Application background
The ratio of the sum of all pore space volumes in the rock sample to the volume of the rock sample is called the total porosity of the rock (core) and is expressed as a percentage. The greater the total porosity of the reservoir, the larger the pore space in the rock (core). From a practical point of view, only those interconnected pores are of practical significance because they not only store oil and gas, but also allow oil and gas to percolate there. Therefore, in the production practice, the concept of effective porosity is proposed. Effective porosity refers to the ratio of the sum of the pore volumes that allow fluid to flow under normal pressure conditions to the total volume of the rock sample, expressed as a percentage. Obviously, the same rock (core) effective porosity is less than its total porosity.
Porosity is one of the important parameters of reservoir evaluation. Nuclear magnetic resonance (NMR) can detect the signal of pore fluid in core, and it has the characteristics of non-destructive fast and accurate. It has advantages that other logging methods can't match in determining formation porosity. Therefore, in the field of petroleum exploration and development, the application of nuclear magnetic resonance (NMR) technology in core analysis, geochemistry and geophysical logging has become increasingly attractive.
The function of nuclear magnetic resonance in the field of petroleum core:
1) conventional core pore structure, pore size distribution and fluid saturation;
2) Pore structure, pore size distribution and fluid saturation of unconventional core (dense core, mudstone, shale);
3) Core sample oily water distribution, oil and water content test;
Application example 1: Glass bead pore model test (T2 relaxation map analysis under different saturation)
Application example 2: conventional core hole penetration test
Figure 2. Sandstone T2 spectrum and cumulative T2 spectrum
It can be seen from the differential spectrum of the sample that manganese is added to the manganese-rich sample to shorten the relaxation time of the water, and no water signal can be collected, and only the oil signal can be collected. Porosity, bound fluid saturation, free fluid saturation can be obtained from the relaxation spectrum of the saturated water sample, and the oil saturation and water saturation can be obtained by combining the original sample and the saturated manganese-like relaxation spectrum.
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