Abstract
With further progress of oilfields' development in China, more and more low permeability reservoirs are being put in production. However, fluid flow in low permeability porous media no longer obeys Darcy's law, so traditional well testing interpretation methods may cause error in estimation of the reservoir parameters.
This paper describes problems encountered when analyzing transient pressure tests in low permeability reservoir. The equation to describe the non-Darcy flow was given according to experimental method and two factors were introduced into the equation to improve the Darcy's law. Based on the modified model, the theoretical well test model for dual-porosity media in low permeability reservoirs with complex fractures was derived which allows for the influence analysis of non-Darcy effect. The model was solved by numerical method and the log-log curves for the pressure responses were plotted. Sensitivity analysis shows that the pressure responses for both Darcy flow and non-Darcy flow conditions are the same for the following parameters: wellbore storage, skin factor, ratio of storativity, and interporosity flow coefficient. Non-Darcy flow mainly affects the transition section between the pure wellbore storage and radial flow region, and the pressure derivative curves exhibit a gentle transition region compared with the Darcy's flow. These type curves give a better interpretation of well testing pressure response in low permeability reservoirs.
