Simulation Study On Wag-Co2 Injection In Light Oil In The Presence Of Asphaltene In Sandstone Reservoir

WAG-CO2 is proven to be a better method than water flooding alone. Injecting water alternately with CO2 helps recover more oil compared to water flooding. Water injection improves the sweep efficiency and gas flooding reduces the effect of viscous fingering. Chen et al. (2009) stated that water injection is used to control gas mobility in order to achieve higher sweep efficiency in macroscopic scale while gas injection gives higher sweep efficiency in microscopic scale. From field experiences, WAG-CO2 injection in light oil will cause asphaltene precipitation problem and one of the reasons is because of pressure and composition changes. This paper is focusing on studying the effect of WAG injection pressure on the precipitation of asphaltene in Malaysian light oil (38.8 API) using sandstone model. Different WAG injection pressure is used ranging from 2000 psia to 3200 psia. Pressure of 2000psia and 2400 psia are used to simulate injection pressure below saturation pressure (2492 psia) while pressure of 2800 and 3200 psia are used to simulate injection above saturation pressure. The result shows that injection pressure higher than saturation pressure resulted in better oil recovery compared to lower injection pressure. This is supported by literature review from experiment conducted by Alian et.al (2011). At higher injection pressure, lesser asphaltene will be precipitated. But for asphaltene deposition using same WAG injection period, same amount of asphaltene is deposited for any of the pressure used due to continuous pressure support at specified pressure ensure no further asphaltene deposited. Thus, higher injection pressure is used to ensure lesser asphaltene precipitation and continuous injection at specified pressure should be made to ensure no further asphaltene deposition from the precipitated asphaltene. Different WAG cycle size was also simulated for this study. WAG cycles of 1 month, 2 months, 3 months and 4 months are used to study the impacts on WAG performance. Results showed that WAG cycle of 1 month gives a bit higher recovery compared to other WAG cycle size. From asphaltene precipitation, WAG cycle does not give significant impact especially at injection pressure higher than saturation pressure. However, other reservoirs might give different results on different WAG cycle size used depending on the reservoir and fluid properties.