Method and system for positioning a trajectory of an ultrasonic logging tool

A method for positioning a trajectory of an ultrasonic logging tool, comprising the following steps:

• S1:
• inputting waveforms and extracting arrival times T;
• S2:
• establishing a coordinate system and initializing a tool trajectory M0;
• S3:
• calculating an initial wave velocity in fluid Vf0 using a least squares method, and calculating a distance D between the tool and a casing and coordinates of casing's inner surface N0 based on the initial wave velocity in fluid Vf0 and time T;
• S4:
• searching for an optimal tool trajectory M1 based on the distance D and the inner boundary coordinates N0, updating a wave velocity in fluid Vf1 according to a perimeter of the inner boundary N0, and updating a distance D between the tool and the casing and coordinates of casing's inner surface N1 based on Vf1 and time T;
• S5:
• repeating step S4 until the update amount of the tool trajectory between two iterations is less than a threshold;
• S6:
• outputting a final tool trajectory M, wave velocity in fluid Vf, and casing's inner surface N.