Gas generation potential of Oligocene source rocks in Yinggehai Basin

For many years, natural gas exploration in Yinggehai Basin has mainly focused on Miocene source rocks, and several exploration successes and insights have been achieved. However, limited research on Oligocene source rocks severely hinders natural gas exploration in the slope zone of the basin. Based on a detailed analysis of the geochemical characteristics of natural gas and source rocks, combined with regional oil and gas geological conditions, basin modeling was used to evaluate Oligocene oil and gas resource potential in the study area. The results indicate the following. First, mudstone source rocks of fair to excellent level were developed in the Oligocene, and high-quality coal measure source rocks were present in certain localities, all of which were gas-prone source rocks. The quality of the source rocks of Yacheng Formation was slightly better than that of Lingshui Formation. Second, the source rocks of the Oligocene can be divided into two types on the basis of their source compositions. One type was mainly composed of terrestrial higher plants, represented by the source rocks of Well L20-1 in Northern Yinggehai Sag, and the other type was mainly composed of lower aquatic organisms, represented by the source rocks of Well Z11-1 in Yingdong Slope. Third, Oligocene source rocks have great potential, with a natural gas resource more than 1.0 × 10¹² m³. They were mainly distributed in Northern Yinggehai Sag and Yingdong Slope. The maximum gas generation intensity can reach 100 × 10⁸ m³/km². We conclude that Oligocene source rock resources in Yinggehai Basin have great potential and that areas with high gas generation intensities are mainly concentrated in Northern Yinggehai Sag and the southern section of Yingdong Slope, which are the main targets for future natural gas exploration.