The tight reservoir and fracture are stress sensitivity medium, and the flow in tight reservoirs obeys the low-velocity non-Darcy flow. Currently, few studies of pressure analysis for volume fracturing well are conducted with simultaneously considering low-velocity non-Darcy flow and stress sensitivity.
In this paper, the dynamic threshold pressure gradient and permeability modulus are respectively utilized to characterize the low-velocity non-Darcy flow and permeability stress sensitivity. And then the model of volume fracturing well in tight reservoirs simultaneously considering low-velocity non-Darcy flow and stress sensitivity is built. After that the finite difference method is used to solve it and the proposed model is verified by comparing the result of this proposed model with that of the commercial software. Finally, the effect related parameters on the dimensionless pressure and pressure derivative are analyzed.
The six flow regimes are identified by the dimensionless pressure and pressure derivative curve. They are fracture linear flow regime, early transition flow regime, radial flow regime, cross flow regime, advanced transition flow regime and boundary controlling flow regime, respectively. The reservoir stress sensitivity and dynamic threshold pressure gradient have a great effect on the dimensionless pressure and pressure derivative curves. With the increase of reservoir stress sensitivity, the dimensionless pressure and pressure derivative move upward at the advanced transition flow and boundary controlling flow stages. The decrease of fluid viscosity results in an increase of the dynamic threshold pressure gradient. The increase of reservoir permeability corresponds to an increase of dynamic threshold pressure gradient and that results in the curves of dimensionless pressure and pressure derivative moving downward. The fracture stress sensitivity has a tiny effect on dimensionless pressure and pressure derivative and can be ignored when the flow rate is small.
This work reveals the effect of dynamic threshold pressure gradient and permeability stress sensitivity on pressure, and provides a more accurate reference for reservoir engineers in pressure analysis when developing tight reservoir by using volume fracturing well.