Sedimentological characteristics and controlling factors on fluvial styles of the Guantao Formation, Kongdian Oilfield, China

Abstract

The Kongdian Oilfield is located in eastern China. More than 30 years have passed since the oil field was discovered in 1979. The majority of the oil is produced from reservoirs of the Guantao Formation (Miocene). A detailed description and interpretation of core, well-logging and 3-D seismic stratal slices data was carried out to analyze sedimentological characteristics of the Guantao Formation and two fluvial styles have been identified encompassing braided channel and meandering channel. Seven main facies associations were defined: (i) upward-fining channel, (ii) braided channel with mid-channel bar, (iii) meandering channel with point bar, (iv) levee, (v) floodplain, (vi) minor channel, (vii) swamp. Vertical changes in fluvial styles of the Guantao Formation were recognized by variations in preserved thickness, channels stacking pattern, regional paleoflow directions, and channel/floodplain ratios. The fluvial succession is 50–70 m thick in the lower Guantao Formation, composed of braided channels and high channel/floodplain ratio. The alluvial succession is 60 m in thickness in the upper Guantao Formation, the dominant fluvial styles change to meandering channels and channel/floodplain ratio reduces. The main factor that may have affected the fluvial style is the base-level changes. With the rise of the base level the fluvial style is believed to have changed from braided channels to meandering channels.