1+Cf12+N1f13+ . . . +Nif1i 2 delta 2 delta g+Af21/3 + Bf2 + Cf22 + N1f23 + . . . + Nif2i 2 delta i 4 delta g+Afi 41/3 +Bfi 4+ N1fi 43 + . . . + Nifi 4i 2 the values of B, C, N1 . . . Ni being considered as equal to zero when only two frequencies are used for the transmission and the values of C, N1 . . . Ni being considered as equal to zero when the number of transmission frequencies is equal to three.

Claim 3

A device for determining characteristics of a geological formation comprising in combination means for transmitting signals in the studied geological formation, these signals travelling through the formations, means for measuring the attenuation of these signals between two points spaced from each other along the direction of propagation of these signals, this attenuation being a function delta of the logarithm of the ratio of the squares of the amplitudes of the signals appearing at said two points respectively, expressed as follows: delta delta g + Af1/3 + Bf + Cf2 + N1f3 + N2f4+ . . . Nifi 2 wherein delta g is the geometrical attenuation factor which depends, in particular, on the degree of fracturation of the formation, A is the attenuation coefficient due to the movement or flow of the fluids through the pores of the formation and which depends on characteristic parameters of the porous medium and of the fluids impregnating the same, B is the attenuation coefficient due to the frictions between solids during the propagAtion of the acoustic signals, C represents the attenuation coefficient due to the frictions between fluids, the series of the terms N1f3, N2f4, . . . , Nifi 2 represents all the attenuation factors which are respectively functions of f3, f4 . . . fi 2, f being the frequency of the transmitted acoustic signals, said transmission means having at least two transmission frequencies f1, f2 . . . f1 4, the number of the transmission frequencies being at least equal to the number of parameters delta g, A, B, C, N1 . . . Ni to be determined, said data processing means being adapted to determine the values of at least the two first of said parameters delta g, A, B, and C complying with the relationships: delta 1 delta g + Af11/3+Bf1 + Cf12 + N1f13 + . . . +Nif1i 2 delta 2 delta g + Af21/3+Bf2 + Cf22 + N1f23+ . . . + Nif2i 2 delta i 4 delta g + Afi 41/3 + Bfi 4+ Cfi 42 + N1fi 43 + . . . + Nifi 4i 2 delta 1, delta 2 . . . delta i 4 being the attenuations measured for the transmission frequencies f1, f2, . . . fi 4 respectively, the values of B, C, N1 . . . Ni being considered as equal to zero when only two frequencies are used for the transmission and the values of C, N1 . . . Ni being considered as equal to zero when the number of transmission frequencies is equal to three.

Claim 4

A device for determining characteristics of a geological formation comprising in combination means for transmitting signals in the studied geological formation, these signals travelling through the formations, means for measuring the attenuation of these signals between two points spaced from each other along the direction of propagation of these signals, this attenuation being a function delta of the logarithm of the ratio of the squares of the amplitudes of the signals appearing at said two points respectively, expressed as follows: delta delta g + Af1/3 + Bf + Cf2 + N1f3 + N2f4+ . . . Nifi 2 wherein delta g is the geometrical attenuation factor which depends, in particular, on the degree of fracturation of the formation, A is the attenuation coefficient due to the movement or flow of the fluids through the pores of the formation and which depends on characteristic parameters of the porous medium and of the fluids impregnating the same, B is the attenuation coefficient due to the frictions between solids during the propagAtion of the acoustic signals, C represents the attenuation coefficient due to the frictions between fluids, the series of the terms N1f3, N2f4, . . . , Nifi 2 represents all the attenuation factors which are respectively functions of f3, f4 . . . fi 2, f being the frequency of the transmitted acoustic signals, said transmission means having at least two transmission frequencies f1, f2 . . . f1 4, the number of the transmission frequencies being at least equal to the number of parameters delta g, A, B, C, N1 . . . Ni to be determined, said data processing means being adapted to determine the values of at least the two first of said parameters delta g, A, B, and C complying with the relationships: delta 1 delta g + Af11/3+Bf1 + Cf12 + N1f13 + . . . +Nif1i 2 delta 2 delta g + Af21/3+Bf2 + Cf22 + N1f23+ . . . + Nif2i 2 delta i 4 delta g + Afi 41/3 + Bfi 4+ Cfi 42 + N1fi 43 + . . . + Nifi 4i 2 delta 1, delta 2 . . . delta i 4 being the attenuations measured for the transmission frequencies f1, f2, . . . fi 4 respectively, the values of B, C, N1 . . . Ni being considered as equal to zero when only two frequencies are used for the transmission and the values of C, N1 . . . Ni being considered as equal to zero when the number of transmission frequencies is equal to three.