Lithologic Reservoirs ›› 2024, Vol. 36 ›› Issue (5): 15-24.doi: 10.12108/yxyqc.20240502

• NEW ENERGY AND ASSOCIATED RESOURCES • Previous Articles     Next Articles

Pore structure characteristics and dehydration evolution of lignite reservoirs of Jurassic Xishanyao Formation in Santanghu Basin

KONG Lingfeng1,2, XU Jiafang1, LIU Ding3   

  1. 1. School of Petroleum Engineering, China University of Petroleum(East China), Qingdao 266580, Shandong, China;
    2. Development Planning Department, China National Petroleum Corporation, Beijing 100007, China;
    3. School of Energy Resources, China University of Geosciences(Beijing), Beijing 100083, China
  • Received:2024-01-23 Revised:2024-03-13 Online:2024-09-01 Published:2024-09-04

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Abstract: It is helpful to accurately predict the operation effect of underground coal gasifier to find out the difference and evolution law of pore structure of coal before and after drying. By selecting water and kerosene as saturated fluids to carry out low-field NMR experiment，the pore structure of the same sample under saturated and dry conditions was tested and compared. The dehydration evolution process of pore structure of coal samples was observed through X-CT technology and an evolution model was established，and pulse attenuation permeability test and low-temperature liquid nitrogen adsorption experiments were conducted to evaluate the mass transfer ability of coal samples. The results show that：（1）During the drying of lignite，pore shrinkage occurs while cracks are produced，and the total pore volume decreases from 0.630 cm3/g to 0.481 cm3/g，while the large pore volume significantly increases from 0.070 cm3/g to 0.420 cm3/g. Dehydration leads to pore concentration，with the large pore volume accounting for 88%.（2）The pore shrinkage during the drying of lignite is controlled by the degree of matrix shrinkage. The dehydration of different coal rock components can be summarized into two types of pore structure evolution models：the dehydration of matrix coal that is prone to shrink develops a large number of cracks at the edges or inside of the components，while the dehydration shrinkage of xylite-rich and charcoal-rich coal is weak，retaining a large number of primary pores and developing fewer cracks.（3）After the drying of the lignite，water is removed and the number of empty pores increases. The seepage state changes from single-phase water to gas-water two-phase and single-phase airflow，forming a good interconnected pore network. The seepage ability of the coal is significantly improved，and the permeability increases from 0.248 to 48.080 mD. The contribution of diffusive mass transfer is increased，with diffusion coefficient of medium and large pores in dry lignite being about 0.09 cm2/s at a temperature of 200 ℃ and a pressure of 0.5 MPa.

Key words: lignite reservoir, pore structure, dehydration evolution law, relaxation spectrum, X-ray CT, seepage ability, underground coal gasification, Xishanyao Formation, Jurassic, Santanghu Basin

CLC Number: 

  • TE122
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