Study On Sequence Stratigraphy And Subtle Reservoir In The Huanghekou Sag,Bohai Bay Basin

In the Bohai Bay Basin, Huanghekou Sag contains abundant oil-gas resources andbecome an important exploration areas in the Bohai Oilfield in recent years, theexploration target have changed from the deep to shallow and found a series of largeand medium-sized shallow oil and gas fields. Therefore, the paper takes the Neocene inHuanghekou Sag as the example, and applys 3-D seismic, log, core and other data, tocarry out the systematic study of the Neogene sequence stratigraphy and sedimentaryfacies. On the basis of establishing the isochronous stratigraphic framework, thegeological-geophysical model of the key target areas and the key layers is establishedfor precise reservoir sandbody prediction and analysis of main control factors. Thefoundation is provided for study of subtle Oil/Gas reservoirs recognition andexploration in Bohai Bay Basin.On the theoretical basis of classical sequence stratigraphy, the analysis of sequenceis made in the lake basin atrophy by using a variety of disciplines and methods. Basedon principle and methods for base level cycle, the drilling, well logging, seismic andpalaeontological data from Huanghekou Sag are analyzed and Neogene can be dividedinto 5 third-order sequences and 10 system tract. 6 sequence boundaries and 5maximum flooding surfaces are identified. The different types of sequence boundaryand stratigraphy character are obtained. On the basis of establishing the isochronousstratigraphic framework, the main depositional system such as braided river, braidedriver shallow-water delta, meandering river, meandering river shallow-water delta, andshallow-water lacustrine are analyzed precisely by means of comprehensive explanationof seismic sections, drilling and heavy mineral assemblages. The laws of sedimentaryevolution and the distribution of depositional system are studied.According to the vertical features of subsequence sets, the low sub-segment ofMinghuazhen formation can be divided into 10～11 subsequences sets in the well areaof BZ29, BZ34 and BZ26, and the subsequences sets sedimentary cycles are controlledby sequence development site. On the basis of statistics of lithology in subsequence sets,by analysing the Lithology distribution characteristics and the sand body 2D forwardmodeling, the relationship of geology-geophysical of genetic sandbody in key area isbuilt up. According to the analysis of genetic sandbody geology-geophysical model andRMS amplitude attribute, the skeletal sand bodies is established in the well area of BZ34 within the third-order sequence and analyzed favorable sand development site ofthe subtle trap. Sequence, relic landform and base level (lacustrine level) are roundlysummarized, and they are the main control factors of shallow-water delta sands.According to analysis of forming conditions of the subtle Oil/Gas reservoirs, thispaper summarizes the hydrocarbon migration and accumulation rules. Tectonic settingsare zones of a long term oil and gas migration. Sequence determine dominantaggregation site of hydrocarbon in Neogene. The effectiveness of subtle trap is subjectto relations of fault and sandbody.