It is a well known fact that nuclear magnetic resonance (NMR) is commonly used in well logging measurements and for routine laboratory core analysis. However, many are not aware of the principle behind NMR and its advantages for the core analyst. It is commonly used to determine porosity and pore size distributions but it is important to note that NMR can also measure fluid mobility parameters such as bound volume irreducible (BVI), free fluid index (FFI), clay bound water (CBW) and effective porosity.
NMR can also easily and effectively measure permeability, capillary pressure, and oil/water and gas/water contents. These parameters are measured with high level of precision using comprehensive software, which is user-friendly and can be easily operated by a novice in NMR. The technical details given below are aimed at introducing NMR to the petrophysicist and core analyst who are not very familiar with NMR.
When a sample is placed in a magnetic field and activated with a quick pulse of radio frequency (RF), NMR signals are generated from liquids such as brine or oil. An NMR signal is formed instantaneously after the pulse, which then dies away with a characteristic decay rate or relaxation time known as T2. The signal amplitude immediately after the pulse indicates the total amount of fluid present. T2 of the signal provides important information about the physical environment of the liquids.
In pores filled with a single fluid, there are two key components to the NMR signal, one signal is generated from the fluid far from the pore walls and another close to the pore walls. The nature of NMR signals in fluids far from the pore walls is similar to those from bulk fluids having comparatively long relaxation times, whereas fluids close to the pore walls undergo a process of adsorption and desorption with the pore walls which has the effect of drastically reducing their NMR relaxation times.
In large pores, the dominant effect is from the bulk fluids, so larger pores have longer NMR relaxation times. In smaller pores, the surface-to-volume ratio is much higher, hence the fluids near the pore wall dominate the NMR signal, and smaller pores display overall shorter NMR relaxation times. This process is illustrated in the figures below.
Of course, practically it may not feasible to take NMR measurements from individual pores. The entire core must be measured at once, hence the resulting NMR signal is a composite of all the NMR signals from the different pore sizes in the core.
MicroMR 2MHz 5MHz Core NMR Analyzer Benchtop NMR System
- 1-inch diameter probe coil is specially designed for 1-inch diameter rock, also suitable for rock cuttings
- Low operation frequency; pulse mode
- All-digital spectrometer
- NMR scanning and analyzing software developed independently according to industry standards
- Customized pulse sequence package
- Exportable raw signal data facilitates data post-processing
- Convenient for export of raw data to Excel
- Automatic and manual calibration of operating frequency
- Automatic and manual calibration of pulse length (90 and 180 pulse)
- Professional ICC(Industrial Control Computer) ensures high stability and fast processing speed
- Compact structure and attractive appearance