Flow rate dependent skin in water disposal injection well: Case study

Re-Injection is one of the most important methods to dispose fluid associated with oil and natural gas production. Disposed fluids include produced water, hydraulic fracture flow back fluids, and drilling mud fluids. Several formation damage mechanisms are associated with the injection including damage due to filter cake formed at the formation face, bacteria activity, fluid incompatibility, free gas content, and clay activation. Fractured injection is typically preferred over matrix injection because a hydraulic fracture will enhance the well injectivity and extend the well life. In a given formation, the fracture dimensions change with different injection flow rates due to the change in injection pressures. Also, for a given flow rate, the skin factor varies with time due to the fracture propagation. In this study, well test and injection history data of a Class II disposal well in south Texas were used to develop an equation that correlates the skin factor to the injection flow rate and injection time. The results show that with time, the skin factor decreases until such a point at which the fracture dimensions are sufficient without further propagation to handle the injected water volume (stationary fracture). A constant skin factor is noted after this point. At higher injection flow rates, the constant skin factor achieved is lower because of the larger fracture dimensions developed at higher injection flow rates.