Petrogenesis And Potential Capacity Of CO₂Sequestration For The Yingcheng Formation Basalts From Xujiaweizi Fault Depression Of The Songliao Basin, North China

The Songliao Basin, situated in the Northeastern China, is the largest Mesozoic-Cenozoic petroleum-bearing basin of Eastern China. The Xujiaweizi (XJWZ) fault depression, located in the northern of the Songliao Basin, cover an area of4300km2, develops large amount of basalts and basaltic hydrocarbon reservoirs. In this paper, the distribution and petrographic charalcter of basalts from the Yingcheng formation were described together with mineralogy, whole rock geochemistry and isotopic composition of these basalts. Then, petrogenesis, mantle sources and tectonic settings for these basalts were discussed and suggested. The formation of the Na-rich character for these basalts and their indication for eruption environments were also be discussed in this paper. Additionally, we evaluate the feasibility of CO2sequestration in petroleum reservoirs of basaltic rocks, and estimate the CO2storage capacity of minerals and oil and gas reservoir of the basalts hydrocarbon reservoir.According to the mineralogy and geochemistry, these XJWZ basalts are mainly calc-alkaline volcanics. These basalts are characterized by enriched large ion lithophile elements and high field strength elements, strong fractionation between light and heavy rare earth elements, no negative Nb anomaly, that resemble to geochemical characters of ocean island basalts. With contract to Mesozoic tectonic settings of the Songliao Basin, it is suggested that basalts from Yingcheng formation were derived from relatively lower percent partial melting of lithosphere under back arc rifting environments. In addition, basalts from the Yingcheng formation generally maintain albites. Albites in these basalts are mostly microcrystalline or irregular-shaped, and should precipitate with the replacement of labradorites. Thus, the Na-enrich character of these basalts might not be their original geochemical property, but the results of alteration by seawater under marine environments. Therefore, it confirmed that a widespread transgressive event were experienced in the northern Songliao Basin during the Early Cretaceous.The Yingcheng formation basalts of XJWZ act as perfect reservoirs for hydrocarbon, because of their great thickness, wide distribution and fine reservior properties. Meanwhile, reservoir spaces and minerals which easy to carbonatization are both favorable destination for CO2sequestration, the cap rocks of hydrocarbon can also prevent the emission of CO2, and the stability of hydrocarbon reservoir can guarantee the safety of CO2injection. Therefore, the basalt hydrocarbon reservoir could serve as an ideal target for CO2sequestration. Combined with the analysis of minerals, chemical composition and reservoir spaces, we preliminary evaluated that, the potential capacity of CO2sequestration of minerals is89.33×108tons, capacity of storing CO2supercritical fluid in this oil and gas reservoir is6.20×108tons, and the total capacity of CO2sequestration in the Yingcheng formation basalt hydrocarbon reservoir is about95.33.40×108tons.