Abstract:

Based on the interpretation of 15s deeper seismic profiles and the anatomy of typical CO₂ gas reservoirs, the distribution law of CO₂ gas reservoirs and its controlling factors have been deeply analyzed in the Songliao basin. Vertically, CO₂ is mainly rich in volcanic rocks of the Yingcheng Formation, and sandstone reservoirs in 3th and 4th Members of Quantou Formation. The beaded distribution feature of CO₂ is mainly dominated by lystric basement faults which are in direct contact with deep thermal fluid: heat-flow diapirs and intrusions, and are depression-controlling and volcanic vent-controlling. Meanwhile, outlet points of CO₂ are controlled by strike infection-points, endpoints and overlap zones of these faults. And CO₂ mainly comes from the deep thermal fluid. The activity of basement faults connected with thermal fluid led to the basin filling by mantle-derived magma, at the same time, the carried CO₂ was released into volcanic rocks erupted earlier and then developed into volcanic CO₂ gas reservoirs of Yingcheng Formation. Considering that faults controlling gas pool are usually basement faults which were active during fault-depression phase and the Late Quantou Formation to the Early Qingshankou Formation, it was speculated that CO₂ reservoirs of Yingcheng Formation were mainly formed between the Late Quantou Formation and the Early Qingshankou Formation. In Songliao basin, the stronge tectonic inversion occurred in the Late Mingshui Formation, and during the declining of compressive force from the SSE to the NNW, the reactivation of basement faults formed positive inversion faults; released from thermal fluid diapirs, CO₂  was migrated upward and then accumulated in inversion structural belts; as the development of fault-style inversion tectonics in the southern part is better than the northern part, and the western is better than the eastern part, CO₂ is richer in the south than in the north, richer in the west than in the east in Songliao basin.

Key words: Songliao basin, carbon dioxide, gas reservoir, distribution law, basement fault, thermal fluid, inversion tectonics