Numerical simulation of skin factors for perforated wells with crushed zone and drilling-fluid damage in tight gas reservoirs

Abstract

Shaped charge perforation is the most widely used method to connect wellbores and reservoir formation. The skin factor is high after perforation tunnel cleaning in some offshore tight-gas reservoirs in China and crushed zones around perforation tunnels might be the cause. We present an efficient workflow for calculating total skin and crushed zone skin factors based on numerical simulation using the finite difference method. Locally refined structured mesh is employed to model the near-wellbore region precisely. The influence of perforation parameters, e.g. penetration length, tunnel cross-sectional area, phase angle and density are analysed both in the presence and absence of crushed zones and drilling-fluid damage. Increasing penetration length is found to be the most effective method for reducing the crushed-zone skin factor until a certain length is reached. Techniques for reducing the crushed-zone damage could be considered together with increasing penetration length to reduce skin efficiently. Our workflow using the finite difference method and structured meshes is convenient to be implemented and a range of configurations can be realised without re-meshing by assigning different properties to cells.