Application of Nuclear Magnetic Resonance in Hydration Damage of Mud Shale

Application of Nuclear Magnetic Resonance in Hydration Damage of Mud Shale

The problem of wellbore instability is a complex problem that has prevailed in oil drilling and has been plaguing the petroleum industry. Wellbore instability encountered during oil drilling can be roughly classified into fracture body instability, plastomer instability, and mud shale instability. Among them, mud shale instability accounts for more than 90%. Therefore, some researchers believe that The problem of wellbore stability is the problem of mud shale stability.
The microscopic structures such as pores and granules of mud shale have changed after water, which promotes the whole process of crack initiation and expansion until the final rupture, which has an important influence on the mechanical properties and engineering properties of shale. The study of the damage evolution from the internal structure of rock to the complete rupture process has been studied by various scholars at home and abroad through various rock meso-mechanical tests.
Nuclear magnetic resonance (NMR) technology is a new type of detection method for studying the mesostructure of rock, which has the advantages of non-destructive, repeated and rapid. NMR obtains information on rock porosity, pore structure characteristics, fluid content, etc. by analyzing the nuclear magnetic resonance relaxation time. MRI can visually observe the development of pore damage inside rock. Currently, nuclear magnetic resonance technology is mainly used in petroleum engineering. Through the study of rock pore structure and reservoir rock pore fluid characteristics, the application of reservoir evaluation and logging logging is carried out.
The following is a brief introduction to the use of nuclear magnetic resonance technology to test the transverse relaxation time and nuclear magnetic imaging of samples with different immersion time. By analyzing the sample mass change, the transverse relaxation time T2 spectrum distribution, the T2 spectral area change and nuclear magnetic imaging, The internal crack damage evolution process of shale after hydration was analyzed and discussed.

Transverse relaxation time T2 distribution

As can be seen from the above figure, as the immersion time is extended, part of the T2 spectrum is 3 peaks, and the second peak of the large-sized micro-crack corresponding to the right side continues to move to the right, indicating that the micro-cracks continue to hydrate. The expansion and bifurcation formed more micro-cracks, indicating that the rock has experienced more serious hydration damage.

After 1 d soaking, in the next few days, the small peak micropores corresponding to the first peak on the T2 distribution map, the amplitude of the peak further increases, indicating that the new micropores are continuously generated and expanded.

Magnetic resonance imaging analysis

The black color in the image is the background color. The whitish area is the area where the water molecules are located, which represents the pore range. The brightness of the image reflects the water content in the rock. The more white bright spots, the larger the rock pores. The smaller the pore

References: “Research on Hydration Damage Evolution of Brack Hard Hard Shale Based on Nuclear Magnetic Resonance”, Geotechnical Mechanics, March 2015, Vol. 36, No. 3