Oil & Gas Geology ›› 2019, Vol. 40 ›› Issue (6): 1215-1225.doi: 10.11743/ogg20190606

• Petroleum Geology • Previous Articles     Next Articles

Characterization,classification and contribution of marine shale gas reservoirs

Xiao Dianshi1, Zhao Renwen1, Yang Xiao2, Fang Dazhi3, Li Bo1, Kong Xingxing1   

  1. 1. School of Geosciences, China University of Petroleum(East China), Qingdao, Shandong 266580, China;
    2. Research Institute of Shaanxi Yangchang Petroleum(Group) Co., Ltd., Xi'an, Shaanxi 710075, China;
    3. Nanchuan Shale Gas Project Department, East China Oil and Gas Company, SINOPEC, Chongqing 408400, China
  • Received:2018-12-20 Revised:2019-08-01 Online:2019-12-28 Published:2019-10-15

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Abstract: The Wufeng-Longmaxi Formations shale gas in Pengshui area,southeastern Chongqing,was studied through several pore characterization experiments including low-temperature carbon adsorption (LTCA),low-temperature nitrogen adsorption (LTNA),nuclear magnetic resonance (NMR),high pressure mercury intrusion porosimetry (MIP),scanning electron microscopy (SEM),and Helium porosity measurement.The shale pore structure was comprehensively described,and the characterization and classification methods of full range of pore size were established to study their individual contributions to shale gas occurrence and migration.The results show that the pore volume by Helium porosity measurement is the largest,followed by LTNA and NMR.The latter two have obvious advantages in characterizing smaller (<10 nm) and larger pores,and thus the combination of LTNA and NMR can be applied to the characterization of full range pore size distribution of shale.The distribution reveals a wide range of shale gas pore distribution,but 70% of the pore volume is concentrated in pores less than 25 nm in diameter.Combined with fractal features,the pores can be divided into micropores,small pores,mesopores and large pores in diameter with a lower boundary of 5 nm,25 nm and 100 nm.The pore throat size is mainly a result of organic matter and clay contents.The larger pores are composed of intergranular pores and inter-clay-layer fractures.The mesopores are also affected by intragranular dissolved pores.The micropores and small pores are the main sites where the shale adsorbed gas and free gas occur.The small pores and mesopores are inter-connected,providing channels for the shale gas to migrate in the matrix.The research results are significant as it may guide the classification of shale gas reservoirs and the understanding of infiltration mechanism.

Key words: nuclear magnetic resonance (NMR), high pressure mercury intrusion porosimetry (MIP), pore characterization, pore classification, shale gas, Wufeng Formation, Longmaxi Formation, Sichuan Basin

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