Sequence Stratigraphy And Hydrocarbon Accumulation Characteristics Of The Lower Cretaceous In Chagan Depression

Based on consulting a number of exploration experience of sag and structure research, we make full use of the theory of sequence stratigraphy to divide sequences, which is foundation framework of examining sedimentary facies and volcanic rock facies, and then we can anlysis the main conditions for oil accumulation by researching reservoir formation characteristics by means of accumulation theory.This paper uses mension seismic data from Chagan area to describe the complex structures. The structural style of this area involve Extensional Structures, reversal structures, strike-slip structures and Compound structures. Basing on the rule of sedimentary compensation, the formation thickness coefficient was advanced to study tectonic movement. The result shows that this area develops a tectonic movement which we named"seesaw". The critical time of this tectonic movement was between the first member of Suhongtu Formation (K1s1) and the second member of it (K1s2). Basing on the conclusion above, Characteristics of Structural Evolution was studied by Analysis the balanced section and it involve 4 stage: faulting stage, faulted depression-depression stage, depression stage and shrinking stage.Based on sequence stratigraphy and analyses of cores, logging and seismic information, the sequence stratigraphy was classified and the sequence stratigraphic framework was established. The lower Cretaceous constitute a second-order sequences that can be further divided into 6 third-order sequences and 16 system tracts. Source orientation was studied by using Basement and fractured surface form, Seismic Reflection structure, Clay Mineral Assemblages, cuttings type and heavy mineral Combination. The result show that the main source of the western Depression come from south direction and north direction and the subordinate source come from XiNi uplift and MaoDun uplift. The main source of the eastern Depression come from east direction named Lang mountain.After establishing the sequence framework and researching source, we studied the distribution and evolution law of sedimentary facies in every system tract. There are different sedimentary facies associations in different formations which developed from earlier to later. The mainly sedimentary facies is the association of nearshore subaqueous fan, fan delta, shallow-semi-deep lake and shore-shallow lacustrine in the K1b. The sedimentary characteristic of K1s is the interbedding of underwater fan, volcanic facies and shore-shallow lacustrine. The association of alluvial fan and fluvial facies play more and more important part in the K1y. Finally the sedimentation model of Chagan basin is set up.Seismic response and recognition model of volcanic rock was established based on the comparison between rock-electricity character and seismic date. volcanic rock facies types mainly include: eruption facies, overflowfacies and volcanic sedimentary facies. We researched the volcanic rock distribution and the result show that the volcanic eruption centers was changed from the BaRen fault at K1s1 to MaoXi fault at early K1s2 then to south BaRen fault at late K1s2 and the volcanic eruption centers located in the Hule fault and Tulage fault crossing area at K1y. At last we established the eruption models including fissure type and central type.Applying the theory of oil accumulation and analysis of the sequence stratigraphy, I make a research, including the characteristic of source rock, reservoir, source-reservoir-cap assemblage, hydrocarbon migration, trap and preservation etc. After comprehensive research, we recognize the main influential factor of oil and gas accumulation and get the conclusion: fault nose trap of WuNan, structural-lithologic trap of WuLiji act as the exploration Favorable Zone.