The validity of the cubic law for laminar flow of fluids through open fractures consisting of parallel planar plates has been established by others over a wide range of conditions with apertures ranging down to a minimum of 0.2 µm. The law may be given in simplified form by Q/Δh = C(2b)3, where Q is the flow rate, Δh is the difference in hydraulic head, C is a constant that depends on the flow geometry and fluid properties, and 2b is the fracture aperture. The validity of this law for flow in a closed fracture where the surfaces are in contact and the aperture is being decreased under stress has been investigated at room temperature by using homogeneous samples of granite, basalt, and marble. Tension fractures were artificially induced, and the laboratory setup used radial as well as straight flow geometries. Apertures ranged from 250 down to 4µm, which was the minimum size that could be attained under a normal stress of 20 MPa. The cubic law was found to be valid whether the fracture surfaces were held open or were being closed under stress, and the results are not dependent on rock type. Permeability was uniquely defined by fracture aperture and was independent of the stress history used in these investigations. The effects of deviations from the ideal parallel plate concept only cause an apparent reduction in flow and may be incorporated into the cubic law by replacing C by C/ƒ. The factor ƒ varied from 1.04 to 1.65 in these investigations. The model of a fracture that is being closed under normal stress is visualized as being controlled by the strength of the asperities that are in contact. These contact areas are able to withstand significant stresses while maintaining space for fluids to continue to flow as the fracture aperture decreases. The controlling factor is the magnitude of the aperture, and since flow depends on (2b)3, a slight change in aperture evidently can easily dominate any other change in the geometry of the flow field. Thus one does not see any noticeable shift in the correlations of our experimental results in passing from a condition where the fracture surfaces were held open to one where the surfaces were being closed under stress.

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VALIDITY OF CUBIC LAW FOR FLUID FLOW IN A DEFORMABLE ROCK FRACTURE - eScholarship

Injecting pure N2 and CO2 to coal for enhanced coalbed methane: Experimental observations and numerical simulation

Methane and CO2 sorption hysteresis on coal: A critical review

A review of microscopic seepage mechanism for shale gas extracted by supercritical CO2 flooding

To study the seepage and deformation characteristics of coal at high temperatures, coal samples from six different regions were selected and subjected to computed tomography (CT) scanning studies. In conjunction with ANSYS software, 3D reconstruction of CT images was used for the establishment of fluid-solid conjugate heat transfer model and coal thermal deformation model based on the microstructures of coal. In addition, the structure of coal was studied in 2D and 3D perspectives, followed by the analysis of seepage and deformation characteristics of coal at high temperatures. The results of this study indicated that porosity positively correlated with the fractal dimension, and the connectivity and seepage performances were roughly identical from 2D and 3D perspectives. As the porosity increased, the fractal dimension of coal samples became larger and the pore-fracture structures became more complex. As a result, the permeability of coal samples decreased. In the meantime, fluid was fully heated, generating high-temperature water at outlet. However, when the porosity was low, the outlet temperature was very high. The average deformation of coal skeleton with different pore-fracture structures at high temperatures showed a trend of initial increase and subsequent decrease with the increase of porosity and fractal dimension. The maximum deformation of coal skeleton positively correlated with connectivity but negatively correlated with the fractal dimension.

Study on seepage and deformation characteristics of coal microstructure by 3D reconstruction of CT images at high temperatures

Permeability variation associated with fines production from anthracite coal during water injection

Physical and analytical modelling of permeability damage in bituminous coal caused by fines migration during water production

A laboratory study of the effect of creep and fines migration on coal permeability during single-phase flow

This paper presents an experimental and modelling study of the adsorption/desorption of pure gases CH4, CO2 and N2 and their binary and ternary mixtures on coal samples obtained from southeast Qinshui Basin, China Results show that the adsorbed amounts of N2, CH4 and CO2 have approximate ratios of 10:13:24, respectively No significant hysteresis from adsorption to desorption is observed for pure N2 and CH4 whereas significant hysteresis is measured for CO2 in CO2-CH4 and CO2-CH4-N2 mixtures and CH4 in the N2-CH4 mixture The experimental observations are modelled using three different models, namely the extended Langmuir (EL), the Langmuir-based ideal adsorbed solution (L-IAS) and the Dubinlin-Radushkevich-based ideal adsorbed solution (D-R-IAS) The models predict well the experimental observations for desorption tests But the measurements for the low adsorbate capacity in binary and ternary mixtures are overestimated by the prediction models It is found that the EL model predicts the CO2-CH4 deso

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Zhenghuai Guo

Papers

Permeability variation associated with fines production from anthracite coal during water injection

Physical and analytical modelling of permeability damage in bituminous coal caused by fines migration during water production

A laboratory study of the effect of creep and fines migration on coal permeability during single-phase flow

Adsorption/desorption characteristics for methane, nitrogen and carbon dioxide of coal samples from Southeast Qinshui Basin, China

Computation of Relative Permeability From In-Situ Imaged Fluid Distributions at the Pore Scale