Accurate Analysis For Complex And Multivariable Logging Response Characteristics Of Chang 6 And Chang 7 Reservoirs In Zhi Dan Oilfield

Low porosity and permeability reservoirs have been one of the typical Mesozoic reservoirs in Triassic Yan chang formation of Ordos Basin.With the development of reservoir prospection and exploitation,high gamma and low-resistivity reservoirs were explored successively,which brought considerable benifits.However,the effective reservoirs could be ignored easily bacause of the characteristics of complex genetic mechanism,it was difficult to identify the real oil layer,even evaluated.Taking chang 6,chang 7 reservoirs of Zhidan oil field in Ordos Basin as examples,for the purpose of analysing the cause to complex and varied logging response by collecting basic geological data,testing data,logging data as well as dynamic production data,in addition,taking “logging” as technical means to divide stratum and sedimentary facies,discuss the four-property relationships,conduct the recognition and assessment techniques as well as construct the model of water satruation.According to these basic work,logging “forward” and “inversion” would be achieved,it would provide effective reference for further exploration and development.Specific research strategies and practical work have been carried out,understandings are acquired as follow:(1)Studies based on reservoirs' characteristics were demonstrated that: mineral components of feldspar,quartz,rock fragments decreased in turn;pore types and structures were multitudinous,logging response characteristics were complex and multivariable,which were embodied in:(1)High gamma sand reservoir was found with oil prospecting in research area;(2)The relationship between oil and water was complex,low resistance oil layer,conventional oil-water layer and the high water resistance layer coexisted.(2)Overlay method and cross-plot method were effective to identify high gamma sand and low resistivity reservoir.The results indicated that spontaneous-acoustic overlay method for high gamma sand identification was proper;calculated natrual potential-spontaneous potential was used for distinguishing oil-water layers validly;deep induction resistivity curve was almost coincide with acoustic time curve generally,however,the phenomenon of negative filling characteristics were found in some typical wells in study area.(3)The complexity of formation water system brought about the difficulties to quantitative interpretation model of oil satruation.On the basis of qualitative recognition of oil-water layers,high resistivity water should be removed as the interference factor,taking the reservoir geological characteristics as the constraint conditions,the parameter Rw which was choosen from the oil field water would be correct.In order to ensure whether litho-electric parameters were pertiment,accurate or not,general oil reservoir and low-resistivity reservoir were necessary to be classified during parameters' calculating processing.