| This thesis takes low permeability reservoir of the2th Member of Xujiahe Formation as the research object, which locates in Hechuan Area, middle of Sichuan Basin.Based on the previous studies,stratigraphic,sedimentary and reservoir characteristics of the2th Member of Xujiahe Formation is described systematically by using lithologic character,physical property,electrical property datas.And then,a reservoir classification evaluation standard is made.The main controlling factors of the reservoir is summarized.On account of the characteristics of reservoir parameter distribution, this paper carries out comprehensive research of reservoir distribution rules,which is the2th Member of Xujiahe Formation.The2th Member of Xujiahe Formation can be divided into two part,six thin layer and belongs to shallow braided river delta-lacustrine depositional system.The property of reservoir is controlled by sedimentary facies obviously.Shallow braided river delta plain is the major sedimentary subfacies and the main river of braided distributary channel is the profitable sedimentary microfacies.The rock types of the2th Member of Xujiahe Formation reservoir take the feldspar lithic sandstones as the main,second are the lithic feldspar sandstone and lithic quartz sandstone.Rock granularity is given priority to medium,of which the lower section is more coarse than the upper section.The structural maturity of composition is middling and the cuttings types give first place to metamorphic lithic.Interstitial material mainiy includes matrix and cements. Low porosity and permeability are the general trait of reservoir physical property. Residual intergranular pores and intragranuar dissolve pores are the commom type of reservoir space. The necking throat,the laminated throat and the control shape throat pertain to throat types and the sand reservoir belongs to fractured-porous type.Combining with the reservoir characteristics, the petrophysical lower limit value of an effective resevoir includes the porosity value6%and permeability value0.03md.Based on then, a classified evaluation on reservoir is maded and the categories of reservoir can be divided into1,11,111,IV,four kinds, which gives priority to Ⅱ、Ⅲ kinds.The main control factors of reservoir is summaried systematically:(1) favorable sedimentary facies master reservior distribution macroscopically;Hasing deposited before the ancient geological characteristics of Xujiahe formation controls of the river of braided distributary channel development and distribution, the river of braided distributary channel is the profitable sedimentary microfacies in this studied area.(2) diagenesis is an essential factor to dominate the reservoir property.The diagenesis mainly includes compaction,solution,cementation,metasomatism and dissolution.favorable diagenesis can protect and improve the reservoir,such as appropriate amount of chlorite rims inhibit the quartz secondary enlargement,which can protect the primary pore space;another example is that with hydrocarbon materials like a large amount of mature organic acid can produce new secondary pore.(3) ectonism and cataclasis is the key to the formation of reservoir.Tectonic fracture effect is helpful to produce microfracture,which can improve the reservoir percolation.The above three kinds of mian control factors comprehensively have an impact on the development degree of reservoir in study area.The thickness of reservoir unevenly distributes in vertical and the connectivity is poor in horizon.The planar characteristics of distribution of each small layer reservoir parameter shows that porosity values, reserve coefficients and reservoir thickness values have a good correlationship,and the high value areas are usually locating in central channel and river interchange which are the main distribution of favorable reservoir areas.Based on the distribution of reservoir parameter,this thesis summarizes the reservoir distribution of the2th Member of Xujiahe Formation,which has an important point to look for high quality reservoir. |
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