Abstract:

The Neogene Shawan formation is one of the important hydrocarbon-rich strata in Chepaizi salient. Based on the analysis of
reservoir distribution and oil nature, coupled with results of previous studies, the accumulation process of Shawan hydrocarbon is
divided into two stages: paleoreservoir stage and secondary adjustment stage. The migration pathway systems and their spatial
combinations are discussed. In the paleoreservoir stage, the Cretaceous basal unconformity and syngenetic reverse faults composed the migration pathway in the Hongche fault zone formed system. The effective thickness of migration zone in the unconformity is thicker in the northern and estern part of the research area while pinching out toward the west; syngenetic reverse faults controlling the formation and development of Hongche fault zone have large fault displacements and beneficial for hydrocarbon migration. In the secondary adjustment stage, sandstone in the first member of Shawan Formation (N1s), epigenetic normal faults in Hongche fault zone, Aika fault zone and Neogene normal fault in Chepaizi salient formed the migration pathway system, the N1s sandstone salient with continuous and stable deposition distributes in the Chepaizi, blanket-like pinching out from the south to the north. As the lowest sandstone bed, the blanket-liked sandstone is the most important transverse migration bed in this stage. Large-scale normal faults in the Hongche fault zone were developed in the late Neogene; Normal faults in the Chepaizi salient were also developed in the same period; the Aika fault zone continued to be active in the Neogene, all of which formed the vertical migration pathway system in the secondary adjustment stage. The dominant migration zones of the Cretaceous unconformity and blanket-liked sandstone migration beds are predicted using
migration pathway index (MPI) and Quantitative Grain Fluorescence (QGF). In the plane, area with MPI greater than 0.3 is regarded as
the dominant migration zone of unconformity migration bed and the area with QGF greater than 3.8 is regarded as the dominant
migration zone of N1s blanket-like sandstone. Based on the analysis of spatial combination of migration pathway systems in different
stages and the relationship between hydrocarbon distribution and migration pathway systems, the control action of migration pathway
system on hydrocarbon accumulation is confirmed prospecting to have. The well P609 area is predicted to have advantages of
hydrocarbon migration, which can be regard as the exploration target of further prospecting.

Key words: Chepaizi salient, migration pathway system, dominant migration zone, hydrocarbon accumulation