Coal Strata Research Articles

Regional Stress Variations in the Pembina-Warburg Area of the Alberta Basin: Implications in Coalbed Methane Exploration

This study documents a comprehensive investigation of the in-situ stress magnitude and orientation data from borehole breakouts, mini- and micro-fracture tests, bulk density logs and other stress data, for strata in or adjacent to the Mannville Group and Edmonton Group coals in a part of the west-central Alberta Basin, Canada. The horizontal in-situ stress orientation data can be used to plan horizontal well trajectories in the coal strata of interest to intersect natural fractures and cleats possessing the highest permeability. Horizontal stress orientation data can also be used to assess the effects of well trajectory or borehole collapse risks during drilling, completions, and production operations. Subtle variations in the vertical total stress in the study area may reflect similar trends in the mean effective stress. However, this would need to be confirmed with more complete horizontal stress magnitude and formation pressure data.

Numerical Simulation of Gas Distribution and Mined Seepage Passage with the Pressure Relief of Short Distance Protective Coal Stratum

With the full consideration of the heterogeneity, existing joints, and cracks in the rock, the coupled gas-rock model for investigating the failure process of coal-rock is established by introducing the related equations governing the evolution of stress, damage and gas permeability along with the deformation of coal and rock. A numerical approach of realistic failure process analysis (RFPA) to simulate the stratum movement, layer separation, the whole collapse progresses, and gas permeability changing of the protected coal seam is proposed. The numerical simulation results well displayed the whole processes of the cracks growth of gas seepage passage and the change of gas permeability for the closed distance protected coal seam. It can be seen from the distribution of acoustic emission in the space that the stratum failure is transferred from deeper to surface. By the analysis of the stress fields changing, the reasons of the gas permeability improvement of the protected coal seam are presented.

A Study on Forming Mechanism of Gas Tunnel in Non-Coal Strata

In addition to the gas tunnel in coal strata, there are a large number of gas tunnel in non-coal strata, these tunnels itself do not through the coal strata, but all encountered the gas problem in the construction process. Because of not a full understanding and preparation on gas of tunnel in non-coal strata zones, and the gas emission is random, uneven distribution of the characteristics, so the gas disaster hazard is larger in such gas tunnel, study on its formation mechanism is great significance. Based on the study of a lot of the gas tunnel has been constructed, summed up three genetic types of the non-coal strata gas tunnel: one type is structural connectivity, according to the different structure types, can be divided into fracture connectivity type, fault type and fold connected connectivity type; Second is surrounding rock metamorphic type; third is compound effects type.

Geological Features of Kailuan Coal Mine and the Laws of Pressure Bump for Deep Mining

Pressure bump in coal mine production safety is a serious disaster. Geological conditions in Kailuan Mine are complex. Coal strata based on the Carboniferous - Permian coal. The roof and floor are made of sandstone and mudstone with poor rigidity. Fault development and mine have large amount of water inflow. Most of mine are already getting into the mining stage over one thousand meters deep. Increasing stress and high stress induced pressure bump as a key factor. In this paper, according to geological characteristics of Kailuan Coal, it analyzes the impact and the laws of pressure bump in the representation of deep mining phase, which have certain reference for coal mine safety production.

Application of the CSAMT Method for Exploring Deep Coal Mines in Fujian Province, Southeastern China

Coal reserve volume in Fujian Province, China, ranks third among the nine provinces in southern China. Over the past decades, most coal mines in uncovered and semi-covered coal strata have been explored and developed. Present exploration mainly focuses on deep coal strata, which are generally covered by older strata and volcanic strata. Because of the terrain and deep targets, seismic prospecting is difficult. The major coal-containing strata that can be excavated in Fujian are within the Tungtzeyan Formation of the Lower Permian Series. The thickness of this formation is greater than [Formula: see text]. The CSAMT (controlled source audio frequency magnetotelluric) method isused to delineate four deep coal strata units. The aim of this prospecting is to delineate the upper and lower boundaries of the stratum containing the coal units. The prospecting target depth is approximately [Formula: see text], which required a frequency range between [Formula: see text] and [Formula: see text] to provide sufficient data coverage. The distance from the transmitter to the survey line was [Formula: see text], with a transmitting current of [Formula: see text] and voltage of [Formula: see text]. The time synchronization between the transmitter and receiver was controlled by a global positioning system. Major static problems were encountered during the CSAMT survey. Both terrain and static corrections were applied during data processing, which smoothed the inverted results for better interpretation. Comparison of the CSAMT interpreted results with available engineering geology information shows a clear difference in electrical properties between coal stratum, upper old stratum, red-beds and volcanic strata. The CSAMT method is useful in identifying the coal strata under these geological conditions.

Macropalaeontology and stratigraphy of lacustrine Miocene deposits at Crnika beach on the Island of Pag (Croatia)

The sequence of Miocene fossiliferous marls of the Crnika beach, along the south west shore of Pag Bay, consists of an alternation of silty and clayey marls, sandstones, coaly clays, coal-bearing strata and sparse intercalations of bentonite in the older part, and of an alternation of calcitic marls and organogenic fossiliferous limestones with several coal strata in the younger part. Some of the strata are highly fossiliferous and rich in various species of freshwater gastropods of the genera Melanopsis, Theodoxus, Pyrgula, Prososthenia, Orygoceras and Valvatawith the new species V. (?Costovalvata) pagana. Bivalves are represented by the genera Congeria, Unio, Pisidium. There is also, a rich ostracod assemblage, and remains of flora: twigs, leaves and seeds of higher and lower plants, and agglomerations of aquatic grasses and algae. Fish bones and teeth, as well as the crocodile tooth, are not particularly common, but they do help to complement the image of the diversity of the biological association that lived in the ancient lake and along its shores. According to facies analysis, the Miocene deposits of the Island of Pag, were deposited on the south-western edge of Paratethys, which has been moved more westward and south-westward within Croatian territory.

3-D seismic identification and characterization of ancient channel morphology

It is easy to identify ancient fluvial morphologic types by the outcrop, log and core data. However, the horizontal distribution and geometry of the channels can only be identified and predicted by relying on the 3-D seismic data. The 3-D seismic horizon slices, especially, can play an important role in the sandstone prediction of meandering rivers, distributary channels and low-sinuosity channels. Every microfacies unit, including main channels, such as sinuous or branching channels, levee, crevasse channels, ligule crevasse splay and floodplain etc. can be identified. Braided channel sandstones are planar tabular lateral-connected sandbodies and the distribution of thick main channel belts can only be identified from 3-D seismic data. As the braided sandstones are ubiquitous, their occurrence and distribution do not need to be predicted. Generally, the coal velocity is so low that it can create a strong amplitude reflection in coal strata. It consequently conceals the amplitude respondence to anastomosing channel sandstone which could be identified from 3-D seismic inversion data sometimes. Case studies of mud-rich low-sinuosity rivers identified with 3-D seismic data indicate that the scales and width-to-thickness ratio of such sandbodies are small, laterally unconnected, and generally occurred on distant or further parts of an alluvial fan under dry climate conditions. Sometimes extraction of seismic attributes of every reflection event along horizons is expected to maximize expression of the spatial evolutions of ancient channels.

Model on surface borehole squeezing deformation fracture

As a good method to solve the problem of high methane on the workface and in the goaf, drawing coal strata methane through a surface borehole is used. However, the excavation affected the overlying rock strata greatly. When the excavation face passed through the surface borehole position, the surface borehole fractures fast. This problem was seriously related to the unformed squeeze effect. Therefore, a squeezing deformation fracture model based on the rock strata squeezing effect was set up. At the same time, a 3DEC simulation model is presented to confirm the theory. The result shows that the model is reliable and has a good engineering application value.

Before the Frank Slide

The Frank Slide occurred on the east limb of the Turtle Mountain Anticline, which was thrust up along the folded and splayed Turtle Mountain Fault. Easterly dipping, Paleozoic limestones and dolomites then rested on sheared, weaker, Mesozoic clastic rocks and coal strata. Cordilleran glaciers steepened the eastern flank of Turtle Mountain but left buttressing kame moraines. These were eroded by the Crowsnest River, which was pushed against Turtle Mountain between its North and South Peaks by the growth of the alluvial fan of Gold Creek. Blairmore Group mudstones and shales beneath the moraines were susceptible to toppling. Photographs of the east slope of Turtle Mountain before the Frank Slide show disturbed vegetation, uneven topography, steep slopes, and rock fall deposits, all consistent with active slope movements. The Frank Slide may have been triggered by the freezing of melting snow in rock joints and by coal mining. Our calculations show that, while individual stopes may have been unstable, the mine pillars and the coal mine itself were stable. Numerical simulations of the coal mining in the Frank Mine suggest mining reduced the strength of the east slope of Turtle Mountain by less than 10% before the Frank Slide.Key words: Rocky Mountains, Frank Slide, coal mining, river erosion, toppling.

MEDAL OF MERIT

J. Wadsworth R. Boyd C. Diessel D. Leckie The Canadian Society of Petroleum Geologists Medal of Merit is awarded annually for the best paper related to Canadian petroleum geology published during the previous publication year, in this case for 2003. The winning paper this year was written by Jennifer Wadsworth, Ron Boyd, Claus Diessel and Dale Leckie and was titled “Stratigraphic style of coal and non-marine strata in a high accommodation setting: Falher Member and Gates Formation (Lower Cretaceous), western Canada”. The paper was published in the September 2003 Bulletin of Canadian Petroleum Geology (v. 51, no. 3, p. 275–303). Non-marine correlations are notorious for the difficulty in defining significant and traceable surfaces and units. The aim of this paper was to develop a summary model of sequence stratigraphic principles that can be used for the non-marine realm, as the authors say: “the next frontier to be modelled”. The paper also forms part of an ongoing study of accommodation and the response of sedimentary sequences done by this group of co-authors and other colleagues in their stratigraphic modelling studies. The Falher/Gates are assumed to represent deposition in a high accommodation region caused by flexural subsidence in western portions of the western Canadian foreland basin with the thick stacked Falher shoreface cycles also providing evidence of high accommodation. This high-accommodation package provides an end-member to low accommodation basins (e.g., Basal Quartz, Zaitlin et al., March 2002 Bulletin of Canadian Petroleum Geology, v. 50, no. 1, p. 31–72; last year’s winning paper) and intermediate accommodation basins (e.g., Upper Mannville, Wadsworth et al., December 2002 Bulletin of Canadian Petroleum Geology, v. 50, no. 4, p. 507–541). The Albian Falher Member and Gates Formation consist of clastic sequences shed …

A NOVEL MICROSTRIP PATCH ANTENNA WITH LARGE IMPEDANCE BANDWIDTH IN VHF/UHF RANG

In this paper a novel antenna is presented. This antenna, employing microstrip circular disc as radiator is seen to perform over a large impedance bandwidth (130 MHz to 876 MHz). The disk resonator is loaded with L-C-R circuit across a selective location in the disk via a thin shorting pin. The theoretical modeling predicts TM01 mode of operation. Therefore the beam pattern shows a null in the broadside direction. The said antenna is proposed to be developed for end use in coal mine where the antenna can be flush mounted on coal strata. Thus it will be able to measure the angle of arrival of any reflective component due to presence of waterbed at a distance. The measured as well as simulated results regarding impedance bandwidth and beam pattern agrees well. The simulated efficiency using IE3D is 48% whereas measured efficiency is nearly 45%.

Natural gas releasing simulation experiment of coal in process of temperature decreasing and decompression and preliminary application in Ordos Basin

Natural gas releasing simulation experiments were carried out in laboratory for researching the gas storage capacity in state of high temperature and high pressure and its gas releasing potential in process of temperature decreasing and decompression. The exiting phase state was studied through measuring gas adsorption of coal and PVT phase calculating of natural gas. Gas volume, gas molecular and isotope compositions in process of temperature decreasing and decompression were measured, natural-gas yields released from the Upper Paleozoic coal strata after later Cretaceous (K3) were calculated and the formation of the reservoir was studied combining with the geological background. The results indicate that natural gas stored in coal has still bigger releasing potential after the uplift of Upper Paleozoic strata. There exists a weak gas supply-effluent equilibrium in the reservoir of Ordos Basin, which is another possible evidence that the Upper Paleozoic gas reservoir may be a deep basin gas reservoir.

Chemical concept of geodynamic shocks in coal strata

A chemical concept of geodynamic shocks in coal strata, accompanied by ejection of coal dust and gas, is suggested.

00/01760 Geochemistry of oils from coal and from the shale in coal measure strata

00/01760 Geochemistry of oils from coal and from the shale in coal measure strata

Electromagnetic radiation method water-infusion control in rockburst-prone strata

An electromagnetic radiation (EMR) method associated with rock fracture was employed to study water infusion in rockburst-prone coal strata. Measurements of EMR activity during borehole drilling revealed that a hole nearing a stress peak excites a sharp increase in EMR activity. Water pressure increase/decrease excited EMR activity up to the coal stratum transition to residual stress. An absence of EMR activity during water pressure changes could be a criterion for water infusion performance.

Time dependent strength of coal strata for long-term pillar stability : Z. T. Bieniawski, M. Alber & G. S. Kalamaras, in: Proc. 13th international conference, ground control in mining, Morgantown, WV, 1994, ed S.S. Peng, (WVU/USBM), 1994, pp 81–90

Time dependent strength of coal strata for long-term pillar stability : Z. T. Bieniawski, M. Alber & G. S. Kalamaras, in: Proc. 13th international conference, ground control in mining, Morgantown, WV, 1994, ed S.S. Peng, (WVU/USBM), 1994, pp 81–90

A numerical analysis of the foot‐floor interaction in long wall workings

AbstractA mathematical and numerical approach for the description of creep and failure of coal around a longwall is given. Two coal strata are considered. They are assumed to be elasto‐viscoplastic. The variation in time of the stress and displacement around the excavation, as well as the limit thickness of the upper stratum which would avoid failure was found.

Inclined shafts in coal strata: the role of the rock mechanics engineer : Vervoort, A; Madden, B; Lear, C Proc 7th ISRM International Congress on Rock Mechanics, Aachen, 16–20 September 1991V2, P1237–1242. Publ Rotterdam: A A Balkema, 1991

Inclined shafts in coal strata: the role of the rock mechanics engineer : Vervoort, A; Madden, B; Lear, C Proc 7th ISRM International Congress on Rock Mechanics, Aachen, 16–20 September 1991V2, P1237–1242. Publ Rotterdam: A A Balkema, 1991

Formation of electromagnetic radiation in coal stratum

More modest success has been achieved in the development of geophysical methods for predicting sudden ejections of coal and gas. Prediction of ejection hazards based on the recording of the acoustic noise [I] has been introduced and widely used in the Donbass. This method, although adequate for evaluating the ejection hazard at the edge of the coal stratum, has some disadvantages. Among these are the complexity of the apparatus, the switching and the subjective interpretation of the results.

Diffusion field in coal stratum

In [i-4] we tried to describe the methane-bearing coal stratum as a methane-coal solid solution. The question of migration of methane within such a system remained unresolved. Complete absence of migration in a methane--coal equilibrium system is impossible. Because of spontaneous fluctuations, there will always be localized ruptures of the bonds between the methane molecules and the coal substance. Due to the migration of the defects in the system, CH~ molecules will have a 'degree of freedom' at certain times. In the assumed analagous model of aerated water (champagne), the migration of the dissolved gas molecules occurs along the system defects. In the liquid medium, the defects were instantaneously closed up, so migration was not observed. It is obvious that small bubbles will combine to form larger bubbles, which are able to rise, overcoming the viscosity of the liquid medium.