Regional Sequence Stratigraphic Correlation And Predication Of Favorable Lithologic & Stratigraphic Traps Zones For Palaeogene In Jiyang Depression

Based on the theory of sequence stratigraphy, regional sequence stratigraphiccorrelation is made for the Palaeogene in Jiyang Depression. And on the basis of subtleoil and gas reservoirs exploration theory for continental rift basin, the paper geneticallymade predications of lithologic & stratigraphic traps zones for Palaeogene in JiyangDepression by means of analysing lateral and longitudinal migration and changes ofsequence boundaries properties within the sequence stratigraphic framework to studysequence boundaries controlling on genetic types and distribution, summarizing thetime-space configuration relationship between sequence boundaries and reservoirdistribution, and discussing the factors of sequence boundaries while forming lithologic& stratigraphic traps.According to the comprehensive research achievements of stratigraphy such asbiostratigraphy, magnetostratigraphy (ESR dating method), seismic stratigraphy andsequence stratigraphy, a regional sequence stratigraphy framework of the Paleogene inJiyang Depression is unified on the basic unit of third-order sequences. Then the analysison the comparison of all second-order sequences and major third-order sequences inwhich subtle reservoirs were most developed, shows that the second-order sequences aredirectly controlled by tectonic episodes in the four sub-sags of the Jiyang Depression,therefore, they are similar in characteristics. The cyclicity of major third-order sequencestratigraphic framework coincides with each other among the four sub-sags, with themarker sediments developed in the same or similar cycle positions. Properties of majorthird-order sequence stratigraphic framework are consistent among four sub-depressions,with marked sediments in the same or similar cycle positions. However, the third-ordersequence boundary properties of T2, T4, and T6 are apparently different among differentsub-sags.On the basis of regional sequence stratigraphic unification, the author does researchon the genetic dynamics mechanisms of the changes of sequence boundary types,sequence boundary sand control, and sequence boundary reservoir control. In this paper,six genetic types of sequence boundaries are divided for the Palaeogene in JiyangDepression for the first time, which are the onlap/truncation construction style, theparallel/truncation construction style, the onlap/parallel construction stytle, theonlap/toplap construction stytle, the parallel/parallel construction stytle, and theconformity construction style. Research shows that the genetic dynamics factorscontrolling the changes of sequence boundaries are the two following aspects: one is themigration and the differences of time and intension of fault activities, the other is themigration of tectonic depocenters and the differences of tectonic subsidence extent. Takethe third member of Shahejie formation in which subtle reservoirs were most developedas an example, the author analyses the sequence boundary types of the three key surfacesT4, T6, and T6' controlling on various genetic types of reservoir sandstones in detail. Onthe basis of analyzing the corresponding relationships between sequence boundary typesand their controlled types of lithologic & stratigraphic traps from exploration matureprovinces and the distribution areas of lithologic & stratigraphic reservoirs in JiyangDepression, sequence boundary reservoir control of the above six types of sequenceboundaries are analyzed.Finally, by using the criterion of "six factors (the changes dynamics of sequenceboundary, sequence boundary sand control, the properties of reservoir sandstones,hydrocarbon generation and expulsion, sedimentary environment, and sequenceboundary reservoirs control) to predict favorable lithologic & stratigraphic traps zones",the author made predications of lithologic &stratigraphic traps and pointed out thefavorable exploration zones for the third member of Shahejie formation in JiyangDepression.