Research On Seismic Sedimentology Characteristics Of Third Section Of Shahejie Formation In Boxing Subsag

In Boxing Subsag, located in the Southwest of Dongying Depression and rich in oil and gas, the third member of Shahejie formation is the main oil exploitation reservoir. However, with the rise in exploitation level and the higher difficulty to exploit the main oil reservoir, currently exploration target in the study area has been diverted from structural hydrocarbon to petroleum reservoirs including lithologic oil-gas reservoir and oil-gas stratigraphic deposits. What is worth mentioning is that the further oil-gas exploitation in this area has been restricted due to lack of sufficient research in superimposed reservoir, sedimentary facies and evolution rules. Targeting at studying Boxing Subsag Es3 sediment system and based on the basic theories and methodology in Sedimentology, Logging Geology, Seismic Sedimentology, Geostatistics and Sequence Stratigraphy, this paper does research in the types of sedimentary facies, logging characteristics, seismic characteristics and sedimentary facies distribution and sedimentary models and controlling factors, through core observation and statistics, analysis of single well facies, division of sequence strata, forward modeling and seismic sedimentology. The conclusions are as follow.Boxing Subsag Es3 are featured by several types of sediments including near-bank submerged alluvial fan, deep water turbidite fan, slip turbidite fan, braided-river delta, semi-deep and deep lacustrine and shallow lake lacustrine. From Es3 early period to Es3 late period, the waters have gradually become shallower and the sediments have been diverted from the deep-water ones to shallow-water ones.According to sequence stratigraphy, Boxing Subsag Es3 is divided into 4 long-term cycles and 8 mid-term cycles to construct refined sequence stratigraphic framework. The study shows that the depocenter is keeping changing in the study area in Es3 sediment period, generally showing the movement from the central section to the northern and northeastern section, figuring out the vertical evolution rule of sedimentary facies and superimposed relationship.The regional structural factor, palaeoclimate and ancient landform controlled sedimentary distribution and evolution rules in Es3 sedimentary study area. In the early time, the water was deep so that near-bank submerged alluvial fan was cultivated around the northern slope of Gaoqing saliment, and in the southwestern part, a strip-shaped braided-river delta was formed. At that time, braided-river delta just covered a small area, which overlapped with near-bank submerged alluvial fan whose front gradually developed into slip turbidite fan. In the middle time, braided-river delta constantly spread towards the study area and the area of near-bank submerged alluvial fan correspondingly declined. In the meantime, developed area of deep water turbidite fan extended towards the north and northeast. With the rise in the area of near-bank submerged alluvial fan, the developed area of semi-deep and deep lake facies shrank and the braided-river delta from the southeastern provenance has passed over the central uplift zone into the sedimentary part located in the western part of Boxing Subsag. In the late period, the braided-river delta from the southeastern and southern provenance overlapped. Simultaneously, in the northwestern part of study area, the deep water turbidite fan was developing but near-bank submerged alluvial fan stopped growing.The study can provide a practical guide for the oil-gas exploitation in Boxing Subsag with a referential meaning about the sedimentary research and oil exploitation in other regions.