Flow Unit Division Of Reef-Shoal Reservoirs In Changxing Formation Of Puguang Gas Field

The Changxing Formation of Puguang gas field is mainly reef beach reservoir.The development mode is mainly perforation gas production in long well section,and the gas production in each layer section in early stage is large and the difference is not obvious.In the later stage of exploitation,due to the strong vertical heterogeneity,the gas production contribution degree of each reservoir section is different greatly,and the overall production degree is different.The production logging shows that the production degree of natural gas reserves in the Changxing formation is only 29.79% and the gas percolation characteristics,contribution to productivity and residual potential in different physical properties are not clear.Based on this,the study of reservoir flow unit can provide support for the subdivision of development strata and the design of development plan.In this study,through the analysis of core,drilling,logging,seismic and analysis test data,combined with the results of indoor dynamic seepage test,the geological characteristics analysis of reef beach reservoir,optimization of flow unit division parameters,flow unit division method analysis and flow unit prediction research are carried out.The conclusions are as follows: 1)It is clear that the Changxing formation is mainly composed of open sea,bioherm(reef base,reef core,reef cover,reef wing),grain beach(bioclastic beach,gravel beach,oolitic beach),inter-tank sea and tidal flat.The reservoir space types are mainly intergranular pore,intergranular inner pore and intergranular inner pore.There are two third-order sequences and two para-sequence groups in the Changxing formation.Two sets of interlayer and four sets of interlayer are identified.The upper limit of physical property of interlayer is 0.03 md through percolation experiment and J-function analysis.2)Four flow unit partition parameters are optimized.Based on the percolation experiment and the analysis of reservoir geological parameters,the percolation index(FI),RQI,R35 and permeability are proposed as the main parameters of flow unit division;3)Clear classification of flow units.Based on cluster analysis,the reef beach reservoir of the Changxing formation is identified as four types of flow units,and the valve of key parameters corresponding to each type of flow unit is defined;4)Based on the permeability and RQI threshold,with reference to the understanding of microfacies,sequence and seepage barrier,the identification of flow unit single well and correlation of connected wells can be realized.The microfacies of type I flow unit are mainly reef cover and beach,the microfacies of type II flow unit are reef base,reef core and beach,the microfacies of type III flow unit are reef wing and beach edge,and the microfacies of type IV flow unit are reef wing and inter beach sea.