Literature review

Gilbert (1954) was the first to propose well analysis with the use of inflow performance relationship where he determined the IPR for different wells on a periodic basis at different inflow and reservoir conditions which indicates the productivity behavior of a well and determines the feasibility of producing that well.Muskat & Evinger (1942) observed that when pressure drops below bubble point pressure, IPR deviates from that of a simple straight line relationship which shows that the straight line IPR is only valid for single phase flow or solution gas drive reservoirs. The various IPR correlations that came into existence after then tried to address this problem.Vogel (1968) introduced empirical relationships for the determination of oil flow rate, and this relationship normalized for ideal absolute flow potential and it can also be referred to as backpressure equation. It is used in two phase reservoirs when reservoir pressure is less than bubble point pressure. In this model the IPR relationship can be formulated if either the absolute flow potential and reservoir pressure are known or if the reservoir pressure and flow rate corresponding the bottomhole pressure are known.The relationship which introduces dimensionless flow rate and pressure is shown in equation 3.(1)The bottomhole pressure is gotten from downhole gauges and the reservoir pressure is derived from buildup tests and they are measured in psig. The equation is also valid for water production; hence the dimensionless flow rate is in this form , where in cases where the water cut is greater than 0.97, which makes it suitable for water production.Vogel method can be used in both saturated and under-saturated reservoirs in combination with the straight line IPR. The major disadvantage of Vogel method is its sensitivity to the match point i.e. the stabilized flow test data points used in generating the IPR curve. Also, the IPR relation is independent of skin factor, which makes it inapplicable to damaged and stimulated wells and also reservoirs with high viscosity fluids. Another disadvantage is that it doesnt take the bubble point into consideration, and cannot be used to forecast future flow rates. Also its a good match using actual field performance but deviates at later stages of the reservoir life hereby affecting the prediction of IPR curve in the case of solution gas drive reservoirs due to the amount of free gas at later life of well.Standing (1970) extended Vogels work and proposed the concept of flow efficiency which helps to relate the IPR relationship to damaged and stimulated wells. Flow efficiency which is a function of reservoir pressure is the ratio of the ideal drawdown of the reservoir pressures to the actual drawdown i.e. as shown in the equation 4 below: = (2)Where, = reservoir pressure= bottomhole pressure of undamaged well (ideal well condition) = bottomhole pressure of damaged wellIn cases when F.E = 1, this means the well is in its ideal state, i.e. undamaged well, also when F.E >1 or F.E