An adaptive method for determining an acquisition parameter t0 in a modified CPMG sequence.

2017 
Abstract The modified CPMG (Carr-Purcell-Meiboom-Gill) pulse sequence is a common sequence used for measuring the internal magnetic field gradient distribution of formation rocks, for which t 0 (the duration of the first window) is a key acquisition parameter. In order to obtain the optimal t 0 , an adaptive method is proposed in this paper. By studying the factors influencing discriminant factor σ and its variation trend using T 2 - G forward numerical simulation, it is found that the optimal t 0 corresponds to the maximum value of σ . Then combining the constraint condition of SNR (Signal Noise Ratio) of spin echo, an optimal t 0 in modified CPMG pulse sequence is determined. This method can reduce the difficulties of operating T 2 - G experiments. Finally, the adaptive method is verified by the results of the T 2 - G experiments for four water-saturated sandstone samples.
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