It is known that the production rate of a well located in the center of the drainage zone and operated in a steady state at a bottomhole pressure higher than the saturation pressure can be determined using the Dupuit equation. If the bottomhole pressure of the production well becomes lower than saturation pressure in the zone where formation pressure is lower than saturation pressure a two-phase flow (gas + liquid) is formed. Formation of two-phases flow leads to a decrease in the well productivity. In this case, the Vogel ratio is usually used to determine the inflow performance, requiring at least one well test for the inflow. The combination of the Dupuit formula and the Vogel relation in calculating the well productivity index makes it possible to obtain a composite Vogel indicator curve. Skin-factor reflects any physical or mechanical phenomenon that reduces the fluid inflow into the well. It depends on partially penetrating well, wellbore damage (skin effect), well slant angle, the manifestation of inertial forces dependent on the production rate, etc. Suppose that using the skin-factor approach, one can take into account not only the degree of change in the properties of the wellbore zone, but also other effects that result to a change in well productivity. One of these effects can be the formation of a two-phase flow zone. The paper presents a generalized Dupuit – Vogel relationship for estimating the oil well productivity at any bottomhole pressure with respect to saturation pressure, as well as evaluating performance of actual oil wells.
References
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