Estimation of reservoir properties taking into account oil degassing in the bottomhole zone

A mathematical model of unsteady oil flow to a vertical well in a circular reservoir taking into account degassing in the bottomhole zone is proposed. The effects of saturation pressure and gas factor on pressure recovery curves and their derivatives are investigated. It is shown that the saturation pressure value characterizes the radius of the degassing zone. The change in permeability in this zone is affected by both the saturation pressure and the gas factor. Based on the proposed model and using the theory of inverse problems, a method was developed for interpreting the results of hydrodynamic studies of vertical wells operating with bottomhole pressure below the saturation pressure. This method can be used to evaluate the saturation pressure and permeability of the reservoir from pressure recovery curves.