Based on the review of exploration history of coalbed methane(CBM)in this region,the main geological factors affecting the CBM recovery are discussed,such as the permeability of coal seam,the ancient and present stress fields,the development of natural fracture in coal seam and the present effective stress,as well as reservoir pressure,isotherm adsorption/desorption,gas saturability and velocity of gas diffusion and so on .

It is concluded that the Gaussian curvature method can reflect the shape variation of coal seam curvature, and the method is effective to forecast natural fracture zones in coal seam.

On the basis of dual-media theory, two-dimensional models of water flow and pollutant migration are established for natural fractural systems both in their fracture domain and porous rock mass domain.

As for the main coal reservoirs of the lower Permian Shanxi Formation in the central-southern Qinshui basin, the permeability gradient of coal reservoirs tends to increase in exponential fanction and the pressure gradient to rise in logarithmic function with the increase of the principal stress difference σ1-σ3 of modern tectonic stress field, which is predominantly controlled by the correlation between the main stress direction and the preferentially developed direction of natural fissures in coal reservoirs.

Cleats are the endogenetic fracture systems which are widely distributed in the coal bed and are of great significance for the coal-bed gas to be produced,being the natural fractures formed by desiccation,coalification,lithification and tectonic force.

A fracture criterion based on finite extension strain energy release rate, is proposed to capture the intrinsic fracture toughness.

Extrapolation of fracture energies to zero additive or porosity levels, as well as analysis of CVD Si3N4 all indicate an intrinsic fracture energy of 20-30J m-2.

A basic statistical fracture description for the intrinsic fracture of whiskers was derived, which predicts a plateau in the intrinsic whisker strength.

Prediction of intrinsic fracture toughness for brittle materials from the apparent toughness of notched-crack specimen

In this investigation, fracture process zone model is used to establish a new relationship to predict the intrinsic fracture toughness from the apparent fracture toughness of a notched-crack specimen.

A stochastic approach is commonly used to generate a synthetic fracture network from the statistics measured at a natural fracture network.

The approach presented herein is able to incorporate the structures found in a natural fracture network into the synthetic fracture network.

A much better understanding of the physics of fluid flow in a natural fracture from a sample of granite has been obtained from metal casts of the complex topography of the surfaces of the fracture as it is subjected to normal stresses up to 85 MPa.

Effect of induced fracturing based on a natural fracture system in a dimension stone quarry in the Offerdal Nappe, Sweden

Little consensus exists on how best to analyze natural fracture spacings and their sequences.

In this Paper the mechanical tests of hard coal samples of Datong coalfield were carried out by using the stiff loading system, and wire strain gages and the microcracks were observed by scanning electron microscope. The results of testing showed that there were many natural microcracks in the coal samples, which developed along their lengths with the increase of the compression stress. When the stress increased to a given level, new cracks occurred in the samples. The relationship between the stress and strain...

In this Paper the mechanical tests of hard coal samples of Datong coalfield were carried out by using the stiff loading system, and wire strain gages and the microcracks were observed by scanning electron microscope. The results of testing showed that there were many natural microcracks in the coal samples, which developed along their lengths with the increase of the compression stress. When the stress increased to a given level, new cracks occurred in the samples. The relationship between the stress and strain was nonlinear. Before reaching the stress peak, the total deformation included mainly elastic deformation and some residual deformation and the latter was represented by closure of the cracks when being compressed. A mechanical model is proposed, which can simulate the nonlinear deformation of coal,the elastic deformation, the residual deformation and the relationship between the stress and strain after the stress peak.

On the basis of dual-media theory, two-dimensional models of water flow and pollutant migration are established for natural fractural systems both in their fracture domain and porous rock mass domain.Expression formulae and calculation methods of the coupling term(r)are discussed separately for cases when the rock mass is of parallelepiped shape, elliptic cylinder shape or irregular shape. Quantitative analyses are made separately for the control and influence of factors like flow speed, diffusivity and porosity...

On the basis of dual-media theory, two-dimensional models of water flow and pollutant migration are established for natural fractural systems both in their fracture domain and porous rock mass domain.Expression formulae and calculation methods of the coupling term(r)are discussed separately for cases when the rock mass is of parallelepiped shape, elliptic cylinder shape or irregular shape. Quantitative analyses are made separately for the control and influence of factors like flow speed, diffusivity and porosity on pollutant migration. Finally, the migration of Cl~- ions in a karstic aquifer of about 85km~2 area in the eastern suburb of Jinan city is simulated, in which rather satisfactory results are obtained.

One of the important reasons that obstruct the application of dual-porosity model is the estimating of parameters in porous blocks and fractures.A set of new equations has been develooed for modeling groundwater flow in dual-porosity aquifers at drawdown and slug conditions, respectively. The transmissivities and storage coefficients in fractures and porous blocks can be determined based on the solutions of the equations.Procedure for estimating the parameters is outlined by using a drawdown test in a karst...

One of the important reasons that obstruct the application of dual-porosity model is the estimating of parameters in porous blocks and fractures.A set of new equations has been develooed for modeling groundwater flow in dual-porosity aquifers at drawdown and slug conditions, respectively. The transmissivities and storage coefficients in fractures and porous blocks can be determined based on the solutions of the equations.Procedure for estimating the parameters is outlined by using a drawdown test in a karst aquifer which has the characters of dual-porosity.