High-resolution Sequence Stratigraphy And Sendimentary Facies Research Of The Fourth Member Of Shahejie Formation Of Weicheng Oilfield

Weicheng oilfield is located on the northern end of the central uplift belt inDongpu depression, The fourth member of Shahejie formation is in the deep part ofthe structure. Wei81block is a fault block reservoir which is like a inverted ridge.The development of Weicheng oilfield becomes increasingly difficult after perennialexploitation and the reservoir prediction demands a higher precision. With theinstruction of sequence stratigraphy, reservoir sedimentation, petroleum geology, thesequence stratus frames of the study area is established, and the types, distribution andevolution of sedimentary microfacies is researched on the base of core, logging andanalytical data, depositional models is established for the further exploitation anddevelopment.Applying the theories and methods of different hierarchical base-level cycles,comebined with tectonic background of Weicheng oilfield, the sequence boundary isrecognized, and on the basis, the fourth member of Shahejie formation is divided intoone long-term cycles, five medium-term base-level cycles and eighteen short-termbase-level cycles. The sequence stratus frames of the fourth member of Shahejieformation in Wei81block is also established.Based on the research of regional geological background, combined with theanalysis of mudstone color value, lithology types and the textural maturity of clasticrocks, this thesis determines sediments in the fourth member of Shahejie formationcome from the northwest and northeast of the study area. The overall depositionalenvironment changes from onshore oxidation environment to underwater reducingenvironment. By observing and describing the core of the study area, and at the sametime, by analyzing logging data, terminal fan and beach bar are recognized. In thelower fourth member of Shahejie Formation，Dongpu depression is at the initial rifting stage with a flat paleotopography. Water body is shallow in the lake basin andthe paleoclimatic is hot and dry. The streamflow of source water system decreasesbecause of evaporation, so the detritus accumulate rapidly to form the terminal fan.The middle zone is dominant in study area, including distributary channel, nearoverbank, far overbank and mudflat as the microfacies. Hydrodynamic force is mainlythe tractive current. Various sedimentary structures develop, because the seasonalrains and flood flow is intermittent, mudstone and sandstone interbed occursfrequently. In the upper fourth member of Shahejie Formation, Dongpu Depressionrifts intensely, the lake basin expands and water body deepens. The underwater uplift,where the study area locates, develops the structural rudiment. The beach bar isformed in the study area. On this basis, combined with the character of sand bodydistribution, the terminal fan depositional model and beach bar depositional model ofthe fourth member of Shahejie formation are established. And moreover, the evolutionrule of sedimentary system in the research area has been cleared about.