A capillary bundle model for the forced imbibition in the shale matrix with dual‐wettability

Abstract

AbstractThe forced imbibition during hydraulic fracturing is one of the main mechanisms of oil production in shale oil reservoirs. However, the shale matrix has complex structures of nanopores and is rich in organic matters. The wettability of nanopores in organics matters is different from the nanopores in inorganic matters, and the characteristic of dual‐wettability leads to complex mechanisms of forced imbibition. This paper proposes a model for describing the imbibition in a dual‐wettability shale oil reservoir based on the capillary tube model. The external displacement pressure gradient is also considered to study the forced and spontaneous imbibition of hydraulic fracturing liquid into oil‐wet organic nanopores and water‐wet inorganic nanopores. The slip effect in organic nanopores and the boundary‐layer effect in inorganic nanopores are considered in this model. The analytical expressions for describing the location of the oil–water imbibition front in an oil‐wet organic nanopore and a water‐wet inorganic nanopore are derived, respectively. The semi‐analytical solution for predicting flow rate in a shale core with an external pressure gradient is given and demonstrated with a case study.