Petroleum Reservoir Evaluation and Development ›› 2023, Vol. 13 ›› Issue (5): 627-635.doi: 10.13809/j.cnki.cn32-1825/te.2023.05.010

• Shale Gas • Previous Articles     Next Articles

Pore scale fracturing fluid occurrence mechanisms in multi-scale matrix-fracture system of shale gas reservoir

XIA Haibang1(),HAN Kening1,SONG Wenhui2(),WANG Wei1,YAO Jun3   

  1. 1. Sinopec East China Oil & Gas Company, Nanjing, Jiangsu 210019, China
    2. School of Petroleum Engineering, China University of Petroleum(Beijing), Beijing 102249, China
    3. School of Petroleum Engineering, China University of Petroleum(East China), Qingdao, Shandong 266580, China
  • Received:2022-11-08 Online:2023-10-26 Published:2023-11-01

Abstract:

After hydraulic fracturing in shale gas reservoir, a significant volume of fracturing fluid retains in the matrix pores and induced fracture network. Currently, the pore scale fracturing fluid occurrence mechanisms are unclear. As a result, it is difficult to accurately understand the difference of fracturing fluid backflow rate of shale gas wells in the backflow process. In this work, the pore scale fracturing fluid occurrence mechanisms analysis method in shale multi-scale matrix-fracture system is developed and the fracturing fluid occurrence mechanisms in shale gas reservoir are elucidated in detail. To understand fracturing fluid occurrence pattern in shale matrix, singe pore gas-water occurrence method is established considering rock-fluid interaction and gas-water capillary pressure and is further extended into the pore network. Invasion percolation is applied to analyze the fracturing fluid occurrence pattern variation during different flowback stages. To understand fracturing fluid occurrence pattern in induced fracture network, the level-set gas-water interface tracking method is applied to calculate gas-water distribution at different flowback pressure based on induced fracture network CT imaging and the fracturing fluid occurrence pattern variation at different flowback stage is studied. Study results reveal that the fracturing fluid flowback rate in shale matrix first increases slowly and then increases fast. In the final stage, the fracturing fluid flowback rate in shale matrix reaches plateau. The fracturing fluid in shale matrix distributes in the forms of water saturated pores, corner water and water film. The fracturing fluid flowback rate in induced fracture network is influenced by pore connectivity around the induced fracture network. The fracturing fluid flowback rate first increases fast and then reaches plateau. The retained fracturing fluid distributes in the dead-end matrix pores around induced fracture network at the final stage.

Key words: shale gas reservoir, digital core, pore network model, fracturing fluid, flowback rate

CLC Number: 

  • TE357