Formating And Distributing Of The Gravel Body, And Conglomerating Of Oil And Gas In The Actic Region Of The Southern Biyang Depression

The Biyang Depression is a small-scale Mesozoic-Cenozoic faulted lacustrine basinabundant in hydrocarbon in the eastern China. After the exploration and production forthirty years and more, the exploration targets are transferred from structural reservoirsand lithological reservoirs in the favorable structural setting to subtle reservoirs. Thethird national resource evaluation indicates that among the residual 1.36×108t resourcein the Biyang Depression, 0.80 × 108t hydrocarbons deposit in the glutenites in the acticregion of the South Biyang Depression. Therefore, it is necessary to build up a set ofrolling exploration methods appropriate to prospecting the glutenites pools in thesouthern actic region.Taking the actic region of the southern Biyang Depression as the major study area,the theory and method of the high--resolution sequence stratigraphy was applied for thefirst time to establish the isochronous stratigraphic framework in the medium-termsedimentary cycle with the ascending and descending semi-cycles as the longitudinalstudy unit. The study suggests that the sedimentary responses of the ascending anddescending semi-cycles are mutually symmetrical, and moreover, the former controlsthe sandstone's retrogradation, while the latter dominates the sandstone's progradation.A research method synthesizing petrographic facies, log facies and seismicfacies was adopted to define the fan delta of abrupt slope type and turbiditesystem. From the source area to the center of lacustrine basin, the braidedchannel of plain subfacies takes on the lenticular configuration andspreads as a strip;the subaquatic distributary channel of the deltaic frontsubfacies, the mouth bar and the sand sheet appears the laminar structureand distributes as a plane;and the fluxoturbidite in the periphery of thecomparatively large deltaic front subfacies takes on a laminar structureand extends as a lobe.The analysis discovers that the tectonic movement and structure of thebasin's boundary faults are the determining factos to control the formationand distribution of the glutenites. The movement's intensity of theboundary faults prescribes the scale of the fan, and the location of thetransfer adjustment zone defines the pathway of the sediment supply of thefan, thus further influencing the characteristics of thepalaeogeomorphology and generating the sedimentary framework of "Largechannel control large fan, and small channel control small fan".The results of systematic study suggests that the sedimentary responsesof the symmetrical medium-term cycle evolves into a beneficialsource-reservoir-caprock assemblage (SRCA) in the actic region, and themultifarious leading systems makes the hydrocarbon accumulationcharacterized with multiform pool types and long oil-bearing horizon.Through the above study, established is a hydrocarbon accumulation modelthat the lithologic hydrocarbon reservoir dominates and diversifiedreservoirs coexist. Two main exploration targets as the newly-discoveredsmall fan and turbidite body are pointed out, for the former is favoredto form the updip wedge-out reservoir in the fan front subfacies and thelatter is beneficial to generate tectum-sealed reservoirs in the fan end.By utilizing the theory of "Channel corresponds with fan" and combiningthe attribute analysis, the flattening horizontal slice analysis, theseismic inversion and other geophysical methods, two potential explorationzones are presented: Liyuan—Pichong—Lishuao small-scale fan zone (ofwhich Pichong fan is newly discovered.) and Pingshi—Yangqiao turbiditefan zone of the deep lake facies in the periphery of sandstone front.Suggestions on well locations are also presented by syntheticallyappraising the advantageous exploration targets.