Quantitative Characterization Of Heterogeneity Of Reef Bank Reservoir For Puguang Gasfiled

The Lower Triassic Feixianguan formation and Upper Permian Changxing formation of Puguang Gasfiled are typical reef bank reservoir,characterized by drastically change in horizontal direction,various pore types,complex pore-throat relationship and high reservoir heterogeneity.The strong heterogeneity certainly lead to unbalanced gas production profile,edge water incursion,increasing water seal gas reserves,which eventually reduce ultimate recovery and stable production period.Thus quantitative characterization research of reservoir heterogeneity is of great significance to gas reservoir connectivity,reserves producing condition and edge water direction.As the reef bank reservoir have complex porosity-permeability relationship,it is difficult to fine interpret and quantitatively predict the reservoir permeability.Using characterization parameters and characterization method of clastic reservoirs further increase the difficulty to quantitatively characterize the reef bank reservoir heterogeneity.The paper is designed to conduct the study on well logging permeability interpretation,quantitative seismic prediction and quantitative evaluation of the reservoir plane heterogeneityConsidering the reservoir petrological characteristics,sedimentary characteristics,reservoir space and physical characteristics,the major factors affecting the reservoir heterogeneity are analyzed from sedimentation,diagenesis and structural fracturing.Based upon the microscopic pore structure characteristics,the reef bank reservoir are divided into three reservoir pore types,intergranular pore types predominate,intragranular pore types predominate,dissolved pores or fractures types predominate.To obtain the accurate reservoir permeability value is the key to quantitatively evaluate the plane heterogeneity of reef bank reservoir.The logging response characteristics of different pore types are analyzed,and the frame flexibility factor is introduced in this paper to characterize the rock physical parameters variation of samples with similar porosity.In order to make fine interpretation and evaluation of reservoir logging permeability,the discrimination standard of reservoir pore types and reservoir porosity-permeability model are established based upon the frame flexibility factor.Rock physical model based on the frame flexibility is finally established by analyzing the relationship between elastic parameters of reservoirs with various pore types and the frame flexibility factor.Quantitative prediction of reservoir permeability with complex pore types is realized by pre-stack geostatistical inversion of permeability based on the porosity and the frame flexibility factor.According to the principle of effectiveness,rationality,comprehensiveness and dissimilarity,five reservoir parameters including percentage of granular rock thickness,number of interlayer,porosity,matrix permeability and fracture permeability are introduced to calculate the heterogeneity parameter.On the basis of reservoir heterogeneity parameter calculation of well points by composite index method,the reservoir heterogeneity 3-D geologic model is established using reservoir permeability data predicted by seismic data volume as constraint.The reservoir heterogeneity model,fourth-order sequence as vertical unit and well block as horizontal unit,can be used to calculate standard deviation of comprehensive evaluation values of all well blocks,and then to quantitative evaluate the plane heterogeneity of reef bank reservoir.The achievements from this research have guided reservoir performance analysis,precaution decision,and offer useful suggestions for similar gas fields.