Well Test Analysis of Two-layered Oil Reservoir in Commingled Flow System

This paper presents multi-layer testing and analysis techniques to obtain layer permeabilities and skin factors using flow rate and transient pressure data which was generated into ECLIPSE100 simulation software. For the purpose of this study, we considered commingled reservoir and is defined as the joint production from two or more layers from a single common wellbore. For simplicity the commingling of two layers is considered, without measuring the individual flow rate from each layer, but measuring the combined flow rate from each layer. This study consists of two-layered radial reservoir model with single phase fluid, with measured reservoir and rock properties. The two-layered testing and analysis techniques are presentend and existing interpretation methods for estimating layer permeabilities; skin factors have been evaluated using the pressure transient data obtained from ECLIPSE100 simulation software. The majority of the reservoirs which are found for exploitation as studied by different investigators suggest that they are exhibiting layering or stratification-a sequence of layers of different properties. The difference between their properties variation may range from high to low. These layers may have different formation properties porosity; permeability; thickness, skin factor and fluid characteristics and are commonly heterogeneous. The boundaries between these layers may usually have significant difference in properties from upper to the lower layer. Therefore the vertical sequence of the different layers may show permeability variations from good to poor. It is very important to identify the type and characteristic of layered reservoir because each layer has different influence on the primary and secondary recovery. There is always a complication of multiple layers testing, the possibility of different skin factors in different layers, the different depletion behaviour of layers with high or low initial pressures. As a reason, it becomes necessary to test multilayered system and analysis is more complex and the results become more ambiguous as compare to the single layer testing. For this reason simulation is a very important tool to minimize the ambiguity in multilayered reservoir testing. By the simulation techniques different layers can be analysed on the basis of each layer contribution to the production during drawdown and build up.