Multi-layer superposed coalbed methane system in southern Qinshui Basin, Shanxi Province, China

Abstract

Multi-coalbed developed in Carboniferous-Permian coal-bearing strata of southern Qinshui Basin, and different coal-bearing segments have different coalbed methane (CBM) reservoiring characteristics. Analysis of previous studies suggests that the essence of an unattached CBM system is to possess a unified fluid pressure system, which includes four key elements, namely, gas-bearing coal-rock mass, formation fluid, independent hydrodynamic system and capping layer condition. Based on the exploration and exploitation data of CBM, it is discovered that the gas content of coal seams in southern Qinshui Basin presents a change rule of non-monotonic function with the seam dipping, and a turning point of the change appears nearby coal seam No. 9, and coal seams of the upper and the lower belong to different CBM systems respectively; well test reservoir pressure shows that the gradient of coal seam No. 15 of the Taiyuan Formation is significantly higher than that of coal seam No. 3 of the Shanxi Formation; the equivalent reservoir pressure gradient of coal seam No. 15 “jumps” obviously compared with the reservoir pressure gradient of coal seam No. 3 in the same vertical well, that is, the relation between reservoir pressure and burial depth takes on a characteristic of nonlinearity; meanwhile, the vertical hydraulic connection among the aquifers of Shanxi Formation and Taiyuan Formation is weak, constituting several relatively independent fluid pressure systems. The characteristics discussed above reveal that the main coal seams of southern Qinshui Basin respectively belong to relatively independent CBM systems, the formation of which are jointly controlled by sedimentary, hydrogeological and structural conditions.

Keywords

multi-coalbed / coalbed methane system / fluid pressure system / equivalent reservoir pressure gradient / formation mechanism

References

[1] Ayers W B. Coalbed Systems, Resources, and Production and a Review of Contrasting Cases from the San Juan and Power River Basins. AAPG Bulletin, 2002, 86(11): 1853-1890.

[2] Che C B. A New Round Evaluation of Nationwide Coalbed Methane Resources. The National Oil and Gas Resources Evaluation Report, 2006 Beijing: Ministry of Land and Resources

[3] Cui K H, Zheng H T. Coalbed Methane Mining, 2009 Beijing: Petroleum Industry Press, 47-48.

[4] Lan F J, Qin Y, Li M, . Abnormal Concentration and Origin of Heavy Hydrocarbon in Upper Permian Coal Seams from Enhong Syncline, Yunnan, China. Journal of Earth Science, 2012, 23(6): 842-853.

[5] Li G B, Li G F. Study on the Differences and Main Controlling Factors of the Coalbed Methane Wells between Single Layer and Multi-Layer Drainage. Journal of China Coal Society, 2012, 37(8): 1354-1358.

[6] Li G H, Zhang H, Zhang P H, . The Renewed Understanding for the Distribution of Coalbed Methane and the Controlling Factor in Jincheng. Journal of China Coal Society, 2010, 35(10): 1680-1684.

[7] Li M, Jiang B, Lin S F, . Structural Controls on Coalbed Methane Reservoirs in Faer Coal Mine, Southwest China. Journal of Earth Science, 2013, 24(3): 437-448.

[8] Li X P. Seepage Mechanics of Underground Oil and Gas, 2007 Beijing: Petroleum Industry Press, 14-19.

[9] Liu H J, Qin Y, Sang S X. Coalbed Methane Geology of Southern Shanxi, China, 1998 Xuzhou: China University of Mining and Technology Press, 74-105.

[10] Lü Y M, Tang D Z, Xu H, . Production Characteristics and the Key Factors in High-Rank Coalbed Methane Fields: A Case Study on the Fanzhuang Block, Southern Qinshui Basin, China. International Journal of Coal Geology, 2012, 96(97): 93-108.

[11] Magoon L B, Dow W G. The Petroleum System. the Petroleum System—From Source to Trap. AAPG Memori, 1994, 60: 3-24.

[12] Meng Z P, Tian Y D, Li G F. Characteristics of In-Situ Stress Field in Southern Qinshui Basin and Its Research Significance. Journal of China Coal Society, 2010, 35(6): 976-981.

[13] Mu F Y, Sun F J, Wang Y B, . Characteristics of Pre-Production Performance and Technical Countermeasures in the Coalbed Methane Gas Field of Qinshui Basin. Natural Gas Industry, 2009, 29(9): 117-119.

[14] Ni X M, Su X B, Li G S. Feasibility of Multi-Layer Drainage for No. 3 and No. 15 Coal Seams in the Fanzhuang Area. Natural Gas Geoscience, 2010, 21(1): 144-149.

[15] Ni X M, Su X B, Zhang X D. Development Geology of Coalbed Methane, 2010 Beijing: Chemical Industry Press

[16] Qin Y. Advances and Reviews on Coalbed Methane Reservoir Formation in China. Geological Journal of China Universities, 2012, 18(3): 405-418.

[17] Qin Y, Fu X H, Wei C T, . Dynamic Conditions of Coalbed Methane Reservoir Formation and Its Controlling Reservoir Effect, 2012 Xuzhou: Science Press, 50-157.

[18] Qin Y, Fu X H, Wu C F, . Reservoir Dynamic Evaluation Techniques of Combined Exploitation of Coalbed Methane on Multiple-Layer Condition. Interim Progress Report of Grand Science and Technology Special Project of China, 2013 Xuzhou: China University of Mining and Technology

[19] Qin Y, Song Q Y, Fu X H. Discussion on Reliability for Co-Mining the Coalbed Gas and Normal Petroleum and Natural Gas: Absorptive Effect of Deep Coal Reservoir under Condition of Balanced Water. Natural Gas Geoscience, 2005, 16(4): 492-498.

[20] Qin Y, Xiong M H, Yi T S, . On Unattached Multiple Superposed Coalbed-Methane System: In a Case of the Shuigonghe Syncline, Zhijin-Nayong Coalfield, Guizhou. Geological Review, 2008, 54(1): 65-69.

[21] Qin Y, Zhang D M, Fu X H, . A Discussion on Correlation of Modern Tectonic Stress Field to Physical Properties of Coal Reservoirs in Central and Southern Qinshui Basin. Geological Review, 1999, 45(6): 576-583.

[22] Seidle J. Fundamentals of Coalbed Methane Reservoir Engineering, 2011 Tulsa: Pennwell Corp Press

[23] Shao L Y, Xiao Z H, Wang H, . Permo-Carboniferous Coalmeasures in the Qinshui Basin: High-Resolution Sequence Stratigraphy and Coal Accumulating Models. Chinese Journal of Geology, 2008, 43(4): 777-791.

[24] Wu C F, Qin Y, Wei C T, . Effectual Stress System of Coalbed Methane in Southern Qinshui Basin. Acta Geologica Sinica, 2008, 82(10): 1372-1375.

[25] Yang Z B. Coalbed Methane Reservoiring Process under Condition of Multi-Coalbeds Overlay: [Dissertation], 2011 Xuzhou: China University of Mining and Technology

[26] Ye J P. Study on Hydrologic Control Mechanism and Evaluation to Coalbed Methane Productivity: [Dissertation], 2002 Beijing: China University of Mining and Technology

[27] Ye J P, Peng X M, Zhang X P, . Exploration Orientation and Development Proposal of Coalbed Methane in Qinshui Basin of Shanxi Province. China Coalbed Methane, 2009, 6(3): 7-11.

[28] Ye J P, Qin Y, Lin D Y, . China Coalbed Methane Resource, 1999 Xuzhou: China University of Mining and Technology Press, 126-189.

[29] Zhang P H, Liu Y H, Wang Z X, . Geological Factors of Production Control of CBM Well in South Qinshui Basin. Natural Gas Geoscience, 2011, 22(5): 909-914.

[30] Zhang X M, Tong D K. The Effects of Pay Formation Combination on Productivity of Coalbed Methane Well in Qinshui Basin. Journal of China Coal Society, 2007, 32(3): 272-275.

[31] Zhao L J, Qin Y, Lin Y C. Abnormal Relation and Its Geological Controls of Coalbed Methane Content to Buried Depth of Coal Seams. Journal of China Coal Society, 2010, 35(7): 1165-1169.

[32] Zhu Z M, Shen B, Yan J F, . Coalbed Methane System: An Unconventional Petroleum System. Coal Geology & Exploration, 2006, 34(4): 30-32.

[33] Zhu Z M, Yang C, Shen B, . The Definition and Characteristics of Coalbed Methane and Coalbed Methane System. Xinjiang Petroleum Geology, 2006, 27(6): 763-765.