Lithofacies Types、Vertical Profile Features and Reservoir Geological Models of Braided Deltaic Sandbodies in Faulted Lake Basin──The Observation on Deposition of Modern Deltas in Daihai Lake, Inner Mongolia

Daihai lake is located in central inner Mongolia and is a modern faulted basin of terrestrial factes.This modern basin is well comparative with the faulted basin of Meozoic and Cenozoic era in the eastern part of China.Deltas is often important infilling sandbodies in faulted basin of terrestrial factes.Therefore, this peper is mainly emphasized on the analysis and Study on the depeitional processes and the favorable reservior sandbodies on different sedimentary scales of two delays in the direction of short axis in Daihai lake basin.One delta, called Yuanzigou delay, is located in thenorthern steep slope of the lake basin, while another one, Bulianghe detla, in the sourthen gentle slope of the lake basin.Both are fluvial-dominated braided deltuic system with coarse deceits.Provenances of two delays are varying form eath other.Yuanzigou river is a short distance ephemeral braided stream and Bulianghe river a long distance ephemeral braided stream.Through element analysis of lithology, grain size, sedimentary structures, thickness of sandbeds, clastic components and color etc., the description and interpretation of the depositional features of two delays are provided.12 lithofacies or genetic factes form two delays have been defined.Their mutual assemblages in verprofile make up different type of lithofaices assemblages or vertical sedimentary sequences, each corresponding to a cerium depeitional process and subenvironment.Therefore, nine sedimentury sequences have been recognized which reflect depositztional features in different perts of two btaided delays.The four sedimentary sub environments or sedimentary factes zones of each delay were distinguished by depeitional features,that is, (1) upper delta plain, (2) lower delta plain, (3) delta front slope and (4) pre-delta.The two delay have been modelled.There are both similarities and differences of depositional features among Yuanzigen delta and Bulianghe delay.Moreever depositional precesses and features between fan delta and braided delta have been discussed in this paper.There exists apparent control of depeitional processes and sedimentary factes zones on the reservoir of two delays.The deltas of the steep and gentle slope in the direction of short axis in the faulted barn have some different features of sedimentary and geometry shape of sandbodies.Finally,through sedimentary sequences, porosity zones and sandbodies geometry of two delays, the sketch model of two delays,sandbody at 3-D sauce extension in each sedimentary zones have been set up.