scholarly journals Low-index Catastrophe Model of Deep Gas-bearing Coal Seams

2020 ◽  
Author(s):  
Tie Li ◽  
Xiyu Pi
Keyword(s):  
High Stress ◽  
Site Investigation ◽  
Gas Migration ◽  
Coal Seams ◽  
Gas Emission ◽  
Gas Channel ◽  
Gas Desorption ◽  
Mining Face ◽  
Ultimate Equilibrium ◽  
Gas Bearing

Abstract Coal and gas outburst always occur as some parameters reach its threshold in the mining process of gas-bearing coal seams. However, low-index catastrophes may happen in the deep mining although the parameters do not exceed its threshold values. This phenomenon has become a challenge for our traditional cognitions. In this paper, the mechanism of low-index catastrophes of high-stress area in the deep gas-bearing seams was investigated by the following methods including literature reviewing, on-site investigation, case analysis, physical experiments and theoretical analysis. The results indicate that there were not only primary state fissures but also many secondary fissures are formed after taking outburst eliminating measures, which is beneficial for improving the desorption performance of methane. A “three-zone” theory of gas migration in Coal Seams is given, coal seam in the front of coal mining face can be divided into three zones: the gas emission zone, the gas channel compaction zone, and disturbance gas desorption zone before reaching ultimate equilibrium, corresponding to coal and gas ejection zone, gas migration zone and gas launching zone after surpassing the limits. Importantly, the stress dike is redefined, and a new concept is proposed that the low-index catastrophe of gas bearing seams is caused by avalanche instability of the stress dikes, meanwhile its three modes are given by over static-load stress dike avalanche caused by hanging arch overlength, stress dike avalanche under roof breakage impact, and stress dike avalanche under floor breakage impact. In deep stress area, stress dike avalanche caused by dynamic-static loading could lead to low-index catastrophes of gas bearing seams. The insufficient residual gas energy could cause unusual gas emission. On the other hand, the sufficient gas energy may lead to coal and gas outbursts.

Use of Destressing Drilling to Ensure Safety of Donbass Gas-bearing Coal Seams Extraction

2019 ◽  
pp. 7-11
Author(s):  
V.S. Brigida ◽  
◽  
Yu.V. Dmitrak ◽  
O.Z. Gabaraev ◽  
V.I. Golik ◽  
...  
Keyword(s):  
Coal Seams ◽  
Gas Bearing

INVESTIGATION OF MAINGATES STABILITY IN STEEP COAL SEAMS AT EXTRACTION LAYOUTS OF DEEP MINE

2020 ◽  
pp. 89-100
Author(s):  
Leonid Bachurin ◽  
◽  
Yuliia Novikova ◽  
Yuliia Simonova ◽  
Vytalyi Dovhal ◽  
...  
Keyword(s):  
Hanging Wall ◽  
Cross Sectional Area ◽  
Practical Significance ◽  
Sectional Area ◽  
Coal Seams ◽  
Cross Sectional ◽  
Deep Mine ◽  
Secondary Support ◽  
The Cross ◽  
Mining Face

Purpose of work. Investigation of maingates stability in different methods of protection on the extraction layouts of a deep coal mine, which develops steeply inclined coal seams. Methods. To achieve this goal, mine experimental observation of maingates stability performed. Conditions for their maintenance are evaluated by the magnitude of the convergence of the side rocks on the contour and changes in the cross-sectional area of the gateroads. Results. As a result of the research the conditions of maingates stability in steep coal seams in protection by pillars or timber sets are substantiated. It is recorded that in the zone of influence of extraction operations, at a distance of l <60 m behind the mining face with the considered methods of protection, the support of the maingates is deformed within the yielding limits and has characteristic flexures the side of hanging wall. At a distance of l≥60 m, the cross-sectional area of the maingates is reduced to 50% of the initial values, and the amount of roof to floor convergence exceeds the flexibility of the support. The increase displacement of rock mass on the contour of the supported roadway behind the mining face depends on the strength and geometry of the secondary support structures above the maingate. Novelty. It is experimentally established that the change in the cross-sectional area of the maingate during protection by timber sets occurs linearly with increasing length of the extraction layout. Practical significance. To ensure the maingates stability, it is advisable to use non-pillar methods of protection, when using yielding secondary support systemsabove the roadway, or backfilling.

Methane Injury-Risk at the Russian Mines

2021 ◽  
pp. 69-74
Author(s):  
V.S. Zaburdayev ◽  
◽  
S.N. Podobrazhin ◽  
Keyword(s):  
Injury Risk ◽  
Electrical Equipment ◽  
Coal Deposit ◽  
Coal Seams ◽  
Mining Operations ◽  
Mining Conditions ◽  
Scientific Substantiation ◽  
And Control ◽  
Gas Bearing ◽  
Engineering Personnel

Conditions are given concerning the development of methane-bearing coal seams in Russia, the chronology of injuries from explosions and outbreaks of methane-air mixtures at the Russian mines for a quarter of a century of developing coal seams at the nine deposits. The emergency was studied in 174 mine incidents, which occurred mainly at the mines of Kuzbass, Vorkuta coal deposit, Eastern Donbass, Chelyabinsk basin, Primorye and Sakhalin. Emergency objects - excavation areas, preparation faces and mined-out areas of the mines. The sources of ignition of methane-air mixture are drilling and blasting works in the faces, malfunctioning of electrical equipment, frictional sparking, endogenous fires, and smoking in the mines. The most injury-risk for methane are steep and steeply inclined mines. The need in the scientific substantiation of the decisions taken for prevention or reduction of the methane injury-risk at the mines is noted in the article. An important role is assigned to the choice of ways to achieve this goal considering the geological and mining conditions of the development of gas-bearing coal seams. As an example, the conditions, methods, and parameters of mining operations at the excavation areas of four mines are given, where occurred the catastrophic explosions of methane-air and methane-dust-air mixtures. The reasons are gross violations of safety rules during mining operations, incompetence of the mine engineering personnel, design, and control organizations in matters of safety during the underground work at the gas-hazardous mines with an extensive network of workings. This resulted in the death of miners and mine rescuers, the destruction of mine workings, equipment and devices, underground fires. Recommendations are given for reducing the level of methane injury-risk at the methane-rich mines.

Optimization of Coal Seam Connectivity via Multi-Seam Pinpoint Fracturing Operations in the Walloons Coal Measures, Surat Basin

2021 ◽  
Author(s):  
Vibhas J. Pandey ◽  
Sameer Ganpule ◽  
Steven Dewar
Keyword(s):  
Coal Seam ◽  
History Matching ◽  
Design Matrix ◽  
Coal Seams ◽  
Major Step ◽  
Well Completion ◽  
Eastern Australia ◽  
Treatment Designs ◽  
Coal Measures ◽  
Gas Bearing

Abstract The Walloons coal measures located in Surat Basin (eastern Australia) is a well-known coal seam gas play that has been under production for several years. The well completion in this play is primarily driven by coal permeability which varies from 1 Darcy or more in regions with significant natural fractures to less than 1md in areas with underdeveloped cleat networks. For an economic development of the latter, fracturing treatment designs that effectively stimulate numerous and often thin coals seams, and enhance inter-seam connectivity, are a clear choice. Fracture stimulation of Surat basin coals however has its own challenges given their unique geologic and geomechanical features that include (a) low net to gross ratio of ~0.1 in nearly 300 m (984.3 ft) of gross interval, (b) on average 60 seams per well ranging from 0.4 m to 3 m in thickness, (c) non-gas bearing and reactive interburden, and (d) stress regimes that vary as a function of depth. To address these challenges, low rate, low viscosity, and high proppant concentration coiled tubing (CT) conveyed pinpoint stimulation methods were introduced basin-wide after successful technology pilots in 2015 (Pandey and Flottmann 2015). This novel stimulation technique led to noticeable improvements in the well performance, but also highlighted the areas that could be improved – especially stage spacing and standoff, perforation strategy, and number of stages, all aimed at maximizing coal coverage during well stimulation. This paper summarizes the findings from a 6-well multi-stage stimulation pilot aimed at studying fracture geometries to improve standoff efficiency and maximizing coal connectivity amongst various coal seams of Walloons coal package. In the design matrix that targeted shallow (300 to 600 m) gas-bearing coal seams, the stimulation treatments varied in volume, injection rate, proppant concentration, fluid type, perforation spacing, and standoff between adjacent stages. Treatment designs were simulated using a field-data calibrated, log-based stress model. After necessary adjustments in the field, the treatments were pumped down the CT at injection rates ranging from 12 to 16 bbl/min (0.032 to 0.042 m3/s). Post-stimulation modeling and history-matching using numerical simulators showed the dependence of fracture growth not only on pumping parameters, but also on depth. Shallower stages showed a strong propensity of limited growth which was corroborated by additional field measurements and previous work in the field (Kirk-Burnnand et al. 2015). These and other such observations led to revision of early guidelines on standoff and was considered a major step that now enabled a cost-effective inclusion of additional coal seams in the stimulation program. The learnings from the pilot study were implemented on development wells and can potentially also serve as a template for similar pinpoint completions worldwide.

COAL SEAM DEGASIFICATION IN QUEENSLAND UTILISING HYDRAULIC FRACTURING WITH FOAM—A CASE HISTORY

1981 ◽  
Vol 21 (1) ◽  
pp. 137
Author(s):  
B. Wilkinson ◽  
L. Barro
Keyword(s):  
Gas Flow ◽  
Gas Production ◽  
Low Permeability ◽  
Gas Flow Rate ◽  
Coal Seams ◽  
Flow Rates ◽  
Coal Deposits ◽  
Early Production ◽  
Design Calculations ◽  
Gas Bearing

Vast reserves of gas-bearing coal deposits are located in Queensland. Owing to the extremely low permeability and porosity of the coal, very low gas flow rates are normally encountered. In an effort to enhance the gas production to economic quantities and to degasify the coal to provide a safer mining environment, four experimental wells were drilled into coal seams near Blackwater, Queensland.Based on extensive laboratory testing of coal samples, computerised fracture design calculations were performed to determine a suitable stimulation programme. The wells were hydraulically fractured with up to 15 000 US gal of foamed stimulation fluid containing 75 per cent nitrogen. To prop open the induced fracture system, 15 000 lb of sand was pumped with the foam. The maximum concentration was eight pounds of 20-40 mesh sand per gallon of fluid. Gas production from the unstimulated wells was too low to measure. Early production data soon after the fracturing suggested a gas flow rate of approximately 50 Mcf/D.

scholarly journals Field Investigation of Hydraulic Fracturing in Coal Seams and Its Enhancement for Methane Extraction in the Southeast Sichuan Basin, China

Energies ◽  
2018 ◽  
Vol 11 (12) ◽  
pp. 3451 ◽  
Author(s):  
Zuxun Zhang ◽  
Hongtu Wang ◽  
Bozhi Deng ◽  
Minghui Li ◽  
Dongming Zhang
Keyword(s):  
Coal Seam ◽  
Hydraulic Fracturing ◽  
Sichuan Basin ◽  
High Stress ◽  
Fluid Pressure ◽  
Field Investigation ◽  
Stress Sensitivity ◽  
Extraction Rate ◽  
Coal Seams ◽  
Methane Extraction

Hydraulic fracturing is an effective technology for enhancing the extraction of reservoir methane, as proved by field experience and laboratory experiments. However, unlike conventional reservoirs, coal seams had high stress sensitivity and high anisotropy. Therefore, the efficiency of hydraulic fracturing in coal seams needs to be investigated. In this study, hydraulic fracturing was performed at Nantong mine in the southeast Sichuan basin, China. The field investigation indicated that the hydraulic fracturing could significantly enhance the methane extraction rate of boreholes ten times higher than that of normal boreholes in one of the minable coal seams (named #5 coal seam). The performance of hydraulic fracturing in three districts revealed that compared with south flank, the fluid pressure was higher and the injection rate was lower in north flank. The methane extraction rate of south flank was inferior to that of north flank. It indicated hydraulic fracturing had less effect on #5 coal seam in south flank. Moreover, the injection of high-pressure water in coal seams could also drive methane away from boreholes. The methane extraction rate of the test boreholes demonstrated the existence of methane enrichment circles after hydraulic fracturing. It indicated that hydraulic fracturing did act on #5 coal seam in south flank. However, due to the high stress sensitivity of coal seams and the high geo-stress of south flank, the induced artificial fractures in #5 coal seam might close with the decline of the fluid pressure that led to a sharp decline of the methane extraction rate.

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