US EPA

4967178 

Journal Article 

The quantitative evaluation method of low permeable sandstone pore structure based on nuclear magnetic resonance (NMR) logging 

Yan Jian-Ping; Wen Dan-Ni; Li Zun-Zhi; Geng Bin; Cai Jin-Gong; Liang Qiang; Yan Yu 

2016 

Yes 

Diqiu Wuli Xuebao / Chinese Journal of Geophysics
ISSN: 0001-5733 

59 

4 

1543-1552 

10.6038/cjg20160434 

WOS:000373864400034 

The low permeability sandstone reservoir, which has been an important target of exploration and development for oil and gas increase in reserves and production, is difficult to identify accurately because of the complex pore structure. The pore structure classification of complex low permeability sandstone and the investigation of the petrol-physical diversity of rock samples in different types are helpful to determine the reservoir type and the fluid properties of low permeability sandstone reservoir.



After the analysis of the pore structure based on physical properties data, mercury injection, nuclear magnetic resonance data and the considering of the properties division level standard of clastic reservoir (SY/T 6285-2011), the low permeability sandstone of Es-4 in the southern slope of the Dongying sag is divided into three types of pore structures. And the diversity of every type in mercury injection, nuclear magnetic resonance (saturated T-2 spectrum, centrifuged T-2 spectrum and free-fluid T-2 spectrum), the pore throat distribution, the porosity and permeability are discussed. Many results indicate that the T-2 spectrum and capillary pressure curves could reflect the pore throat distribution in some degree. Meanwhile the T-2 spectrum could be used to evaluate the pseudo capillary pressure curve to get the pore throat radius. However, it's large of the deviation between the pore throat distribution from this way and mercury injection because of the membrane bound water affect. In fact, the free-fluid T-2 spectrum and the pore throat distribution of mercury injection correspond much better. Based on this feature, after the comparing of the free-fluid T-2 spectrum and the pore throat distribution of mercury injection in different pore structure types, the conversion relationship is established between the relaxation time and the pore throat distribution of mercury injection in different pore structure types and the pore size scale (large scale-linear relationship; small scale-piecewise exponential function). Meanwhile, the electrical standards and identification methods of every pore structure are also established based on the cross-plot analysis of logging response.



Therefore, the pore structure could be identified along the well hole, and then the pore throat distribution of different pore structure can be quantitatively calculated by using nuclear magnetic resonance logging data. Not only the segment of pseudo-capillary curve's building is avoided, but also the identification of pore structure could be more effective. Overall, this research provides a direct evidence to recognize the low permeability reservoir and sheds a new light on quantitative reconstruction of microscopic pore structure with well logging. 

Nuclear magnetic resonance; Low permeable sandstone; Mercury injection; Free fluid; Pore structure