Gas Flow In Pores Research Articles

Simulation of gas flow in organic-rich mudrocks using digital rock physics

Organic-rich mudrock systems play an important role in the world's volatile petroleum industry. Due to their complex pore structures with a large portion of nano pores, the flow mechanics of gas flow in the pore space may involve nanoscale effects that could not be accounted for by classic Darcy's law. It is also very difficult to experimentally probe the transport properties of extremely low permeability rock samples. Digital rock physics (DRP) obtains a direct view of the internal structure of reservoir rock sample by digitized high resolution images to compute their properties, such as porosity and directional permeability, and hence to enable the studies of multi-scale flow mechanics in mudrocks. In this study, we present a parallel lattice Boltzmann method (PLBM) for studying nanoscale effects on a three dimensional (3D) tube flow, and then to simulate the flow process of the gas flow in real 3D pore geometry of two perpendicularly cored mudrock samples (S62H and S62V), combining with some image processing methods in DRP. The pore geometry is obtained by 3D digital image data based on ultra-high resolution X-ray computed tomography (XCT) imaging. The numerical advantages of lattice Boltzmann method (LBM) make it a powerful tool to simulate gas flow in such nano pores and estimate the absolute permeability. The new parallel implementation has been successfully performed on a powerful high performance computing cluster (HPCC) and validated with the analytical solution of a 3D tube flow model, which is taken as the elementary model for the pore networks. By simulating the nanoscale effects of rarefaction, slippage and roughness on gas flow in a nano tube model, we propose some more realistic parameters for simulating the gas flow in real mudrocks to study the flow mechanics, and to calculate the apparent directional permeability. The results show: 1) the simulated porosities (7.66% for S62H and 2.58% for S62V) are close to measured porosities (5.00% for S62H and 1.76% for S62V); 2) the estimated apparent permeability of S62H is 0.032 mD, which is close to the measured permeability of 0.02 mD; 3) the apparent directional permeability of S62V is not able to be estimated because the identified pores of subsamples are not connected in any direction with the image resolution of 65 nm/voxel; 4) the permeability anisotropy of S62H is clearly observed through the velocity field visualization and calculated permeability values; 5) the characteristics of pore geometry, flow velocity distribution and transport properties can be captured using DRP and the PLBM is an effective way to simulate complex gas flow in kerogen pores and estimate the apparent directional permeability.

Influence of gas generation in electro‐osmosis consolidation

SummaryThis paper presents a numerical model for the elasto‐plastic electro‐osmosis consolidation of unsaturated clays experiencing large strains, by considering electro‐osmosis and hydro‐mechanical flows in a deformable multiphase porous medium. The coupled governing equations involving the pore water flow, pore gas flow, electric flow and mechanical deformation in unsaturated clays are derived within the framework of averaging theory and solved numerically using finite elements. The displacements of the solid phase, the pressure of the water phase, the pressure of the gas phase and the electric potential are taken as the primary unknowns in the proposed model. The nonlinear variation of transport parameters during electro‐osmosis consolidation are incorporated into the model using empirical expressions that strongly depend on the degree of water saturation, whereas the Barcelona Basic Model is employed to simulate the elasto‐plastic mechanical behaviour of unsaturated clays. The accuracy of the proposed model is evaluated by validating it against two well‐known numerical examples, involving electro‐osmosis and unsaturated soil behaviour respectively. Two further examples are then investigated to study the capability of the computational algorithm in modelling multiphase flow in electro‐osmosis consolidation. Finally, the effects of gas generation at the anode, the deformation characteristics, the degree of saturation and the time dependent evolution of the excess pore pressure are discussed. Copyright © 2016 John Wiley & Sons, Ltd.

页岩气渗流过程中的多场耦合机理

The deficiencies in present mathematic models of shale gas flow are outlined briefly. Based on the linear poroelasticity, the transfer of free gas in nanopores, surface diffusion of adsorbed gas, nonlinear and non-equilibrium gas adsorption-desorption kinetics as well as the rock deformation are all coupled to formulate a new mathematic model to unlock the true potential of shale-gas development. The stress-and-pressure dependent permeability and porosity models of matrix containing random fractures, together with the non-equilibrium adsorption-desorption kinetics, are also deduced in this paper. Numerical method is applied to solve the model and analyze the impacts of stress-and-pressure sensitivity, surface diffusion and non-equilibrium adsorption on shale gas flow. The results suggest: (1) The fracture density in the shale matrix plays an important role in the permeability and porosity, the stress-and-pressure sensitivity of shale rock itself can be ignored; (2) compared with the free gas flow in pores, the surface diffusion of adsorbed gas can be ignored; (3) the recovery time during non-equilibrium sorption process relies heavily on equilibrium coefficient and rock porosity, and the desorption rate significantly impacts the gas flow rate.

Low-velocity detonation modes of grained pyroxylin powder

It is well known that low-velocity detonation excited by the explosion of a thin layer of a plastic explosive within charges of grained pyroxylin powder is propagated with a velocity that is practically constant along the charge. However, it varies depending on the power of the initiating pulse. The present paper is devoted to the elucidation of the mechanism of this unusual feature of detonation process. Experiments were carried out on charges of VTM grade grained single-channel powder with different initial density and were added by numerical modeling. It is shown that the property studied is the consequence of the relatively low intensity of the chemical transformation and the limited charge length (120 mm in the experiment and calculations). The reaction zone of the detonation wave has no time to form completely under these conditions, and the development process is interrupted at a stage when the wave characteristics change actively. The wave evolution was distinctly revealed on pressure profiles; however, the front trajectory, if excluding the initiation area, has an almost linear form. The wave velocity, close to constant, corresponds to this. To form a stationary wave with characteristics that are not dependent on the initiation conditions in a range corresponding to lowvelocity detonation mode, charges with much greater length are necessary. As regards the mechanism of the excitation of chemical transformation in the wave front, as numerical modeling showed, high-porosity charges operate by the gas-phase mechanism (the compression and heating in the high-speed gas flow in pores). In the case of compacted charges with a porosity of 0.2 and lower, heating and ignition of the powder occur by the solid-phase mechanism (because of dissipation at plastic deformations of the porous layer). Details of both mechanisms are considered.

Conductive thermal conductivity of fibrous materials under transient gas flow

The results are reported from computational studies of the conductive thermal conductivity of fibrous materials working at pressures correspnding to transient gas flow in pores.