Abstract:

The Yushulin Oilfield, located in the Sanzhao Depression of the Songliao Basin, developed large shallow-water deltas at
the time when the Fuyu Reservoir deposited within the Member 4 of the Lower Cretaceous Quantou Formation. Based on 12 well
cores and 2268 well loggings, by ways of single-well facies, logging facies, connecting-wells and plane sedimentary microfacies,
well-developed shallow deltas were recognized in the study area in which can be further subdivided into delta plain, internal front,
external front, predelta, and delta plain subfacies. Main sedimentary microfacies are plain distributary channel and internal front
subaqueous distributary channel. These two types of channelized sandstone bodies interlaced into a network. During the early
stage of the Member 3 of the Fuyu Reservoir, the studied area was dominated by shallow-water delta internal front subfacies which
was sourced from north only. Later, the delta prograded towards south, and the studied area changed into delta plain subfacies. At
the time of the third layer in the Member 3 of the Fuyu Reservoir, source from south appeared and intersected with the northern
source. This sedimentary condition continued to the latest stage of the first mewber of the Fuyu Reservoir FⅠ At the time of the
third layer of the Member 1, both the northern and southern deltas retrograded due to the sudden rise of lake level. In the middle
part of the studied area, delta internal front, external front, and predelta were developed in proper order.

Key words: Yushulin Oilfield, Fuyu Reservoir, shallow-water delta, sedimentary characteristics, Lower Cretaceous