Abstract
The Gulong shale oil reservoir in the Daqing Oilfield of China is characterized by well-developed fracture bedding planes. Studying the distribution and evolution of Gulong shale oil, specifically the size of oil-bearing pores, the content of oil in organic and inorganic pores, and the evolution of oil distribution during gas displacement, can aid in the development of shale oil. To this end, this study employed T1-T2 NMR spectra for the aforementioned investigations. A Gulong shale core is tested in this experiment. NMR T1-T2 and T2 spectral scans are conducted on the cores in both before and after it saturated with oil. Then gas displacement experiments are conducted, and NMR scans are taken. The oil distributions in the organic and inorganic pores are characterized using the T1-T2 spectra. The evolution of oil distribution under gas displacement in the shale cores is characterized by NMR T2 spectra. The T1-T2 spectra results revealed that the oil in both organic and inorganic pores was distributed in two distinct regions with different T2 value intervals. The oil in the organic pores consisted of residual heavy oil components and saturated oil, and they were distributed in a small T2 value interval and different T1/T2 value interval. On the other hand, the oil in the inorganic pores was primarily composed of saturated oil. Mobile oil was observed in the inorganic pores and was distributed in the largest T2 value interval among all oil phases. Additionally, the T2 spectra further revealed the displacement efficiency of different pores in shale core. Furthermore, Micromodel flooding and imbibition experiments have been conducted to study the flow dynamics of water in porous, which demonstrated the high recovery of water flooding for nanopores in shale oil reservoirs.
