Rock-Physics Model And Heterogeneity Characterization Of Donghe Sandstone Reservoir In DH1 Oilfield

The clastic reservoir with littoral facies found in Carboniferous Donghe sandstone in DH1 oilfield is the first marine block reservoir with bottom water discovered in China.However,the studies about reservoir characteristics are short of integrity,the key controlling factors to heterogeneity and its genetic mechanism are lack of understanding and the heterogeneity characterization based on conventional permeability model is unable to truly reflect the interwell variation of reservoir characteristics.Therefore,this dissertation starts with the analysis of sedimentation,diagenesis and structural evolution to reclassify the main controlling factors of reservoirs with different types and determine the formation mechanism of microscopic reservoir space.Combined with rock physics study,core,logging and seismic data are used to rock physical characterization of different reservoir types.Donghe sandstone is littoral deposition with delta sedimentary background.According to the difference in sedimentary environment,littoral reservoir can further be divided into 12 microfacies with different genetic types.Through the thin section analysis,4 diagenetic types including compaction,cementation,metasomatism and dissolution are developed in Donghe sandstone reservoir,the reservoir undergoing five diagenetic stages including syngenetic,early-compaction,hypergene diagenetic,eogenetic and mesogenetic stages and now evolve in period A of mesogenetic stage.Six different diagenetic facies types can be identified in Donghe sandstone.Comprehensive analysis of sedimentary facies and diagenetic facies reveal that the superimposed area of channel-modified bar,mouse bar-modified bar and clay envelope cementation has the best physical properties;reservoirs in this area has good pore-throat connectivity and weak heterogeneity.Through the overlay of sedimentary facies and diagenetic facies,Donghe sandstone can be divided into 8 types of petrophysical facies,and type PF2 has the best macro property and good micro pore-throat connectivity.Reservoir characteristics analysis of Donghe sandstone indicates that rock matrix of Donghe sandstone is mainly composed of quartz,feldspar,cuttings and interstitial materials,pore types in Donghe sandstone are mainly residual original intergranular pore,secondary intergranular dissolved pore and intragranular dissolved pore,pore fluid is oil-water two phase.On the basis of above analysis,the rock-physics model of Donghe sandstone reservoir is established.Combined with the theoretical formula derivation of rock physics,the quantitative relationship between micro reservoir characteristics and macro rock elastic modulus is determined.On this basis,S-wave velocity is estimated based on the rock-physics model of Donghe sandstone,and compared to other prediction methods,this method has higher precision.Through the overlay analysis of sedimentary facies and diagenetic facies and consider the unity of data with different scale,this study eventually divides Donghe sandstone into 3 types of petrophysical facies on core,logging and seismic scale.Reservoirs with different petrophysical facies have different logging response and seismic AVO characteristics.Based on this phenomenon,the characterization method of quantitative parameter of petrophysical facies using data with different scale is established with rock physics analysis and this method can avoid the solution of dry rock modulus.With the quantitative parameter as a constraint,permeability model is reconstructed and this process achieves the high accuracy characterization of heterogeneity.Finally,pre-stack seismic data is used for rock-physics parameter,porosity and permeability inversion based on rock physics analysis.Integrated with static geological analysis,the potential preferential pathways are forecasted.