High Resolution Sequence Stratigraphy Analysis And Subtle Reservoir Prediction Of Lower Tertiary In Changdi Area, Shengli Oilfield

Changdi area lies in the northeast of Zhanhua depression of Jiyang superdepression. It is a NNE-strike low buried-hill draping structural belt on the Mesozoic buried hill at the last phase of Yanshan movement. Aiming at subtle reservoir, this subject applies the theory and technology of high resolution sequence stratigraphy to solve the problems in research of deposition and reservoir of lower Tertiary. By integrative analysis of the cores, drilling and three-dimension seismic interpretation data, the Lower Tertiary of the study area is divided into two cycles of structural base level compsed by Es4-Es3 and Es2-Esl-Ed respectively. Es3-Ed comprises of three long term base-level cycles(secondary sequences ) and eight middle term base-level cycles (tertiary sequences ). The three long term base-level cycles are approximately equivalent to Es3,Esl and Ed, therein Es3 is composed of three middle term base-level cycles, Esl one cycle; and Ed four cycles. Based on the stratigraphic correlation of different order base-level, the sequence stratigraphic framework is built in Changdi area, which can meet the needs of subtle reservoir prediction.Based on middle-term cycles, the paper discussed the distribution and evolution of the depositional facies in study area. Five types of depositional facies in the Lower Tertiary are recognized. They are offshore subaqueous fan, beach sandbar, fan delta , turbidite fan and fluvial facies. The regularly vertical evolution of depositional facies has close relationship with the regional structure evolution and lake surfacechanges. During Es3 period, offshore subaqueous fan mainly developed in the west and south of the area. During Esl, the development of dipositonal facies experienced bioclastic sandbar, beach bar and semi-deep lake deposits was developing. During Ed, there was a progressive model from pre-fan delta, fan delta to fan delta plain and braided river at last.Being enclosed by hydrocarbon-generating subdepressions, Changdi buried-hill draping structural belt is of excellent conditions of reservoir. The reservoirs found in the Lower Tertiary are mainly structural and stratigraphic type. The main oil-bearing layer is Shahejie Formation. The middle fan sand in Es3, the bioclastic beach bar at the bottom of Esl, the river sand in Ed formed very best reservoir. In the area, oil and gas are enriched in "two side and one bulge and one slope". The rich layer and buried depth have an ascending tendency from south to north. Vertically, there are many thick oil-bearing beds with different enrichment. The enrichment of oil and gas is controlled by many factors including structural background, faults, lithology, stratigraphic unconformity, regional seal bed and so on. The reservoir-generating system in this area can be divided into two systems; the first is in the central west, the second east. Each of them has different sources, different fill factors and conceal conditions. Consequently, correspondent reservoir-generating models have been established.To guide the practice of production, the research analyzed the potential in oil and gas exploration, pointed out the main explorative directions, evaluated favorable areas and beds, which have made important explorative breakthroughs in these areas covering Zhuang 47, Zhuang 8-18 and Zhuang l-x41 blocks. At the same time, the study suggests eight favorable targets for next exploration, specifies the location of more than 10 prospective and developing wells with predicted petroleum geologic reserves 12600000 tons.