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摘要
In order to further our understanding of the physical properties of tight carbonate and to explore the use of NMR to identify different rock types, in this study we use thin-section observations, scanning electronic microscopy (SEM), helium porosity, helium pulse decay permeability, mercury injection capillary pressure (MICP), and nuclear magnetic resonance (NMR) to conduct petrographic and petrophysical characteristics studies on 12 carbonate samples. Our results show that nano/micropores are widely distributed between the micrite and/or dolomite crystals. The correlation between the permeability and porosity of the tight carbonates is poor, while the r(apex), which is the apex of the hyperbola in Pittman (1992), is well correlated with the threshold entry pressure, the maximum pore-throat radius, and the average pore-throat radius. On the basis of new cutoff values, we have identified three types of pores: nanopores, which mainly correspond to the intercrystalline pores; micropores, which may be related to the bioerosion or mechanical erosion process of the aragonitic bioclasts; and mesopores, which mainly consist of well-preserved intraparticle porosity related to the diagenetic shielding effect, dissolved intragranular pores, and a few intercrystalline pores. The dissolved bioclastic packstone and dolostone exhibit similar unimodal behavior with a broader wave, while each of the other four lithofacies has a unique NMR signature. The microstructures and diagenesis processes result in different NMR responses in the different rock types. Micrite envelope, neomorphism, and moderate recrystallization of the micrite matrices result in a higher T-2 spectrum value and a longer relaxation time, while the high clay content and stylolite have the opposite effect. The dissolved bioclastic packstone has a shorter relaxation time than dolostone, with a similar pore throat distribution. Geological knowledge is needed for the NMR-based core-facies classification and for evaluation of the physical properties of the tight carbonate.
- 出版日期2018-3
- 单位中国地质大学（北京）
