High-frequency sequence division reveals the intergrowth development regularity between source rocks and reservoirs of deep lake facies strata in the faulted depression:Taking the Eocene Liushagang 2 interval in Haizhong Depression,Beibuwan Basin as an exa
Taking the deep lake sedimentary system of the Eocene Liushagang 2 interval in the Haizhong De-pression,Beibuwan faulted lacustrine basin as an example,guided by the theory of high-resolution sequence stratigraphy,the high-frequency sequence division of the Liushagang 2 interval was carried out by means of the utilization of the maximum entropy spectrum analysis and wavelet transform analysis techniques;further,the source-reservoir intergrowth regularity of the deep lake strata in the faulted lacustrine basin was discussed,on basis of the analysis of the development rules of sedimentary system,and also the analysis of the development regularity of deep lake facies source rocks and sublacustrine fan gravity flow sandstones in the high-frequency grade-5 sequence of the Liu 2 interval.The research suggests:INPEFA spectrum analysis and wavelet trans-form analysis technology can be effectively applied to the high-frequency sequence division in deep lake facies strata in the faulted lake basin;the Liu 2 interval in Haizhong depression of Beibuwan Basin can be divided into one grade-3 sequence,two grade-4 sequences and five grade-5 sequences,with the grade-4 sequence be-ing divided into two system tracts of the lake expansional system tract(TST)and the lake contraction system tract(HST),which are interfaced by the maximum flooding lake surfurce(Mfs);High-quality thick source rocks in faulted lacustrine basins were often developed in the initial grade-5 sequence at the first lake flooding surface in the lower part of the lake expansional system tract of grade-4 sequence.Although the source rocks developed in the two grade-5 sequences closely under or over the maximum lake flooding surface at the top of the lake expansional system tract of grade-4 sequence are large in areal extent,but thin in thickness,which can thus be served as the secondary source rocks and most well cap rocks.The grade-5 sequence at the middle part of the grade-4 sequence in the lake expansion system tract often developed sublacustrine fan gravity flow facies reservoirs,which are sandwiched between the two sets of source rocks nearing the initial lake flooding surface and the maximum lake flooding surface,while all these together could form a good sandwich type source-reservoir-cap assemblage,which should be a follow-up field of unconventional oil and gas prospection.
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