Study On Geological Model Of Low Permeability Glutenite Reservoirs Of The Wutonggou Formation In Yubei Area

Yubei area is located in the southwest of the Taibei Sag,Turpan-Hami Basin.The Permian Wutonggou Formation is divided into the third member（P₃w₃）,the second member（P₃w₂）and the first member（P₃w₁）from top to bottom,with a burial depth of about 4000-6000m.It is deeply buried reservoirs dominated by low permeability glutenite,with relatively poor physical properties.At present,the reservoir characteristics,genesis and oil distribution of the Wutonggou Formation are less studied,which restrict the next exploration work.In response to these problems,comprehensive uses of cores,testing,logging,seismic and other data,the following results and understanding have been achieved in the analysis of sedimentary facies characteristics,reservoir characteristics and genesis,reservoir parameter acquisition,reservoir geological model development and verification,and favorable areas prediction.（1）The type and distribution of sedimentary facies of low permeability glutenite reservoirs of the Wutonggou Formation in Yubei area were clarified.The gravity slump characterized glutenite at the bottom of P₃w₃ are deposits of braided channel in nearshore subaqueous fan,and glutenite developed in P₃w₁ with multi-stage superposition are the deposition of underwater distributary channel of fan delta front.P₃w₁ is mainly developed in the fan delta front subfacies,and the thick glutenite of underwater distributary channel are mainly distributed in the central and southern part of Yubei area.The mudstone of underwater interdistributary bay are dominant in the northeast.P₃w₂ is dominated by the shore-shallow lacustrine subfacies,and the underwater distributary channel of fan delta front are only distributed in the northwest and southeast parts.The glutenite in the braided channel in nearshore subaqueous fan at the bottom of P₃w₃ are thick and have good lateral continuity,and are widely distributed in Yubei area.（2）The characteristics and genesis of low permeability glutenite reservoirs of the Wutonggou Formation were elucidated.The reservoir compositional and structural maturity of the Wutonggou Formation are low.And storage spaces are dominated by the residual intergranular pores,dissolved pores in grains and microcracks developed in the deep layers,which are significantly influenced by compaction,followed by cementation and dissolution.The reservoirs as a whole show low porosity and low permeability characteristics.Tectonics and sedimentation cause the Wutonggou Formation to gradually increase in depth to the northwest and the complex pore structure of the reservoirs.Compaction directly leads to the deterioration of reservoir properties,which is the main control factor for the low permeability of the glutenite reservoirs,while cementation enhances the low permeability degree of the reservoirs.（3）The four properties of the Wutonggou Formation reservoirs were clarified.The physical and oil content properties of glutenite in the Wutonggou Formation are the best,followed by fine sandstone,with good exponential correlation between porosity and permeability.The oil content grade increases significantly with better physical properties.The glutenite,fine sandstone and siltstone in the reservoirs have different logging response characteristics,and the glutenite have better oil content and significantly larger deep induction resistivity variation.（4）Logging interpretation models were developed.Based on seismic interpretation and seismic attribute analysis,the interpretation of strata in the Wutonggou Formation was completed.Seismic attributes such as average energy,half energy,maximum amplitude and RMS amplitude were used to predict reservoir parameters such as sandstone thickness and reservoir porosity in the Wutonggou Formation.The reservoir parameters of low permeability glutenite reservoirs of the Wutonggou Formation were accurately obtained and used in geological modeling studies.（5）The innovative proposal is based on seismic attribute analysis and well seismic combination to develop geological model of low permeability glutenite reservoirs.It is believed that the joint constraints of variogram analysis,3D acoustic impedance data,and seismic prediction parameters can improve the prediction accuracy of facies and reservoir parameters.Structural and attribute models were developed to describe structural morphology,reservoir distribution and parameter characteristics of the low permeability glutenite reservoir.The depth distribution of the Wutonggou Formation in Yubei area is large,and the overall slope structure is high in the southeast and low in the northwest.The reservoir porosity and permeability of each member of the Wutonggou Formation decreases from top to bottom,with a decreasing trend with increasing burial depth.The oil content saturation distribution varies greatly,and the oil content saturation of the sand body at the bottom of P₃w₃ is relatively the highest.（6）The rationality test of the model improved the model accuracy and pointed out the favorable exploration areas.The mean errors of well data and model parameters are small and the distribution patterns are similar.The average compliance rate between test oil data and model parameters is 90.98%,and the correspondence between oil formation and model parameters is good.The distribution of attribute model profiles before and after well data thinning is basically consistent,indicating that the reservoir geological model test is reasonable.P₃w₃ in the northeast and P₃w₁ in the northwest of Yubei area are potential high-quality reservoirs,and the northeast and northwest areas without well pattern control are favorable exploration areas.