Study On The Sequence Stratigraphy And Sedimentary Systems Of Es₃～Es₄　of Baxian Drepression

In order to explore the lithologic or stratigraphic reservoirs in mid-depth formations of Baxian Depression, sequence stratigraphy and depositional system of the third member of Shahejie Formation (Es3) to the fourth member of Shahejie Formation (ES4) which is the target formation of this research were discussed. This study will be helpful for increase in oil reserve and production. Under the guidance of classic sequence stratigraphy, high-resolution sequence stratigraphy and sedimentology, the isochronal stratigraphic framework of Es3to Es4is established with the help of relevant method and techniques. Depositional facies and depositional systems were studied and discussed in isochronal frame of sequence stratigraphy. It will lay the foundation for oil and gas exploration in the future.The sequence stratigraphic division was done systematically on the premise that a huge mass of data of core, well drilling, well logging and seismic were studied. Es4is one2nd order sequence which can be subdivided into two3rd order sequences, including sequence1and sequence2. ES3is the other one2nd order sequence, and which can be divided into three3rd order sequences, sequence3, sequence4and sequence5.There are three systems tract in every one3rd order sequence which are low stand system tract, transgressive system tract as well as high stand system tract. Finally, distributional features of strata within the sequence stratigraphic framework and the controlling factors of stratigraphical distribution were analyzed and summarized.According to the observation and analyses of all sorts of facies marks, Es3and Es4mainly contain four types of sedimentary facies which include braided river delta facies, fan-delta facies, lacustrine and the nearshore subaqueous fan. Further, sedimentary facies were divided into12subfacies and29microfacies. There are many provenances from different directions, such as the east, the north-west, west, south east and south-west, Wenan slope in the north-west and Niutuozhen salient in the east are two main provenances. On thebasis of single phase and section phase, the isopach of ratio of sandstone and formation wasconsidered as a basic gist to finish the plane graph of sedimentary facies, meanwhile, seismicattributes, palaeogeomorphology and previous studies in this field are referred.There are fiveplane graphs of sedimentary facies from sequence1to sequence5, and there are nine planegraphs of sedimentary facies of system tract within sequence3to sequence5. Finally, thecharacter of the distribution of plane and the evolutive law of different plane graphs ofsedimentary facies were discussed. Fan-delta facies is distributed mainly in sequence1andsequence2, braided river delta facies is distributed mainly in sequence3, sequence4andsequence5, lacustrine is developed in every sequence, and the nearshore subaqueous fan isdistributed mainly in sequence3and sequence4. The distribution of favorable sand body inthe study area is forecasted at last.