A NMR-based porosity calculation method for low porosity and low permeability gas reservoir
Mao Zhi-qiang1,2,3, Zhang Chong Xiao liang1,2
1. State Key Laboratory of Petroleum Resources and Prospecting,China University of Petroleum,Beijing City 102249,China;
2. Beijing City Key Laboratory of Earth Prospecting and Information Technology,China University of Petroleum,Beijing City 102249,China
Abstract：Many low porosity and low permeability gas reservoirs developed in Xujiahe Formation in central Sichuan Basin,core analysis results show that the porosity of the reservoir is from 4% to 8%,and the permeability is from 0.1 to 1 mD.For this type of reservoirs,accurately calculating their porosity is of great significance.As the reservoirs are gas-bearing,it is difficult to accurately calculate the reservoirs' porosity with single type of well logging data.According to the NMR basic principles and analysis for rock volume physical model which is based on acoustic time difference well logging and by integrating acoustic time difference with NMR well logging data a method to calculate real porosity of low porosity and low permeability gas reservoir was developed in this paper.Application of the field data shows that the porosity calculated from the new method matches the core analysis results very well,and the calculation results could objectively reflect the porosity of the gas-bearing reservoirs.
