Study on the Evidences for Episodic Expulsion of Overpressure-Heat Fluid Associated with the Formation of Gas Chimneys in Baiyun Depression of Deep-Water Area of Pearl River Mouth Basin, South Chian Sea
Department of Petroleum Geology and Gngineering, Faculty of Earth Resources, China University of Geoscience, Wuhan Hubei P.R. China; E-Mail: [email protected]
The gas chimneys which mainly originate from the main source rocks of Wenchang and Enping Formations widely exist at the Baiyun Depression of deep-water area of Pearl River Mouth Basin. The bright spots distributing at the top or on both sides of the gas chimneys have a positive relationship with the nature gas reservoirs and it is confirmed by the drilled wells in the north of the Baiyun Depression. The condensate oil and natural gas in the north of the Baiyun Depression mainly derive from the source rocks of Engpin Formation and the accessory source rocks are the mudstones of Wenchang Formation. The overpressured hot fluid activities associated with the formation of gas chimneys are evidenced by the data of vitrinite reflectance (Ro), smectite-illite mineral abnormal transformation and fluid inclusion homogenization temperature. The numerical modeling of formation pressure evolution presents that there are 3 episodic stages of overpressure releases which occurs at 40-37Ma, 33-31Ma and 16-0Ma due to the effects of the tectonic movements of the second phase of Zhuqiong movement, Nanhai movement and Dongsha movement. The hydrocarbon charging times are coincident with the third episodic stage of overpressure release during 16-0Ma. As results of overpressure releases, many faults are formed leading to hydrocarbon vertical migration and accumulation around the gas chimneys. All the geological evidences indicate that the gas chimneys are mainly developed with the overpressure releases from the Paleocene and Eocene formations with the organic-matter rich source rocks in Baiyun Depression.
AAPG Search and Discovery Article #90083 © 2008 AAPG Foundation Grants in Aid