ESTIMATION OF RESERVOIR PROPERTIES TAKING INTO ACCOUNT OIL DEGASSING IN THE BOTTOM-HOLE ZONE

A mathematical model of unsteady oil flow to a vertical well in a circular reservoir taking into account degassing in the bottom-hole zone is proposed. The effects of saturation pressure and gas/oil ratio on pressure recovery curves and their derivatives are investigated. It is shown that the saturation pressure characterizes the radius of the degassing zone. The change in permeability in this zone is affected by both the saturation pressure and the gas/oil ratio. Based on the proposed model and the theory of inverse problems, a method was developed for interpreting the results of pressure transient analysis of vertical wells producing at bottom-hole pressure below the saturation pressure. This method allows evaluating the saturation pressure and permeability of a reservoir from pressure recovery curves.