Reservoir Evaluation and Development ›› 2023, Vol. 13 ›› Issue (1): 64-73.doi: 10.13809/j.cnki.cn32-1825/te.2023.01.007

• Methodology and Theory • Previous Articles     Next Articles

Physicochemical mechanism of water phase imbibition in shale reservoirs

LI Ying(),LI Maomao(),LI Haitao,YU Hao,ZHANG Qihui,LUO Hongwen   

  1. Southwestern Petroleum University, Chengdu, Sichuan 610500, China
  • Received:2021-10-22 Online:2023-02-26 Published:2023-01-30
  • Contact: LI Maomao E-mail:yingingli@163.com;limaomao819@163.com

Abstract:

Shale gas reservoirs, which develope micro-nano pore throats and fractures, have high clay mineral content, and strong heterogeneity of porosity. Therefore, large-scale hydraulic fracturing is usually needed to realize the effective exploitation. In the process of hydraulic fracturing, the spontaneous imbibition of the water phase will trigger a series of physical and chemical effects on the shale gas reservoir, changing the pore structures, physical and chemical properties of shale gas reservoirs, thereby affecting the production of shale gas. In order to further clarify the influence mechanism of water phase imbibition in shale gas reservoirs, multiple repetitive imbibition experiments were carried out. Based on the changes in rock sample quality caused by mineral dissolution, the visual characteristics of samples from scanning electron microscope, the observation of nuclear magnetic resonance pore structures, and the change of physical properties, the impact of imbibition on the microscopic pore structure, permeability and porosity of shale are revealed. The results show that: ① Water imbibition causes fractures in shale, thus changing the pore structure; ② The proportion of macropores increases in shale samples with significantly improved porosity, which indicates that water imbibition will increase the pore space in shale; ③ The imbibition capacity is positively correlated with the porosity and permeability of shale, and the physical properties of shale are significantly improved after imbibition. In addition, the time index is found to be able to quantitatively characterize the influence of imbibition on the pore-throat connectivity of shale.

Key words: shale gas reservoir, fracture, water phase imbibition, physical and chemical effect, microscope structure of pore

CLC Number: 

  • TE341