Research On Depositional System And Favorable Sandstone Prediction Of The Upper Of The Third Member Of The Shahejie Formation In The North Of Dongpu Depression

Dongpu depression is one of prolific oil-gas salt lake basin in the southwest of Bohai Bay basin, China. Though at the high-maturity exploration phase, Dongpu depression still has large potential for resource exploration. And the remaining oil and gas mainly existed in the lithologic hydrocarbon reservoir, the upper of the third member of Shahejie Formation is rich in lithology reservoir with commercially value in the northern part of depression.There are still some problems which prevent the further exploration of lithologic hydrocarbon reservoir. For example, there is lacking of a systematic regional study of sequence stratigraphy and the distribution of depositional system. Sand body and deposition system controlling mechanism of different combinations in fault system, especially of different styles of contemporaneous fault complex are unclear, meanwhile the distribution between the salt and thin sand layer is unknown.In order to resolve the mentioned problems, combined with regional geological setting and the history of Tectonic evolution, the thesis studied the sequence stratigraphic division, the distribution of depositional systems and favorable sand body, lithologic traps prediction in the upper of the third member of Shahejie Formation based on core, logging, seismic, geochemical and practical means of production data in the guide of sequence stratigraphy and reservoir sedimentology.The third member of the Shahejie Formation was divided into a long-term base-level cycle and two medium-term base-level cycles using cores, well logging and seismic data. The sequence stratigraphic framework was set up, meanwhile the development model of sequence stratigraphy. in three different sub-region was also studied.There were many source systems composed of northern, eastern, western and southern parts under a comprehensive analysis of trace elements, conglomerate distribution, heavy mineral composition and tectonic setting in the third member of Shahejie Formation, the central uplift was a multi-source convergence zone.On the base of fine observation of cores of 29 drilled wells, well logging and seismic data, the study showed that there were fan delta depositional system, braided river delta depositional system, delta depositional system, lake depositional system, storm depostional system and salt lake deposition system in the third member of Shahejie Formation, Dongpu Depression.Generally, fan delta was deposited in the east of Dongpu depression. While braided river delta in west and normal delta in eastern limb of the center uplift zone and Liuzhuang-Qiaokou area. Many provenances were convergent in the center uplift zone. The lacustrine deposition mainly formed in each sag and turbidite fan in deep water mainly formed in the downthrown block of the trunk fault. The sand body was classified and the study showed that distributary channel sandbody and mouth bar in various types of delta front, turbidite sand and beach sand were favorable.According to the tectonic evolution setting, the characteristics of fault combinations, cores, well logging, seismic data and geochemical data, there were many factors that controlled the sand body’s formation and distribution, that was the structure belt types, transfer zone, Paleo-geomorphic, paleo-climate, paleo-water depth and depositional facies types controlled various types of sand body’formation and distribution.From the comprehensive analysis, we considered that the downthrow sides of the 1first Wenxi fault with the second Wenxi fault in southern Wenliu area and around the Pu-Wei sag belt where the delta front was developed, the downthrow side of Changyuan fault in Xingzhuan area where the braided river delta front sand body and turbidity sand body were developed and the downthrow side of Lanlao fault where fan delta front were the favorable zones for favorable sand body. The east sag belt, the west sag belt, the two limbs of the center uplift zone and around the Pu-Wei sag belt were the favorable zones where favorable sand body and the lithologic trap developed well.