Application of Sequence Stratigraphy to Subtle Oil‐Gas Reservoir Exploration: Take Example of the Third Member Shahejie Formation Dongpu Depression

high mature stage and subtle reservoirs exploration has become a major target.Finding out the distribution of subtle reservoir is extremely important. Sequence stratigraphy take research from causes perspect provide an effective method for analyzing subtle reservoirs distribution. By recogniting different scale sequences、 system tracks, hydrocarbon and the sedimentary bodies of system becomes established in the evolution of time and spatial configuration, making the prediction of subtle and gas pool more effective. This study takes Dongpu depression as an integrated system and is carried out by the comprehensive research of sequence stratigraphy and sedimentary system using the method of sequence stratigraphy to find out subtle reservoir by exploring the space distribution of various types of sand bodies. At the same time.the key areas of Dongpu depression will be analyzed by high resolution sequence stratigraphy to know the internal relationship between source sequence and reservoirs and to forecast favorable distribution of subtle reservoirs. The research of subtle reservoir in Dongpu depression by sequence stratigraphy, usually start from seismic sequence interpretation. Seismic interpretation and well logging interpretation would be linked by synthetic seismic record to divide the sedimentary sequence and system tract. Then sequence stratigraphic framework would be build by recognizing the quasi sequence, quasi sequence group and intensive period in combination with biostratigraphic data and isotope age data. Lately, inspect and complete the result of seismic and log analysis by outcrop and core data to carry out the fine comparison of wellbore formation and the analysis of sedimentary facies in sequence stratigraphic framework. Combining with reservoir property and the plane distribution characteristics of sand body, the effective range of subtle trap and prospective area would be predicted. Lastly, point out the favorable blocks and goals by analyzing the forming conditions of hydrocarbon accumulation and accumulation pattern and exploring the relationship between sequence stratigraphy and subtle trap. 12 seismic section including 7 cross section and 5 longitudinal section have been confirmed to carry out the study of sequence stratigraphy. Palaeogene in Dongpu depression has been divided into 3 secondary sequence and 9 tertiary sequence by the recognition of sequential interface and the calibration of logging curve and 2D and 3D seismic data.Besides. Es3 in Dongpu depression is devided into 3 tertiary sequence and 9 system domain according to well-logging data and 15 parasequences are recognized in system domain by parasequence superposition pattern. Then sequence stratigraphic framework of the whole region and Es3 is build. Finally, forecast the subtle reservoir by the research of depositional facies and microfacies and the analysis of the internal relationship between source sequence and reservoirs, the distribution of sand body and the characteristics of faults. The study points out the main type of Dongpu depression subtle reservoir is fault-cutting type, slope, sublacustrine fan lithologic and gypsum closed reservoir. System tract in northern region of Dongpu depression develops well ;while system tract in southern region only develops HST and lake transgression system but lacks LST and source rocks, so it is bad for the development of subtle reservoir.West Slope is favorable areas of subtle reservoir because of the development of lowstand sandbody and mainly develops slope belt lithologic traps and faults cutting reservoirs. Central uplift belt develops beach bar and delta of LST. Salt sand interbeded with terrestrial sandstone and mudstone in a way of finger crossed. It mainly develops gypsum closed reservoirs and faults cutting reservoirs. Lanliao fault controls sedimentation strongly. Fall plate has obvious sedimentary slope break and up-throw side develops lowstand sandbody. The structural-lithologic reservoir often develops in the cutting zone of Lanliao fault and LST sandbody. JI Youliang ZHOU Sheng and CHENG Tongran, 2015. Application of Sequence Stratigraphy to Subtle Oil-Gas Reservoir Exploration: Take Example of the Third Member Shahejie Formation Dongpu Depression. Acta Geologica Sinica (English Edition), 89(supp.): 395.