Factors Affecting and Correction Methods for Porosity Measured by NMR Logging in the J Oilfield of Bohai Bay

doi:10.11938/cjmr20192770

Abstract

Abstract: The porosity of reservoir bed and core in the Shahejie formation of the J oilfield of Bohai bay measured by nuclear magnetic resonance (NMR) logging were found to be lower than those measured by the reference helium method, affecting the application of NMR logging. NMR experiments on the core samples were performed to study the contributions of potential affecting factors, including instrument acquisition parameters, wellbore environment and reservoir fluid properties. The main reason for the lower porosity measured by NMR logging was found to be the intrusion of high salinity mud filtrate. The effects of brines with different salinity on NMR T₂ spectrum were analyzed, and the results were used to determine the lower limit of salinity required for morphological correction of the NMR T₂ spectrum. In view of that the intrusion of high salinity mud filtrate could affect the NMR T₂ spectrum during actual logging, a model for morphological correction of the NMR T₂ spectrum and a method to correct the NMR porosity at different salinity were established. The experimental results demonstrated that the average relative error of the NMR porosity reduced from 13.56% to 2.81% after correction.

Key words: nuclear magnetic resonance (NMR) logging, porosity, influencing factors, T₂ spectrum, correction model

CLC Number:

P631

LIU Huan, XU Jin-xiu, ZHENG Yang, XIONG Lei. Factors Affecting and Correction Methods for Porosity Measured by NMR Logging in the J Oilfield of Bohai Bay[J]. Chinese Journal of Magnetic Resonance, 2020, 37(3): 370-380.

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