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Experiments on coal permeability with saturated water under tri-axial stress were conducted. The relationship between stress and permeability under tri-axial stress was analyzed on the rock mechanical experimental rig (GAW-2000). After the experiments on permeability, the fracture characteristics were researched by X-ray computerized tomography, which shows that the bituminous coal normally has high fractal dimensions (generally over 1.8) and wide aperture. The results for permeability reveal that bituminous coals always have variable permeability characteristics under incremental axial stress due to its inherent fracture features. It can be divided into two types: type I, at the linear and nonlinear elastic deformation and peak stage, the permeability keeps rising, which is represented by FYGY8 #. The main control factor of permeability should be related to coal microfractures and coal compositions. Type II, which is represented by sample YCLZ2#, in the initial linear elastic stage, there is a decrease trend in the permeability performance, and then permeability gradually rise when it comes into the stage of nonlinear elastic deformation. The permeability will keep go down after coal becomes soften under the action of confining pressure, compaction.

Low-field nuclear magnetic resonance (LFNMR) is a rapid, nondestructive analytical method which has been proved to be attractive for its application in brittle and easily compressed coals. In this paper, the relationships between NMR parameters and coal pores were analyzed by the NMR measurements of six coal samples with different ranks using AniMR with the resonance frequency of 12.15MHz. Results show that NMR porosity usually compare well to water porosity and be lower than He porosity, and the NMR porosity at echo spacing of 0.3ms sometimes underestimates the coal sample, lower than water porosity by >1 porosity unit. In contrast, the NMR porosity at echo spacing of 0.1ms is acceptable for characterization of coal reservoir. The difference of NMR porosity at different echo spacing may relate to the vitrinite content. Based on the T2c model, the transverse surface relaxivity of coal is calculated and it ranges from 0.25 to 20 um/s, commonly lower than 5um/s. The producible porosity could be a parameter used to estimate coal permeability, however there still needs a lot of work to construct a perfect method for this.

Jixi basin is one of the important coal basins in China. To explore the gas accumulation characteristics and its geological controls, it’s important for further exploration and development of coalbed methane (CBM). The gas content of Jixi Basin is high viable from 4.78 to 11.94 m3/t, indicating high gas content in the north and west but low gas content in the south and east. The further analysis results show that the delta plain and lake are favorable sedimentary environments for coal accumulation. The Chengzihe and Muleng formation are formed in these environments. Moreover, massive magmatic intrusion heat activities and subsequent continuous subside of strata increase coal rank of the coals. In the area of Pingma reverse fault and the area with thick Muleng formation, mud seals are favorable for CBM preservation. In these areas, CBM is sealed and accumulated by hydrodynamic condition. Finally, a comprehensive evaluation model for CBM was found. Based on the evaluation model, the most favorable zone for CBM exploration is forecasted to be J idong depression.

Coal petrologic structure is important for the prediction of coal and the associated coalbed methane outburst during coal mining. This paper discusses the relationship between the response characteristics of natural gamma (GR), laterlog deep (LLD) and compensation density curve (RHOB), and the coal structures. Results show that the tectonic-coals (the coals with high breakage degree by tectonic structures) can be identified by the logging characteristics of low amplitude of GR (20-90 API), high amplitude of LLD (300-1800 Ωm), and low amplitude of RHOB (1.25-1.5g/cm3). It was found that with increasing degree of the breakage, coal pores and fractures become well developed, and thus reduce the bulk density of coal and the content of radioelement but more gas within the coal. This is the reason for logging performances of low amplitude of GR and RHOB, as well as high amplitude of LLD for the tectonic-coals.

This paper discusses the structural characteristics and tectonic evolution, as well as the accumulation history and preservation conditions of coalbed methane (CBM) in Zhengzhuang block located in southeastern Qinshui basin. Deformed by the Hercynian, Indo-China, Yanshan and Himalayan four tectonic movements, the study area emerges the structure pattern that folds developed in northwest of the block, while faults in the southeast. The area near the syncline axis is the favorable region of CBM accumulation with good sealing condition. The Sitou fault has an effect on the diffusion of CBM. The geological controls of gas accumulation were concluded by a conceptual model, which provides a basis for further exploration and development.

Southern Shizhuang Block has simple structure characteristics, relatively thick coal seams (3.1-10.5 m, 6 m in average), and favorable burial depth (450-900 m). The gas content of the No.3 coal seam in the Shanxi formation ranges from 6-20 m3/t, and it increases from the southeast to northwest area in the southern Shizhuang Block. Gas content is high in the structural low in the area, which means the gas accumulation is controlled by the geological characteristics of local structure and hydrogeologic conditions.

Mercury injection capillary pressures (MICP) on the coal samples were measured with a variety of pressure regimes. The goal was to compare the effects of different pressure regimes for determining the compressibility of the coal. The two samples were taken from Northeast China. MICP profiles up to 204 MPa were measured on two different crushed samples of the same size. Three linear regimes namely, at 10-40 MPa, 40-100 MPa and P>100 Mpa are defined, corresponding with the diameters of mesopore and microspore. The standard deviations of the compressibility values were less than 20%. The results from the present study suggest that the different pressure regimes affect the compressibility values slightly.

Based on the gas analysis results of coalbed methane (CBM) wells in the Weibei CBM field, two main recoverable target seams (Nos. 5 and 11) were evaluated for the potential of exploration and exploitation by using the grey correlation analysis method. The main influnce factors on the CBM potential by increasing importance are gas content, gas saturation, buried depth, methane concentration, critical desorption pressure,reservoir pressure and coal thickness for the No.5 coal seam; while they are gas saturation, gas content, critical desorption pressure, methane concentration, buried depth, reservoir pressure and coal thickness for the No.11 coal seam. The exploration potential of No.5 coal seam is better than that of No.11. The favorable area for CBM exploration are the areas including Well block W2, W3, W4 and W8 in the middle of Weibei CBM field.

This paper discusses how sedimentary controls on accumulation of coal and coalbed methane in Hancheng CBM field. Two major coal-bearing strata include the Upper Carboniferous Taiyuan formation (a marine and terrestrial sedimentation) and the Lower Permian Shanxi formation (a terrestrial sedimentation). The favorable sedimentary environments for accumulation of coalbed methane by decreasing order are the shallow marine and barrier island system, the delta system, and the shallow marine and plane coast system.

For finding out favorable coalbed methane development districts, the evaluation of geological controls of CBM distribution and accumulation is essential during CBM exploration and development. In this paper, the No. 3 coal seam in the Zhengzhuang coal zone located at southern Qinshui Basin, China, was selected as a focus for comprehensively evaluating geological controls of CBM. The findings of this study are: (1) Coalbed gas contents increase with increasing mudstone roof thickness (ranging from 0-9 m), and will always be as high as 20 m3/t in the coal reservoirs with the mudstone roof thickness greater than about 9 m. (2) The weak transmission and stagnant coalbed water are favorable for CBM accumulation in coal reservoirs resulting from the typical hydraulic preservation of CBM. (3) High coalbed gas contents will commonly occur in vitrinite-rich and low-ash yield coals with high CH4 adsorptive capacity.

The Boli basin has coalbed methane (CBM) resource of 57×108m3 at a coal-bearing area of about 7200km2. Although the basin has huge CBM development potential, the study on the characteristics of coal reservoirs is still deficient. In the paper, the physical properties (including coal petrography, rank, quality, porosity and permeability) of the coals were studied by: (1) measuring vitrinite reflectance, coal maceral composition and coal quality; (2) quantitatively counting microfractures; (3) porosity and permeability tests; and (4) low-temperature N2 isotherm adsorption/desorption and mercury porosimetry analyses. Results show that: (1) coal maceral composition is dominated by vitrinite (77.0-95.1 %); (2) the maximum vitrinite reflectance of coals ranges from 0.48 to 1.76 % Ro, max; (3) coal is composed of high carbon content (63.43-85.14%), low hydrogen content (3.23-4.56%), extremely low moisture content (0.18-1.18%) and widely varied ash yield (7.54 to 29.23%); (4) Coal pores are dominated by micropores (40.6-69.3%), and the pores with a diameter of 0-10nm are dominant (59.6-80.9%); (5) coal permeability values vary from 0.04 to 3.92mD with an average of 1.98mD. In addition, according to the mercury porosimetry analysis, pore-fractures size distribution was summarized as four types: Types Ⅰ and Ⅲ are favorable for developing CBM and represent good pore-fracture structures.

The Late Paleozoic coalbed methane (CBM) reservoirs for high-rank coal in North China have the characteristic of high CBM content. But due to the differences between CBM reservoirs in several aspects such as physical property and gas accumulation condition, CBM was developed for commercialization only in the south of Qinshui Basin. Coal samples were systematically collected from Qinshui Basin, Jiaozuo Coalfield, Yongxia Coalfield and Xinggong Coalfield, and then tested on coal petrology, porosity-permeability characteristics and isothermal adsorption, etc. Based on the analyses of these test data, this paper discusses the forming conditions and mechanisms of the favorable CBM reservoirs for high-rank coals. These factors like the coal petrology characteristics, reservoir physical property and gas accumulation conditions were detailedly discussed. The difference characteristics of the favorable CBM reservoirs in North China were comprehensively evaluated as conclusions. The result shows that in comparison with other high-rank coal areas, coals in Qinshui Basin have undergone slight tectonic destruction, which induces the widespread development of primary- and cataclastic-structured coals, developing better microfractures. Moreover, the Qinshui coals have not only the well-developed exogenetic fractures, but also well sedimentary and tectonic conditions at the key accumulation period of CBM. These factors resulted in the formatting of better CBM reservoir in Qinshui Basin when comparing to other high coal rank areas in North China.