The impact of sedimentation

diagenesis and tectonic activities upon reservoir quality in Putaohua oil layer of Daqingzijing area

southern Songliao Basin

was studied based on sequence stratigraphic theories through analyses of drilling and logging data

core and thin section observation

SEM images as well as lab testing results.The result shows that the sequence stratigraphic framework of Putaohua oil layer is mainly composed of a low stand system tract and a lake transgression tract

with the former containing some high-quality sandstone reservoirs in distributary channels and forks of the main stream and the latter with quality sandstone reservoirs in underwater distributary channels.Sedimentation constrained by the framework was found to control the vertical and horizontal distribution of sedimentary microfacies and the scales of sandbodies in these system tracts.Vertically

sandstone layers at the upper part of the low stand system tract are large in scale and good in connectivity

thus contain relatively high-quality reservoirs; and horizontally

reservoir properties of the main distributary channel sandstone and fork sandstone are better for oil and gas accumulation.Diagenesis and compaction were suggested to be the direct reason behind the low-permeability of Putaohua oil layer

while the sequence stratigraphic framework

which controlled an early diagenesis environment in both system tracts

was regarded to be a factor that strengthened to some extent the carbonate cementation of sandstone layers in the lake transgression system tract.The range and extent of dissolution there were thought to be determined by the properties of reservoirs

distribution of source rock-rooted faults and distance to these faults.Relatively high-quality reservoirs in the oil layer were controlled jointly by four factors

namely the sequence stratigraphic framework

sedimentation

diagenesis and tectonic activity

i.e. the main distributary channels at the central and upper part of the low stand system tract that were near to the source rock-rooted faults or bounded by the faults served as the major spots for high-quality reservoirs to take shape.