A semi-analytical model for simulation of fluid flow in tight rock with irregular fracture geometry

Numerous micro-seismic and laboratorial studies show that hydraulic fracture is usually with complex geometries, such as plugged fracture, asymmetry and non-plane. It is a challenging task to recognize the complex fracture and obtain reliable fracture parameters through transient pressure analysis. In this work, we extend the semi-analytical model by Zhou et al. (2013) to analyze transient pressure behavior of a fractured vertical well with complex fracture geometries. We verified the semi-analytical model by a numerical reservoir simulator on a planar fracture. Then, based on this model, we made a systematical discussion about the transient pressure behavior of the planar fracture with varying conductivity, asymmetric fracture and non-planar fracture. Results show that when the fracture conductivity is varying along the fracture path, the influence of fracture zone conductivity on the transient pressure behavior gradually decreases with the distance from the wellbore growing. Besides, we found that the fracture asymmetry is against for the fluid flow in the fracture, and it decreases the slope of transient pressure behavior curve and enlarge pressure drop. In addition, the non-planar fracture is usually with severe fracture width restriction around the wellbore, which will induce pseudo-radial flow in the fracture at early times and large pressure drop in the fracture. Furthermore, the influences of varying conductivity, fracture asymmetry and non-plane on transient pressure behavior are obvious for fracture with average small-to-middle conductivity (average dimensionless fracture conductivity ranging from 0.1 to 50); the influences become negotiable for fracture with average high-to-infinite conductivity (average dimensionless fracture conductivity ranging from 50 to 1000). This work can provide critical insights into understanding the effect of complex fracture geometry on transient pressure behavior of fractured vertical well in tight oil reservoir.