Permeability (earth sciences)

About: Permeability (earth sciences) is a research topic. Over the lifetime, 15424 publications have been published within this topic receiving 288535 citations.

Mapping permeability over the surface of the Earth

Abstract: [1] Permeability, the ease of fluid flow through porous rocks and soils, is a fundamental but often poorly quantified component in the analysis of regional-scale water fluxes Permeability is difficult to quantify because it varies over more than 13 orders of magnitude and is heterogeneous and dependent on flow direction Indeed, at the regional scale, maps of permeability only exist for soil to depths of 1–2 m Here we use an extensive compilation of results from hydrogeologic models to show that regional-scale (>5 km) permeability of consolidated and unconsolidated geologic units below soil horizons (hydrolithologies) can be characterized in a statistically meaningful way The representative permeabilities of these hydrolithologies are used to map the distribution of near-surface (on the order of 100 m depth) permeability globally and over North America The distribution of each hydrolithology is generally scale independent The near-surface mean permeability is of the order of ∼5 × 10−14 m2 The results provide the first global picture of near-surface permeability and will be of particular value for evaluating global water resources and modeling the influence of climate-surface-subsurface interactions on global climate change

Stimulating Unconventional Reservoirs: Maximizing Network Growth While Optimizing Fracture Conductivity

Abstract: A significant portion of gas production in North America comes from unconventional reservoirs such as gas shales, coalbed methane (CBM) deposits and tight gas sands. Due to their limited permeability, stimulation processes are needed for economic recovery from wells drilled into these formations. This paper described some of the technology-based solutions that have been used to successfully exploit these reservoirs, such as horizontal drilling, multi-stage completions, innovative fracturing, and fracture mapping. Economic production depends on the matrix permeability of these reservoirs as well as the conductivity that can be generated in hydraulic fractures and network fracture systems. Simulations have shown that a fracture network of moderate conductivity is needed in ultra-low shale permeabilities. The spacing between fractures must be small to obtain reasonable recovery factors. Such networks are achievable according to results of microseismic mapping. In contrast, tight gas sands may be successfully depleted without inducing complex fracture networks because they have orders of magnitude greater permeability than gas shales. However, the recovery in tight gas sands is complicated by other issues of damage and zonal coverage in these reservoirs. It was concluded that fracture mapping can help improve the understanding of fractures and improve the ability to change the fracture complexity through operational changes to the well design and treatment implementation. 47 refs., 15 figs.

Nanoscale simulation of shale transport properties using the lattice Boltzmann method: permeability and diffusivity

Abstract: Porous structures of shales are reconstructed using the markov chain monte carlo (MCMC) method based on scanning electron microscopy (SEM) images of shale samples from Sichuan Basin, China. Characterization analysis of the reconstructed shales is performed, including porosity, pore size distribution, specific surface area and pore connectivity. The lattice Boltzmann method (LBM) is adopted to simulate fluid flow and Knudsen diffusion within the reconstructed shales. Simulation results reveal that the tortuosity of the shales is much higher than that commonly employed in the Bruggeman equation, and such high tortuosity leads to extremely low intrinsic permeability. Correction of the intrinsic permeability is performed based on the dusty gas model (DGM) by considering the contribution of Knudsen diffusion to the total flow flux, resulting in apparent permeability. The correction factor over a range of Knudsen number and pressure is estimated and compared with empirical correlations in the literature. For the wide pressure range investigated, the correction factor is always greater than 1, indicating Knudsen diffusion always plays a role on shale gas transport mechanisms in the reconstructed shales. Specifically, we found that most of the values of correction factor fall in the slip and transition regime, with no Darcy flow regime observed.

Atmospheric pressure effects on 222Rn transport across the Earth-air interface

Abstract: The effect of large-scale atmospheric pressure changes on the 222Rn flux across the soil-air interface is investigated. Field data collected during 1972 and 1973 show that pressure changes of 1–2% associated with the passage of frontal systems produce changes in the 222Rn flux from 20 to 60%, depending upon the rate of change of pressure and its duration. A simple model of molecular diffusion combined with pressure-induced transport in the soil has been confirmed by laboratory experiments using a vertical column of 226Ra-bearing sand. On the basis of this model, pressure changes of 10–20 mbar occurring over a period of 1–2 days produce Darcy velocities of the order of 10−4 cm s−1 near the surface of a soil having a permeability of 10−8 cm2. The corresponding variations in the 222Rn flux predicted by the model are in agreement with those observed from valley alluvium in central New Mexico.

Permeability of Compacted Clay

Abstract: The effects of molding water content, density, degree of saturation, method of compaction, and thixotropic hardening on the permeability of compacted silty clay have been determined. The formation of a dispersed structure in samples compacted wet of optimum may result in a coefficient of permeability two or three orders of magnitude less than for the same soil compacted dry of optimum. The actual decrease in permeability wet of optimum appears to correlate well with the degree of shear strain applied to the soil during compaction. In line with this, it was found that for samples compacted wet of optimum kneading compaction gave significantly lower values of permeability than did static compaction. Thixotropic hardening was accompanied by an increase in permeability, a result compatible with the concept that thixotropic hardening involves a change to a more flocculent structure. As much as a five-fold increase in permeability may accompany an increase in saturation from the as-compacted state to the fully saturated condition. Because of the great variability in permeability with compaction conditions, selection of an appropriate value for use in problems involving seepage or pore pressure dissipation will be difficult.