The Impact of Accumulation Condition of CO2 on Authigenic Minerals of Paleogene Clastic Reservoir at Actic Area, Qin Nan Sag

Abstract

In the paper, the accumulation condition of CO₂, and its impact on authigenic minerals of clastic reservoir at the actic area of Qin Nan Sag were studied. The elevated δ13C CO₂, R/Ra values and 40Ar/36Ar values show that CO₂ was mantle derived. CO₂-bearing inclusions were associated with hydrocarbon inclusions, and CO₂-bearing inclusions included hydrocarbon components, showing migration and filling of CO₂ and hydrocarbon were at the same stage. Basin modeling and homogenization temperature of the inclusions indicated that the time of hydrocarbon and CO₂ accumulation was mainly less than 3 Ma, with the temperature over 100 degrees centigrade. The above accumulation condition produced remarkable influence on authigenic minerals. The late-filling CO₂ led to intense dissolution of feldspar and carbonate cements, showing as high content of intragranular dissolution pores and high proportion of intergranular primary pores, which mostly were contributed by carbonate cements dissolution. Acidic environment inhibited illite growth, and promoted the dissolution of feldspar and the formation of authigenic kaolinite, thereby, the content of kaolinite, which can exceed 70%, is much higher than that at the similar stratum. In addition, the late accumulation of CO₂ and hydrocarbon, the long-term acidic reservoir environment and the high temperature resulted in weak cementation of dawsonite, as well as ankerite, which is different from most CO₂-bearing reservoirs which are characterized by intense dawsonite and ankerite cementation in eastern basins of China. Dissolution of feldspar and carbonate cements, inhibition of illite growth, the high content of authigenic kaolinite and low content of dawsonite and ankerite, played a decisive role on improving reservoir quality.

AAPG Datapages/Search and Discovery Article #90217 © 2015 International Conference & Exhibition, Melbourne, Australia, September 13-16, 2015