Effective porosity

About: Effective porosity is a research topic. Over the lifetime, 1199 publications have been published within this topic receiving 26511 citations.

Quantification of free gas in the Kumano fore‐arc basin detected from borehole physical properties: IODP NanTroSEIZE drilling Site C0009

Abstract: The Kumano fore-arc basin overlies the Nankai accretionary prism, formed by the subduction of the Philippine Sea Plate beneath the Eurasian plate offshore the Kii Peninsula, SW Honshu, Japan. Seismic surveys and boreholes within the framework of the Nankai Trough Seismogenic Zone Experiment (NanTroSEIZE) project show evidence of gas hydrates and free gas within the basin. Here we use high-quality borehole sonic data from Integrated Oceanic Drilling Program (IODP) Site C0009 to quantify the free gas distribution in the landward part of the basin. The Brie theory is used to quantify gas content from sonic logs, which are calibrated from laboratory measurements on drill cores. First, we show that the sonic data are mainly sensitive to the fluid phase filling the intergranular pores (effective porosity), rather than to the total porosity that includes water bound to clay minerals. We then compare the effective porosity to lithodensity-derived porosity that acts as a proxy for total porosity. The combination of these two data sets also allows assessment of clay mineralogy of the sediments. Second, we compute free gas saturation and find a gas-rich interval that is restricted to a lithological unit characterized by a high abundance of wood fragments and lignite. This unit, at the base of the fore-arc basin, is a hydrocarbon source that should be taken into account in models explaining gas distribution and the formation of the bottom-simulating reflector within the Kumano fore-arc basin.

The determination of aquifer parameters with the aid of radioactive tracers

Abstract: The effective porosity of a dolomite aquifer was determined by tracing a pulse of radioactive K3Co60(CN)6 between two wells 250 meters apart. Coordinate transformation of the obtained activity curve was applied for the calculation of the porosity from experimental results. The experiment indicates the usefulness of radiotracer techniques for medium-scale field experiments.

Soil Water Retention Curves Characterization of a Natural Forested Hillslope using a Scaling Technique Based on a Lognormal Pore‐Size Distribution

Abstract: Heterogeneous water flow is known to be an important factor of hydrological processes in a natural forested hillslope. To model heterogeneous water flow, the characterization of spatial variability in water retention curve (WRC) is required. The scaling technique introduced by Miller and Miller is effective to characterize it for conditions of constant standard deviation (STD) in pore-size distribution and porosity, but this is not necessarily appropriate for forested hillslopes. We tested the conventional scaling method and the two proposed methods that presume that field soils do not exhibit constant STD and porosity. The observed WRCs were fitted using a model, which assumes a lognormal pore-radius distribution and contains three parameters: the matric pressure head related to the median pore radius, ψ m ; the STD of the log-transformed pore radius distribution, σ; and the effective porosity, θ e . In Method 1, which corresponds to the conventional scaling method, ψ m was optimized for each soil, whereas the values of σ and θ e were common for the whole data set. In Method 2, σ was optimized for each soil, and in Method 3, θ e was optimized for each soil, whereas the values of the remaining parameters were common for the whole data set. Method 3 produced the best description of spatial variability in the WRCs. This result indicates that in the natural forested hillslope, variability in the pore-size distribution is characterized by variability in effective porosity. In practical aspect, we suggested an alternative simpler method to Method 3. In this method, the θ e for each location was estimated from soil penetration resistances measurable in situ. This method explained 59.3% of the spatial variability in WRCs on the studied natural forested hillslope.

A Tracer Method to Determine Hydraulic Conductivity and Effective Porosity of Saturated Clays Under Low Gradients

Abstract: Based on the column tracer test, we developed a research method to determine the hydraulic conductivity and effective porosity of saturated clays under low hydraulic gradients or small flow rates. Derived from Darcy's law and the solute transport equation, this method evaluates the hydraulic conductivity through measuring solute concentrations rather than by measuring flow rates. And the effective porosity is determined by applying an analytical solution of the one-dimensional uniform flow equation. Two types of experimental data drawn from a review of the literature and four sorts of accuracy test data carried out in the laboratory are used to examine the proposed method. The reproducibilities of accuracy tests for hydraulic conductivity determination indicate a consistency within a 5.5% error margin. The experimental results further indicate that hydraulic conductivities determined using the tracer method are more precise than those from the conventional flowmeter method. In addition, with the assistance of the proposed tracer method, we argue that the effective porosities may be overestimated as shown in the drawn example cases due to mistaking total pore volumes as the effective pores. The results of the accuracy tests further indicate that the effective porosities of saturated clay specimens are significantly smaller than the total porosities, at least when the samples are allowed to swell freely.

The occurrence state of moisture in coal and its influence model on pore seepage

Abstract: Moisture is one of the most important factors that influences coal seepage and coal-bed methane (CBM) extraction. To obtain the water occurrence state and dynamic processes of water change in coal, a series of microscopic observation experiments of Wei Jiagou coal by using field-emission environmental scanning-electron microscopy (ESEM) was conducted under the condition of a fixed point. Afterwards, a mathematical model to explain the influence of water on porosity and permeability was proposed based on the ESEM observations. It was found that there were three main types of water occurrence state: a crescent shape, a full filled shape and an annulus shape, which can provide powerful evidence to explain the influence of water on porosity and starting pressure gradient. As well as this, the box counting reached a minimum at a chamber pressure of 520 Pa and the box counting reduced after water wetting. Based on the mathematical model analysis, the water-occupied area of crescent shapes would reach a peak value with an increase of the contact angle, which has a critical impact on the effective porosity. The influence model that we built matched well with experimental data, which in turn demonstrated the validity of the mathematical model. The prominent combined effect of strain and water saturation appeared on the ridge of the permeability contour, while strains have little influence on permeability at a large initial porosity. Furthermore, a model for contact angle and wetting height was proposed and discussed, and contact angles with different improving fluids were tested. It also can be shown that using better wettability improving-fluid can save the cost of volume and have a good performance on the results of hydraulic technology based on model and experimental tests.