Radio frequency antenna receiving method and device for a downhole three-dimensional scanning nuclear magnetic resonance imager

1. A radio frequency antenna receiving device for a downhole three-dimensional scanning nuclear magnetic resonance imager, comprising:

an array antenna for receiving a nuclear magnetic resonance echo signal, an antenna interface circuit, a receiving and amplifying circuit for amplifying the echo signal, an analog-to-digital conversion circuit for converting an analog signal to a digital signal, a signal collecting circuit and a control circuit; wherein

the array antenna comprises N antenna units, where N≥4, and the N antenna units correspond to different circumferentially sensitive regions;

the array antenna, the antenna interface circuit, the receiving and amplifying circuit, the analog-to-digital conversion circuit, and the signal collecting circuit are sequentially connected;

four ports of the control circuit are respectively connected to the antenna interface circuit, the receiving and amplifying circuit, the analog-to-digital conversion circuit and the signal collecting circuit, for controlling the antenna interface circuit, the receiving and amplifying circuit, the analog-to-digital conversion circuit and the signal collecting circuit, and the control circuit is connected to a logging ground acquisition system; and

the antenna interface circuit is configured to select one antenna unit in the array antenna according to a control instruction of the control circuit.

2. The device according to claim 1 , further comprising an isolation circuit, wherein the isolation circuit is connected in series between the antenna interface circuit and the receiving and amplifying circuit, and the isolation circuit is connected to the control circuit; and

the isolation circuit is configured to disconnect the connection between the antenna interface circuit and the receiving and amplifying circuit when the array antenna transmits a signal.

3. The device according to claim 1 , further comprising a memory for storing signals collected by the signal collecting circuit, the memory being respectively connected to the signal collecting circuit and the control circuit.

4. The device according to claim 1 , further comprising a filter circuit, the filter circuit being connected in series between the receiving and amplifying circuit and the analog-to-digital conversion circuit.

5. The device according to claim 1 , wherein the antenna interface circuit comprises: a selection switch circuit for selecting an antenna unit in the array antenna, a tuning circuit for generating different resonant frequencies, and a coupling circuit for impedance matching; wherein

the selection switch circuit, the tuning circuit and the coupling circuit are sequentially connected;

the selection switch circuit is respectively connected to the array antenna and the control circuit;

the tuning circuit is connected to the control circuit; and

the coupling circuit is coupled to the receiving and amplifying circuit.

6. The device according to claim 5 , wherein the tuning circuit comprises a plurality of capacitors in parallel, and the tuning circuit controls the capacitors to be connected or disconnected according to a control instruction of the control circuit.

7. The device according to claim 5 , wherein the antenna interface circuit further comprises a limiting circuit, the limiting circuit comprises two diodes, and the two diodes are connected in series between the tuning circuit and the coupling circuit after the two diodes are connected in an anti-parallel manner.

8. The device according to claim 1 , wherein the receiving and amplifying circuit comprises: a pre-amplifying circuit and a program-controlled amplifying circuit which are sequentially connected, wherein the pre-amplifying circuit is connected to the antenna interface circuit, and the program-controlled amplifying circuit is respectively connected to the analog-to-digital conversion circuit and the control circuit;

the pre-amplifying circuit is configured to perform amplification on the echo signal by a fixed multiple; and

the program-controlled amplifying circuit is configured to determine a amplification multiple according to a control instruction of the control circuit and an amplitude of the echo signal, and amplify the echo signal according to the determined amplification multiple.

9. A radio frequency antenna receiving method for a downhole three-dimensional scanning nuclear magnetic resonance imager, which is applied to the radio frequency antenna receiving device for a downhole three-dimensional scanning nuclear magnetic resonance imager according to claim 1 , comprising the following steps:

selecting one antenna unit in an array antenna, wherein the array antenna comprises N antenna units, where N≥4, and the N antenna units correspond to different circumferentially sensitive regions; and

receiving an echo signal in a circumferentially sensitive region corresponding to the one antenna unit.

10. The method according to claim 9 , wherein before the receiving an echo signal in a circumferentially sensitive region corresponding to the one antenna unit, the method further comprises:

transmitting a signal to the circumferentially sensitive region corresponding to the one antenna unit.