关键词: 扇三角洲, 地层层序, 沉积模式, 过程响应机制, 双河油田

Abstract:

Fan deltas in the 3rd member of Hetaoyuan Formation in Shuanghe oilfield have the characteristics of shelf-type fan deltas, where the strtigraphic sequences, as a whole, are developed in anticyclic sequences, but the single layer appear to be in positive rhythm. This kind of sequences are neither typical fluvial deposits, nor typical river mouth bar deposits. They are deposited as a result of axial efflux from river channel to lake basin under the condition of shelf-type fan delta with midly sloping lake floor. The energy and speed of axial efflux gradually decrease toward the axial direction and both sides, and the grain sizes of sediments decrease along with lowering of water flow energy, the deposits get thinner and evolve from subaquous distributary channel deposits into distributary mouth bar deposits. The deposits in the leading edge of mouth bar spread out and become sheet sand. In fact, the river mouth bar is a complex composed mainly of river mouth bar,and 6 microfacies, including core, lateral margin, margin,front edge,sheet sand and interbar. The bars get higher vertically and migrate laterally when the main stream line or location of channel migrate, resulting in plenty of sequence patterns.

Key words: fan delta, stratigraphic sequence, mode of deposition, process response mechanism, Shuanghe oilfield