Method and system for testing oil-water capillary pressure curve of compact rock core

Abstract

The invention discloses a method and a system for testing an oil-water capillary pressure curve of a compact rock core. The system comprises a magnet, a gradient coil, a sample moving platform, a nuclear magnetic resonance radio frequency coil, a nuclear magnetic resonance spectrometer, a radio frequency power amplifier, a gradient amplifier, a power supply, a water cooling machine, a computer comprising a host and a display, and a pre-amplifier. Awater cooling system is arranged in the gradient coil. By designing a pure phase coded pulse sequence with short echo time, quick attenuation signals in the compact rock core are collected, fluid saturation distribution in the compact rock core when oil and water phases coexist is obtained in combination with centrifugal equipment, and the systemis used for testing an oil-water capillary pressure curve of the compact rock core and is more suitable for being used in an oil reservoir development field.

Description

technical field [0001] The invention belongs to the technical field of nuclear magnetic resonance, and relates to a method and a system for testing the oil-water capillary pressure curve of a dense rock core. Background technique [0002] As an unconventional oil and gas resource, tight oil has abundant reserves, which has greatly changed my country's energy structure. It has very important strategic significance and commercial development prospects. The test and analysis of the physical parameters of the reservoir core is particularly important. The capillary pressure curve is an important physical property of the core. It plays a very important role in the fields of seepage mechanism research, reservoir development evaluation, reservoir accumulation exploration and other fields. [0003] At present, in the testing method of capillary pressure curve nuclear magnetic resonance, the test of the fluid saturation distribution of the sample is carried out through conventional med...

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Problems solved by technology

[0004] Due to the physical properties of tight cores such as small porosity (low fluid abundance), low permeability, high clay content, and mostly small pore sizes, the excited NMR signal has low intensity and fast attenuation (i.e., relaxation time is short), there are few relaxation components above 10ms, and the echo time TE (Time to Echo, echo time), an important parameter of conventional medical magnetic resonance imaging technology, is longer. Taking 0.3T nuclear magnetic resonance imaging equipment as an example, its For one-dimensional imaging pulse sequences see figure 1 , the echo time TE-3 is jointly determined by the 90°soft pulse-1, 180°soft pulse-2, sampling time-4, and readout gradient compensation gradient-5 in the figure. The shortest echo time TE-3 is fundamentally determined by The limitation of the frequency encoding method, even if the hardware level is improved, because TE is positively correlated with the resolution, it determines that the high resolution and short TE of this method cannot be taken into account at the same time.

The shortest echo time in one-dimensional imaging is about 15 ms, and it is mostly used for MRI analysis of long relaxation features such as muscle, fat, and tissue fluid, while tight cores have short relaxation times, and the transverse relaxation time T2 is less than 1 ms. The existing capillary pressure curve NMR test technology is not suitable for the NMR analysis of the capillary pressure curve of tight rock cores, and the existing capillary pressure curve NMR test technology is difficult for the oil-water two-phase coexistence in the core during the actual development and production of the petroleum industry. Test and analyze the capillary pressure curve

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