Improving recovery efficiency by CO2 injection at late stage of steam assisted gravity drainage

The high recovery performance of steam-assisted gravity drainage (SAGD) makes it a popular option for heavy oil resources. Currently, most of the heavy oil reservoirs developed by SAGD in China are in the late development phase, with high energy consumption due to reduced thermal efficiency. The use of SAGD wind-down processes involving CO2 in combination with steam for heavy oil recovery is considered as a viable alternative to limit energy consumption, and also reduce the amount of greenhouse gas emissions by leaving CO2 behind in the reservoir. Study reveals that the dissolution and demulsification of CO2 steam chamber temperature reaches 200 ◦C, the amount of solid phase deposition induced in crude oil can reduce the viscosity of emulsified heavy oil by more than 50%. When the by CO2 extraction is only 0.016 kg/m3 , the rock wettability changes from lipophilic to hydrophilic, and the higher the reservoir temperature, the stronger the hydrophilicity is, which reduces the adhesion power of the oil phase and facilitates the stripping of crude oil from the rock surface. Numerical simulation studies have been carried out utilizing STARS to obtain energy efficient utilization and improved steam chamber characteristics. Heat loss from SAGD baseline is 1.77 times that with CO2 injection process, but the recovery factor is only 2.48% higher. At the initial stage with CO2 injection, the steam chamber continues its lateral expanding, which increases the recovery factor at the initial stage of CO2 injection by about 6%. One year after CO2 injection, gas channeling results in lower recovery than traditional SAGD process, and 38.4% of the injected CO2 is stored in the reservoir from this study.Cited as: Gong, H., Yu, C., Jiang, Q., Su, N., Zhao, X., Fan, Z. Improving recovery efficiency by CO2 injection at late stage of steam assisted gravity drainage. Advances in Geo-Energy Research, 2022, 6(4): 276-285. https://doi.org/10.46690/ager.2022.04.0

Shale Microstructure Characteristics under the Action of Supercritical Carbon Dioxide (Sc-CO₂)

Supercritical carbon dioxide (SC-CO2) is suitable to extract low-polar organics and to assist in the dissolution of pores and fractures in shale. In this work, we investigate the effect of temperature on the structure of five shale samples via high pressure reaction assisted with SC-CO2. Shale samples were analyzed using X-ray diffraction, field emission scanning electron microscopy, and ImageJ software. Due to the extraction of CO2, after Sc-CO2 treatment, carbonate and clay content decreased, while quartz and plagioclase increased slightly, which improved gas and oil flow in microscopic pores and shale cracks. Shale samples showed an increase in surface fracture area as experimental temperature increased. Since Sc-CO2 fluid density and solubility increase with temperature, more organics can be extracted from shale pores and fractures, resulting in newly formed pores and fractures. As a result, the threshold temperature for shale high-temperature Sc-CO2 cracking was confirmed to be 400 °C, and the fracture area increased by more than 45% at this temperature. Based on the findings of this study, Sc-CO2 technology can be used to potentially recover low-maturity shale oil efficiently