Managing Gas-Injection-Induced Excessive Water Production in Tight OilReservoirs by Optimizing Operational Constraints

摘要

A CO2 huff-n-puff pilot implemented in the Midland Basin demonstrated a significant oil rate improvement,but also witnessed an escalation in water-cut up to 0.3.A compositional model was established to considerthe complex physics including cyclic stress changes,reopening of water-bearing layers,reopening ofunpropped fractures and its resulting relative permeability shift.Our previously published work suggestedthat the reopening of unpropped fractures and its resulting relative permeability shift contributes most tothe abnormal water cut surge after gas injection.In this study,we further proposed several operationalconstraints to manage such high water-cut occurrence after gas injection.The optimized simulation resultssuggested that around 1.5 times increase in recovery factor can be achieved after six CO2 huff-n-puff cycles.Sensitivity analysis was subsequently conducted regarding parameters such as soaking time,injection time,and bottom-hole pressure.It was found that soaking time and bottom-hole pressure did not have muchinfluence on cumulative oil production.Setting injection time as 150 days in each cycle can achievethe highest net present value.The primary objective of this study is aimed at optimizing techniques forconducting CO2 huff and puff process to maximize oil production and minimize CO2 emission.