Investigating the effect of fracture-matrix interaction in underground gas storage process at condensate naturally fractured reservoirs

Depleted oil and gas reservoirs are used for underground gas storage. Accurate prediction of fractured reservoir efficiency during storage period is of great importance due to complex phase behavior of fluids and existence of fractures. The reservoir model should be representative of the reservoir behavior, the interaction between fracture and matrix and it should be capable of exact prediction of reservoir deliverability. Despite comprehensive studies performed on fractured reservoirs, the effect of fracture matrix interaction on underground gas storage capacity and reservoir injectivity is not yet investigated. In this paper, the role of fracture on storage capacity and fluid distribution is determined by investigating the behavior of a fractured gas condensate reservoir using different models during gas storage. The single-porosity compositional model of a real reservoir is constructed and validated. The reservoir is simulated using dual-porosity and dual-permeability models and reservoir performance is compared for different storage periods. The primary objective of this study is to determine the fracture influence on fractured reservoir simulation, as compared to matrix in underground gas storage. The water production, gas invasion in the reservoir during injection, condensate production, and relative permeability which are known to have high impact on the gas behavior are all affected by the changes in the system used for model construction. The results of this study show that although petrophysical properties, the volume of gas in place, and reservoir pressure drop are the same during reservoir depletion, different storage capacities and injectivity are predicted in gas storage periods. Fractures result in wider spread of injected gas (improvement of injected gas invasion) in the field and gas movement is easier during injection and production periods, mainly owing to the absence of water in fractures. (C) 2014 Elsevier B.V. All rights reserved.