一种基于核磁共振测井计算低孔低渗气层孔隙度的新方法

A NMR-based porosity calculation method for low porosity and low permeability gas reservoir

川中地区须家河组发育大量的低孔低渗气藏,岩心分析结果表明,储层孔隙度为4%～8%,渗透率为0.1～1mD。对于这类低孔低渗气层,准确地计算储层孔隙度显得尤为重要。考虑到储层含气的影响,利用单一测井资料难以准确地计算储层孔隙度,本文从核磁共振测井基本原理和基于声波时差测井的岩石体积物理模型分析出发,提出了一种新的结合声波时差—核磁共振测井资料计算低孔低渗气层真实孔隙度的方法。实际资料应用表明,利用该方法计算的孔隙度与岩心分析结果吻合较好,计算结果可以真实地反映实际地层孔隙度。

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.