地质科技通报 (May 2021)

Water mobility of the main coal seam and its control of porosity and permeability in Jixi Basin

  • Wenyu Zhou,
  • Xiaoming Wang,
  • Fangui Zeng,
  • Zheng Dang,
  • Chong Zhu,
  • Wenwen Chen,
  • Zhizhuang Wang,
  • Mingkai Tu

DOI
https://doi.org/10.19509/j.cnki.dzkq.2021.0305
Journal volume & issue
Vol. 40, no. 3
pp. 124 – 131

Abstract

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Water mobility is an important factor affecting the production of coalbed methane. It is of great significance to analyze the effect of porosity and permeability on water mobility for the development of coalbed methane in Jixi Basin. In order to analyze the influence of porosity and permeability of coal reservoir on the water mobility, we performed low field NMR, permeability and water saturation experiments on the main coal seams of different mining areas in Jixi Basin.The results show that: ①Adsorption pores are relatively developed and the average proportion is 58.36%, while the seepage pores and fractures are similarly developed, with the average proportion of 21.23% and 20.41%, respectively.The seepage pores and fracture are well connected; ②The centrifugal force that makes the studied coal seam reach the bound water state is 1.38 MPa, under which the movable water can be discharged from half-open or open pores with a radius of more than 0.1 μm.By which the movable water saturation is 27.84%-60.87%, with an average of 37.86%; the irreducible water saturation is higher which is calculated as 39.13%-72.16%(av.62.14%).With the increase of pressure, the movable water flows first along the fracture, and then flows out through the seepage pores, while the irreducible water mainly existing in the adsorption pores is difficult to flow because of the large capillary resistance during centrifugation; ③There are obvious differences in water mobility and occurrence in coal samples with similar metamorphic degree, which may be one of the reasons for the difference of water and gas production in different block's CBM wells; ④The movable water in the study area is easy to flow out from coals with higher movable water saturation, greater permeability and more developed pore throat of more than 1 000 nm, but the water is difficult to flow out from coals with lower movable water saturation and more developed pore throat of 0-100 nm in which water is trapped.

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