Abstract:

The petrological records of mantle-magmatic CO₂ leakage, which occurred in Honggang anticline, southern Songliao basin, can be revealed by studing on spatial distribution and the occurrence of dawsonite cements and also the characteristics of fluid inclusions in dawsonite-bearing sandstones. In Honggang anticline, dawsonite is widespread in Qingshankou Formation, in Quangtou Formation and Yaojia Formation come second. Most of the dawsonite-bearing sandstones do not contain CO₂, while some of the dawsonite-bearing layers contain oil. There is a weak positive association between the content of dawsonite cements and bitumen, which distribute in both oil and dry layers. Two different diagenetic associations, belong to pre-injection and post-injection of CO₂, respectively, can be distinguished in dawsonite-bearing sandstones. The first phase hydrocarbon inclusions which are mainly liquid hydrocarbon inclusions, can be found in the preinjection association, while in the post-injection association, the second phase hydrocarbon inclusions develop, which are liquid-gas phases inclusions by primary. The CO₂ leakage on a large-scale can be recorded by the existences of dawsonite cements occurrence  on non-CO₂ gas reservoir, and the bitumen. Among them, the bitumen can be the result of separating of the light-heavy components which induced by the decreased of the strata pressure when the CO₂ leaked. As a consequence, the channel for CO₂ leakage is Honggang fault, while the leakage time should be early than the second section of Mingshui Formation.

Key words: southern Songliao basin, Honggang anticline, CO₂ leakage, dawsonite, bitumen, mineralogy