Mitigation of near wellbore gas-condensate by CO2 huff-n-puff injection: A simulation study

Abstract

Accumulation of gas-condensates in near wellbore regions, and consequently, the reduction of gas production rates, is a well-known phenomenon in most gas reservoirs all around the globe. In this study, the injection of CO2 in “huff-n-puff” (HnP) mode and its potential advantages of removing accumulated gas-condensates are thoroughly investigated. A compositional simulator was used to capture the near wellbore fluid flow physics causing the condensate dropout under various wellbore/field operational conditions. The severity of condensate blockage was evaluated using detailed sensitivity and uncertainty analyses of various key static and dynamic influencing parameters such as porosity, permeability, fluid composition, boundary flux, and flowing bottomhole pressure. Under various scenarios of condensate blockage, studies related to effectiveness and optimization of CO2 slug-size, soaking-time, and flowback rate are conducted. As a proof of concept, it is observed that miscibility of CO2 in condensates, and near wellbore re-vaporization of accumulated liquids, are two of the main mechanisms of removing the condensate blockage. Because of these two mechanisms an improvement in effective permeability to gas can be expected. It is also concluded that CO2 is relatively more effective in removing near wellbore condensates as compared to far-field regions. Finally, based on various optimization analyses, a viable approach to adopt HnP CO2 injection scheme is suggested.