Characterization of thermal evolution of pores and fluids in shales using NMR 2D measurement


H. Jiang, Daigle, H., Zhang, B., and Tian, X., “Characterization of thermal evolution of pores and fluids in shales using NMR 2D measurement,” Unconventional Resources Technology Conference. Society of Petroleum Engineers/Society of Exploration Geophysicists/American Association of Petroleum Geologists, Houston, TX, 2018.


The evolution of pores and fluids due to thermal effects is a key factor for predicting shale gas production. However, different fluid types and a wide range of pore sizes pose difficulties for characterization. We experimentally changed the fluid distribution and maturity of shales by pyrolysis on an Eagle Ford sample and a northern Rocky Mountains sample. Initial fluid conditions of shale samples were determined by NMR T1-T2 measurement. The samples were heated at 110°C, 250°C, 450°C, and 650°C, and T1-T2 measurements were performed after each level. The obtained T1 and T2 distributions were mapped to T1/T2 ratio (R) and secular relaxation time (Ts) for better characterization of different fluid distributions. Further, a difference index was used to quantify the overall distribution difference in R-Ts space.

According to the results, the Eagle Ford sample is dominated by an oil signal, whereas the northern Rocky Mountains sample has a mixture of oil, water and organic matter signal. Fluid volume decreases with increasing temperature. Heating at 110°C or 250°C reduces the fluid volume through the course of evaporation of water and hydrocarbon. The signal of OM is also revealed due to the fluid evaporation. Heating at 450°C and 650°C will alter the maturity of OM, resulting the change of distribution shape of T1-T2 due to change of pore structure. The thermal effects lead two samples to have a similar evolution pattern during thermal maturation.


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