Localized method and device for the precise determination of the acoustic impedance of material situated in proximity to the wall of a borehole

Claim 3

A method according to claim 1, further comprising the step of determining the porosity of a formation by generating, in response to said resultant signal representative of the acoustic impedance of said formation, a signal representative of the porosity of said formation, said signal being proportional to the function

Claim 6

A device according to claim 3, wherein said surface apparatus comprises: means for producing a resultant electric signal representative of the acoustic impedance of a geological formation traversed by a borehole, said means being connected with means for producing a signal representative of the porosity phi of the formation, wherein

Claim 7

A device according to claim 3, wherein said first means and said second means consist of a single transducer of the piezo-electric type for supplying an incident acoustic impulse upon receiving an electric signal supplied by said control means and for supplying an electric signal representative of said reflected acoustic impulse reflected when receiving the latter.

Claim 8

A device according to claim 5, wherein said transducer is adapted to supply an acoustic impulse having a frequency between 0.1 MHz and 5MHz.

Claim 9

A device according to claim 6, wherein said transducer is composed of a piezoelectric element made of barium titanate.

Claim 10

A device according to claim 7, wherein said second intermediate element consists of a material having an acoustic attenuation coefficient with a value between 0.3 and 3 decibels per millimeter and an acoustic impedance of a value comprised between 3 and 15 kilograms per square meter per second.

Claim 11

A device according to claim 6, wherein said transducer is composed of a piezo-electric element made of lead zirconate.

Claim 12

A device according to claim 5, wherein said transducer is adapted to supply an acoustic impulse having a frequency approximately equal to 1 MHz.

Claim 13

A device according to claim 10, wherein said second intermediate element has a contact surface with said transducer placed in the path of said incident acoustic impulse, and wherein the acoustic impedances of the materials constituting said transducer and said first and second intermediate elements have values such that the acoustic reflection coefficient of the contact surface of said second intermediate element and of said transducer has a value approximately equal to zero and that the acoustic reflection coefficient of the contact surface of said first and second intermediate elements has a value between 0 and 1, and in that the product of the attenuation coefficient, measured in decibels per millimeter of the second intermediate element, by the distance separating the contact surfaces of said second intermediate element with, respectively and piezoelectric element and said first intermediate element, is sufficient to cause a rapid decrease of the amplitudes of the reflected acoustic impulses originating from the successive reflection of the acoustic impulses on the contact surface of said intermediate elements, in such a manner that the acoustic impulses intercepted or collected by said piezo-electric element originaTe essentially from the reflections of the acoustic impulses on the contact surface of said first element and of said material traversed by the borehole.

Claim 14

A device according to claim 11, wherein said acoustic reflection coefficient of the contact surface of said first and second intermediate elements has a value approximately equal to 0.5.

Claim 15

A device according to claim 12, wherein the apparatus for processing the data supplied by the sonde comprises a recording circuit for indicating the signal supplied by the sonde; an circuit for integrating the signal supplied by the sonde, and a recording circuit connected to said integrating circuit and recording the signal supplied by said integrating circuit as a function of the depth of the sonde within the well.

Claim 16

A device according to claim 11, for controlling cementing of a lining placed inside a well, wherein said first intermediate element consists of said lining.

Claim 17

A device according to claim 11, for the determination of the acoustic impedance of geological formation traversed by a well the wall of which is covered with a mud-cake, wherein said first intermediate element consists of said mud cake.

Claim 18

A device according to claim 11, wherein said apparatus for processing the data being supplied by the measuring sonde comprises: an impulse selector circuit for supplying on a first output terminal thereof the portion of the signal furnished by the measuring sonde, representative of the first reflection of the incident acoustic impulse on the contact surface between said intermediate elements and, on at least a second and third output terminal thereof, the portions of the signal being respectively representative of two successive reflections of the incident acoustic impulse on the contact surface between said first intermediate element and the material for which the acoustic impedance is intended to be determined; measuring circuits each connected to one output terminal of said selector circuit, said measuring circuits each furnishing at least one signal being representative of the portion of the signal which appears on the corresponding output terminal of said selector circuit; a first circuit, connected to said selector circuit, for supplying a resultant signal from a signal proportional to the attenuation coefficient of the acoustic impulses in said first intermediate element, a signal proportional to the acoustic reflection coefficient of the contact surface between said intermediate elements and signals furnished by said measuring circuits connected to said second and third output terminals of said impulse selector circuit; said resultant signal being proportional to the value of the reflection coefficient of the contact surface between said first intermediate element and said material, and a second circuit, connected to said first circuit, for producing from a signal proportional to the acoustic impedance of said first intermediate element and the signal delivered by said first circuit, a resultant signal representative of the acoustic impedance of said material.

Claim 19

A device according to claim 16, wherein each of said measuring circuits provides a second signal representative of the instant of arrival at said transducer of the reflected acoustic impulse corresponding to the portion of the signal received by the measuring circuit, and in that it comprises: a third circuit, connected to said measuring circuits, and adapted to produce, from said second signals corresponding to the portions of the signal appearing on said second and third output terminals of said selector circuit, a signal proportional to the attenuation coefficient of the acoustic waves in said first intermediate element, and a fourth circuit, connected to said measuring circuit, corresponding to said first output terminal of said selector circuit, adapted to produce a signal proportional to the value of the acoustic reflection coefficient of the contact surface of said intermediate elementS, the output terminals of said third and fourth circuits being connected to the input terminals of said first circuit.

Claim 20

A device according to claim 17, wherein said third circuit is composed of a first circuit element receiving said second signals provided by the measuring circuits corresponding to said second and third output terminals of said selector circuit and supplying a signal proportional to the difference of the signals which are applied thereto, a second circuit element connected to said first circuit element and supplying a signal proportional to the product of the value of said signal which is applied thereto by the value of the speed of acoustic propagation in said first intermediate element and a third circuit element receiving the signal supplied by said second circuit element and furnishing a signal, representative of the product of the signal received by a predetermined value proportional to the damping coefficient of the acoustic impulse in said first intermediate element.

Claim 21

A device according to claim 17, wherein said fourth circuit consists of a first circuit element supplying a signal proportional to the reverse of the attenuation of a reflected acoustic impulse a second circuit element connected to said measuring circuit corresponding to the first output terminal of said selector circuit and dividing said first signal of said measuring circuit by a coefficient representative of the amplitude of the incident impulse emitted by said transducer multiplied by the square of the value of the acoustic transmission coefficient of the contact surface of the transducer and of said second intermediate element, and a third circuit element connected to said first and third circuit elements and supplying a signal representative of the product of the signals which are transmitted thereto.

Claim 22

A device according to claim 13, wherein said first circuit consists of a first circuit element at the input terminal of which there is applied a signal representative of the acoustic attenuation coefficient of said first intermediate element and which generates a signal proportional to the reverse of the acoustic damping of a reflected impulse in said first intermediate element, a second circuit element receiving on a first input terminal thereof the signal furnished by said first circuit element and on a second input terminal a signal proportional to the value of the acoustic reflection coefficient of the contact surface between said intermediate elements, said second circuit element furnishing a signal proportional to the ratio of the signal applied on its first input terminal and of that applied on its second input terminal and, a third circuit element connected to said measuring circuits of said selector circuit and receiving, on two input terminals, the first signals supplied by said measuring circuits corresponding to said second and third output terminals of said impulse selector circuit, said third circuit element supplying a signal proportional to the ratio of the first signal furnished by said measuring circuit corresponding to the third output terminal of said selector circuit and that furnished by said measuring circuit corresponding to the second output terminal of said selector circuit, and a fourth circuit element connected to said second and third circuit elements and furnishing a signal proportional to the product of the signals supplied by said second and third circuit elements.

Claim 23

A device according to claim 13, wherein said second circuit consists of a first and a second circuit element connected to said first circuit, the first circuit element supplying a signal whose value is equal to that of the signal supplied by said first circuit increased by one unit, said second circuit element supplying a signal whose value is equal to that of the signal supplied by said first circuit with a change in the sign thereof, a third circuit element connected to said second circuit element and supplying a signal whose value is equal to that of the signal sUpplied by said second circuit element reduced by one unit, a fourth circut element connected to said first and third circuit elements and supplying a signal proportional to the ratio of the signals supplied by said first and third elements, a fifth circuit element receiving on a first input terminal the signal issued from said fourth circuit element, and on a second input terminal a signal proportional to the acoustic impedance of said first intermediate element, said fifth circuit element producing a signal proportional to the ratio of the signals which are applied on its second and its first input terminal and which is representative of the acoustic impedance of said material traversed by the borehole.

Claim 24

A device according to claim 11, for the determination of the acoustic impedance of geological formations traversed by a well, wherein said first intermediate element is integral with said sonde and has a contact surface with said intermediate element.

Claim 25

A device according to claim 5, wherein said measuring sonde comprises at least one measuring pad displaceable with respect to the body of the sonde so as to be applied against the wall of the well, said pad having a housing for at least said second transducer and said intermediate element integral with respect to each other, and elastic means interposed between said pad and said transducer.

Claim 26

A device according to claim 3, wherein said first intermediate element has a deformable surface in contact with the wall of the well.