Preselecting initial guesses for multi-step inversion using electromagnetic measurements

1. A electromagnetic well measurement system comprising:

an electromagnetic transmitter, wherein the electromagnetic transmitter 1s an antenna and is operable to transmit a low frequency electromagnetic field of 1 KHz (Kilohertz) to 250 KHz for 100 feet to 500 feet into a formation or a high frequency electromagnetic field of 250 KHz to 2 MHZ (Megahertz) into the formation at a depth of 1 foot to 100 feet;

an electromagnetic receiver, wherein the electromagnetic receiver is an antenna and is operable to record the high frequency electromagnetic field or the low frequency electromagnetic field; and

an information handling system configured to:

produce a deep electromagnetic measurement from the measured low frequency electromagnetic field and a shallow measurement from the high frequency electromagnetic field;

perform an inversion with the deep electromagnetic measurements and the shallow measurement to find a formation resistivity model;

set a first threshold for the formation resistivity model and visually identify the deep electromagnetic measurements and the shallow measurement that are within the threshold;

set a second threshold for the formation resistivity model and visually identify the deep electromagnetic measurements and the shallow measurement that are within the second threshold;

set a third threshold for the formation resistivity model and visually identify the deep electromagnetic measurements and the shallow measurement that are within the third threshold;

identify at least one area on the formation model that has the same resistivity measurements from the first threshold, the second threshold, and the third threshold;

truncate the at least one area;

create a random initial guesses of a formation property range;

compare the random initial guesses that have a misfit for a deep inversion; and

run the deep inversion with the random initial guesses that have the misfit.

2. The electromagnetic well measurement system of claim 1 , further comprising a downhole tool, wherein the electromagnetic transmitter and the electromagnetic receiver are disposed on the downhole tool.

3. The electromagnetic well measurement system of claim 2 , wherein the electromagnetic transmitter is disposed 100 feet to 500 feet from the electromagnetic receiver.

4. The electromagnetic well measurement system of claim 2 , wherein electromagnetic transmitter is disposed 1 foot to 100 feet from the electromagnetic receiver.

5. The electromagnetic well measurement system of claim 1 , further comprising a first downhole tool and a second downhole tool.

6. The electromagnetic well measurement system of claim 5 , wherein the second downhole tool each has an electromagnetic transmitter and an electromagnetic receiver.

7. The electromagnetic well measurement system of claim 6 , further comprising a third downhole tool and a fourth downhole tool.

8. The electromagnetic well measurement system of claim 7 , wherein third downhole tool and a fourth downhole tool each have an electromagnetic transmitter and an electromagnetic receiver.

9. The electromagnetic well measurement system of claim 1 , further comprising a bottom hole assembly and a drill bit.

10. The electromagnetic well measurement system of claim 9 , wherein the electromagnetic transmitter and the electromagnetic receiver are disposed on the bottom hole assembly.

11. A method for preselecting initial guesses for multi-step inversion from electromagnetic measurements:

disposing an electromagnetic well measurement system into a wellbore, wherein the electromagnetic well measurement system comprises:

an electromagnetic transmitter, wherein the electromagnetic transmitter is an antenna;

an electromagnetic receiver, wherein the electromagnetic receiver is an antenna;

transmitting a high frequency electromagnetic field from the electromagnetic transmitter into a formation, wherein the high frequency electromagnetic field has a frequency of KHz (Kilohertz) to 2 MHZ (Megahertz) at a depth in the formation of 1 foot to 100 feet;

recording a high frequency electromagnetic field with electromagnetic receiver; transmitting a low frequency electromagnetic field from the electromagnetic

transmitter into the formation, wherein the low frequency electromagnetic field has a frequency of 1 KHz to 250 KHz for a depth into the formation of 100 feet to 500 feet;

recording a low frequency electromagnetic field with electromagnetic receiver, wherein the reflected low frequency electromagnetic field is recorded as a measurement of the formation;

performing a shallow inversion on the low frequency electromagnetic field and the high frequency electromagnetic field to form a formation resistivity model;

setting a first threshold for the formation resistivity model and visually identifying the deep electromagnetic measurements and the shallow measurement that are within the threshold;

setting a second threshold for the formation resistivity model and visually identifying the deep electromagnetic measurements and the shallow measurement that are within the second threshold;

setting a third threshold for the formation resistivity model and visually identifying the deep electromagnetic measurements and the shallow measurement that are within the third threshold;

identifying at least one area on the formation model that have the same resistivity measurements from the first threshold, the second threshold, and the third threshold;

truncating the at least one area;

creating a random initial guesses of a formation property range;

comparing the random initial guesses that have a misfit for a deep inversion; and

running the deep inversion with the random initial guesses that have the misfit.

12. The method of claim 11 , wherein the electromagnetic well measurement system further comprises a downhole tool, wherein the electromagnetic transmitter and the electromagnetic receiver are disposed on the downhole tool.

13. The method of claim 12 , wherein the electromagnetic transmitter is disposed about feet to 500 feet from the electromagnetic receiver.

14. The method of claim 12 , wherein electromagnetic transmitter is disposed 1 foot to 100 feet from the electromagnetic receiver.

15. The method of claim 11 , further comprising a first downhole tool and a second downhole tool.

16. The method of claim 15 , wherein the second downhole tool has an electromagnetic transmitter and an electromagnetic receiver.

17. The method of claim 16 , further comprising a third downhole tool and a fourth downhole tool.

18. The method of claim 17 , wherein third downhole tool and a fourth downhole tool each have an electromagnetic transmitter and an electromagnetic receiver.

19. The method of claim 11 , further comprising a bottom hole assembly and a drill bit.

20. The method of claim 19 , wherein the electromagnetic transmitter and the electromagnetic receiver are disposed on the bottom hole assembly.