Abstract:
Songliao Basin is a key area for increasing oil and gas reserves and production in China with a high level of conventional oil and gas exploration. There is an urgent need to explore new fields for resource replacement. Songliao Basin has great shale oil and gas potential, but the shale oil and gas are hosted in tight spaces with poor fluid mobility. The clay mineral content is high and the brittleness is low in these rocks, making it difficult in engineering stimulation and oil and gas breakthrough. The authors in this paper took public-benefit oil and gas geological survey in Songliao Basin and adjacent areas since the 13th Five-Year Plan as the main line, and focused on the new frontiers of continental shale oil in the Upper Cretaceous Qingshankou Formation and continental shale gas in the Lower Cretaceous Shahezi Formation. The strategic survey breakthroughs were systematically summarized in Qingshankou Formation continental shale oil of Qijia, Gulong, Changling, Sanzhao sag and Shahezi Formation continental shale gas of Lishu fault depression. In addition, multiple new discoveries of shale oil and gas have been made in adjacent areas including Shuangyang, Tonghua, Fuxin, and Jinyang basins, as well as in the Meso-Neoproterozoic strata of the northern Hebei-western Liaoning. The study proposed two high-efficient enrichment models for deep lacustrine shale oil-the "laminated type" and the "fissile type", and clarified the distribution pattern of shale oil in deep lacustrine facies of open freshwater lake basins. Besides, a model of nutrient element migration from volcanic ash during the post-depositional diagenetic stage was established, and the formation mechanism of high-quality mixed shale during volcanic activity periods was revealed. It confirmed that the deep Shahezi Formation shale in Songliao Basin has the resource base for continental shale gas enrichment. Hydrocarbon detection technology based on two-phase medium wave equation theory was developed, and precise geosteering technology for long horizontal sections with thin target layers was established. An innovative supercritical CO
2 composite fracturing technology suitable for high-clay continental shale reservoirs was developed. These advances have promoted the geological understanding of continental shale oil and gas as well as the progress of exploration and development technologies. The survey breakthroughs and theoretical progress of shale oil and gas in Songliao Basin and its peripheral areas could provide theoretical and technical support for strategic surveys of continental shale oil and shale gas across China, and offer references for shale oil and gas exploration in other regions.