Hydraulic fracturing improves well productivity by creating a highly conductive pathway that allows fluids to flow more easily from the reservoir to the wellbore. After a fracture is created, fluid first flows from the reservoir into the fracture and then along the fracture toward the well. For the fracture to significantly improve production, it must offer very little resistance to flow.
The ability of the fracture to transmit fluids is quantified using the dimensionless fracture conductivity, defined as:
Where:
- \(\boldsymbol{F_{CD}}\): dimensionless fracture conductivity
- \(\boldsymbol{k}\): reservoir permeability
- \(\boldsymbol{k_f}\): fracture permeability
- \(\boldsymbol{w_f}\): fracture width
- \(\boldsymbol{x_f}\): fracture half-length
The term kfwf represents the conductivity of the fracture, while kxf represents the reservoir's ability to supply fluid to the fracture. Therefore, FCD compares the flow capacity of the fracture to that of the reservoir.
If FCD is small, the fracture itself restricts flow, and the production improvement will be limited. If FCD is large, the fracture provides an efficient pathway for fluid flow and behaves as a high-conductivity fracture.
In practice, a typical design range is 1 < FCD < 10, which provides significant productivity improvement while maintaining realistic fracture properties.
The improvement in well performance therefore depends mainly on fracture half-length (xf), which determines how far the fracture extends into the reservoir, and fracture conductivity (kfwf), which determines how easily fluid flows within the fracture.
