New Insights into spontaneous imbibition processes in unfractured and fractured carbonate cores with stress-induced apertures

Spontaneous imbibition (SI) experiments in fractured and unfractured Indiana limestone cores were performed to evaluate the impact of fractures in oil recovery. Numerical simulations were performed to reproduce the experimental setting and to history match fracture and matrix properties. Tracer tests were carried out to investigate the effect of changing stresses in hydraulic fracture conductivity. The pore space and connected pores in the fractured plug were analyzed via microscopic computed tomography (micro-CT) scan, and a thin petrography analysis was carried out to observe the matrix heterogeneity of the samples. Relative permeability, capillary pressure, and fracture properties were estimated numerically to match the SI curves measured at a temperature of 58.7°C. The investigation shows that the fractured core has suffered deformation under higher stress conditions, impacting the fracture aperture and the initial values of total permeability measured in the laboratory at a constant net stress. This deformation has led to decreased flow rates in the fracture and oil trapping in the fracture channel. At the field scale, this phenomenon could lead to decreased oil recovery rates in the initial stages of production.