The Variation Law of Shape Factor for Fractured Carbonate Reservoirs

Shape factor of fractured porous media is crucial to characterize fluid flow in fractured carbonate reservoirs. However, due to the complex structures of matrix and fracture systems in fractured porous media, how to efficiency predict shape factor of fractured porous media is an open question. In this paper, a transient flow model with matrix deformation coefficient, considering stress sensitivity characteristics of the reservoir, has been established to express shape factors for fractured oil reservoirs. The shape factor computation expression has been derived. And the influence of different sensitivity parameters on the shape factor has been Analyzed. The research results show that shape factor is not a constant but is time varying. Shape factor is influenced by the sensitivity factors such as fracture interval, matrix deformation coefficient, matrix compressibility factor and matrix average pressure. In the early production, the shape factor decreases rapidly with the increase of time. And shape factor tends to be stable after the production time reaching a certain value. Shape factor reflects the geometric of the matrix block and fluid exchange capacity between matrix system and fracture system. The geometric of the matrix block varies with fracture interval. The cross-flow between matrix system and fracture system will be affected by the factors such as matrix deformation coefficient, matrix compressibility factor and matrix average pressure. The derived model in this paper can provide an insight into the shape factor for fractured carbonate reservoirs.