Characteristics of in situ stress and its influence on coal seam permeability in the Liupanshui Coalfield, Western Guizhou

Song

Energy Science & Engineering

et al. 2022

In situ stress and groundwater have important effects on the deformation and stability of deep underground rock masses. Therefore, it is extremely important to study the mechanical properties and permeability evolutionary processes of rocks under hydromechanical (HM) coupling. The purpose of this study was to investigate the mechanical properties and permeability evolution of sandstone using triaxial compression tests under different confining and seepage pressures. The test results show that the confining pressure can increase the strength of sandstone, whereas the seepage pressure has the opposite effect. The initial and maximum permeabilities were positively correlated with seepage pressure and negatively correlated with confining pressure. The confining and seepage pressures had little effect on the change in initial permeability. As a common parameter of acoustic emission (AE), cumulative AE counts can intuitively reflect the permeability evolutionary process in the sandstone failure process. A permeability evolutionary early warning model for the sandstone failure process under HM coupling is proposed. The results are helpful for understanding the influence of in situ stress and seepage pressure on deep sandstone and the permeability evolutionary mechanism, and they can be used to provide early warning of water inrush disasters in deep underground structures.

Section: Equipment and Methodsmentioning

confidence: 99%

Experimental study on the mechanical properties, acoustic emission characteristics, and permeability evolution of sandstone under triaxial hydromechanical coupling

Song

Energy Science & Engineering

et al. 2022

Energy Science & Engineering

“…This depth is also consistent with that of the high-low-permeability transition zone studied by predecessors in eastern Yunnan and western Guizhou (Figure 4B). 15,41,42 For combinedlayer drainage, the interval between layers is a factor that cannot be ignored. The layer spacing should be controlled within a certain range, and for the Laochang mining area, the maximum layer spacing should be controlled within 80 m (Figure 4C).…”

Section: Influence Of Geological Factors On the Productivity Of Cbm W...mentioning

confidence: 99%

“…11,12 The stress regimes of shallow strike-slip and deep normal fault types were revealed. [13][14][15] Coal structure is affected by coal thickness, in situ stress, geological structure, and coal mine goaf; furthermore, the homogeneity of primary structural coal is better than tectonic coal. 16,17 The development degree of coal-seam fractures has significant anisotropy in both horizontal and vertical directions, which is related to the complex tectonic stress in this area.…”

Section: Introductionmentioning

confidence: 99%

“…On this basis, a quantitative classification and rating index system for the development of unit divisions considering the key parameters of coal reservoirs has been formed 11,12 . The stress regimes of shallow strike‐slip and deep normal fault types were revealed 13–15 . Coal structure is affected by coal thickness, in situ stress, geological structure, and coal mine goaf; furthermore, the homogeneity of primary structural coal is better than tectonic coal 16,17 .…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Impact factors and contributions of commingled production in multiple coal seams

Jin

Fang

et al. 2022

Self Cite

The multilayer development of coalbed methane (CBM) is affected by many factors, and the gas production contribution of each seam is unclear. In this study, 12 geological and 10 engineering parameters were adopted to reveal the key factors affecting the combined-layer drainage productivity of CBM wells before using numerical simulation to clarify the contribution of each coal seam. The results show that the coal reservoir in the Laochang mining area exhibited the advantages of high gas content, intact coal body structure, and large thickness of the combined coal seams, and it was deficient with low saturation and ratio of critical desorption pressure to reservoir pressure. The medium permeability after fracturing and the influence of a small range of fracturing leads to the steep and deep pressure drop funnel of the coal reservoir, and most of the reservoir pressure drop is ineffective; this may be the reason for the unstable production and rapid attenuation of most CBM wells in the study area. The gas production of the Nos. 13 and 18 coal seams is stable and makes a significant contribution, and they can be used as the key objects of follow-up CBM exploration and development in this area. Geological factors, such as coal body structure, ratio of critical desorption pressure to reservoir pressure, thickness of combined coal seams, and gas saturation, as well as engineering factors, such as permeability and half length of fractures after fracturing, are the main factors affecting the productivity of the CBM wells in the Laochang mining area.

“…Coal seam permeability is one of the most important bases for evaluating the degree of CBM development and the effect of mine gas drainage, , but its measurement and evaluation are very difficult . Scholars have carried out many studies on the influencing factors and prediction of coal permeability. − In situ stress, , gas pressure and type, , and the anisotropic characteristics of coal reservoirs , determine the permeability of coal to varying degrees, and there are relevant coal permeability evaluation models , to theoretically discuss the mechanism of its seepage law. However, most of the above coal permeability acquisition and evaluation methods are still in the laboratory measurement stage.…”

Section: Introductionmentioning

confidence: 99%

Relationship between Dielectric Relaxation Time and Permeability of High-Rank Coal in the Jiaozuo Mining Area

Zhang

Lei

2022

ACS Omega

To evaluate the permeability of coal by the complex resistivity method, the real part of complex resistivity (R), the imaginary part of complex resistivity (X), capacitance (C), permeability (k), and strain (ε) of coal in different directions under variable pressure were measured. Based on the physicochemical structure characteristics of coal and its conductivity and dielectric mechanism, the experimental phenomenon was analyzed and correlated with the permeability of coal. The results demonstrated that (1) the R–X curve is U-shaped. With increasing frequency, the amplitude first decreases and then increases, forming an obvious trough. C decreases with increasing frequency. (2) The R–X curve is affected by pressure and directivity. The absolute value of the R–X curve amplitude gradually decreases and shifts to the left as the pressure increases; meanwhile, it decreases and shifts to the left in the order of the vertical bedding direction (z direction), the vertical main fracture direction in parallel bedding (y direction), and the main fracture direction in parallel bedding (x direction). There is also a related change law for C. (3) The dielectric relaxation time (τ) was optimized as the electrically sensitive parameter of coal. τ continues to decrease as pressure increases and decreases in the order of the z, y, and x directions. (4) The permeability of coal is strongly correlated with the dielectric relaxation time, and the relationship between them conforms to a logarithmic function. The relationship of strain and the dielectric relaxation time verifies the strong correlation between permeability and the dielectric relaxation time. This study provides an experimental basis and theoretical support for the subsequent accurate prediction and evaluation of coal permeability using the dielectric relaxation time.