Study on shale imbibition characteristics experiment from Longmaxi Formation of Southeastern Chongqing in Sichuan Basin

Shale belongs to low-porosity and low-permeability reservoir, so it is difficult for fluid to enter pores through displacement. However, in the process of shale hydraulic fracturing, most of the fracturing fluid does not flowback after entering strata. It indicates that reaction may take place when fluid enters into strata, resulting in low flowback rate of fracturing fluid. Imbibition experiment and physicochemical properties test show that there is imbibition effect in shale. There are two stages: one is the initial rapid water absorption, while the other is later osmotic water absorption. The first stage is affected by the seam network system, while the other stage is mainly affected by the content of clay minerals. As clay minerals swell by absorbing water, the original fracture network system gradually expands, and porosity grows, permeability improves and recovery rate increases. The physicochemical properties test shows that (1) imbibition is influenced by both capillary force and mineral components. The higher the clay content is, especially the content of chlorite and illite/smectite (I/S) , the stronger the imbibition capacity is. (2) Shale with strong imbibition capacity also has strong seam-making capacity, which not only provides convenience for hydraulic fracturing but is more conducive to exploitation.