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Ma D.-M.,Xian University of Science and Technology | Ma D.-M.,State Energy Key Laboratory of Joint Exploitation of Coal and Coal bed Methane | Li L.-X.,Shaanxi Coalbed Methane Development Corporation Ltd. | Li X.-P.,Team 131 of Shaanxi Coalfield Geology Bureau | And 4 more authors.
Meitan Xuebao/Journal of the China Coal Society | Year: 2014

The study investigated the technology of the replacement of CH4 by CO2 in order to rapidly reduce the coalbed methane content in coal seam 4 at Dafosi Coal Mine and improve the recovery factor of the ground coalbed methane wells. Contrastive experiments on adsorption and desorption of CH4 and CO2 of cylinder raw coal and 60-80 mesh equilibrium water samples at different temperatures are conducted using the samples collected from the working face 40114 at Dafosi Coal Mine. The results indicate: the adsorption and desorption of CO2 on coal pore surface is consistent with that of CH4, the pressure-rising process abiding by Langmuir equation and the pressure-dropping process being described by desorption expression. Based on thermodynamic calculation, in cylinder raw coal during pressure-rising process, the adsorption heat of CO2 is 56.827 kJ/mol while that of CH4 is 12.662 kJ/mol. During pressure-dropping process, the adsorption heat of CO2 is 115.030 kJ/mol while that of CH4 is 23.602 kJ/mol. In both processes, the adsorption heat of CO2 is far greater than that of CH4, which proves that CO2 is more competitive over CH4 in their adsorption on coal pore surfaces, leading to replacement desorption. The conclusion is verified by the calculations of adsorption potential and adsorption space. The technology of replacing CH4 by CO2 is feasible with strong theoretical ground, and useful for improving the recovery factor of coalbed methane. Source


Tian Y.-D.,State Energy Key Laboratory of Joint Exploitation of Coal and Coal bed Methane | Tian Y.-D.,Shanxi Lanyan CBM Group Co. | Wu J.,Shanxi Lanyan CBM Group Co. | Wu J.,Shanxi Province Key Laboratory of Coal and Coalbed Methane Simultaneous Extraction
Meitan Xuebao/Journal of the China Coal Society | Year: 2014

In order to achieve a high-efficient exploitation of CBM in the southern Qinshui Basin, the velocity sensitivity, water sensitivity, alkaline sensitivity and stress sensitivity of the main coalbed 3 were investigated and analysed. The results show that: the degree of velocity sensitivity damage at the coalbed 3 varies from medium to weak. In the actual CBM development process, the velocity sensitivity damage is due to the transportation of coal powder produced by the coalbed washout of the fracturing fluid containing sand. The degree of water sensitivity damage at the coalbed 3 varies from medium to weak. Adding a small amount of KCl to the working fluid can reduce the water sensitivity effect. The coalbed 3 is a weak alkaline sensitive reservoir, however, the high pH fluids will dissolve quartz sand and reduce the support effect. The coalbed 3 is a strong stress sensitivity reservoir. According to the comparison of permeability change in the step-up and step-down phases, the irreversible damage rate is 55.88%. In the coalbed methane development process, in theory, strengthening reservoir protection can increase the coalbed methane production. Source


He J.-H.,Wuhan University | Chen L.-C.,Wuhan University | Hu Q.,Wuhan University | Wang S.-W.,Wuhan University | And 4 more authors.
Meitan Xuebao/Journal of the China Coal Society | Year: 2014

In order to accurately analyze the impact of natural fracture surface characteristics on the effect of hydraulic fracturing in coal reservoir, based on the observations of eight coalbed methane wells and the natural fracture surface characteristics in southern Qinshui Basin, the authors observed and contrasted the natural fracture surface features from two coalbed methane wells (F1 and F2). The natural fracture surface features of F1 shows a tortuous and rough feature and with many secondary cracks, while F2 demostrates the opposite feature. The authors found that the coal reservoir fracturing fracture morphology are more short and wide than the surface monitoring value and the theoretical model projections; the natural fracture surface is straight, smooth and the surface does not develop secondary cracks obtained more long and narrow fracture. The results show that the unique natural fracture surface characteristic of coal reservoir is one of the main factors that cause the actual fracture more short and wide. The different natural fracture surface characteristics influence the fracturing process by affecting the fluid pressure gradient that in turn affects the final fracturing result. Source


Li R.,Wuhan University | Wu X.-M.,Wuhan University | Li J.,Wuhan University | Wang S.-W.,Wuhan University | And 4 more authors.
Meitan Xuebao/Journal of the China Coal Society | Year: 2014

In order to find out the variation characteristics and flow laws of two-phase fluid in coalbed methane (CBM) wells, the fluid parameters detector was developed, which had the functions to not only monitor the fluid pressure, temperature, fluid level, velocity, density distribution and bubbles forms of two-phase fluid, but also provide actual data to forecast the variations characteristics or show flow laws of two-phase fluid in coalbed methane wells. Based on the working principles and structures of the detector parts, the detection methods of the key two-phase fluid parameters including density distribution, bubbles forms and flow were established. Therefore, the detector can be applied in CBM and shale gas drainage, as well as in intelligent gas drainage. Source


Meng Z.-P.,China Three Gorges University | Meng Z.-P.,China University of Mining and Technology | Hao H.-J.,State Energy Key Laboratory of Joint Exploitation of Coal and Coal bed Methane | Zhang D.-K.,State Energy Key Laboratory of Joint Exploitation of Coal and Coal bed Methane | And 2 more authors.
Meitan Xuebao/Journal of the China Coal Society | Year: 2014

At Chengzhuang mine field in Jincheng mining area, the fracture pressure of coal floor rock, in situ stress, the hydraulic pressure of aquifer in the coal floor and the aquifuge thickness were analyzed after coal-bed methane (CBM) development. The theory and method for evaluating water inrush risk in coal floor after CBM development were developed. The influence mechanism of CBM vertical wells development on coal floor water inrush during coal mining was obtained. The results show that the completion depth of CBM wells, the underground pressure in coal mining and the water pressure make the aquifuge in the coal floor break through rupture. If the minimum horizontal stress in aquifuge is greater than the hydrostatic pressure of confined water, the water inrush would not occur, otherwise, the water inrush would occur. If the completion depth of CBM wells and the underground pressure in mining and the water pressure of confined water do not make coal floor aquifuge break through rupture, the ratio of water pressure of the aquifer in the coal floor to effective aquifuge thickness between coal seam and the aquifer determines the water inrush risk of the coal floor. According to key parameters of the fracture pressure of coal floor rock, water pressure and the ratio of water pressure to aquifuge thickness, the water inrush risk in the coal floor is divided into four types: safety (I), medium safety (II), poor safety or danger (III) and extremely dangerous (IV). The distance between No. 15 coal seam of Taiyuan formation and the Ordovician limestone aquifer is small, and the variation is large. The coal mining after CBM vertical wells development is threatened by the confined water in Ordovician limestone. Water inrush from No. 3 coal floor does not occur in coal mining after CBM development. If the completion depth of CBM wells for No. 9 coal seam and the coal floor damage depth caused by the coal mining are same according to the calculation under coal floor 15 m, the water inrush risk of coal floor is mainly the type of medium safety, however, there is a water inrush risk in the deep area. Source

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