The High-resolution Sequence Stratigraphy And Depositional System Of Dongying Formation In Northern Liaozhong Depression

Northern Liaozhong depression is located in the middle-northern of Liaodongwan basin. Dongying formation is very thick, one of the main interval interest. Due to high exploration cost, the degree of exploration of interested region is unbalanced. Therefore, to study the sedimentary facies distribution of Dongying formation is significant to future exploration. Based on the theory of sequence stratigraphy, this thesis studies the paleo-lake feature in Oligocene Epoch, constructs isochronic strata frame of Dongying formation, and analyzes the of sedimentary faces distributing characteristics of different stratum, and points out favorable exploration direction of different district according to the condition and rule of petroleum accumulation.On the ground of the identification of different hierarchy sequence interface, we subdivide the sequence of the Dongying formation in northern Liaozhong depression. We divide Dongying formation into three 3rd-order sequence and six 4th-order sequence. In the same time, we first divide 4th-order sequence of the Dongying formation in northern Liaozhong depression using regression surface of seismic profile as sequence interface. Through comparing the sequences of key wells and seismic profile, we build sequence strata frame.Utilizing the off-shore onlap change on seismic profile and different palynologic fossil statistics, we study paleo-lake feature in Oligocene Epoch. We find that there are four large lake-level cycle in Oligocene Epoch and the last two cycle were in Dongying stage. Seven obvious climate cycle are found in Dongying stage. Dongying early tectonic subsidence rate is large, but tectonic subsidence rate became small at later stage. Analyzing the relationship between paleo-lake characteristics and every sequence, we obtained that tectonic subsidence can control large scale lake-level change, and that climate cycle can control small scale and high frequency lake-level change. The lake-level change is the most direct reason to form sequency.Using the combination method of core face, log face and seismic face, we recognize that the main facies types of Dongying formation are delta facies, turbidite fan facies and lake facies, and clear up sedimentary faces distribution characteristics. The distribution characteristics of sedimentary faces are controlled by tectonic movement, lake-level change, sedimentary supply and palaeogeomorphology etc.According to different tectonic location, we divide the study area into six different district, analyze petroleum accumulation condition, and identify main accumulation factors. We put forward range of exploration profitability.