Dawsonite occurrences related to the age and origin of CO 2 influx in sandstone reservoirs: A case study in the S ongliao B asin, NE C hina

Dawsonite is often associated with CO 2 ‐rich gas reservoirs, and it is regarded as a “trace mineral” for recording migration and accumulation of CO 2 . Following accepted petrological, mineralogical, and geochemical principles, we used several methods (described herein) to study the Cretaceous dawsonite‐bearing sandstone reservoirs in the Songliao Basin, China. We used the ideas of “sequencing” and “timing” to verify the influx stages of CO 2 and hydrocarbons, dividing their influx sequence pattern and building a CO 2 ‐influx timeframe. First, we determined the stable isotopic ratios of dawsonite and CO 2 in gas and oil reservoirs, and found that the CO 2 in? dawsonite is of a mantle‐derived magma origin. Second, we differentiated an early/late‐stage oil and gas influx and a midmantle source influx through the study of diagenetic paragenetic sequences, formation water, and fluid inclusions in the dawsonite‐bearing sandstones. Combining burial/thermal‐history curves and illite K‐Ar dates from the study area, we determined that the early‐stage oil and gas influx, late oil and gas influx, and medium CO 2 influx occurred at 85–58.8 Ma, 41–20 Ma, and 58.8–41 Ma (Paleocene and Eocene), respectively. Finally, we observed a coupling relationship between CO 2 influx and Shuangliao volcanic activities and material compositions, as constrained by volcanic activity history in the basin since the Late Cretaceous.