Oil Recovery and Permeability Reduction of a Tight Sandstone Reservoir in Immiscible and Miscible CO₂ Flooding Processes

Abstract

In this paper, oil recovery and permeability reduction of a tight sandstone reservoir in immiscible and miscible CO2 flooding processes are experimentally studied. First, a series of saturation tests are conducted to determine the onset pressure of asphaltene precipitation from a light crude oil−CO2 system. Second, the vanishing interfacial tension (VIT) technique is applied to determine the minimum miscibility pressure (MMP) between the light crude oil and CO2. Third, a total of nine CO2 coreflood tests under immiscible and miscible conditions are performed through the so-called dry, secondary, and tertiary oil recovery processes, respectively. It is found that the onset pressure of asphaltene precipitation is much lower than the MMP. In the CO2 secondary oil recovery process, the coreflood test data show that, when the injection pressure is between the onset pressure of asphaltene precipitation and the MMP, the oil recovery factor is higher but the oil effective permeability reduction is larger at a higher injection pressure in the immiscible CO2 flooding. They both reach almost constant maximum values in the miscible CO2 flooding (P ≥ MMP). It is also found that, in three different miscible CO2 oil recovery processes, the CO2 tertiary flooding process gives the lowest oil recovery factor but the largest oil effective permeability reduction. This is attributed to the most severe codeposition of asphaltenes and metal carbonates. However, the CO2 dry or secondary flooding process has a significantly higher oil recovery factor but a much smaller oil effective permeability reduction due to asphaltene deposition alone in the former process or codeposition of asphaltenes and metal carbonates in the latter process.

Experimental investigation of miscibility conditions of dead and live asphaltenic crude oil–CO2 systems

“…This reduction was related to extraction of light component. Nevertheless, a comprehensive technical justification of the reason behind the slope change was not offered in the literature (Wang and Gu 2011;Wang et al 2010). Besides IFT studies, another research group investigated the conditions of miscibility for a crude oil through core flooding experiments, who comprehended that the point of slope change approaches to the asphaltene precipitation onset pressure (Cao and Gu 2013a).…”

“…In the literature, several investigations of CO 2 -asphaltenic crude oil IFT versus pressure have been performed. The observed results show different linear slopes at different temperatures (Escrochi et al 2013;Wang and Gu 2011). The starting point of slope variation of the VIT curve corresponds to the onset of the asphaltene precipitation (Escrochi et al 2013).…”

“…In addition, CO 2 injection process is more attracted due to the reduction of greenhouses gas emissions (Aycaguer et al 2001;Gui et al 2010;Rao and Rubin 2002). The CO 2 flooding process, depending on the highest possible operating pressure and minimum miscible conditions, can be performed at both miscibility and immiscibility conditions (Wang and Gu 2011). The oil recovery mechanisms that occur in CO 2 injection include the oil viscosity reduction, light-component extraction, IFT reduction, immiscible and miscible displacements and improving the oil swelling (Cao 2012;Holm and Josendal 1974;Mungan 1981;Simon and Graue 1965).…”

On the application of NiO nanoparticles to mitigate in situ asphaltene deposition in carbonate porous matrix

“…Studies performed on asphaltene precipitation under dynamic CO 2 injection also report permeability reduction in sandstone cores in immiscible CO 2 state (Wang et al 2013). Recently, Wang and Gu (2011) performed dynamic CO 2 flooding tests in sandstone cores in both miscible/immiscible states. It was concluded that the onset pressure of asphaltene precipitation is much lower than the minimum miscible pressure (MMP).…”

“…Moreover, the oil recovery factor was determined to be higher and the oil effective permeability reduction to be larger at a higher injection pressure (in immiscible CO 2 case) while reaching nearly constant maximum values in the miscible CO 2 case (P C MMP). For a comprehensive review of the subject the reader is referred to the article by Wang and Gu (2011) and the references therein.…”