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Dual-spacing hydrogen index correction method for neutron gamma density measuring in LWD
ZHANG Quanying1, ZHANG Feng1,2, WANG Yuwei3, LIU Juntao1, JIA Wenbao4, TI Yongzhou5, LI Jing6
(1.School of Geosciences in China University of Petroleum, Qingdao 266580, China;2.Laboratory for Marine Mineral Resources, Qingdao National Laboratory for Marine Science and Technology, Qingdao 266071, China;3.Exploration Company of Xinjiang Oilfield Company, Karamay 834000, China;4.College of Materials Science and Engineering, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China;5.Zhengzhou Key Laboratory of Isotope Tracing and Detecting, Isotope Research Institute of Henan Academy of Sciences Company Limited, Zhengzhou 450015, China;6.Department of Biology, Guta Branch School of Mongolian Senior High School, Chaoyang 122300, China)
Abstract:
To resolve unstable density measurements using single detector hydrogen index correction calculation in neutron gamma density logging, a dual-spacing hydrogen index correction method is studied. The neutron and gamma ray distribution in different hydrogen index and formation conditions is simulated by a Monte Carlo method. A hydrogen index correction calculation model is established by the dual-spacing count rate ratio of capture gamma ray, hydrogen capture gamma ray and thermal neutron. The results of hydrogen index correction and the impact of caliper and salinity are compared. As a result, the accuracy in the density measurements after hydrogen index correction has improved significantly. Among them, the precision and accuracy from thermal neutron correction is the highest. The accuracy from hydrogen capture gamma correction is slightly higher than that of the capture gamma; on the contrary, the precision of hydrogen capture gamma is far less than that of the capture gamma and the thermal neutron. The error of dual-spacing hydrogen index correction increases with the increasing caliper and salinity. The results from thermal neutron correction are less sensitive to caliper and salinity, while the results from capture gamma and hydrogen capture gamma correction are considerably are on the opposite. The research provides correction methods for obtaining neutron gamma density accurately in LWD.
Key words:  pulsed neutron source  dual-space  density  hydrogen index  Monte Carlo simulation