Reservoir Architecture Of Chang 8₂-chang 9 And Comprehensive Reservoir Evaluation With Multi Factors Coupling In Shijiawan-Buziwan Area,Ordos Basin

Ordos Basin is rich in unconventional oil and gas resources,but also faces huge exploration and development challenges.With the deepening of the research,the low porosity and ultra-low permeability reservoirs represented by Chang 8₂-Chang 9 in Shijiawan-Buziwan area of Jiyuan oilfield have attracted much attention.A series of problems have emerged,including complex and changeable sedimentary context,unclear genetic structure of sand body,fuzzy reservoir characteristics and quality evaluation criteria,which seriously restrict the current exploration and development process.Therefore,this paper starts with the sedimentary characteristics and sand body architecture to study the macro characteristics of this kind of reservoir,and then combined with a large number of experiments to study the reservoir characteristics,diagenesis,micro pore throat structure and seepage characteristics.Finally,the comprehensive evaluation of the reservoir is completed on the basis of multi coupling quantitative characterization of macro and micro factors.In general,this study has a certain value in solving the exploration and development contradictions of unconventional reservoirs,breaking the theoretical barriers and improving oil and gas recovery.Finally,the following main understandings were obtained.The intersection of the northwest and northeast bidirectional provenance systems makes the deposits of different regions and different layers in the study area different.The Chang 8₂sub-member is dominated by shallow delta front sediments.The Chang 9 member is composed of the braided river delta plain in the northwest and the meandering river delta frontal deposits in the northeast,which have experienced a relatively large flooding process on the whole.The development characteristics of each sedimentary cycle in different regions are different,with significant facies differentiation.After establishing the description method of single genetic sand body corresponding to ultra short term cycle,eight kinds of fourth-order architectural elements are identified,and the correlation is formed between each layer and each area.The quantitative characterization method of architectural elements is established by using logging data,and the architectural distribution mode is summarized.The lithology of Chang 8₂and Chang 9 reservoirs is the same,but the component content is different.The content of chlorite,iron calcite and siliceous is higher,but the content of Chang 9 laumontite is higher.The structure maturity and composition maturity were mainly medium.The average porosity and permeability of Chang 8₂reservoir is 11.24%and1.57×10^-3?m²respectively,while that of Chang 9 reservoir is 11.97%and 4.7×10^-3?m²respectively.The reservoir develops four types of diagenesis,which are mainly compaction,cementation,metasomatism and dissolution.The diagenesis stage is middle diagenetic stage A.The densification process of the reservoir is mainly by compaction and pore reduction,followed by cementation,while dissolution and pore increase are relatively Weaker.Four and five dominant diagenetic facies were identified in the Chang 8₂and Chang 9 reservoirs respectively,and the Fisher discriminant function was established after combining with litho-electric calibration,which realized the quantitative characterization of diagenetic facies,and summarized the spatial relationship between architectural elements and diagenetic facies Later,the spatial distribution model of diagenetic facies was established.The pore types are mainly inter-granular pore and solution pore,and the pore combination is solution pore plus inter-granular pore.High pressure mercury injection can be divided into four types of pore throat structure.The pore throat structure of chang 9 is better than that of Chang 8₂,but the connectivity of pore throat is poor,and the heterogeneity of pore throat structure is significant.Four kinds of movable fluid characteristics are classified by NMR.The T₂relaxation time of Chang 9 is significantly longer than that of Chang 8₂,and the movable fluid saturation is relatively high.After joint characterization,it is found that there are more large and medium pore throats in Chang 9 reservoir.The seepage characteristics of Chang 9 reservoir are significantly better than that of Chang 8₂reservoir,and all kinds of characteristic parameters match well with physical properties;Chang 9 multi-phase flow is mainly homogeneous,while Chang 8₂multi-phase flow is mainly reticular.Both of them have strong overall flow capacity and high displacement efficiency.Nine representative parameters are selected from macro and micro factors.The multi-factor comprehensive classification coefficient F_iis used to classify and evaluate the reservoir,and the quantitative evaluation standard of various reservoirs is established.