Hydrate risk assessment during CO2 injection on legacy wells in a highly depleted gas field

Abstract

Summary CO2 storage in depleted gas reservoirs is a major topic in the context of European efforts to reduce CO2 emissions by geological storage. Injection of CO2 in such fields often leads to significant difference between the injected CO2 and the initial reservoir temperature. Moreover, cold CO2 injection can promote hydrate formation that will impair the well injectivity. The main goal of this study is to assess the hydrate formation risk during CO2 storage operations on legacy wells of a highly depleted gas field. To assess if a well is subject to hydrate risk, dynamic pressure and temperature profiles in the formation are analysed using hydrate phase diagrams (P-T paths technique). The hydrate formation condition is flagged if the P-T paths enter the hydrate stability zone at the place where water is present. The method application is presented for a gas producer well and a water dump disposal well. The hydrate formation risks were studied in a simplified in-house well-reservoir coupling model and through sensitivity analysis of reservoir-simulator model including the influence of injection conditions (rate and bottom-hole temperature). Results show how the hydrate formation may be foreseen depending on P-T condition, injection rate and water saturation distribution in near-wellbore region.