Effect of Nano-Pore Wall Confinements on Non-Ideal Gas Dynamics in Organic Rich Shale Reservoirs

摘要

The advancements in horizontal well drilling and multistage hydraulic fracturing technology enabled us to unfold major sources of hydrocarbon trapped in ultra-tight formations such as tight sands and organic rich shales. Tremendous gas production from these reservoirs has transformed today's energy landscape. To effectively optimize the hydrocarbon production from these ultra-tight formations, it is essential to study and model the fluid transport and storage sealed in multiscale pore structure of these formations, i.e. micro-, meso- and macro-pores. In shale gas reservoirs, Kerogen, the finely dispersed organic nano-porous material with an average pore size of less than 10 nm holds bulk of the total gas in place (GIP) in an adsorbed state. The molecular level interactions between fluid-fluid and fluid-solid organic pore walls govern the transport and storage in these organic nano-pores. Among different methods used to model gas dynamics in organic nano-pores such as the multi-continuum, molecular dynamics and Monte Carlo, the lattice Boltzmann method (LBM) is a more effective method with much less computational cost relative to other techniques. This is due to the applicability of this technique in wide range of flow regimes and ease of handling complex boundary conditions such as incorporation of the molecular interactions in porous media.;The objective of this research is to develop a two-dimensional LBM of organic rich shales that can be used to quantify the effect of organic pore wall confinement on non-ideal gas flow and storage in organic nano-pores of the shale reservoirs. This method incorporates the involvement of molecular forces between fluid particles such as, adsorptive and cohesive forces. Using the Langmuir-slip boundary condition at capillary walls, slippage of free gas molecules and surface transport of adsorbed molecules are studied. This effect is investigated in a large range of Knudsen numbers from continuum flow to transition flow regime with varying capillary width sizes from 100 nm to 5 nm.;Simulation results concentrates on the molecular phenomena like- adsorptive/cohesive forces, and the kinetic energy of the fluid molecules at different pressures, and reservoir temperatures. The LBM model results displays a clear indication that the gas transport in the capillary tube is depends on the pore width size. A critical Knudsen number exists with changing reservoir conditions, where the anticipated fluid velocity profile in organic nano-pores alters showing higher flow rate as capillary widths reduces due to the underlying effect of molecular phenomena of double slippage and wall confinement, introduced earlier by Fathi et al. These results are compared with traditional continuum Hagen-Poiseuille law, Klinkenberg slip theory, and recent modified version of Klinkenberg slip flow equation. This work is not only important for the advancement of shale gas flow simulator, but also for organic rich shale characterization.