Well Tests analysis is a useful tool to estimate and "visualize" properties and performance of reservoirs under production induced stress-sensitivity. Formation damage due to the irreversible nature of rock deformation reduces the permeability, and consequently alters the oil/gas production.
The objective of this study is to assess well tests analysis in stress-sensitive reservoirs to determine the mechanism of permeability reduction and the subsequent well formation damage along with production depletion. Therefore, conventional well test analysis must be modified to include the governing equations describing rock deformation and changing pore pressure.
In this work a 3D fully coupled fluid-flow/geomechanical model accounting for well testing and formation damage has been developed. The numerical model performs well test analysis such as draw-down, pressure build-up and multi-rate tests describing the permeability reduction in stress-sensitive reservoirs. The governing equations were developed in cylindrical coordinates to better simulate the flow geometry that characterize the drainage area in most well tests. Furthermore, it is assumed that the mechanical rock properties are function of the mean effective stress (i.e., nonlinear rock deformation).
For typical field conditions, the results show that a combined effect of rock deformation -caused by pore pressure depletion, and reservoir compaction -caused by the overburden, generates high formation damage approximately within 9.5 feet around the wellbore. This damage is irreversible, and the permeability can only be improved a few feet near the wellbore through well stimulation. It is observed that conventional well-test analysis techniques may lead to erroneous estimations of well performance due to formation damage in stress-sensitive reservoirs. New results illustrate that Reservoir Pressure Distribution plots can be used as a "visualization" tool to identify formation damage by deformation/compaction in well test analysis. Premature diagnosis of the above-mentioned combined effect will provide evaluation and picturing of formation damage for field development strategies.