In recent years, interest has grown in developing and producing shale gas reservoirs. These reservoirs are increasingly becoming more important as gas sources in many countries. All shale gas reservoirs must be hydraulic fractured to be able to produce gas. Because these wells are characterized by long periods of transient flow it is common to supplement rate and recovery predictions done by decline curve analysis with numerical simulation. Furthermore, nano-Darcy permeability requires that hydraulic fractures be explicitly represented by small, highly permeable grid blocks to accurately capture flow characteristics. For the most part, shale gas wells are modeled using proven algorithms in conventional simulators.

The well index formulation normally used by reservoir simulators for vertical wells was developed by Peaceman. The Peaceman approach has been shown to suffer from some artifacts when simulating transient linear flow behavior because the method is based on an assumption of radial geometry. Because the Peaceman equation uses fracture permeability to calculate the wellblock radius (ro), in some cases the value of ro will be less than the actual wellbore radius. This error can generally be overcome by assigning an arbitrarily large well index for the fractured well. Perhaps more importantly the Peaceman formulation does not allow the fracture face skin to be assigned directly.

This paper presents a new well equation for accurately computing well index and modeling fracture face skin based on the fracture half-length and matrix permeability. The simulation result shows good match with the analytical solution for different values of fracture face skin. The new equation will be useful in modeling well test design by reservoir simulation with and without the effect of fracture damage.

You can access this article if you purchase or spend a download.