Hydrocarbon generation potential and sedimentary environment for the source rocks along the Changshe Mountain oil shale section in North Qiangtang Basin

Abstract: Located in North Qiangtang Basin in the northern part of the Shengli River-Changshe Mountain oil shale belt (currently the largest marine oil shale belt in China), the Changshe Mountain oil shale section mainly consists of oil shale, micrite limestone, black shale and marl. In order to determine the content of total organic matter, organic matter type, thermal maturity and sedimentary environment of the source rocks along the Changshe Mountain oil shale section, the authors collected twenty samples for multiple organic geochemistry tests. The results show that the oil shale has the best hydrocarbon generation potential, followed by the black shale and micrite limestone. The total organic carbon (TOC) content varies from 0.41% to 9.49%, with an average of 4.02%, and the oil shale samples have the highest values (ranging from 4.53% to 9.49%), with an average of 7.74%. Chloroform bitumen “A” varies from 0.0252% to 0.3403%, and the average value of the oil shale sample is 0.27%, indicating moderate to good source rocks. The kerogen types assessed from organic element composition and organic petrography data show that there is mainly typeⅡ1 kerogen, with small amounts of type Ⅱ2 and Ⅲ kerogen. The distribution of Ro ranges from 1.08% to 1.43%, with an average of 1.27%, demonstrating a mature to overmature stage of the organic matter, with the Ro gradually becoming higher along the oil shale section. The source rocks along the Changshe Mountain oil shale section were deposited in a reductive and high-saline water environment, and the organic source material was mainly low-grade hydrobios.