Nuclear Techniques ›› 2015, Vol. 38 ›› Issue (8): 80502-080502.

• NUCLEAR PHYSICS, INTERDISCIPLINARY RESEARCH •

Effect of pair production on D-T induced gamma density measurement

YU Huawei1 ZHANG Li2 HOU Boran1

1. 1(College of Geo-Resources and Information, China University of Petroleum, Qingdao 266580, China) 2(Department of Resources and Civil Engineering, Shandong University of Science and Technology, Tai'an 271019, China) 3(School of Science, China University of Petroleum, Qingdao 266580, China)
• Received:2015-04-07 Revised:2015-05-30 Online:2015-08-10 Published:2015-08-13

Abstract: Background: The D-T controllable neutron source is used to replace the chemical gamma source to measure the formation density in oil exploration. Purpose: The paper aims to study the effect of pair production on density measurement accuracy using the D-T neutron induced gamma ray. Methods: Firstly, the theory of traditional chemical source density logging method is analyzed, and the difference of the mass attenuation coefficient between Compton scattering and pair production is compared. In addition, the measurement accuracies of both traditional density log and neutron induced gamma density log are studied using Monte Carlo simulation method. And then the source of error and its correction are analyzed. Results & Conclusion: The measurement accuracy of neutron induced gamma density is worse than the traditional density log, the reason is that the contribution of gamma comes from not only the Campton scattering, which is employed in traditional density log, but also pair production. Moreover, the pair production of gamma ray is sensitive to the formation lithology, and the measurement accuracy could be increased if the lithology correction was added.