Coal quality related to microfractures identified by CT image analysis

Heriawan, Mohamad Nur; Koike, Katsuaki

doi:10.1016/j.coal.2015.02.001

Cited by 72 publications

(23 citation statements)

References 18 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Dispersion of X-ray attenuation and partial volume effects can cause an expansion of the anomaly over adjacent voxels that gather this "missing attenuation" (Johns et al, 1993) and, in particular for larger fractures, represent a large portion of the entire anomaly. According to that, Johns et al (1993) suggested a calibration-based linear relationship between aperture width and the integral of the full measured anomaly which was subsequently confirmed in several fracture aperture studies (Bertels et al, 2001;Heriawan and Koike, 2015;Huo and Benson, 2015;Keller, 1997;Van Geet and Swennen, 2001;Vandersteen et al, 2003;Weerakone and Wong, 2010) and physically established by Huo et al (2016). Accordingly, the linearity between missing attenuation (CT MA ) and fracture aperture a can be simply described as…”

Section: Image Processingmentioning

confidence: 99%

Simulating stress-dependent fluid flow in a fractured core sample using real-time X-ray CT data

et al. 2016

View full text Add to dashboard Cite

Abstract. Various geoscientific applications require a fast prediction of fracture permeability for an optimal workflow. Hence, the objective of the current study is to introduce and validate a practical method to characterize and approximate single flow in fractures under different stress conditions by using a core-flooding apparatus, in situ X-ray computed tomography (CT) scans and a finite-volume method solving the Navier-Stokes-Brinkman equations. The permeability of the fractured sandstone sample was measured stepwise during a loading-unloading cycle (0.7 to 22.1 MPa and back) to validate the numerical results. Simultaneously, the pressurized core sample was imaged with a medical X-ray CT scanner with a voxel dimension of 0.5 × 0.5 × 1.0 mm 3 . Fracture geometries were obtained by CT images based on a modification of the simplified missing attenuation (MSMA) approach. Simulation results revealed both qualitative plausibility and a quantitative approximation of the experimentally derived permeabilities. The qualitative results indicate flow channeling along several preferential flow paths with less pronounced tortuosity. Significant changes in permeability can be assigned to temporal and permanent changes within the fracture due to applied stresses. The deviations of the quantitative results appear to be mainly caused by both local underestimation of hydraulic properties due to compositional matrix heterogeneities and the low CT resolution affecting the accurate capturing of sub-grid-scale features. Both affect the proper reproduction of the actual connectivity and therefore also the depiction of the expected permeability hysteresis. Furthermore, the threshold value CT mat (1862.6 HU) depicting the matrix material represents the most sensitive input parameter of the simulations. Small variations of CT mat can cause enormous changes in simulated permeability by up to a factor of 2.6 ± 0.1 and, thus, have to be defined with caution. Nevertheless, comparison with further CT-based flow simulations indicates that the proposed method represents a valuable method to approximate actual permeabilities, particularly for smooth fractures (< 35 µm). However, further systematic investigations concerning the applicability of the method are essential for future studies. Thus, some recommendations are compiled by also including suggestions of comparable studies.

show abstract

Section: Image Processingmentioning

confidence: 99%

Simulating stress-dependent fluid flow in a fractured core sample using real-time X-ray CT data

et al. 2016

View full text Add to dashboard Cite

show abstract

“…However, these studies did not consider the changes in the pore structures during methane adsorption. Recently, X-ray CT (Computed Tomography) scans have been widely used in the research into the mesostructures of coal [1][2][3][4]. Compared with the methods of MIP and N 2 adsorption, the methodology of X-ray CT scan has the advantage of studying the mesostructure deformation in coal during methane adsorption to infer the nature of the methane distribution in coal.…”

Section: Introductionmentioning

confidence: 99%

Temperature and deformation changes in anthracite coal after methane adsorption

Feng

Cai

Zhou

et al. 2017

Fuel

View full text Add to dashboard Cite

Micropores are the primary sites of methane adsorption in coal, and the heterogeneous mesostructures of coal create the non-uniform distribution of the micropores in coal. Using a thermal infrared imager, the temperature distribution on the surface of an anthracite sample during methane adsorption/desorption was tested in this paper, and a new method is advanced to calculate methane adsorption capacity in coal based on its temperature increment. The results confirm the strongly non-uniform distribution of methane adsorption in coal. A X-ray CT scan test demonstrates that the volumetric zones of coal sample with a strong methane adsorption capacity have a lower average density. In these regions, the clay minerals with developed micropores also have a strong methane adsorption capacity. During the coal skeleton deformation of methane adsorption, the high density is hard to be squeezed, while low density areas are likely to be squeezed. Therefore, the complexity density distribution in coal leads to the incompatibility of deformation, which make the direct determination of regional uptake a challenge; From the SEM micrographs of the same coal sample with different densities determined by the X-ray CT scan, the mesostructures of cell cavity pores with non-compact packing of the clay minerals appear to be the primary sites of methane adsorption in coal, and the telocollinite with fewer pores has a lower methane adsorption capacity.

show abstract

“…The pores above mesopores and micro-fractures in high-rank reservoirs are the key voids for reservoir connectivity. CT analysis studies have indicated that the mineral content within coal is proportional to the number of micro-fractures (Heriawan and Koike, 2015). The authors found that the influences of minerals within the high-rank coal in the Qinshui basin on pores and fractures have unique characteristics.…”

Section: Effect Of Minerals On the Development Of Pores And Fracturesmentioning

confidence: 99%

Occurrence and genesis of minerals and their influences on pores and fractures in the high-rank coals

Tian

Sang

Liu

et al. 2016

Energy Exploration & Exploitation

View full text Add to dashboard Cite

Pores and fractures constitute connected networks for fluid migration and production in or from coal reservoirs. The existence of minerals in coal not only increases the heterogeneity of the reservoir but also influences the development and connectivity of pores and fractures in the coal. By applying X-ray diffraction environmental scanning electron microscopy and field emission scanning electron microscopy with an energy dispersive X-ray spectrometer type, the occurrence modes and geneses of minerals were investigated in representative high-rank coals from the Qinshui basin, North China. Additionally, their impact on the development and connectivity of pores and fractures was explored in the high-rank coal. The results show that illite and kaolinite are the dominant minerals, comprising 57.74% of the mineral volume on average. The minerals fall into three genetic types, including detrital, syngenetic, and epigenetic, of which syngenetic minerals are the most common. The occurrence modes of the minerals depend on their geneses. The detrital minerals are mostly granular; the syngenetic minerals are agglomerates, stripped aggregates, and disseminated fine particles, and the epigenetic minerals are fracture fillings. At the micro-scale, the influences of the minerals on pores and fractures in the high-rank coals are mainly denoted by micro-fracture fillings, development of mineral pores, and generation of differential deformation pores and fractures. Differential deformation pores and fractures appear at the boundaries between clay and brittle minerals or clay and organic matter due to their physical and chemical property differences related to the regional thermal metamorphism of the coal. The coal samples are always connected by thermogenic pores and mineral pores, favoring connectivity of the pores and fractures in the coal. Moreover, the dissolved pores and intercrystalline pores are largely interconnected. This study focused on the effects of minerals on the pore and fracture structure of the high-rank coal reservoir. The results provide a better understanding of the

show abstract

Coal quality related to microfractures identified by CT image analysis

Cited by 72 publications

References 18 publications

Simulating stress-dependent fluid flow in a fractured core sample using real-time X-ray CT data

Simulating stress-dependent fluid flow in a fractured core sample using real-time X-ray CT data

Temperature and deformation changes in anthracite coal after methane adsorption

Occurrence and genesis of minerals and their influences on pores and fractures in the high-rank coals

Contact Info

Product

Resources

About