Application solution of low field nuclear magnetic resonance technology in conventional core analysis [first bullet of petroleum energy application] | | Core analysis is a necessary means to understand the geological characteristics of oil and gas layers. As a porous medium, rock's internal pore structure, the movement state of molecules in the pores, the reaction process and other phenomena are important for core analysis. Question. In recent years, low-field NMR core analysis technology has become an important means to quickly measure rock physical parameters. It is suitable for laboratory research and oilfield field applications, and has been widely recognized by the petroleum industry, and its application fields are increasingly widespread. | | Fundamental:
Low-field NMR techniques use hydrogen or nucleus in oil or water to resonate in a magnetic field and produce signal characteristics to detect oil, gas, water, and their distribution and petrophysical parameters. In the rock, different sizes of pore throats constitute rock pores, and the relaxation time shows the characteristics of pore size. Therefore, the T2 spectrum shows the pore size distribution of the rock. The larger the pore size, the longer the corresponding relaxation time, the more the T2 distribution curve is to the right side; the smaller the pore size, the shorter the corresponding relaxation time, and the more T2 distribution curve Close to the left. | | 
| | Compared with other methods, the gas field adsorption method, the mercury intrusion method, the gas porosity method and the like, the low field nuclear magnetic method has many advantages such as rapid, non-destructive, green and the like. | | Application direction
1. Core hole, seepage and saturation measurement
2, oil, water saturation
3. Determination of wettability
4, core imaging
5. Analysis of oil content in drilling fluid
6. Study on the mechanism of rock freeze-thaw loss
7. Study on mechanical properties of triaxial compression damage
8. Core high temperature and high pressure displacement experiment... | Test Methods | advantage | Disadvantage | Gas adsorption method | 1. The micro and mesopores are more accurate, 0.4nm-50nm
2. The BET multi-molecular layer adsorption theory is close to the actual adsorption state, and the formula is more accurate.
3, select the corresponding calculation principle to describe different apertures | 1. It is impossible to characterize the pore distribution and structural characteristics of macropores.
2, the test time is long
3. The test results are affected by the selected model, and the accuracy difference is large.
4. The throat and the pore itself cannot be distinguished in the measurement of pore distribution. | Nuclear magnetic resonance | 1, fast, non-destructive testing, can measure the aperture of 2nm-1μm
2, the operation is simple, the application is universal
3. The characterization is relatively accurate throughout the pore scale
4, can obtain more accurate pore structure image | Paramagnetic substances have a greater impact on the signal | Mercury intrusion | 1, the test speed is fast, the principle and operation are relatively simple
2, the mercury density is large, easy to enter the pores of the rock sample
3, can measure the aperture of 3nm-400μm | 1. Nano-level pore test error is large
2, high pressure mercury can cause artificial cracks, affect measurement accuracy, and mercury is toxic
3. The measured maximum opening size of the pores, the presence of the pores causes the measurement pore size to deviate |
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