Reservoir Evaluation Of Chang 4+5 Member In West Jiyuan Oilfield In Ordos Basin

Based on previous achievements,core,logging and analytical data,this dissertation will probe into the distribution,the feature and the main controlling factors of Chang 4+5 oil reservoir in west Jiyuan oilfield.Finally,the classification and evaluation criterions of the reservoir here will be set up.Meanwhile,the area of advantageous reservoir shall be delineated.Previous researches show that it was shallow water delta front environment in west Jiyuan oilfield during Chang 4+5 period,including micro-facies such as submerged natural levee,submerged distributary channel and tributary bay.The leading rock type of Chang 4+5 is lithic arkose sandstone,arkose sandstone and feldspathic lithic sandstone rank the second place.The separation of the grain ranges from medium to fine.The rounding degree appears as subangular.Line contact and porous cementation are the most common scene when observing under the microscope.The rocks of the reservoir have medium structural maturity and inferior-medium componential maturity.Chang 4+5 reservoir experienced diverse diagenesis such as compaction,replacement,cementation,and corrosion,and it's between middle diagenesis stage A and early diagenesis stage B.The original intergranular pores and intragranular pores are the dominating types of reservoir space.The average porosity is 11,82%and average permeability is 0.68×10^-3?m².The lower limit porosity and permeability of effective reservoir hits 8.6%and 0.11×10^-3?m² respectively.The upper and lower reservoir have better physical property quality in contrast to the middle part.Combined with microfacies,the area of high prosity and peemeability usually locates in submerged distributary channel,then the submerged natural levee.The tributary bay always belongs to the area of worst physical property.The sedimentation has the basic effects on reservoir's physical property,and process of diagenesis finally decides the quality of reservoir.On a micro level,the mineral constituents,the interstitial material,the clay content and the grain size of the deposits are closely related to the porosity and permeability of reservoir.In the research area,the reservoir could be divided into four categories or six subgenera.The type of III plays a leading role among all reservoirs.The layer Chang 4+5₂^2-2,Chang 4+5₂^2-1 and Chang 4+5₁^1-2 have better physical property than the rest.Finally,this dissertation delineated the area of advantageous reservoir for the follow-up oil-gas exploration.