Experimental Study on Permeability and Stress Sensitivity of Different Lithological Surrounding Rock Combinations

Abstract

The different lithological combinations of the surrounding rock of coal seams play a key role in controlling the enrichment and migration of coalbed methane (gas), and their permeability and stress sensitivity have important theoretical guiding significance for the regional election and evaluation of coalbed methane development. In this paper, the HB-2 type coal rock sample pore permeability adsorption simulation measurement device is used to carry out the sensitivity experiment of the permeability of different surrounding rock combinations on the effective stress of the No. 3 coal seam roof in the Daping coal mine area, Luan, Shanxi. The sensitivity coefficient of permeability to effective stress, the maximum damage rate of permeability, and other parameters are defined to characterize the response mode of permeability to effective stress and the dynamic change rule of permeability, and reveal the control mechanism of effective stress on permeability change of different surrounding rock combinations. The results show that the permeability of the roof of No. 3 coal seam is highly sensitive to the effective stress, and the permeability of different surrounding rock combinations decreases with the increase of the effective stress, and there is a strong negative exponential correlation between the permeability and the effective stress; the stress sensitivity coefficients of different surrounding rock combinations under unloading stress are higher than those under loading; the permeability changes of specimens with different combinations of surrounding rock under the same experimental conditions are varied and the differentiation phenomenon is significant; the permeability is affected by lithology, pore fissure degree, and different combinations of surrounding rock, among which different combinations of surrounding rock are the main controlling factors for the dynamic change of permeability.

Dewatering Optimization of Coal Seam Gas Production Wells: A Review and Future Perspectives

“…A high dewatering rate will result in a significant rise in the effective stress at the near-wellbore area and cause the reduction of cleat aperture and permeability, a phenomenon called the stress-sensitivity permeability, ,− as described by the curve from P i to P rb in Figure . This is detrimental to the dewatering efficiency and the pressure propagation, leading to a low production rate and small drainage radius. ,, If the stress concentration around the wellbore is excessive, it can lead to permanent (i.e., irrecoverable) permeability damage, resulting in long-term loss to the gas well productivity. ,,− An example of the impact of stress sensitivity during CSG production was presented by Yang et al via a numerical simulation. Their results show that (i) the existence of stress sensitivity can reduce the pressure funnel radius and decrease the production rate evidently, as presented in Figure , and (ii) increasing the dewatering rate is not always beneficial to gas production.…”

True triaxial experimental study on the influence of axial pressure on coal permeability

“…Simultaneously, different structural phenomena such as folds and small faults are encountered in the coal mining process. These structures form stress concentration areas, which are the ideal areas for gas occurrence and coal and gas outbursts (Meng and Li, 2017;Shi et al, 2018;Yan et al, 2019;Lv et al, 2022;Tatyana et al, 2022;Wang et al, 2018). This phenomenon is caused by the distribution of in situ stress having an impact on the permeability of coal seams, which reduces the permeability of local coal seams and forms gas accumulation zones (Guo et al, 2019;Lin et al, 2022;.…”