Influence of coupled effect among flaw parameters on strength characteristic of precracked specimen: Application of response surface methodology and fractal method

Abstract

a b s t r a c tHydraulic slotting is an effective method for enhanced coalbed methane (ECBM) recovery, and it has been widely employed in China. Although there have been many studies of this technique, the influence of slot parameters on the strength characteristic of the coal, which is an important factor that affects the permeability enhancement effect, has rarely been studied. Thus, only limited information is available regarding the pressure relief and permeability enhancement mechanisms of this technique. In the current study, the influence of flaw parameters on the compressive strength of a precracked sample under biaxial compression is discussed. The results indicate that an increase in the flaw length and width has a negative effect on the compressive strength, whereas an increase in the flaw inclination angle has a positive effect on the compressive strength. The results of the response surface methodology (RSM) indicate that the interactions among the flaw parameters have a significant influence on the compressive strength. The propagation patterns of cracks are quantified by the fractal dimension, which is used to explore the mechanism of compressive strength variation with changes in the flaw parameters. The study results indicate that the variation in the flaw parameters changes the propagation pattern of cracks, resulting in different compressive strengths. In addition, an opposite variation trend of the compressive strength and fractal dimension with flaw parameters is also observed. The research results are expected to guide the field application of hydraulic slotting.

Coupled analysis about multi-factors to the effective influence radius of hydraulic flushing: Application of response surface methodology

“…Response surface methodology (RSM), which is a combination of mathematical and statistical techniques, is widely applied for analyzing the influence of various factors on one system (Liu et al, 2015a;Sodeifian et al, 2014;Kirmizakis et al, 2014). To explore the relationship between the borehole radius (X 1 ), the initial pressure (X 2 ), the original permeability (X 3 ) and gas drainage effects, a mathematical model was designed using Design Expert 8.0.5b software.…”

“…(13)] could explain the experiment data at a 95% confidence level (Liu et al, 2015a;Kirmizakis et al, 2014). The analysis of variance regression parameters of the RSM quadratic model for the effective influence radius were listed in Table 4.…”

“…In this study, the ratio of 32.789 was obtained (suggesting "adequate signal"), which indicated that this model could be used to navigate the design space. The fit of the model was controlled by the coefficient of determination R 2 (Liu et al, 2015a;Kirmizakis et al, 2014). As could be seen in Table 4, R 2 of the model was 98.65%.…”

Microscopic mechanism for enhanced coal bed methane recovery and outburst elimination by hydraulic slotting: A case study in Yangliu mine, China

“…Gas drainage has been widely accepted as an effective way of solving the aforementioned problems and obtaining a kind of environmentally friendly energy. However, the permeability of most coal seams in China is in the range of 10 −4 –10 −3 mD, which is three orders of magnitude lower than that of Australia and four orders of magnitude lower than that of the United States . The geological reason for such a low permeability is that most coal seams in China were formed during Carboniferous‐Permian period.…”

“…Liu et al . investigated the mechanical characteristics of slotted coal using the Particle Flow Code ( PFC 2D ) method . Their results indicated that the parameters of the flaw had a significant effect on the slotted coal strength.…”