Dealing With the Challenges of the Rate-Dependent Skin Phenomenon in a Gas Condensate Reservoir: A Simulation Approach

Abstract

Skin is one of the most challenging problems in oil and gas production, resulting in a reduction in reservoir deliverability. Mechanical skin is introduced to the pay zone during the drilling and completion phase, while rate-dependent skin comes into play as production starts, and is caused by infracting basic Darcy assumptions in a gas reservoir. Dissimilar to conventional gas reservoirs, the formation of condensate jots in a gas condensate reservoir when the bottomhole pressure drops below the dew point causes higher skin, which imposes a greater pressure drop. The authors investigated dependency of skin to flow rate in gas condensate reservoirs through a simulation approach. A radial synthetic reservoir compositional model was developed by using rock and fluid properties and well data based on information from a real gas condensate field in south Iran. A well test analysis was utilized to verify the validity and accuracy of the model. Due to heterogeneity existence in particular field, the authors tried to consider different reservoir and wellbore characteristics in reservoir simulation models. A wide range of rock permeabilities and mechanical skins were examined in different irreducible water saturations. Moreover, all the scenarios were run in two different initial reservoir pressures individually. The result of numerous simulations showed a similarity between the trends of rate-dependent skin versus flow rate for the entire tested model. It was also illustrated that in low-permeable gas condensate reservoirs, the existence of mechanical skin leads to inefficient production. Because mitigation of some kind of mechanical skin types are not efficient, the same simulation study should be performed before starting the drilling operation in a gas condensate reservoir to assess the effect of mechanical skin.