Abstract:

Based on core observation, combined with 135 exploration wells data, various sedimentary microfacies signs were identified. All these showed that Fuyu reservoir mainly developed meandering river-shallow water delta depositional system in Shuangcheng area, Northern Songliao Basin, furtherly divided into 5 subfacies and 11 microfacies. With the guidance of high resolution sequence stratigraphy, using the technologies of rock-electric combination, well-seismic combination and so on, several sequence boundaries were identified. Fuyu reservoir can be divided into 2 long-term base level hemicycles and 7 middle-term base level cycles, and in this way, isochronous sequence stratigraphy framework has been established. Taking middle-term base level cycle as compilation unit, combined with the analysis of seismic attribute, lithofacies paleographic maps in different period were compiled and depositional model was established. Research show that Fuyu reservoir in study area mainly experienced two evolutionary stages: during the period of Q3-sq1—Q4-sq1, shallow delta plain gradually converted to meandering river; while during the period of Q4-sq2—Q4-sq3, meandering river depositional system converted to delta plain subfaceis and delta front subfacies. All these reflected a lake retreat-lake transgression depositional process during which the sedimentary water is firstly shallowing then gradually deepening. The results of above studies provide an important guidance for recent oil and gas exploration.

Key words: Shuangcheng area, Fuyu reservoir, stratigraphy framework, lithofacies paleographic map, depositional model