Using pressure changes in offset wells for interpreting fracture driven interactions (FDI)

Abstract

Infill completions have been used in the field to enhance ultimate recovery of unconventional low permeability reservoirs. The stimulation of the infill wells can cause pressure increase in nearby wells. Most available studies have focused on the propagation of fractures from infill wells and pressure changes in treatment wells rather than offset wells which their pressure data may reveal important signatures of fracture-driven interactions (FDI). In this study, we looked at different signatures of FDI data collected in the field and then used a numerical approach to model the pressure fluctuations in offset wells induced by fracturing infill wells and provide insight into how field operators can use the pressure data from nearby wells to identify different forms of FDI, including frac/frac connections and fracture shadowing. The trajectory of a fracture propagating from an infill well is modeled using the extended finite element methods (XFEM). This method allows us to model change of fracture propagation direction due to the rotation of stress field caused by the production of the offset wells. Then, we calculate the pressure response after the fracture intersection using a multi-phase flow model. We investigate the effect of several parameters on the pressure behavior such as the fracture intersection location, the vertical well offset and the fluid compressibility. Typically, a sudden increase in the offset well pressure over a short period is interpreted as a fracture intersection. However, our numerical examples reveal that a gradual increase in the offset well pressure may also indicate a frac/frac connection, especially if the offset well is initially pressurized by injection of fluid before stimulating the infill well. Therefore, only looking at the magnitude of the pressure increase may not be very definitive to make a judgement. Thus, we propose to use diagnostic pressure plots to differentiate fracture connection and fracture shadowing. The proposed analytical model for frac/frac connection pressure threshold and the pressure diagnostic plots can be combined to quickly assess fracture's connections.