Xuehai Fu

Fractal classification and natural classification of coal pore structure based on migration of coal bed methane

According to the data of 146 coal samples measured by mercury penetration, coal pores are classified into two levels of <65 nm diffusion pore and >65 nm seeping pore by fractal method based on the characteristics of diffusion, seepage of coal bed methane(CBM) and on the research results of specific pore volume and pore structure. The diffusion pores are further divided into three categories: <8 nm micropore, 8–20 nm transitional pore, and 20–65 nm minipore based on the relationship between increment of specific surface area and diameter of pores, while seepage pores are further divided into three categories: 65–325 nm mesopore, 325–1000 nm transitional pore, and >1000 nm macropore based on the abrupt change in the increment of specific pore volume.

Vertical Diversity of Coalbed Methane Content and its Geological Controls in the Qingshan Syncline, Western Guizhou Province, China

The distribution of methane content in the coalbed is complex in the Qinshan Syncline of western Guizhou Province. Analyses of factors controlling on the distribution of gas content are made in this paper. Coal ranks and geo-structure in the region showed strong controls on the gas distribution. Coals with higher degree of metamorphism or located in syncline most likely have higher gas content. With the concept of coalbed methane content unite thickness (CBMCUT), those factors such as coal seam buried depth and coal structure present positive relations with gas content. Results indicated that the variation of CBMCUT is not fixed in different research areas or in different coal structures. Namely, the variation follows “v-shaped” correlation with the increasing coal buried depth in the region of Qinshan Syncline. However, the trend is smooth for the coals in the Panzhuang mining area. Usually, the critical value for primary-texture coal and mylonitized is different based on the analysis of the relationship between coal structure and CBMCUT in those two areas described above. The value is commonly higher in mylonitized coal and lower in those mainly primary-texture and fragmented coals.

Evaluation of favorable regions for multi-seam coalbed methane joint exploitation based on a fuzzy model: A case study in southern Qinshui Basin, China

The coalbed methane resources in the Taiyuan Formation account for 55% of total coalbed methane reserves in the southern Qinshui Basin, China; however, the resources have yet to be utilized basically. The joint exploitation of coalbed methane in the Taiyuan Formation and the Shanxi Formation can accelerate the process of coalbed methane scale development in this region. The productivity characteristics of commingling drainage are controlled by various geological factors. Thus, to select favorable regions for multi-seam coalbed methane joint exploitation, the impacts of some geological factors such as coal thickness, burial depth, gas content, reservoir pressure gradient, and reduced water level on the gas production were analyzed and estimated based on a bivariate correlation analysis. Analysis results show that the two coal seams of the high production rate wells of commingling drainage usually have the following conditions: total coal thickness > 9.5 m; average burial depth < 640 m; average gas content > 14 m3/t; reservoir pressure gradient difference < 0.05 MPa/100 m; reduced water level difference < 55 m. Based on the correlation analysis results, the potential of multi-seam coalbed methane exploitation in the study area was evaluated by using a multi-objective fuzzy matter-element model. At last, taking the evaluation coefficient 0.75 as the critical value, unfavorable zones, relatively favorable zones, favorable zones, and extremely favorable zones for multi-seam coalbed methane joint exploitation were identified in the southern Qinshui Basin.