[CCoE Notice] PhD Defense: MOLECULAR MODELING OF SHALE GAS STORAGE AND TRANSPORT MECHANISMS IN SHALE NANOPORES

[Grayson, Audrey A]

PhD DEFENSE STUDENT: Shuai He

DATE: Thursday, November 16, 2017

TIME: 1:00 PM

PLACE:  Energy Research Park (ERP) Building 9, Room 129

DISSERTATION CHAIR: Dr. Guan Qin

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TITLE:

MOLECULAR MODELING OF SHALE GAS STORAGE AND TRANSPORT MECHANISMS IN SHALE NANOPORES



Shale reservoir contains different rock components that exhibit multi-scale hierarchical pore structure and complex mineralogical compositions, in which the experimental evidence has indicated that the majority of the natural gas in shale is adsorbed in the clay and organic matter nanopores. The impact of different geological features and adsorption effect on fluid transport mechanism is yet poorly understood. In this dissertation, we present a molecular modeling on fluid flow at nanoscale and investigate the impact of different features on gas transport, which further facilitates large-scale shale reservoir property characterization.

We first apply boundary-driven non-equilibrium MD simulation (BD-NEMD) to estimate the gas transport diffusivity in slit-like clay and kerogen nano-pores. We scrutinize the performance of six temperature control schemes in BD-NEMD simulation. Then, we examine the validity of the Knudsen model for predicting transport diffusivity under the effective temperature control schemes. Results indicate that the reservoir models based on Knudsen theory fail to predict the shale gas production accurately because it neglects to account for the adsorption effects.

Second, we apply external field NEMD (EF-NEMD) to estimate gas transport diffusivity in nano-scale digital rocks with complex pore structure, which is reconstructed by Markov Chain Monte Carlo (MCMC) simulation or Focused Ion Beam Scanning Electron Microscope (FIB-SEM). On top of their dependence on Knudsen number, gas transport diffusivity coefficients are found to be sensitive to the pore geometry factors (e.g. surface area, pore tortuosity, etc.), where an effectiveness factor has been proposed to modify the Knudsen diffusivity.

Third, we apply fractional partial differential equations (F-PDEs) to model the shale gas sub-diffusion process in micron-scale digital rocks with nanometer resolutions. Time-fractional PDE is able to accurately capture the transient state of gas sub-diffusion process which occurs in heterogeneous porous media with strong confinement. Integrate workflow has been developed where the transport diffusivity for each grid block is obtained from MD simulation. Slow rate of transport has been identified and the effective transport diffusivity in such micron-scale digital rock has been estimated. Such reservoir properties are then adopted to scale up the parameters to core plug scales for practical applications.


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