Visualization and Analysis of Interaction of Carbonate Reservoirs with Carbon Dioxide During CO₂ Enhanced Gas Recovery Process

This paper presents simulation based analysis for CO₂ Huff-n-puff and Enhanced Gas Recovery (EGR) process in carbonate rocks that are representative of the Middle East’s aquifers and oil/gas reservoirs. The objective of this study is to study the development of condensate in the near wellbore region of a wet gas carbonate reservoir and to subsequently study the feasibility of using CO₂ injection for removing this condensate phase.

Changes in oil saturation, gas saturation, gas permeability, and gas productivity were used to quantify the effect that CO₂ has on wet gas carbonate reservoirs. Carbonate reservoir systems have complex structures and to represente these, two reservoir models were constructed that had the characteristics of typical carbonate reservoirs.

Condensates appeared in wet gas systems once the pressure reduces below the dew point pressure. This can be remedied in two ways: (1) repressurizing the reservoir above the dew point and (2) lowering the dewpoint pressure by changing the fluid properties of the reservoir fluid. Both of these remedies can be achieved by using CO₂. Results show that CO₂ has the ability to repressurize a reservoir and the ability to lower the dew point of a wet gas fluid. Results also show that carefully timing the start of CO₂ injection and its duration can significantly improve the economics of enhanced gas recovery process.