title: An adaptive method for determining an acquisition parameter t0in a modified CPMG sequence.
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 t0(the duration of the first window) is a key acquisition parameter. In order to obtain the optimal t0, an adaptive method is proposed in this paper. By studying the factors influencing discriminant factor σ and its variation trend using T2-G forward numerical simulation, it is found that the optimal t0corresponds to the maximum value of σ. Then combining the constraint condition of SNR (Signal Noise Ratio) of spin echo, an optimal t0in modified CPMG pulse sequence is determined. This method can reduce the difficulties of operating T2-G experiments. Finally, the adaptive method is verified by the results of the T2-G experiments for four water-saturated sandstone samples.
authors.affiliation: School of Geosciences, China University of Petroleum, Qingdao 266580, China; Laboratory for Marine Mineral Resources, Qingdao National Laboratory for Marine Science and Technology, Qingdao 266071, China; CNPC Key Well Logging Laboratory, China University of Petroleum, Qingdao 266580, China.
authors.forename: Donghui
authors.initials: D
authors.lastname: Xing
authors.affiliation: School of Geosciences, China University of Petroleum, Qingdao 266580, China; Laboratory for Marine Mineral Resources, Qingdao National Laboratory for Marine Science and Technology, Qingdao 266071, China; CNPC Key Well Logging Laboratory, China University of Petroleum, Qingdao 266580, China. Electronic address: fanyiren@upc.edu.cn.
authors.forename: Yiren
authors.initials: Y
authors.lastname: Fan
authors.affiliation: Middle East Department of Research Institute of Petroleum Exploration and Development, Beijing 100083, China.
authors.forename: Jianfei
authors.initials: J
authors.lastname: Hao
authors.affiliation: School of Geosciences, China University of Petroleum, Qingdao 266580, China; Laboratory for Marine Mineral Resources, Qingdao National Laboratory for Marine Science and Technology, Qingdao 266071, China; CNPC Key Well Logging Laboratory, China University of Petroleum, Qingdao 266580, China.
authors.forename: Xinmin
authors.initials: X
authors.lastname: Ge
authors.affiliation: PetroChina Research Institute of Petroleum Exploration and Development, Beijing 100083, China.
authors.forename: Chaoliu
authors.initials: C
authors.lastname: Li
authors.affiliation: PetroChina Research Institute of Petroleum Exploration and Development-Langfang, Langfang 065007, China.
authors.forename: Yufeng
authors.initials: Y
authors.lastname: Xiao
authors.affiliation: Shanghai Niumag Corporation Ltd., Shanghai 200333, China.
authors.forename: Fei
authors.initials: F
authors.lastname: Wu
keywords: Adaptive method; Discriminant factor; Internal magnetic field gradient; Maximum value; Modified CPMG pulse sequence; Numerical simulation