High-Resolotion Sequence Stratigraphy And Reservior Strata Prediction In The Boxing Sub-depression

Boxing sub-sag is one of main hydrocarbon gathering areas of Dongying sag. There are many kinds of hydrocarbon reservoirs, which have been found, such as structural, stratigraphical, lithological and complex reservoirs. After having been explored and developed for more than forty years, the degree of exploration is high. The new found reserves from structural reservoirs are becoming less and less, and on the other hand, those from lithological reservoirs are going up increasingly.During the sedimentary period of Es3, Boxing sub-sag was going down. The delta system was growing, whose substantial sources mainly came from Luxi uplift. And at that time, multi-period slump turbidite fans were formed in its front , where are the main hydracarbon distributing areas of lithological reservoirs in Boxing sub-sag.This paper focused on the analysis of sequence stratigraphy of the 3rd member of Shahejie formation, in the west of Boxing sub-sag, with the technologies of high-resolution sequence stratigraphy which reference to base level.Due to the lack of unconformities, a new word" turnaround surface" are proposed. Furthermore, the types of turnaround surface are listed and relations between turnaround surface and unconformities are explained. Five sequence boundaries and four flooding surfaces are recognized in the 3rd member of Shahejie formation. According to these surfaces, the member is divided into four long-term base level cycles. Moreover, eight medium-scale base level cycles are divided by recognizing the inner turnaround surfaces of the long-term base level cycles. High-resolution sequence stratigraphy framework is constructed according to correlations between wells and seismic profiles. And the characters of sequences are analyzed in the sequence framework.Three main sources systems are recognized. Gaoqing delta system is from Luxi uplift, which is a braided-river delta. Big turbidite fans are formed in the sub depression due to the slip of delta front sandbody. The source from Qingcheng uphill is less, which formed near-bank submerged alluvial fans. Later, the source from southeast delta entered into study area.There are three main types of sedimentary facies: braided-river delta, slip turbidite fan, near-bank submerged alluvial fan. The distribution and composition of sedimentary facies and the depositional systems are analyzed in the sequence framework, using units of medium-scale base level cycles. The distribution of reservoir sandbody is determined.Based on the analysis above, the high- resolution sequence stratigraphy models from braided river delta to turbidite fan are constructed. Braided river deltas and turbidite fans have the upgrading characters ; braided river deltas are distributed in slope areas and turbidite fans are more distributed in depression areas; braided river deltas are concentrated in the falling hemi-cycles of base level and turbidite fans are more concentrated in the rising hemi-cycles of base level. The Scales of turbidite fans are more related to lake flooding surfaces.After having analized the position of the discovered oil and gas in sequence stratigraphy, we draw a conclusion comprehensively, turbidite fan is the most favorable sandbody to lithologic exploration, and near-bank submerged alluvial fan and delta leading edge sandbody are the second. The favorable members are in the rising hemi-cycles of MSC5, MSC6, MSC7, MSC8. The favorable areas to lithologic traps are the depression areas under the slope break of south slope of Boxing sub-sagStudy on distribution discipline of reservoir sandbody shows that tectonic movements, depositional systems, paleotography and paleo-geomorphology, sandbody position are the main factors which control the distribution of reservoir sandbody. At the same time, "distribution of sandbody controlled by flooding surface" are proposed. A series of geology technologies for reservoir sandbody predication are summarized as technologies for reservoir sandbody predication according to characters of sequence boundary, sandbody position in the sequence framework, paleo-geomorphology and sandbody recognition on seismic profiles which are based on sequence stratigraphy. These technologies are based on sedimentary dynamics, so the accuracy of reservoir predication is enhanced.Seven favorable exploration targets are proposed and forecasted oil reserves of 6400>