Miscible gas flooding is the most commonly used enhanced oil recovery (EOR) method. One of the most important experimental parameters for miscible gas injection is minimum miscibility pressure (MMP). Many times, the MMP of a system can be very high. Instead of raising the pressure to achieve miscibility, injection gas may be enriched with intermediate components. The enrichment level at which the gas-oil system becomes miscible is called minimum miscibility enrichment (MME). Regardless of the values of MMP and MME, gas injected into a reservoir will most likely induce asphaltene precipitation, which may potentially cause formation damage and reduce flow in the production tubing.
In this paper, reservoir fluid from a Kuwait reservoir was analyzed to check for the feasibility of miscible gas injection. First, a series experiments were conducted to measure MMP with various gases using different techniques and MME testing with slimtube experiments. Moreover, the benefits, disadvantages, and applicability of each experimental method for EOR testing with gas injections were compared. Second, asphaltene precipitation upon gas injection was investigated in detail by measuring the precipitation onset conditions. Asphaltene precipitation onset was measured using a near infrared (NIR) light-scattering technique and a high-pressure microscope system to analyze the measured data. Finally, the asphaltene precipitation locus on a pressure-temperature (PT) diagram and the amount of precipitation were modeled for the reservoir fluid with different concentrations of injection gas. The modeling was carried out using a composition-based cubic equation-of-state approach. The experimental and modeling results indicated that an increase in concentration of injection gas appears to aggravate asphaltene precipitation.