Calculation of porosity from nuclear magnetic resonance and conventional logs in gas-bearing reservoirs |
| |
Authors: | Liang Xiao Zhi-qiang Mao Gao-ren Li Yan Jin |
| |
Institution: | 1.Ministry of Education,Key Laboratory of Geo-detection (China University of Geosciences, Beijing),Beijing,People’s Republic of China;2.State Key Laboratory of Petroleum Resources and Prospecting,China University of Petroleum,Beijing,People’s Republic of China;3.Beijing City Key Laboratory of Earth Prospecting and Information Technology,China University of Petroleum,Beijing,People’s Republic of China;4.Research Institute of Exploration & Development, Changqing Oilfield Company,PetroChina,Xi’an Shaanxi,People’s Republic of China;5.Southwest Oil and Gas Field Branch Company,PetroChina,Chengd, Sichuan,People’s Republic of China |
| |
Abstract: | The porosity may be overestimated or underestimated when calculated from conventional logs and also underestimated when derived
from nuclear magnetic resonance (NMR) logs due to the effect of the lower hydrogen index of natural gas in gas-bearing sandstones.
Proceeding from the basic principle of NMR log and the results obtained from a physical rock volume model constructed on the
basis of interval transit time logs, a technique of calculating porosity by combining the NMR log with the conventional interval
transit time log is proposed. For wells with the NMR log acquired from the MRIL-C tool, this technique is reliable for evaluating
the effect of natural gas and obtaining accurate porosity in any borehole. In wells with NMR log acquired from the CMR-Plus
tool and with collapsed borehole, the NMR porosity should be first corrected by using the deep lateral resistivity log. Two
field examples of tight gas sandstones in the Xujiahe Formation, central Sichuan basin, Southwest China, illustrate that the
porosity calculated by using this technique matches the core analyzed results very well. Another field example of conventional
gas-bearing reservoir in the Ziniquanzi Formation, southern Junggar basin, Northwest China, verifies that this technique is
usable not only in tight gas sandstones, but also in any gas-bearing reservoirs. |
| |
Keywords: | |
本文献已被 SpringerLink 等数据库收录! |
|