Abstract
In 1968, Vogel used a computer program to predict inflow performance relationships (IPR) of a well producing from a wide variety of solution-gas drive reservoirs. In dimensionless form, these curves relating flowing bottom-hole pressures to oil production rates were found to share a common characteristic shape which was correlated by a parabola. Because Vogel studied cases of differing rock and PVT properties, his work became well accepted in the industry. Most of the papers published on inflow performance deal with vertical wells and should not be applied to horizontal wells without verification. There are no analytical models available at present to compute IPRs from two phase flow theory. In such a case, it is necessary to use numerical simulation. Unfortunately, most commercial black oil simulators do not include the feature necessary for predicting IPRs of horizontal wells.
In this paper1, two commercial simulators are utilized to develop IPRs for horizontal wells producing from solution-gas drive reservoirs. The development parallels the work of Vogel for vertical wells. First, a base case is considered with typical fluid, rock and reservoir properties. Then, variations from the base case are investigated. Changes from the base case, in fluid properties included variations in relative permeability and PVT properties. Changes in reservoir properties included variations in drainage area, pay thickness, and absolute permeability. Changes in well properties included variations in skin, well location, and well length with respect to reservoir boundaries. The resulting IPRs were made dimensionless in order to compare their curvature, or the rate of change of oil production rate with flowing bottom-hole pressure. These curves were found to be sensitive to the stage of reservoir depletion. However, they were not affected significantly by changes in the fluid reservoir, or well properties.
An attempt was made to develop a simple correlation to represent numerical results. Both Vogel's and Fetkovich's equations were tried, but neither of them fully reproduced the characteristic shape of the dimensionless IPRs. A new two-parameter equation, that results from combining the two previous equations was found to provide an adequate correlation.
