A discrete model for prediction of radon flux from fractured rocks

Ajayi, Kayode M.; Shahbazi, Khosro; Tukkaraja, Purushotham; Katzenstein, K.

doi:10.1016/j.jrmge.2018.02.009

Cited by 27 publications

(6 citation statements)

References 58 publications

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“…This calculated mass flow rate seems relatively low because there are only two boundary fractures (8–6 and 9–7) connected to B4. However, the fractured zone is often denser with a likelihood of more fractures (internal and external nodes), which increases the fracture areas for methane desorption; a recent study on radon gas shows that, a 10% increase in the fracture density increases the radon boundary flux by a factor 15% [ 39 ]. Even though this is different gas, it gives an insight on the impact of fracture density on gas flux and opens up more opportunities for future work on this study.…”

Section: Results and Discussion For Low-velocity Transportmentioning

confidence: 99%

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Transport model for shale gas well leakage through the surrounding fractured zones of a longwall mine

Ajayi

Schatzel

2020

International Journal of Mining Science and Technology

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The environmental risks associated with casing deformation in unconventional (shale) gas wells positioned in abutment pillars of longwall mines is a concern to many in the mining and gas well industry. With the recent interest in shale exploration and the proximity to longwall mining in Southwestern Pennsylvania, the risk to mine workers could be catastrophic as fractures in surrounding strata create pathways for transport of leaked gases. Hence, this research by the National Institute for Occupational Safety and Health (NIOSH) presents an analytical model of the gas transport through fractures in a low permeable stratum. The derived equations are used to conduct parametric studies of specific transport conditions to understand the influence of stratum geology, fracture lengths, and the leaked gas properties on subsurface transport. The results indicated that the prediction that the subsurface gas flux decreases with an increase in fracture length is specifically for a non-gassy stratum. The sub-transport trend could be significantly impacted by the stratum gas generation rate within specific fracture lengths, which emphasized the importance of the stratum geology. These findings provide new insights for improved understanding of subsurface gas transport to ensure mine safety.

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Section: Results and Discussion For Low-velocity Transportmentioning

confidence: 99%

“…As a starting point, this study focuses on developing an analytical model of the second transport scenario considering both advection and diffusion [ 39 , 40 ]. The hypothesis is that the methane flux from a compromised casing could jeopardize compliance with mandated methane concentrations, which impacts safety.…”

Section: Introductionmentioning

confidence: 99%

Transport model for shale gas well leakage through the surrounding fractured zones of a longwall mine

Ajayi

Schatzel

2020

International Journal of Mining Science and Technology

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“…This effect, however, was mainly contributed to the underlying soil. A recent study by Ajayi et al [4], with focus on radon generated in fractured rocks, imply that an increase in fracture density (m/m 2 ) of 10% for a fractured rock may increase the radon flux (radon generated) by 15%. The effect of fractures/cracks density consequently has a large impact on the radon exhalation rate.…”

Section: Ionizing Radiation and Healthmentioning

confidence: 99%

Effect on Radon Exhalation Rate Due to Cracks in Concrete

Döse

Silfwerbrand

2019

Nordic Concrete Research

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The second largest cause of lung cancer in the World is related to radon (222Rn) and its progenies in our environment. Building materials, such as concrete, contribute to the production of radon gas through the natural decay of 238U from its constituents. The Swedish Cement and Concrete Research Institute (CBI), part of RISE (Research Institute of Sweden AB), has examined the effects of cracks in concrete on two different concrete recipes where an Ordinary Portland Cement, OPC-CEM-I concrete (REF) and an OPC concrete including a hydrophobic additive (ADD) were addressed. Two concrete prisms from each concrete recipe were examined. The radon exhalation rate was measured in the pristine state and after concrete cracks had been induced into the concrete prisms. Measurements were performed with an ATMOS 33 ionizing pulsation chamber. The results indicate a strong influence of cracks on the radon exhalation rate. An increase in radon exhalation rate was calculated for every test prism. The increase in radon exhalation rate varied between 80 and 260 %. The crack apertures may play a significant role on the exhalation rate. The concrete prisms with the largest apertures (ADD) also generated the highest radon exhalation rates. The results imply that there could be a substantial variation in the exhalation rate, due to numerous factors, but nonetheless, the results should, raise the awareness of the impact cracks in concrete structures, may have on the final exhalation rate of radon. The exhalation rate of the recipe with an additive (ADD) also showed a lower exhalation rate than for the reference recipe (REF), when compared in a pristine state. This was in part expected. However, the effect of induced cracks and its aperture, seemingly trumps the effect that an additive may play on the radon exhalation rate, when cracks are induced. The hypothesis is in part verified in view of the results of the prism for the ordinary Portland recipe (REF-prisms), were an increase of approximately 100 % would be expected due to the total surface increase. The results also indicate this. The major increase in the radon exhalation rate of the ordinary Portland recipe including an additive, implies however other factors, such as minor internal cracks, that may substantially contribute to the final exhalation rate.

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“…It is well known that the influence of fractures on the blockiness level is considerable, especially in the spacing, size, and statistical distribution of fractures (Elmouttie and Poropat, 2011;Zhu et al, 2014;Ajayi et al, 2018). The sizes and distributions of fractures in rock masses are diverse (Hu et al, 2022;Yang et al, 2022).…”

Section: Introductionmentioning

confidence: 99%

The influence of normal distribution dispersion of fracture size on blockiness and REV of fractured rock masses

Xia²

2023

Front. Earth Sci.

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The fractures of different sizes in rock masses are important for describing rock fragmentation. The distribution dispersion of fracture size influences the blockiness level of the rock masses. Based on a normal statistical distribution, the volume ratio of blocks to rock (B) was obtained to describe the blockiness level. For exploring the effect of the dispersion of fracture size on blockiness level and the representative elementary volume (REV) of rock masses, the laboratory model and numerical simulation were established, and the theory of statistics and the method of analytical solution were applied. In addition, 4,525 practical rock models were established to qualitatively reproduce the behavior of B with changing domain size. The results show that by comparing the degree of convergence, the REV of a rock mass is determined by the fracture size rather than the degree of fracture dispersion. The value of B increases with the distribution dispersion of fracture size, indicating a higher blockiness level. From the experimental analysis of coin tossing, when the number of trials exceeds 69, the random results are nearly stable. In this study, 100 calculations were performed. A formula to calculate the blockiness by considering the dispersion degrees of fracture size was obtained. Moreover, a positive linear correlation between B and the coefficient of variation of fracture size was obtained. The rate of increase in B has a parabolic relationship with the ratio of fracture size to fracture spacing (L).

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A discrete model for prediction of radon flux from fractured rocks

Cited by 27 publications

References 58 publications

Transport model for shale gas well leakage through the surrounding fractured zones of a longwall mine

Transport model for shale gas well leakage through the surrounding fractured zones of a longwall mine

Effect on Radon Exhalation Rate Due to Cracks in Concrete

The influence of normal distribution dispersion of fracture size on blockiness and REV of fractured rock masses

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