摘要：

Successful breakthroughs have been made in shale oil exploration in several lacustrine basins in China, indicating a promising future for shale oil exploration and production. Current exploration results have revealed the following major conditions of lacustrine shale oil accumulation: (1) stable and widely distributed shale with a high organic abundance and appropriate thermal maturity acts as a fundamental basis for shale oil retention. This shale exhibits several critical parameters, such as total organic carbon content greater than 2%, with optimal values ranging from 3% to 4%, kerogen Ⅰ and Ⅱ₁ as the dominant organic matter types, and vitrinite reflectance (R_o) values greater than 0.9% (0.8% for brackish water environments). (2) Various types of reservoirs exhibiting brittleness and a certain volume of micro-nanoscale pores are critical conditions for shale oil accumulation, and these reservoirs have porosities greater than 3% to 6%. Moreover, when diagenesis is incipient, pure shales are not favorable for medium-to-high maturity shale oil enrichment, whereas tight sandstone and hybrid rocks with clay content less than 20% are favorable; however, for medium-to-late-stage diagenesis, pure shales with a clay content of 40% are favorable. (3) The retention of a large amount of high-quality hydrocarbons is the factor that best guarantees shale oil accumulation with good mobility. Free hydrocarbon content exceeding a threshold value of 2 mg/g is generally required, and the optimum value is 4 mg/g to 6 mg/g. Moreover, a gas-oil ratio exceeding a threshold value of 80 m³/m³ is required, with the optimal value ranging from 150 m³/m³ to 300 m³/m³. (4) High-quality roof and floor sealing conditions are essential for the shale oil enrichment interval to maintain the overpressure and retain a sufficient amount of hydrocarbons with good quality. Lacustrine shale oil distributions exhibit the following characteristics: (1) major enrichment areas of shale oil are located in semi-deep to deep lacustrine depositional areas with external materials, such as volcanic ash fallout, hydrothermal solutions, and radioactive substances with catalytic action, as inputs; (2) intervals with “four high values and one preservation condition” govern the distribution of shale oil enrichment intervals; and (3) favorable assemblages of lithofacies/lithologies determine the distribution of enrichment area. According to preliminary estimates, China has 131×10⁸ to 163×10⁸ t of total shale oil resources with medium-to-high thermal maturity, among which 67×10⁸ to 84×10⁸ t is commercial. These resources are primarily located in the Chang 7¹⁺² interval in the Ordos Basin, Qing 1+2 members in Gulong sag in the Songliao Basin, Kongdian and Shahejie formations of Cangdong sag, Qikou sag and the Jiyang depression in the Bohai Bay Basin, and Lucaogou Formation in the Junggar Basin.