Abstract:
The Chang 7 shale oil in the Yanchang Formation of Ordos Basin was studied using X-ray diffraction, scanning electron microscopy, high pressure mercury penetration, and gas isothermal adsorption. The formation was compared with typical shale oil in North America from four aspects including geological conditions, source rock characteristics, mineral composition, and reservoir space types. The results showed that both the Chang 7 shale oil and the typical shale oil in North America were deposited in a low energy environment, and the stable sedimentary environment was beneficial to shale oil accumulation. The organic matter type and maturity of source rocks in Chang 7 and North America are similar. The TOC content of Chang 7 shale oil is 2% to 18%, which is higher than that of the Eagle Ford shale. Thus, the Chang 7 source rocks are considered to have a great potential for oil production. The brittle mineral content of Chang 7 shale oil is 69.73%, only 1.27% lower than the typical shale oil in North America, indicating that the shale of Chang 7 formation is amenable to fracturing. Compared with the typical shale oil in North America, the Chang 7 shale oil has poor porosity and permeability (0.5%-2.1% and (0.000 4-0.03)×10
-3 μm
2, respectively). Micro-cracks and organic pores were well developed in typical shale oil in North America, while the organic pores in Chang 7 shale oil are scattered, and the reservoir space is mainly composed of intergranular pores, intragranular pores and micro-cracks. It can be concluded that the Chang 7 shale oil has the same oil accumulation pattern and mineral composition as the typical shale oil in North America. However, the Chang 7 shale oil has poor physical properties and a dense reservoir. Therefore, it has great resource potential and high development difficulty.