One of the main parameters in reservoir engineering science is drainage area or drainage volume and its properties. Drainage area or volume is a region around each well, which the fluid from this part of reservoir drains to the well. So, all ofthe reservoir parameters that can be gained by well testing are belonging to this region.
For a better understanding of the drainage area concept, it can be considered that when a well starts to produce, a pressure disturbance is moving from the well to the boundaries. In this part of time, wells drainage area will become large. Then the disturbance will meet the boundary. When all sides of boundary are met, the wells drainage area will keep a constant shape, as long as the wells flow rates are constant.
A lot of equations in reservoir engineering science consist of a parameter that relate to drainage area and shape. So accuracy in determining drainage area will cause accurateresults for reservoir engineering problems.
But it must be said that estimates for drainage area are still more guesses than scientific deductions. Even the relatively expensive well test procedure often reveals very little about the drainage area.
The aim of this study is to review the all various methods of drainage properties determination and showing the best method used for one of the Iranian south oil field (Ab-Teymur). Also the benefits of drainage area and geometry determination that cause more attention to drainage area will be demonstrated.
Ab-Teymur field located 25-km southwest of Ahwaz field in southern onshore Iran, was placed on production during November 1991. This field contains two important formationswith good potential, which named Ilam and Sarvak. During these years, a total of 29 wells were drilled on Ab-Teymur structure. Out of these numbers, 26 wells were completed and opened to flow naturally with solution gas drive mechanism. The oil gravity varies between 23 and 24 degree API and is highly undersaturated with gas. The current reservoir pressure is about 4900 psi and the crude oil bubble point pressure is 1680 psi.
During the production, the engineers have understood that this field has a complex behavior in its natural flow. So all thesimulation studies on this field have some errors and the simulators can not describe the reservoir behavior. One of the main reasons for bad results of the simulators is non-accurate input data and this is because of high degree of heterogeneity inthis field. So the first step in perfect simulation of this field is determination of the properties of each part of reservoir. This means that by using modern well test analysis, the reservoir parameters around each well can be determined. But first of all, this region around each well that well test will give its properties must be determined. This region is drainage volume or area that in this study after some general theories about it, the various methods for its determination will be described and finally the best method for determination of well drainage area properties of Ab-Teymur oil field will be demonstrated.