Showing papers on "Permeability (earth sciences) published in 2014"
TL;DR: In this article, the effects of confining stress and pore pressure on permeability were examined on intact core samples from the Barnett, Eagle Ford, Marcellus, and Montney shale reservoirs.
Abstract: Predicting long-term production from gas shale reservoirs has been a major challenge for the petroleum industry. To better understand how production profiles are likely to evolve with time, we have conducted laboratory experiments examining the effects of confining stress and pore pressure on permeability. Experiments were conducted on intact core samples from the Barnett, Eagle Ford, Marcellus, and Montney shale reservoirs. The methodology used to measure permeability allows us to separate the reduction of permeability with depletion (because of the resultant increase in effective confining stress) and the increase in permeability associated with Knudsen diffusion and molecular slippage (also known as Klinkenberg) effects at very low pore pressure. By separating these effects, we are able to estimate the relative contribution of both Darcy and diffusive fluxes to total flow in depleted reservoirs. Our data show that the effective permeability of the rock is significantly enhanced at very low pore pressures ( []) because of the slippage effects. We use the magnitude of the Klinkenberg effect to estimate the effective aperture of the flow paths within the samples and compare these estimates to scanning electron microscopy image observations. Our results suggest effective flow paths to be on the order from tens of nanometers in most samples to 100–200 nm, in a relatively high-permeability Eagle Ford sample. Finally, to gain insight on the scale dependence of permeability measurements, the same core plugs were crushed, and permeability was again measured at the particle scale using the so-called Gas Research Institute method. The results show much lower permeability than the intact core samples, with very little correlation to the measurements on the larger scale cores.
422 citations
TL;DR: In this article, the authors map and analyze permeability and porosity globally and at high resolution for the first time, based on a recently completed high resolution global lithology map that differentiates fine and coarse-grained sediments and sedimentary rocks.
Abstract: The lack of robust, spatially distributed subsurface data is the key obstacle limiting the implementation of complex and realistic groundwater dynamics into global land surface, hydrologic, and climate models. We map and analyze permeability and porosity globally and at high resolution for the first time. The new permeability and porosity maps are based on a recently completed high-resolution global lithology map that differentiates fine and coarse-grained sediments and sedimentary rocks, which is important since these have different permeabilities. The average polygon size in the new map is ~100 km2, which is a more than hundredfold increase in resolution compared to the previous map which has an average polygon size of ~14,000 km2. We also significantly improve the representation in regions of weathered tropical soils and permafrost. The spatially distributed mean global permeability ~10−15 m2 with permafrost or ~10−14 m2 without permafrost. The spatially distributed mean porosity of the globe is 14%. The maps will enable further integration of groundwater dynamics into land surface, hydrologic, and climate models.
208 citations
TL;DR: In this article, a laboratory study has been conducted to investigate the transport of gases and water in the matrix of Lower Toarcian Posidonia Shale samples from three shallow boreholes in northern Germany.
190 citations
TL;DR: In this article, a method to compute the full permeability tensor of three-dimensional discrete fracture and matrix models is described, based on the element-wise averaging of pressure and flux, obtained from a finite element solution to the Laplace problem, and validated against analytical expressions for periodic anisotropic porous media.
Abstract: The reduction from three- to two-dimensional analysis of the permeability of a fractured rock mass introduces errors in both the magnitude and direction of principal permeabilities. This error is numerically quantified for porous rock by comparing the equivalent permeability of three-dimensional fracture networks with the values computed on arbitrarily extracted planar trace maps. A method to compute the full permeability tensor of three-dimensional discrete fracture and matrix models is described. The method is based on the element-wise averaging of pressure and flux, obtained from a finite element solution to the Laplace problem, and is validated against analytical expressions for periodic anisotropic porous media. For isotropic networks of power law size-distributed fractures with length-correlated aperture, two-dimensional cut planes are shown to underestimate the magnitude of permeability by up to 3 orders of magnitude near the percolation threshold, approaching an average factor of deviation of 3 with increasing fracture density. At low-fracture densities, percolation may occur in three dimensions but not in any of the two-dimensional cut planes. Anisotropy of the equivalent permeability tensor varies accordingly and is more pronounced in two-dimensional extractions. These results confirm that two-dimensional analysis cannot be directly used as an approximation of three-dimensional equivalent permeability. However, an alternative expression of the excluded area relates trace map fracture density to an equivalent three-dimensional fracture density, yielding comparable minimum and maximum permeability. This formulation can be used to approximate three-dimensional flow properties in cases where only two-dimensional analysis is available.
183 citations
TL;DR: In this paper, the authors investigated the relationship between apparent water permeability and hydrate saturation (Sh), accounting for hydrate pore-scale growth habit and meso-scale heterogeneity.
Abstract: Permeability is a critical parameter governing methane flux and fluid flow in hydrate-bearing sediments; however, limited valid data are available due to experimental challenges. Here we investigate the relationship between apparent water permeability (k′) and hydrate saturation (Sh), accounting for hydrate pore-scale growth habit and meso-scale heterogeneity. Results from capillary tube models rely on cross-sectional tube shapes and hydrate pore habits, thus are appropriate only for sediments with uniform hydrate distribution and known hydrate pore character. Given our pore network modeling results showing that accumulating hydrate in sediments decreases sediment porosity and increases hydraulic tortuosity, we propose a modified Kozeny-Carman model to characterize water permeability in hydrate-bearing sediments. This model agrees well with experimental results and can be easily implemented in reservoir simulators with no empirical variables other than Sh. Results are also relevant to flow through other natural sediments that undergo diagenesis, salt precipitation, or bio-clogging.
182 citations
TL;DR: In this article, the authors performed history matching with two field gas production data from Barnett Shale and Marcellus Shale, and first analyzed the positive contribution of gas desorption and the negative effect of geomechanics on gas production, respectively, and then compared these two effects with the purpose of identifying which effect is dominant in the whole process of gas production.
182 citations
TL;DR: In this article, the authors explore the interactions of stress and damage that contribute to changes in coal permeability through imaging with X-ray computed tomography (X-ray CT), acoustic emission (AE) profiling together with the concurrent measurement of P-wave velocities.
173 citations
TL;DR: In this paper, the authors present results from a laboratory study investigating the fluid (gas/water) transport properties in the matrix system of the Scandinavian Alum Shale, showing that the intrinsic permeability coefficients measured parallel and perpendicular to bedding were within the range previously reported for other shales and mudstones.
167 citations
TL;DR: In this article, the porosity of a porous medium is described by an effective hydraulic pore radius in the porous medium, the fluctuation in local hydraulic radii, the length of streamlines, and the fractional volume conducting flow.
Abstract: In this article we investigate the permeability of a porous medium as given in Darcy’s law. The permeability is described by an effective hydraulic pore radius in the porous medium, the fluctuation in local hydraulic pore radii, the length of streamlines, and the fractional volume conducting flow. The effective hydraulic pore radius is related to a characteristic hydraulic length, the fluctuation in local hydraulic radii is related to a constriction factor, the length of streamlines is characterized by a tortuosity, and the fractional volume conducting flow from inlet to outlet is described by an effective porosity. The characteristic length, the constriction factor, the tortuosity, and the effective porosity are thus intrinsic descriptors of the pore structure relative to direction. We show that the combined effect of our pore structure description fully describes the permeability of a porous medium. The theory is applied to idealized porous media, where it reproduces Darcy’s law for fluid flow derived from the Hagen–Poiseuille equation. We also apply this theory to full network models of Fontainebleau sandstone, where we show how the pore structure and permeability correlate with porosity for such natural porous media. This work establishes how the permeability can be related to porosity, in the sense of Kozeny–Carman, through fundamental and well-defined pore structure parameters: characteristic length, constriction, and tortuosity.
143 citations
TL;DR: In this paper, a series of experiments were performed to investigate the variation of permeability in gas hydrates-bearing sediments, and the experimental results were compared with several theoretical models using both the quantitative and graphical analyses.
140 citations
TL;DR: In this article, a node-bond pore-network flow model was developed for gas flow where it is the only fluid phase, and the flow conductance equation includes the usual Darcy flow terms, and additional terms that capture the contributions from slip flow to Knudsen diffusion.
TL;DR: In this article, an analytical model was proposed to represent the anisotropic permeability evolution of coal due to effective stress change and gas sorption, and this model captured both mechanical properties and gas-sorption-induced directional strains.
TL;DR: In this article, a new well testing model for multiple fractured horizontal wells (MFHW) in shale gas reservoirs with consideration of desorption, diffusive flow, viscous flow and stress-sensitivity of reservoir permeability is presented.
TL;DR: In this paper, the effect of pressure on gas permeability in the pore network structure was investigated using non-equilibrium molecular dynamics (NEMD) simulations with an external driving force imposed on the 3-D carbon pore networks generated atomistically using the Voronoi tessellation method.
TL;DR: In this paper, a volume-averaging model for the electrical conductivity was used to determine intrinsic formation factor and surface conductivity of Fontainebleau sandstone, a clean sandstone with relatively coarse ( ∼ 250 μm ) and well-rounded silica grains and silica cement.
Abstract: The electrical conductivity of clay-free sandstones is customarily assumed to have negligible surface conductivity contribution. The Fontainebleau sandstone, a clean sandstone with relatively coarse ( ∼ 250 μm ) and well-rounded silica grains and silica cement, exhibits surface conductivity along the electrical double layer coating the surface of the grains. A recently developed volume-averaging model for the electrical conductivity was used to determine intrinsic formation factor and surface conductivity from electrical conductivity measurements performed at seven salinities with NaCl solutions. The bulk tortuosity of the pore space influenced the surface conductivity in a predictable way. Formation factor and permeability can be determined as a function of the porosity using the equations developed by Archie for the formation factor, and Revil and Cathles for the permeability. In both the cases, the data emphasize the existence of a percolation threshold of about 0.02 (2%) in porosity. Once corrected for the effect of this percolation threshold, the porosity exponent of Archie’s equation was approximately equal to 1.5 as predicted from the differential effective medium theory for a pack of spherical grains suspended in an electrolyte. We illustrated that permeability can be predicted, within one order of magnitude, from surface conductivity, porosity, and formation factor. Spectral-induced polarization data indicated that the in-phase conductivity was nearly frequency-independent (in the frequency range from 1 to 10 kHz) whereas the quadrature conductivity displayed a relationship between the surface conductivity and a peak frequency likely related to the pore throat size determined from mercury porosimetry measurements.
TL;DR: In this article, the authors investigated the nature of helium permeability change on 14 coal cores under a varying effective stress from 4 to 12 MPa in laboratory, and found that the gas permeability of coals varies with effective stress increase, matrix shrinkage/swelling due to gas desorption/adsorption, gas slippage and other factors.
TL;DR: In this article, the authors reconstructed the porosity, pore size distribution, specific surface area and pore connectivity of shales from Sichuan Basin, China using scanning electron microscopy (SEM) images of shale samples.
Abstract: Porous structures of shales are reconstructed based on scanning electron microscopy (SEM) images of shale samples from Sichuan Basin, China. Characterization analyzes of the nanoscale reconstructed shales are performed, including porosity, pore size distribution, specific surface area and pore connectivity. The multiple-relaxation-time (MRT) lattice Boltzmann method (LBM) fluid flow model and single-relaxation-time (SRT) LBM diffusion model are adopted to simulate the fluid flow and Knudsen diffusion process within the reconstructed shales, respectively. Tortuosity, intrinsic permeability and effective Knudsen diffusivity are numerically predicted. The tortuosity is much higher than that commonly employed in Bruggeman equation. Correction of the intrinsic permeability by taking into consideration the contribution of Knudsen diffusion, which leads to the apparent permeability, is performed. The correction factor under different Knudsen number and pressure are estimated and compared with existing corrections reported in the literature. For the wide pressure range under investigation, the correction factor is always greater than 1, indicating the Knudsen diffusion always plays a role on the transport mechanisms of shale gas in shales studied in the present study. Most of the values of correction factor are located in the transition regime, with no Darcy flow regime observed.
TL;DR: In this paper, two improved models are proposed, one is under constant effective stress and the other is under reservoir condition, which shows that the proportion of change due to Klinkenberg effect is greater than the result from original model.
TL;DR: In this paper, a set of triaxial testing measurements on 38 mm diameter fractured sub-bituminous and bituminous coal cores exposed to CO2 were performed and the results were analyzed with a poromechanical model in which coal matrix microporosity and adsorption-induced phenomena were embedded into a fractured reservoir rock with transverse isotropic properties.
TL;DR: In this paper, the authors present new experimental results on the drying of rocks induced by continuous injection of large amount of dry gas (N2) in deep saline aquifers and study slow and fast drying rates and capillary effects on drying.
TL;DR: In this paper, a collection of cores was retrieved from three wells intersecting these units and characterisation of their flow properties complemented the current evaluation of the Perth Basin by adding new data on effective porosity, pore size distribution and pore geometry according to a comprehensive facies classification scheme.
TL;DR: In this paper, a detailed comparison of permeability data derived from a selection of commonly used Hassler cells and probe permeameters is presented, where typical aberrations and transform equations are elaborated.
Abstract: . Permeability is one of the most important petrophysical parameters to describe the reservoir properties of sedimentary rocks, pertaining to problems in hydrology, geothermics, and hydrocarbon reservoir analysis. Outcrop analogue studies, well core measurements, and individual sample analysis take advantage of a variety of commercially available devices for permeability measurements. Very often, permeability data derived from different devices need to be merged within one study (e.g. outcrop minipermeametry and lab-based core plug measurements). To enhance accuracy of different gas-driven permeability measurements, device-specific aberrations need to be taken into account. The application of simple one-to-one correlations may draw the wrong picture of permeability trends. For this purpose, transform equations need to be established. This study presents a detailed comparison of permeability data derived from a selection of commonly used Hassler cells and probe permeameters. As a result of individual cross-plots, typical aberrations and transform equations are elaborated, which enable corrections for the specific permeameters. Permeability measurements of the commercially available ErgoTech gas permeameter and the TinyPerm II probe permeameter are well-comparable over the entire range of permeability, with R2 = 0.955. Aberrations are mostly identified in the permeability range
TL;DR: In this article, the authors presented an experimental study on relative gas and water permeabilities of ordinary concrete versus its saturation degree, which showed the influence of the saturation degree of concrete on the variation of water and gas permeabilities.
TL;DR: The interaction and the coupling of slip-flow of gases, a fluid dynamic phenomenon, and the cleat volume compressibility, a poro-elastic effect, have been investigated on two sister samples from the Taroom coal measure, Surat Basin, Queensland Australia as discussed by the authors.
TL;DR: In this article, a study of 16 corefloods with piecewise constant flow rate was performed under increasing flow rate, and it was found that the mobilised particles drift with speeds significantly lower than the carrier fluid velocity, resulting in long permeability stabilisation periods.
TL;DR: In this article, a dual-permeability model was proposed for the analysis of the experimental data based on the theory of poroelasticity, where coal permeability is determined by the effective stress only.
TL;DR: In this article, the authors simplified the Beskok and Karniadakis equation to describe the relationship between flow velocities and pressure gradient, which considers the molecular collisions with the pore walls.
TL;DR: In this paper, the Gamma test was used as a non-parametric nonlinear smooth modeling tool to choose the best input combination of seismic attributes to estimate k and ϕ, and the best combination of well-logs to estimate 1/Q.
TL;DR: In this paper, the authors investigate the underlying mechanics by generating well- controlled, repeatable permeability enhancement in laboratory experiments, and they conclude that a flow-dependent mechanism associated with mobilization of fines controls both the magnitude of the pore enhancement and the recovery rate in their experiments.