Traditionally, formation damage has been associated with the presence of a flow reduction around the wellbore area due to drilling and completion operations; however factors such as variation in pore pressure can induce a response in the geomechanical behavior of the reservoir and thermodynamic behavior of fluid, which causes additional decrements on the flow capacity of the well drainage area. A procedure has been developed that determines the damage caused by changes in permeability due to variations in pressure. The procedure requires two parameters: the permeability modulus and the damaged caused by drilling and completion operations; these parameters are obtained using a coupled fluid-geomechanical simulator, the Numerical Transient Simulator (NTS), by the interpretation of a well transient analysis. The NTS was developed by the Applied Geomechanics Research Group (GIGA) of the Petroleum Engineering Program at the National University of Colombia – Medellín Campus. With the use of the NTS software it is possible to interpret a well test in a non-conventional way and then decompose the total skin into two components, one of them is the damage due to drilling and completion operations, and the other one is due to changes of permeability caused by pressure variations. The later component can be additionally decomposed into the geomechanical damage and thermodynamic damage as well. By disaggregating the formation damage, it is possible to know the factor that is having a major impact on the flow reduction. Therefore, the methodology presented in this paper can be used for the selection of the most appropriate well-stimulation procedure. This paper presents the theory and results of the application of this procedure for studying the damage in several wells of a field at the Colombian eastern foothill.

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