Study on Oil Composition Variation and Its Influencing Factors during CO2 Huff-n-Puff in Tight Oil Reservoirs

Abstract

With immense potential to enhance oil recovery, CO2 has been extensively used in the exploitation of unconventional tight oil reservoirs. Significant variations are observed to occur in the oil’s composition as well as in its physical properties after interacting with CO2. To explore the impacts of oil properties on CO2 extraction efficiency, two different types of crude oil (light oil and heavy oil) are used in CO2 huff-n-puff experiments. Moreover, numerical simulation is implemented to quantitatively inspect the impacts of different influencing factors including production time, reservoir pressure and reservoir temperature on physical properties as well as on the oil composition variation of the crude oil. The findings of the experiments demonstrate that, whether for the light oil sample or for the heavy oil sample, hydrocarbon distribution becomes lighter after interacting with CO2 compared with the original state. In addition, it is also discovered that the hydrocarbon distribution variation is more significant for the light oil sample. The findings of the numerical simulation suggest that production time, reservoir pressure and reservoir temperature have significant impacts on the produced oil composition and properties. The hydrocarbon distribution of the oil becomes lighter with the increasing of production time and formation pressure, while it becomes heavier with the increasing of reservoir temperature. At the very beginning of the oil production, the properties of the produced oil are worsened. Compared with the original state, the oil density and viscosity are 25.7% and 200% higher, respectively. It is suggested that viscosity reducers are added into the well to improve the oil properties in this period. With the continuing of the oil production, the oil properties are continuously promoted. At the end of the simulation time, the oil density and viscosity are 3.5% and 15.1% lower compared with the original oil, respectively. This paper has great significance for the implementation of CO2 huff-n-puff in tight oil reservoirs.

Mechanism and Main Control Factors of CO2 Huff and Puff to Enhance Oil Recovery in Chang 7 Shale Oil Reservoir of Ordos Basin

“…This paper investigates the potential of CO 2 huff-n-puff to enhance oil recovery in the challenging context of the Chang 7 shale oil reservoir, characterized by low natural energy and high heterogeneity. Most shale oil reservoirs are depleted using horizontal wells and hydraulic fracturing technology, which typically yield recoveries of less than 10%, and are less effective at improving recovery [1][2][3]. CO 2 has a low density and excellent all-around performance, and it is easy to obtain at a low cost.…”