Fracturing in Coal-beds

The production of natural gas from coal typically requires a stimulation with hydraulic fracturing. Basic studies on the effectiveness of various treatment methods for coal-beds have been presented in the literature [398,1424]. 

Treating a coal seam with a well treatment fluid containing a dewatering agent will enhance methane production through a well. This additive enhances the permeability of the formation to water production and binds tenaciously to the coal surface so that the permeability-enhancement benefits are realized over a long production term. 

Dewatering surfactants can be polyoxyethylene, polyoxypropylene, and polyethylene carbonates [1348] or p-tert-amylphenol condensed with formaldehyde, or they can be composed of a copolymer from 80% to 100% alkyl methacrylate monomers and hydrophilic monomers [777]. Such a well treatment fluid may be used in both fracturing and competition operations to enhance and maintain fracture conductivity over an extended period of production. 

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Cleats are natural opening-mode fractures in coal beds. They account for most of the permeability and much of the porosity of coal bed gas reservoirs and can have a significant effect on the success of engineering procedures such as cavity stimulations. Because permeability and stimulation success are commonly limiting factors in gas well performance, knowledge of cleat characteristics and origins is essential for successful exploration and production. 

Cleats Natural opening-mode fractures in coal beds, which account for most of the permeability and much of the porosity of coalbed gas reservoirs. 

Mr. Koppe This was not done, but it would be helpful to do so. The coal examined is highly fractured in the bed. Often samples were scooped up with a thin paint spatula. Studying oriented block material was impractical for the area in the time available. 

A system of joint planes is often observed in coal formations, and these joint planes (cleats) are usually perpendicular to the bedding planes. Thus, cleat joints are usually vertical. The main system of joints is more commonly called the face cleat, whereas a cross-system of jointing is called the butt cleat. Furthermore, the cleat system in coal has a pronounced effect on the properties of a coal deposit. For example, holes drilled into coal perpendicular to the face cleat are said to yield from 2.5 to 10 times the amount of methane gas from the formation as holes drilled perpendicular to the butt cleat. Also, the cleat system of fracture and the frequency of cleats may determine the size of run-of-mine coal. In general, a pair of cleats will be oriented at about 90° to each other, and the orientation of the cutting elements influences the output of coal-mining machines (Figure 8.4). 

The initial compression and plastic deformation zone. This zone begins about 90 m in front of the face. As the face advances, the top coal undergoes vertical compression and deformation under the influence of the initial coal mining operation. The deformation is derived mainly from the compression of the inherent horizontal fractures in the coal seam. As the face continues to advance, the front abutment pressure also continues to increase, plastic deformation and lateral deformation begin to occur in the top coal. This process produces micro-cracks in the coal. Field measurements showed that there are no bed separations between the immediate roof and top coal, and within the top coal. 

The intensive compression and damage zone. This zone, approximately from 20 m to 40 m in front of the face, is located within the peak pressure area of the front abutment pressure. Due to the increasing roof pressure, the inherent fractures in the coal open up further. So are the microcracks induced in the initial compression and plastic zone. Many new fractures are also produced and developed to the full extent. As a result, top coal is damaged gradually. Field measurements showed that bed separations in this zone are well-developed between the immediate roof and top coal, and within the top coal. 

Endogenetic cleats are normal to the bedding plane of coal and generally occur in pairs. There are at least two sets of near perpendicular fractures that intersect the coal to form an interconnected network throughout a coal bed. These two fracture systans are known as face and butt cleats. The shorter butt cleat normally terminates at a face cleat, which is the prominent type of cleat. 

Blast mining (sometime referred to as conventional mining) is an older practice in which explosives (such as dynamite) are used to fracture the coal seam, after which the coal is gathered and loaded on to shuttle cars or conveyors for removal to a central loading area. This process consists of a series of operations that begins with cutting the coal bed so it will break easily when blasted with explosives. 

ABSTRACT The present mining depth reaches about 600 m and inreases 12 m per year to deep part in key coal mines of eastern North China. Being the basement of coal measure strata in North China coal mine, the Ordovician karst aquifer is the baleful source of water for exploiting the Carboniferous coal bed (deep coal seam). The coal mines that the exploitation transfers into the deep stratum will be threaten by the deep high or superhigh pressure (8-12 MPa) confined water from Ordovician. Meanwhile, the researched area has the Coal Chemical Industry (CCI) which demands a mass of water. This paper analy-sised the current situation of water resources in the researched area and hydraulic, hychemical feature of deep Ordovician fracture-karst aquifer. The concept of Water and Coal Simultaneous Extraction (WCSE) was put forward. The feasibility test of WCSE was put into effect in study area. Einally, the water pressure of deep karst aquifer was reduced for the deep coal mined safely by means of dewatering, which could supply sufficient water for the CCI. 

Most gas in coal is stored on the internal surfaces or organic matter. Because of its large internal surface area, coal stores 6-7 times more gas than the equivalent rock volmne of a conventional gas reservoir [1]. ( s content generally increases with coal rank, with depth of the coalbed, and with reservoir pressure. Fractures or cleats that permeate coalbeds are usually filled with water the deeper the coalbed, the less water is present, but the more saline it becomes. In order for gas to be released from the coal, its partial pressure must be reduced, and this is accomplished by removing water from the coal bed. Large amounts of water are produced from coalbed methane wells, especially in the early stages of production. While economic quantities of n thane can be produced, water disposal options that are environmentally acceptable and yet economically feasible become a concern. 

Anthracite, a form of coal q.v), contains fi om 90 to 95% carbon with low oxygen and hydrogen content. It is black with a sub-metallic lustre, conchoidal fracture, banded strucmre and does not mark the hands when handled. Anthracite is formed when coal-bearing beds are subject to low-grade metamorphism, so, for instance, in the South Wales coalfield transitions from... 

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