Nuclear Magnetic Resonance Experiment on the Influence of Confining Pressure on Spontaneous Imbibition of Water in Coal

Abstract

Residual water after hydration measures can wet a coal sample to lead to spontaneous imbibition; it is a common phenomenon in the process of extracting coalbed methane using hydraulic measures. To study the characteristics of the microscopic pore structure of a coal body and spontaneous imbibition of water in the pore structure by simulating the actual deposition environment, the T 2 spectra and spatial distribution of water in the imbibition process of coal samples under different circumferential pressure conditions were obtained by online testing using the low-field NMR technique. Results show that during the process of coal sample imbibition, the T 2 spectra shows the characteristics of multi-peak distribution, and the number of adsorption and seepage pores is considerably higher than the fracture. Moreover, the influence of confining pressure on imbibition mainly appears in the seepage pore. The spontaneous imbibition behavior at different stages is accurately described by the Handy equation combined with the NMR signal; the higher the confining pressure, the worse the imbibition ability of the coal sample. The rate of water migration to the end of coal sample will be higher than the rate of migration to the surrounding. Finally, the three-dimensional signal distribution indicates that the imbibition is not a piston advance but a wave advance, and the rate of water migration in the longitudinal direction is higher than the rate of diffusion in the lateral direction.

Imbibition Behavior of Oil-Saturated Rock: Implications for Enhanced Oil Recovery in Unconventional Reservoirs

“…Nuclear magnetic resonance (NMR) can distinguish the liquid content in pore spaces, which is ascribed to liquid having a short relaxation time in small pores and a long relaxation time in large pores. − Because of this merit, NMR plays an important role in monitoring the liquid distribution and has been widely used to observe the process of liquid displacing gas. For example, NMR can be used to monitor the liquid distribution during co-current and counter-current imbibition, which shows that the order of liquid filling into pores varies with different rock types, including sandstone, volcanic rock, shale, coal, and hydrate sediments. − NMR with slicing method can reflect the water content along the sample axial direction and indicate that the water saturation away from the water contact surface increases gradually with time . Similar to NMR with slicing method, computed tomography (CT) is used to monitor the variation of water saturation in diatomite, implying the waterfront moves uniformly in the beginning and differently in the late period .…”

Novel Discrete Fracture Network Model for Multiphase Flow in Coal

“…Gas/water relative permeability has been analyzed on the basis of in situ dynamic microcomputed tomography imaging technology . Ma et al studied the spontaneous imbibition of water using a nuclear magnetic resonance experiment, and Zhao et al stimulated relative permeability of two immiscible fluids flowing in a porous media using the lattice Boltzmann method . Jing et al simulated multiphysics gas flow in coal using a pore network model (PNM) .…”