Coal Seam Structure Research Articles

The Feasibility Research on Ascending Mining under the Condition of Multi-Disturbances

Abstract This study focus on the feasibility of ascending mining under the condition of multi-disturbances for the Zhengyi coal mine. Firstly, the empirical methods are used to calculate and analyze the feasibility, and in order to make up for the deficiency of these empirical methods not considering the influence of overlying strata lithology and structure of upper coal seam on ascending mining then numerical simulation method is used to calculate and verify the feasibility. It is found that the empirical methods are appropriate for the Zhengyi coal mine and the ascending mining can be carried out under the condition of multi-disturbances for the Zhengyi coal mine based on the comprehensive analysis of empirical and numerical methods.

Gas Geology Law and Gas Forecast in Yongju Well Field

This paper takes gas as a geological-mass to study, using gas geology theory, by analysising the geological conditions of Yongju mine in ShanXi, combining with the coal seam gas content data which measured underground to study the relationship between geological conditions and gas occurrence, reveal the gas occurrence factors: geological structure, roof and floor lithologic of coal seam, buried depth of coal seam and thickness of coal seam. Finally, using the measured data of gas content and gush, regression analysis, the gas gush is forecasted, playing a guiding role in the gas control and production safety .

Management of Major Influential Factors on Safe Coal Mining

A couple of factors affecting coal mining are investigated. These factors include but are not limited to thickness, structure and stability of coal seam, roof, floor as well as their stability, hydrogeology, gas and coal dust, temperature. How each of these factors affects coal mining is deliberated. Finally, the paper concludes that it is important to have these factors in mind when a coalmine proceeds with its mining operations and put them under control. Moreover, safety management plays an important role in work safety in coal mines.

Quantitative prop support estimation and remote monitor early warning for hard roof weighting at the Muchengjian Mine in China

The complex coal seam structure and hard roof at the Muchengjian Mine were studied, and the equivalent tensile strength of the roof was determined by a retrospective analysis of similar roof cave-ins. The prop spacing or number of hydraulic props required per unit area were obtained by analyzing the roof caving span and thickness. The early warning threshold bedding vertical separation velocity for hard roof caving at the Muchengjian Coal Mine was determined to be about 14 mm/day, and the newly invented “bedding separation remote monitoring system” (BSRMS) was used for the first time for early warning of a roof fall. A total of 48 trials of early warning roof weighting were performed at the Muchengjian Mine. It was found that not only were all the early warnings accurate, but the support system was also safe and reliable.

Seismic wave propagation through surface basalts – implications for coal seismic surveys

Seismic reflection surveying is one of the most widely used and effective techniques for coal seam structure delineation and risk mitigation for underground longwall mining. However, the ability of the method can be compromised by the presence of volcanic cover. This problem arises within parts of the Bowen and Sydney Basins of Australia and seismic surveying can be unsuccessful. As a consequence, such areas are less attractive for coal mining. Techniques to improve the success of seismic surveying over basalt flows are needed.In this paper, we use elastic wave-equation-based forward modelling techniques to investigate the effects and characteristics of seismic wave propagation under different settings involving changes in basalt properties, its thickness, lateral extent, relative position to the shot position and various forms of inhomogeneity. The modelling results suggests that: 1) basalts with high impedance contrasts and multiple flows generate strong multiples and weak reflectors; 2) thin basalts have less effect than thick basalts; 3) partial basalt cover has less effect than full basalt cover; 4) low frequency seismic waves (especially at large offsets) have better penetration through the basalt than high frequency waves; and 5) the deeper the coal seams are below basalts of limited extent, the less influence the basalts will have on the wave propagation. In addition to providing insights into the issues that arise when seismic surveying under basalts, these observations suggest that careful management of seismic noise and the acquisition of long-offset seismic data with low-frequency geophones have the potential to improve the seismic results.

Sub-basalt coal seam structure imaging - results from numerical modelling

Tertiary volcanic basalts (high velocity layers) exist in both the Bowen and Sydney Basins of Eastern Australia. The use of conventional seismic for coal mine planning is often compromised and produces sub-surface images of variable quality because the wave propagation through these heterogeneous basalt layers becomes complex. The difficulty of exploring beneath the Tertiary volcanics makes these areas less attractive for coal mining exploration. Workers involved in sub-basalt imaging in the petroleum sector, mainly give the following reasons for the difficulties in imaging beneath high-speed surface layers: 1. The strong impendance contrast between the basalts and the underlying sedimentary rocks prevents the penetration of seismic energy into target zones (Fruehn et al., 1998; Behera, 2006). 2. The roughness of the basalt boundaries causes significant disruption and scattering of the transmitted wavefield (Behera, 2006). 3. The scattering of heterogeneity of the basalt (Ziolkowski et al., 2001; Hobbs, 2002). To improve seismic imaging in these cases, modifications to data acquisition and data processing procedures which improve data quality and increase S/N were proposed (Fliedner and White, 1999; Hu et al., 2003). Commonly used techniques involve long offset, low frequency and converted wave data acquisition (Ryu, 1997; Wombell et al., 1999; Hanssen et al., 2003; Lau et al., 2007; Spitzer et al., 2008). In data processing, procedures such as pre-stack depth migration, have improved the quality of sub-basalt images (Fruehn et al., 1999; Reshef et al., 2003; Gallagher and Dromgoole, 2008). Wave-equation modelling techniques have also been used to investigate the influence of high speed layers on seismic wave propagation (Battig and Hearn, 2001; Hanssen et al., 2003). In this paper, we use a 2D finite-difference-based full elastic wave-equation forward modelling algorithm to further investigate the effects and characteristics of seismic wave propagation under different basalt settings. Our objective is to provide some insights into the seismic wave propagation and guidance for improving the quality of seismic sections for coal mine investigations.

Coal Seismic Depth Conversion for Mine Data Integration: a Case Study From the Sandy Creek 3D Seismic Survey

When seismic data are presented as two-way reflection times, these times are not easily directly scalable to depths, because of spatial variations of seismic velocity. Apparent structures in the time domain can be misleading. Correct conversion of seismic time sections to depth sections removes this ambiguity. In general, seismic depth conversion is a complex process requiring careful use of NMO and migration velocities, the study of well data, and the generation of synthetic seismograms. The process is usually iterative, especially when the structures are complex. In this paper, we present a depth-conversion algorithm designed for coal seismic data. Our method exploits the relatively simple structure of coal seams and the availability of many exploration boreholes to constrain the process. Once converted to depth, the seismic data can be exported into mine-planning software and used to provide seam elevations for tasks such as in-seam drilling and other mine activities. Our method has been implemented into an MS Windows-based program, and allows new boreholes to be incorporated without the need to go back to a seismic processing centre.A 3D seismic data set from Xstrata‘s Sandy Creek coal mine is used to demonstrate our method. The results show that the depth-conversion algorithm can accommodate differences in seismic processing. The depth-converted seismic data agrees with the geological model based on the borehole results and underground mine surveys. Given confidence in the depth conversion, it is possible to look more closely into the seismic data in order to make interpretations that are more detailed.

Coal seismic depth conversion for mine data integration: a case study from the sandy creek 3d seismic survey

When seismic data are presented as two-way reflection times, these times are not easily directly scalable to depths, because of spatial variations of seismic velocity. Apparent structures in the time domain can be misleading. Correct conversion of seismic time sections to depth sections removes this ambiguity. In general, seismic depth conversion is a complex process requiring careful use of NMO and migration velocities, the study of well data, and the generation of synthetic seismograms. The process is usually iterative, especially when the structures are complex. In this paper, we present a depth-conversion algorithm designed for coal seismic data. Our method exploits the relatively simple structure of coal seams and the availability of many exploration boreholes to constrain the process. Once converted to depth, the seismic data can be exported into mine-planning software and used to provide seam elevations for tasks such as in-seam drilling and other mine activities. Our method has been implemented into an MS Windows-based program, and allows new boreholes to be incorporated without the need to go back to a seismic processing centre. A 3D seismic data set from Xstrata?s Sandy Creek coal mine is used to demonstrate our method. The results show that the depth-conversion algorithm can accommodate differences in seismic processing. The depth-converted seismic data agrees with the geological model based on the borehole results and underground mine surveys. Given confidence in the depth conversion, it is possible to look more closely into the seismic data in order to make interpretations that are more detailed.

Microcosmic analysis of ductile shearing zones of coal seams of brittle deformation domain in superficial lithosphere

The ductile shearing zones of coal seams in a brittle deformation domain in superficial lithosphere are put forward based on the study on bedding shearing and ductile rheology of coal seams. The macrocosmic and microcosmic characteristics include wrinkle fold, mymonitized zones and ductile planar structure of coal seams, etc., while the microcosmic characteristics may also include different optic-axis fabrics and the anisotropy of vitrinite reflectance as well as the change of chemical structure and organic geochemistry components. The forming mechanism is analyzed and the strain environment of ductile shearing zones of coal seams discussed. The result indicates that, in the superficial brittle deformation domain, the coal seams are easy to be deformed, resulting in not only brittle deformation but also ductile shearing deformation under the action of force. Because of simple shearing stress, the interlayer gliding or ductile rheology may take place between coal seams and wall rocks. Therefore, many ductile shearing zones come into being in superficial lithosphere (<5 km). The research on ductile shearing zone of brittle deformation domain in superficial lithosphere is significant not only theoretically for the study of ductile shearing and ductile rheology of the lithosphere but also practically for the structural movement of coal seams, the formation and accumulation of coal-bed methane, and the prevention and harness of gas burst in coal mine.

Imaging coal seam structure using 3-D seismic methods

Coal mining and production is a very large industry within Australia with over 100 active collieries. However, to run at a profit, the coal mines must have continuous production and fulfil large annual quotas. This is generally achieved through the use of the capital intensive, underground, longwall mining technique. This technique requires that the coal seam structure be accurately known ahead of the extraction coal face. Any unknown faulting, unstable roof conditions or gas accumulations encountered while mining can lead to equipment damage, down-time and injury to workers. Thus, the responsibility is on the mine geologist to ensure that the coal seam structure is accurately mapped ahead of mining, to provide a safe mine plan. Before the introduction of the seismic method in coal mining, all coal seam mapping was done using surface boreholes. This is an expensive method to use and provides only a low level of lateral resolution.Seismic methods are gradually replacing boreholes and becoming more common place in coal industry as an accurate and cost effective alternative method for imaging the seam structure. Burton Downs colliery in central Queensland, was one such mine to take advantage of this method as apart of an Underground Feasibility Study for their northern, Kerlong mine area. With no previous seismic work done in the area, reverse vertical seismic profiling (RVSP) and two-dimensional (2-D) surveys were initially shot. RVSP results showed that the seismic method was viable, imaging the coal seam of interest and provided acquisition parameters for the 2-D surveys. The 2-D lines gave high-resolution images of the coal seams within the mine area, and showed a complex faulting system which included low-angle reverse faulting and normal faulting. The success of the 2-D profiles prompted the acquisition of a three-dimensional (3-D) survey. After processing the 3-D depth volume, a much more complete structural interpretation and hence, mine plan could be made.

High resolution seismic for resolving coal seam structure in difficult terrain

This paper describes a high-resolution seismic survey in the Southern Coalfields of New South Wales over rugged terrain in areas yet to be mined. The aim of the survey was to identify faults in the working seam, which are very disruptive to longwall mining operations. Rapidly changing topography with deep gorges, swamps and dense bush create access and environmental difficulties for seismic operations. For the first time, attempts have been made to acquire seismic data across difficult gorge and swamp country. The techniques used were successfully adapted from previous surveys carried out in less difficult terrain. Current indications are that there will be minimal impact on the environment. The data collection and processing parameters developed enabled good coherent data to be obtained across deeply incised terrain. Faults with various throws have been interpreted.

Coal seam structure delineation by downhole-crosshole seismic methods : Hawkins, L V; Wootton, P; Holmes, W H Geoexploration V24, N4/5, Nov 1987, P409–419

Coal seam structure delineation by downhole-crosshole seismic methods : Hawkins, L V; Wootton, P; Holmes, W H Geoexploration V24, N4/5, Nov 1987, P409–419

Geotomography for the delineation of coal seam structure : Rogers, P G; Edwards, S A; Young, J A; Downey, M GeoexplorationV24, N4/5, Nov 1987, P301–328

Geotomography for the delineation of coal seam structure : Rogers, P G; Edwards, S A; Young, J A; Downey, M GeoexplorationV24, N4/5, Nov 1987, P301–328

Coal seam structure delineation by downhole-crosshole seismic methods

Very high resolution profiling of coal seams by seismic reflection methods requires wide band-width sources and the avoidance of transmission through weak or weathered material, which strongly attenuates high frequencies. The system described here uses a marine sparker source and hydrophone seismometers in boreholes below the weathered layer to achieve sub-metre resolutions. The survey techniques include vertical and crosshole logging as well as Yo-Yo profiling. Problems with tube waves can be removed by F-K filtering and other processing techniques. In particular, multi-channel data acquisition allows beam steering techniques to be used to improve resolution and remove interference. The migration of Yo-Yo data is also discussed.

Geotomography for the delineation of coal seam structure

The in-seam and surface reflection methods of seismic delineation of disruptions to coal seams have recently been extended by the use of seismic sources and receivers located in boreholes. Both reflection and transmission (tomographic) borehole seismic data, as well as borehole EM attenuation data, can assist in forming improved pictures of coal seam structure in the vertical plane. This paper examines the problems associated with imaging of geological features via tomography. Computer simulations of crosshole and surface-to-borehole (offset VSP) seismic surveys are used to illustrate the effect on tomographic images of the parameters of the survey geometry, particularly the range of depths sampled by in-hole sources and receivers, the distance between boreholes and the in-hole and surface sampling density. We find that it is essential to include surface-to-borehole data in addition to crosshole data to be able to see lateral seam disruptions. We illustrate how the recovery of tomographic images from field data can be improved by constraining them during processing, using velocity information and information about the survey geometry. Finally, we address the question of picking travel times from transmission seismograms recorded in a sedimentary environment and illustrate the necessity of accounting for waveform distortions due to the complex propagation conditions in order to extract travel times from a transmission data set that are suitable for tomographic reconstruction.

Determination of contributors to coal seam structure in Sullivan County, Indiana

The structure of coal seams in Sullivan County, Indiana is subject to local variability controlled by differential compaction. Underlying Silurian reefs contribute to the maximum vertical variation and the underlying Mississippian unconformity surface controls the distribution of the most extensive and mappable structural features. The vertical magnitude, orientation, and lateral extent of the features should be considered during mine layout. Potential underlying Silurian reefs can be distinguished from other contributors to coal seam structure for the purposes of petroleum exploration.

Shallow seismic reflection investigations of coal in the Sydney Basin

Surface reflection profiling with the Mini‐SOSIE technique successfully mapped shallow coal seam structure in the western Sydney Basin, New South Wales. Several minor faults and zones of fracturing were detected. In regions of thick Triassic sandstone cover, data quality was poor and unsuitable for geologic interpretation. Synthetic seismograms based on nearby borehole and petrophysical control show excellent agreement with the Mini‐SOSIE sections and illustrate the deleterious filtering effects of coal seams and sequences. To establish a phenomenological basis for seismic wave propagation in shallow coal measures, two vertical seismic profiles (VSPs) which used small explosive charges were recorded with high spatial and temporal sampling. Numerous multiple reflections were observed in the downgoing wave display. The isolated upgoing waves were migrated to yield blurred images of the main coal seams. The subsurface velocity function, also deduced from the VSP, shows broad correlation with the geologic log. The VSP seismograms are not simple because of the combined effects of wave absorption, scattering, and interference. Such problems impede recovery of fine structural detail from seismic data in the shallow environment, particularly when a surface energy source is used.

Gravity log — A simpler representation of coal quality and seam structure : Chatterjee, D R J Mines Met Fuels, V30, N7, July 1982, P370–390

Gravity log — A simpler representation of coal quality and seam structure : Chatterjee, D R J Mines Met Fuels, V30, N7, July 1982, P370–390

Applications of reflection seismics to mapping coal seam structure and discontinuities : Proc 1st Conference of Ground Control in Mining, Morgantown, 27–29 July 1981, P160– 166. Publ Morgantown: West Virginia University, 1981

Applications of reflection seismics to mapping coal seam structure and discontinuities : Proc 1st Conference of Ground Control in Mining, Morgantown, 27–29 July 1981, P160– 166. Publ Morgantown: West Virginia University, 1981

Internal structure of coal seams and mechanical stability : CIM Bull, V75, N841, May 1982, P71–75

Internal structure of coal seams and mechanical stability : CIM Bull, V75, N841, May 1982, P71–75