Establishment Of Braided River Delta Mouth Bar Prototype Model Based On Physical Simulation

At the later stage of development in eastern China, Old oil fields generally shows high water cut, high oil production rate, high degree of recovery, low yield, low level, low formation pressure, and additional the complex geological structure, For further guidance on tapping the potential of remaining oil, to strengthen research on reservoir architecture, large lacustrine physical simulation provides a powerful complement to the study of reservoir architecture.This research selected8stratum of ES2in block No.2of Shegntuo Oilfield.Shengtuo oilfield is reverse drag anticlinal structure oilfield,locating in northern Chennan-Shengbei zone of the Dongying recession in Jiyang depression, is controlled by Shengbei fault,a branch fault of the nearly EW strike Chennan listric normal fault.8stratum of ES2in block No.2of Shegntuo Oilfield belongs to Deepwater Braided River Delta front mouth bar deposits, sediment source come from Qingtuozi bump. Selected64square kilometers area in ES2-in block No.2of Shegntuo Oilfield as the research target,we make physical simulation about Formation, evolution and internal architectural structure of Braided River Delta, focusing on hydrodynamic condition of delta front mouth bar formation, single mouth bar size, shape, internal architectural structure and composite mouth bar stacking patterns, providing the geological basis for tapping the potential of remaining oil in Shengtuo oilfield.Through the Shengtuo oilfield Braided River Delta physical Simulation experiment studying on mouth bar architectural structure, we obtain the following conclusions:1) Delta front mouth bar formation is controlled by the bottom slope, sediment supplyment, flow rate, substrata subsidence, relative lake-level fluctuation;2) Bottom slope is steep, the water depth changes greater, and the mouth bar sand body thickness change greater. Front delta mud in the overlying mouth bar sand body under the action of gravity will be compressed or stretched. If the bottom slope steep increases further, Influenced by gravity and water level decline, mouth bar will be slumped,and not easy to preserve.3) Discharge rate difference will be influenced mouth bar development rate and scale. Under the condition of the dry season or distributary channel is more in the middle water level, mouth bar development speed is slow and mouth bar shows small scale. Flood period or flowing water relatively concentrated in the middle water level, mouth bar growth rate is high, and the development of mouth bar are also larger scale;4) substrate deposition increases the lake basin accommodation space, Delta retrogradation occurs, increase the vertical extent of stacked mouth bar. Base remains the same vertical sedimentary river is restricted, vertical accretion and lateral accretion.5) When the lake level is relatively stable, the Delta all directions developmental rate roughly equal and the longitudinal development fastest. Mouth bar thickness variation is small. The lake level rose,delta mouth bar retrogradation, covering the pre-mouth bar above, the genesis of a single mouth bar thinly thickness. The lake level decline will cause the bottom of the deposition shaped slope gradient amplify, river erosion cutting the early formation of the mouth bar, and sand material to be cut off as the newly generated source material of the mouth bar;6) summarizes the four modes of the estuary swing, estuary not swing,estuary swing small amplitude-way swing, the slight swing around and substantial one-way swing, each swing mode corresponds to a mouth bar development mode. The mold common feature of these four developmental and mouth bar extends forward some distance, due to the loss of slope advantage, mouth bar formed by the estuary lateral swing, swing is a special case, that river diversion force the mouth bar termination of development.7) According to the river configuration, the delta front mouth bar sedimentary sand body is divided into three-tier interface, four-tier interface and five-tier interface. The three-tier interface is mouth bar accretion sand body; the four-tier interface is single mouth bar sand body, and the top interface is for estuary dam crest and argillaceous sediment. Because simulation argillaceous sediments is thin, so top interface and overlying sedimentary sand body coincide with each other and bottom interface is for the lower prodelta argillaceous sediment..The five-tier interface is for estuary-dam complex, and the top interface is wide distribution of argillaceous sediments,but under sedimentary simulation experiment, it’s top interface is the erosion surface of river channel for dam crest;the bottom interface is the interface of widely distributed predelta mud from each deposit and mouth bar sand body.8) To sum up the contiguous mechanism of delta front mouth bar sand body including mouth bar formed by several rivers at the same period,as well as mouth bar formed by single river at different period.9) According to the actual area of Es28of Block Sheng2, the designed simulation experiment plane scale is1:1000, vertical scale is1:200.Simulation results show estuary dam is between450m and2100m long, the average length is1270m; and it is between300m and150m wide, the average width is760m with good correlation. Mouth dam thickness spreads across9.2m to16m.