The Songliao Basin is located in Northeastern China surrounded by the Greater Khingan, Lesser Khingan, and Changbai mountains. The Songliao basin originated between the late phase of Indonesian movement and the early stage of Yanshan movement. The development stage took place between mid-late Yanshan movement and early Himalayan movement. It is a sedimentary basin characterized with high surroundings and a low center. The low center is comprised of Cretaceous strata distributed under Cenozoic strata. The reserve is rich in oil and oil shale, accounting for more than half of China's already proven oil reserves. The Songliao Basin holds two of China's most prized oil fields - Daqing and Jilin.
History of The Songliao Basin
The Songliao Basin can be easily split into two parts. The northern half of the basin is dedicated to exploration of the Daqing Oilfield while the southern half is dedicated to exploration of the Jilin Oilfield. The Songliao Basin experienced two phases of thermal evolution. The first stage consisted of a gradual increase of heat flow from the Late Cretaceous to the end of the Cretaceous. The second phase has been a gradual decline in heat flow since the Neogene. At the end of the Late Cretaceous, source rock began to generate a lot of hydrocarbon due to the rapid increase in heat. Since the Neogene the maturity has maintained the characteristics of the end of the Cretaceous. The structural style and formation of oil shale reservoirs happened during the cooling events in the late Nenjiang period and the late Mingshui period.
Daqing and Jilin Oilfields
The Daqing Oilfield is the largest producing oil area in China. The crude oil is paraffin based with a high wax content, high freezing point, and a low sulfur content. The source bed of the Daqing is primarily Mesozoic Cretaceous sandstone of continental facies. A commercial flow began producing around 1960. The Daqing Oilfield was producing 50 million tons of crude oil annually for 30 years. Output is diminishing, but there are plans for new shale oil production in different areas of the Daqing. The Jilin Oilfield began producing around 1960 as well. Jilin Oilfield consists of 23 oil and gas fields. It has an annual output of 7.5 million tons of oil.
The Songliao Basin was a primarily freshwater lake. The water level and salinity increased during the sedimentation of the source rock. Salinity stratification occurred leading to sulfate reducing activity caused by the increase in sulfates. The lake water dissolved the oxygen so much that living species could not be supported. This resulted in an accumulation of organic matter followed by the formation of large source rocks. The most abundant source rock in the Songliao Basin is mudstones rich in organic matter. Two secondary source rocks are black shale and oil shale.
Oil and gas released from the source rocks and migrated through the sandstone beds and structural fractures to enter the traps and accumulate in the reservoirs.
The Songliao Basin is trapped by anticlinal and nose-shaped folds, fault barriers, and lithofacies changes. These structural traps were created by late Cretaceous and early Tertiary compressional tectonic movement. These structures paired with pinchouts of nearshore lacustrine and fluvial sandstone created the traps in the Songliao Basin's petroleum system. Future exploration will likely be focused in the anticlinal noses as most drilling has occurred in anticlinal domes.
The reservoir rocks of the Songliao Basin are fluvial and deltaic sandstone consisting of quartz, feldspar, and detrital clastics. The highest producing pay zones of the basin are the Shaertu, Putaohua, and Gaotaizi reservoirs located in the Daqing Oil Field. Intergranular porosity is the main porosity type. As the shale content increases moving south porosity and permeability of the reservoir sandstone becomes poorer.
Most seal rocks in the petroleum system are source rocks. Black shale and mudstone serve as seals for oil and gas.
Geologic Risks and Uncertainties
There are a lot of uncertainties about the Songliao Basin. Detailed stratigraphic information and data on exploratory drilling are not available. Petroleum recovery and potential are simply estimates based on the limited information that is available. Due to the political system in China, businesses, land, etc. are controlled by the state. Chinese media is one of the most heavily controlled in the world. There are more than 60 regulations that limit access to the internet and control what does appear. Until 2020 China limited exploration and production to the Chinese state energy giants. In 2020, China began allowing foreign oil and gas companies to join upstream and midstream production. However, this will likely not excite global companies, because the Songliao basin has an average decline rate of 2.9% per year and the remaining recoverable hydrocarbons are depleted.
- Aizhu, Chen, and Muyu Xu. “China Opens up Oil and Gas Exploration, Production for Foreign, Domestic Firms.” Reuters, Thomson Reuters, 9 Jan. 2020, https://www.reuters.com/article/us-china-oil-mining/china-opens-up-oil-and-gas-exploration-production-for-foreign-domestic-firms-idUSKBN1Z806Q.
- Daqing Oil Province - CNPC. https://www.cnpc.com.cn/en/operatediol/201405/f96f221bb538428f9b1b7f4869c8f576.shtml.
- Energy . This Paper Citation for the ... - Diva-Portal.org. http://www.diva-portal.org/smash/get/diva2:317938/FULLTEXT02.
- Liu, Yuchen, et al. “Modeling of Tectonic-Thermal Evolution of Cretaceous Qingshankou Shale in the Changling Sag, Southern Songliao Basin, NE China.” Frontiers, Frontiers, 1 Jan. 1AD, https://www.frontiersin.org/articles/10.3389/feart.2021.694906/full.
- Petroleum Geology of the Songliao Basin, Northeast ... - USGS. https://pubs.usgs.gov/of/1986/0502/report.pdf.
- Qingshankou-Putaohua/Shaertu and Jurassic Coal ... - USGS. https://pubs.usgs.gov/bul/b2203-a/B2203-ALayout.pdf.
- “Songliao Basin.” China National Petroleum Corporation, PetroChina Information Technology Service Center Beijing, https://www.cnpc.com.cn/cnpc/index.shtml.
- Xu, Zhihe, et al. “The Cretaceous Stratigraphy, Songliao Basin, Northeast China: Constrains from Drillings and Geophysics.” De Gruyter, De Gruyter Open Access, 1 Jan. 2020, https://www.degruyter.com/document/doi/10.1515/geo-2020-0188/html?lang=en#j_geo-2020-0188_fig_002_w2aab3b7e2233b1b6b1ab1b1b3Aa.