Geological controls over coal-bed methane well production in southern Qinshui basin

The reserves of Coalbed Methane (CBM) in Qinshui Basin are quite promising, but the outputs from CBM wells are quite small even after massive hydraulic fracturing. Herein the fracture system with #3 and #15 coal seams in Qinshui basin was analyzed, and it was found that both of the macro-scale fractures and micro-scale fractures are filled with clay and carbonate minerals, which explains the low productivity of CBM wells after conventional hydraulic fracturing. Acid fracturing has long been an effective method for carbonate gas reservoir to improve the gas well production. However, there were few reports about the application of acid fracturing in coal bed methane field. Based on the mineral identification and acid sensitivity test, the feasibility of acid fracturing demonstrated that the acid does more help than damage to increase the permeability of coal seams in Qinshui basin. Onsite operations have shown that acid fracturing is applicable for the CBM wells in Jincheng Mining Area. It was also observed from the microseismic survey that when applying the acid fracturing treatment, the stimulated reservoir area depends on the acid volume pumped in the first stage, which is crucial to the success of the stimulation. Evaluación piloto de fractura ácida en depósitos de gas metano de carbón en el suroeste de la cuenca Qinshui, China ResumenLas reservas de gas metano de carbón (CBM, del inglés Coalbed Methane) en la cuenca Qinshui son más que prometedoras, pero la producción en los pozos es muy pequeña, incluso después de fracturas hidráulicas masivas. En este trabajo se analizaron los sistemas de fractura de las vetas de carbón #3 y #15 de la cuenca Qinshui y se encontró que tanto las fracturas a macroescala como aquellas a microescala están cubiertas con arcillas y minerales carbonatos, lo que explica la baja productividad de los pozos de gas metano de carbón después de la fractura hidráulica convencional. La fractura ácida ha sido un método efectivo en los depósitos de gas carbonato para mejorar la producción en el pozo de gas. Sin embargo, existen pocos informes sobre la aplicación de la fractura ácida en el campo del gas metano de carbón. De acuerdo con la identificación mineral y las pruebas de sensibilidad ácida, la factibilidad de la fractura ácida demostró que el ácido es reparador en el incremento de la permeabilidad en las vetas de carbón de la cuenca Qinshui. Las operaciones in situ han demostrado que la fractura ácida es aplicable para los pozos de gas metano de carbón en el área minera de Jincheng. También se observó en el sondeo microsísmico que cuando se aplica un tratamiento de fractura ácida, el área del depósito estimulada depende del volumen de ácido bombeado en primera instancia, lo que es determinante en el éxito de la estimulación.

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Reservoir Simulation to Diagnose the Causes of Reduced Well Production Efficiency in Coal Bed Methane

Journal of Earth Science & Climatic Change ◽

10.4172/2157-7617.1000248 ◽

2015 ◽

Vol 06 (01) ◽

Author(s):

Ismail Iqbal Md Gupta DK

Keyword(s):

Reservoir Simulation ◽

Production Efficiency ◽

Coal Bed ◽

Coal Bed Methane ◽

Well Production

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Numerical analysis of drainage rate for multilayer drainage coalbed methane well group in Southern Qinshui basin

Energy Exploration & Exploitation ◽

10.1177/0144598720946494 ◽

2020 ◽

Vol 38 (5) ◽

pp. 1535-1558

Author(s):

Qiujia Hu ◽

Shiqi Liu ◽

Shuxun Sang ◽

Huihuang Fang ◽

Ashutosh Tripathy ◽

...

Keyword(s):

Pressure Drop ◽

Coal Seam ◽

Coalbed Methane ◽

Gas Production ◽

Hydraulic Pressure ◽

Qinshui Basin ◽

Well Production ◽

Drainage Rate ◽

Southern Qinshui Basin ◽

Cbm Production

Multilayer drainage is one of the important technologies for coalbed methane (CBM) production in China. In this study, a multi-field fully coupled mathematical model for CBM production was established to analyze the multilayer drainage of CBM well group in southern Qinshui basin. Based on the numerical simulation results, the characteristics of CBM well production under different drainage rates and key factors influencing the CBM production were further discussed. The results show that the effect of an increased drainage rate on gas production of CBM wells and CBM recovery of No.3 coal seam is not significant. However, it significantly improved the gas production of CBM wells and CBM recovery of No.15 coal seam. After a long period of production, the CBM content in No.3 coal seam has reduced to a low level and the pressure drop potential of No.3 coal seam is insignificant, which are important reasons for the insignificant increase of CBM production even under a drainage rate of 2 to 7 times. Conversely, No.15 coal seam has larger residual CBM content and increasing the drainage rate can significantly improve the pressure drop and superimposed well interference of No.15 coal seam, which means No.15 coal seam has greater production potential than No.3 coal seam. Therefore, it is recommended to improve the gas production and CBM recovery in No.15 coal seam by increasing the drainage rate, and the average hydraulic pressure drop should be 0.018–0.031 MPa/day. The influence of effective stress is weak in No.3 and No.15 coal seam, and the coal seam permeability is largely influenced by the shrinkage of coal matrix caused by CBM desorption. This indicates the feasibility of increase in gas production from CBM wells by increasing the drainage rate.

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Permeability Prediction in Deep Coal Seam: A Case Study on the No. 3 Coal Seam of the Southern Qinshui Basin in China

The Scientific World JOURNAL ◽

10.1155/2013/161457 ◽

2013 ◽

Vol 2013 ◽

pp. 1-10 ◽

Cited By ~ 9

Author(s):

Pinkun Guo ◽

Yuanping Cheng

Keyword(s):

Coal Seam ◽

Effective Stress ◽

Axial Stress ◽

Gas Pressure ◽

Coal Bed ◽

Stress And Strain ◽

Qinshui Basin ◽

Coal Permeability ◽

Permeability Prediction ◽

Southern Qinshui Basin

The coal permeability is an important parameter in mine methane control and coal bed methane (CBM) exploitation, which determines the practicability of methane extraction. Permeability prediction in deep coal seam plays a significant role in evaluating the practicability of CBM exploitation. The coal permeability depends on the coal fractures controlled by strata stress, gas pressure, and strata temperature which change with depth. The effect of the strata stress, gas pressure, and strata temperature on the coal (the coal matrix and fracture) under triaxial stress and strain conditions was studied. Then we got the change of coal porosity with strata stress, gas pressure, and strata temperature and established a coal permeability model under tri-axial stress and strain conditions. The permeability of the No. 3 coal seam of the Southern Qinshui Basin in China was predicted, which is consistent with that tested in the field. The effect of the sorption swelling on porosity (permeability) firstly increases rapidly and then slowly with the increase of depth. However, the effect of thermal expansion and effective stress compression on porosity (permeability) increases linearly with the increase of depth. The most effective way to improve the permeability in exploiting CBM or extracting methane is to reduce the effective stress.

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