Hydraulic conductivity changes and influencing factors in longwall overburden determined by slug tests in gob gas ventholes

Sequential Gaussian co-simulation of rate decline parameters of longwall gob gas ventholes

“…Of course, it can be argued that correlation coefficients based on 10 wells are in the order of ~0.7 and thus nugget and ranges may not be exactly the same. This argument is partly taken care of by generating a range of correlation coefficients around the mean that will reflect on results and is also supported by the influence of surface elevation on production and decline characteristics discussed in [10,34]. Thus, as continuation of the above approach approximating the parameters of the primary semivariogram, the same shape of the secondary semivariogram, which is given in Fig.…”

“…They also have higher rates when the GGVs eventually enter the forecast period, which means that even though these GGVs may have rates sufficient to sustain production, they can cease production due to other problems that high overburden can create such as lower fracture permeabilities and larger strains on the wellbore that may promote casing failure. In fact, [34] showed that calculated hydraulic conductivities in GGV-11 to GGV-15 shown in Fig. 1 decreased at higher overburden depths as the longwall face was approaching.…”

“…Subsidence caused by longwall mining results in tension and compression of the nearsurface zone, increasing or decreasing the fracture transmissibility, especially in valley bottoms, suggesting that GGVs drilled in the valleys may be more productive [33]. Based on an earlier integrated study evaluating hydraulic properties of underground strata and their potential responses to longwall mining, Karacan and Goodman [34] concluded that GGVs drilled in the valleys might be more productive than those drilled on hilltops. They also observed that the borehole location affected fracturing during dynamic subsidence in such a way that hilltop GGVs seemed to fracture earlier than valley-bottom wells.…”

A Novel Caving Model of Overburden Strata Movement Induced by Coal Mining

“…Severe conflicts of interest are especially noteworthy regarding human life and the exploitation of energy resources [12][13][14][15][16][17][18][19][20][21][22][23][24]. Exploitation activities inevitably cause ground subsidence, water loss, building damage, and a series of other problems, especially in some eco-environmental fragile areas [3,[25][26][27][28][29][30][31][32][33][34][35].…”

“…As can be seen in Figure 1, the process of mining involves the total exploitation of large, rectangular panels of coal several kilometers long and hundreds of kilometers wide, leaving only a movable hydraulic support behind to support the roof strata and further leading to land and strata subsidence and the hydro-geomechanical response of the long and hundreds of kilometers wide, leaving only a movable hydraulic support behind to support the roof strata and further leading to land and strata subsidence and the hydro-geomechanical response of the overlying aquifers [4,5,15]. The redistribution of the overburden stress regime caused by longwall mining brings about general increases in fracture porosity and permeability owing to the development of fractures, joints, and bedding separations, resulting in the disruption of the natural groundwater flow system to a great extent [12,15,16,44]. Currently, a variety of methods, ranging from analytical methods and field experiments to numerical and physical simulation, have been used that mainly focus on the mining-induced effects on the movement of overburden strata, the generation of fractures, and subsidence [2,13,29,30,[45][46][47].…”