A new nuclear magnetic resonance permeability model of shale of Longmaxi Formation in southern Sichuan Basin

Key words:  shale gas  nuclear magnetic resonance (NMR)  nuclear magnetic resonance (NMR) permeability  Coates model  SDR model

Abstract:

In order to measure the shale permeability more effectively and quickly, 22 shale samples from Lower Silurian Longmaxi Formation in southern Sichuan Basin were collected and used in the low field nuclear magnetic resonance (NMR) and high-speed centrifugal experiments. The results show that the relative error of the four rocks NMR permeability model currently used are very large, and is small only in the extended SDR model. Therefore the four conventional NMR models are not suitable for the NMR permeability calculation of shale. In order to reduce the calculation error, a single parameter model of shale NMR permeability is set up based on the SDR model. The correlation coefficient of this new model reaches 0.967, and the average relative error of pulse decay permeability is about 18.31%. It is concluded that the new model can calculate the permeability of gas shale more accurately, which provides a fast, nondestructive and effective experimental methodology for shale permeability test.