Effective porosity

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

Simulation Analysis on Water’s Micro Seepage Laws under Different Pressure Gradients Using Computed Tomography Method

Abstract: The aim of this paper was to develop a model that can characterize the actual micropore structures in coal and gain an in-depth insight into water’s seepage rules in coal pores under different pressure gradients from a microscopic perspective. To achieve this goal, long-flame coals were first scanned by an X-ray 3D microscope; then, through a representative elementary volume (REV) analysis, the optimal side length was determined to be 60 μm; subsequently, by using Avizo software, the coal’s micropore structures were acquired. Considering that the porosity varies in the same coal sample, this study selected four regions in the sample for an in-depth analysis. Moreover, numerical simulations on water’s seepage behaviors in coal under 30 different pressure gradients were performed. The results show that (1) the variation of the simulated seepage velocity and pressure gradient accorded with Forchheimer’s high-velocity nonlinear seepage rules; (2) the permeability did not necessarily increase with the increase of the effective porosity; (3) in the same model, under different pressure gradients, the average seepage pressure decreased gradually, while the average seepage velocity and average mass flow varied greatly with the increase of the seepage length; and (4) under the same pressure gradient, the increase of the average mass flow from the inlet to the outlet became more significant under a higher inlet pressure.

Some Methodological Modifications of Determination of Diffusion Coefficients in Compacted Bentonite

Abstract: The results of 3H, 36Cl and 137Cs diffusion experiments through compacted bentonite using a new design of diffusion cell and a new methodology of diffusion coefficients evaluation are presented. The diffusion cell was made from the stainless steel and enables to connect it directly to the input and/or output reservoirs without any tubing. The evaluation of diffusion coefficients utilizes a compartmental model developed in the environment of the GoldSim transport code. It enables to determine diffusion coefficients for various types of boundary conditions, including also input and output filters. The influence of the diffusion through filters on the determined values of both effective (D e ) and apparent (D a ) diffusion coefficients was numerically demonstrated for the through diffusion method. This effect is most important for D a , the value of which would be underestimated using standard ways of evaluation for neutral and positively charged species, mainly in the case of high effective porosity. The comparison of standard and the newly developed method of evaluation of diffusion coefficients showed a significant influence of diffusion in filters for HTO. Contrary to the standard method of evaluation, the evaluation taking into account filters showed here no difference between total and effective porosity. The effect of filter resistance was negligible for Cl-, especially at high dry density of compacted bentonite, due to the anion exclusion effect. The numerical model developed enabled to determine D a values of Cs+ from the concentration change in the inlet reservoir.

Microstructural Analysis From X-Ray CT Images of the Brae Formation Sandstone, North Sea

Abstract: During deposition and subsequent diagenesis, reservoir rocks develop sediment texture and cement phases are formed during the precipitation of secondary minerals such as microcrystalline quartz, calcite and clay fibrous over-growths that contain secondary porosity. The grain size distribution and presence of secondary microporous material can influence the reservoir porosity and permeability. Using 3D X-ray microtomographic images we analyze the grains and pore space in Brae Formation sandstones from the South Viking Graben in the North Sea. The samplesderived from two cored wells (16/7b-20 and 16/7b-23), and located within the depth interval between 4040 m and 4064 m-display mean grain sizes between 315-524 microns (1.78-1.05 φ units), classifying them as predominantly medium-grained sands, with moderate to well sorting (0.51-0.7 φ units). From our models we calculate the upper and lower bounds of the micropores on the pore connectivity and permeability. Our samples show total porosities between 10 and 18% of which 6 and 13% are effective, leading to a permeability range between 1 and 400 mD through the effective macropore network. We found that the fraction of effective porosity and effective permeability shows a nonlinear reduction with increase in microporous cement volume fraction. Above a threshold cement volume of approximately 5.5% the effective pore network is disconnected and percolation is no longer possible. Based on our observations and modeling results we propose that cement precipitation can be a positive consequence of mineral trapping from sequestered CO2 , which can be important for reducing reservoir quality and ensuring efficient long term storage.