Prediction And Evaluation Of Stratigraphic Traps In Paleogene Of Liaohe Beach Area

The paper takes full use of cores, well logs and seismic data, and integrates geological and geophysical research methods to analyze systematically Paleogene in the beach area of Liaohe Depression, so as to find out the controlling factors for the reservoir and the distribution law of reservoir sand bodies by tracing the sequence stratigraphic framework, furtherly to get prediction and evaluation of favorable lithologic and stratigraphic traps.In the beach area of Liaohe Depression, the Paleogene reservoirs comprise mainly feldspathic lithic sandstone and lithic sandstone, and have lots of secondary pores developed, which bring on two depth segments with abnormal high values of porosity. The study shows that the first segment is at the stage B of the early diagenesis to the stage A1 of late diagenesis, when the organic maturing make organic acid, which led to the dissolution of carbonate cement, feldspar and rock fragment, and give many secondary pores. The second one is at the stage A2 of late diagenesis, when well-matured organic acid gave off CO2, and make the formation water alkalescent, which result in the dissolution of silica components, and make the secondary pores larger to a great degree. In addition, the sedimentary microfacies and the system tracts in sequence stratigraphy are also main effective factors controlling on porosity of sandstones. In the different sedimentary microfacies, the porosity and permeability of sandstone is obviously different, distributary channel sandstone is the highest, followed in the order of quality by those of debouch bar, underwater distributary channel, delta distal bar, delta front sheet. Base-level cycles also affect the porosity and permeability of sandstone, and the sandstones near the interface of the sequences have better porosity because the interaction therein between accommodation space and sediment source supply can bring up a good formation properties.Slope break zone and system tracts control the development of stratigraphic trap model. Some fan-shaped lithologic traps, which belong to low system tracts (LST), develop at the bottom of the depress. Stratigraphic overlap trap and complex traps from transgressive sand sealed by faults arise upward slop break zone. Downward to the slop breaks, there are some slump fan traps and some complex traps from delta front sealed by faults in the high system tracks(HST), some channel-fill deposit in the LST. Amongst all, complex traps from every type of delta front sealed by faults are the most important stratigraphic lithologic traps, and have bigger size of single trap. Specifically, in the western depression, complex traps lie in bi-jia-ling slope region, Huludao bulge’s eastern slop region and Yuedong bulge’s slope, they are delta front sands separately of braid delta, fan delta and fan delta. There are some fan shaped lithologic trap belonging to LST and HST in the deep zone. In the eastern depression, there are fault-sealing compound traps from various types of deltas located in the eastern slope region. Some fan shaped traps of slumps, complex traps of fault sealt delta and channel-fill deposit are founded in the region of deep zone, overlapping stratigraphic traps of beach bar sand in the east slope of the central bulge.