Study On Mid-deep Reservoir Characteristics Of Paleogene Shinan Slope In Bozhong Depression

Reservoir with high porosity and permeability was developed in mid-deepPaleogene Shinan slope of Bozhong depression, Bohai Bay basin. Guided by thetheories from sedimentology, reservoir geology and petroleum geology, thisdissertation systematically studied the sedimentary, petrology, reservoir and diagenesischaracteristics of the mid-deep reservoir using the methods of thin section analysis,casting thin section identification, scanning electron microscopy, mercury-injection test,cathodoluminescence, X-ray diffraction, mercury injection analysis and physicalproperty analysis. Then it discussed the effect of sedimentation, diagenesis, abnormalhigh pressure and early hydrocarbon filling on pore evolution, and determined the mainfactors that controlling good reservoir development in deep strata in the study area.The research of reservoir sedimentology characteristics suggests that there arefour kinds of sedimentary systems, braided river delta, fan delta, turbidite fan andlacustrine facies in Paleogene Shinan slope. The favorable sedimentary facies areconsidered as underwater distributary channel of braided delta front, beach bar ofshallow shore lacustrine facies, underwater distributary channel of fan delta front andmouth bar of braided river delta front based on the study of sedimentary systemdistribution in each sequence.According to the reservoir petrology characteristics, sandstone in the reservoir isdominated by debris-feldspar and feldspar-debris sandstone, with clastic particlescharacterized by poor quartz and rich feldspar. In member Sha1-Sha2of Paleogene inwell QHD36-3-2, lacustrine beach bar carbonate was developed and dominated bysparry terrigenous elastics dolomite and sparry terrigenous elastics-containingdolomite.Main reservoir spaces of mid-deep Paleogene strata in the study area are residualprimary intergranular pore, dissolved pores among and in grains, moldic pores,dissolved matrix pores and microfissure, and were dominated by the former three types.Secondary pores give more contribution to the reservoir than the primary ones. High-quality reservoir interval was developed in mid-deep Paleogene strata in the area,with porosity of about20%and permeability of10×10-3ìm2～1000×10-3μm2. Thepore structure is principally large, mid pore-mid, fine throat, classified as high porosityand permeability reservoir. Three secondary pore belts were encountered in themid-deep reservoir at the depth of2500m～2800m,3200m～3400m and3700m～3900m.The diagenesis evolution of the reservoir had experienced three stages,contemporaneous diagenesis, early diagenesis A, early diagenesis B, and now isbetween middle diagenesis stage A and B. The reservoir diagenesis is complex,including compaction, cementation， dissolution, metasomatism, the formation ofauthigenic mineral and so on, where the former three are the main diagenesis thatinfecting reservoir development. Pore and diagenesis evolution have couplingrelationship, with the first secondary pore accumulated belt formed in middlediagenesis substage A1， the second one in substage A2，and the last in stage B.High-quality reservoir in the mid-deep strata of Shinan slope is mainly controlledby sedimentation, diagenesis, abnormal high pressure and early hydrocarbon filling.Sedimentation is the premise and basis for formation of high-quality reservoir. There isa coupling relationship between the evolution of pore and diagenesis. Dissolution is themost direct reason for good reservoir formation, while abnormal high pressure andearly hydrocarbon filling are the cofactors.