Recovery of Gas Condensate by Nitrogen Injection Compared With Methane Injection

Abstract

Summary: Methane injection or gas cycling is the recovery process of choice for gas-condensate reservoirs. For economic reasons, however, this process can often not be implemented. An alternative injection gas may be nitrogen, which is relatively cheap and available everywhere. Nitrogen, however, causes stronger liquid drop-out in the mixing zone between the gas condensate and the injected gas, which could reduce recovery. This paper presents the results of slim-tube experiments and numerical simulations of the displacement of a model gas condensate at reservoir conditions by both nitrogen and methane. The gas condensate used is a three-component hydrocarbon system representative of a North Sea reservoir. The phase behavior and physical properties of mixtures of the gas condensate and injection gas were calculated with an equation of state tuned by some selected pressure/volume/temperature (PVT) experiments. The main conclusion of this study is that the displacement of gas condensate by both nitrogen and methane is a developed miscible process, which results in high condensate recoveries. The recovery is adversely affected by dispersion; nitrogen is more sensitive to this than methane.