Research On Diagenesis Difference And Productivity Evaluation Of Low Permeability Sandstone Reservoir

Multi-stage superimposed sand bodies developed in the Ordos Basin.The sedimentary sand bodies were strongly transformed by later diagenesis,which directly affected the pore evolution of the reservoir and controlled the physical properties and oil-bearing properties of the reservoir,Clarification of differential diagenesis of reservoirs is important for oil and gas exploration.The purpose of this paper is to offer a useful reference for further research on the genesis and distribution of reservoirs through the study of the differential diagenesis of different reservoirs,thereby improving the efficiency of exploration and development of tight sandstone reservoirs.The research object of this thesis is the formation of Yan 10 member in Maling region,Chang 2 member in Jiyuan region,and Chang 6 member in Wuqi region.According to the diagenesis process of low-permeability sandstone,the pore evolution of different reservoirs and the microscopic reservoir characteristics corresponding to typical diagenetic facies are analyzed.The thesis mainly carries out reservoir basic geological characteristics analysis,petrological characteristics and physical properties analysis,diagenesis and porosity evolution research,diagenetic facies division and sedimentary and diagenetic characteristics research,micropore structure of different types of diagenetic reservoirs,different diagenetic reservoirs Microscopic seepage characteristics research and production dynamic analysis.The main knowledge obtained is as follows:(1)According to the unified classification criteria,combined with the quantitative calculation results of pore evolution during the diagenesis process and the level of pore permeability,the study was divided into four types of diagenetic facies reservoirs and named,which are low-permeability,mesopore compaction and weak cementation.Erosion phase,ultra-low permeability-low-porosity medium compaction and cementation dissolution phase,ultra-low permeability-low-porosity medium-strong compaction cementation phase,ultralow permeability-ultra-low-pore strong compaction carbonate cementation phase.The proportions of typical diagenetic facies reservoirs of type ?-? are: 38.18%,14.55%,32.73%,14.54%.(2)Quantitative analysis of porosity evolution of reservoirs of different diagenetic facies types: The initial porosity of the four types of diagenetic facies zones are close to 43.53%,41.43%,42.41%,and 41.79%,respectively,and the differences are not large;the remainder after compaction The porosity in turn is: 18.92%,17.37%,16.28%,15.89%,and the gap gradually widens;mainly after the early cementation-metastatic interaction,the remaining porosity has differentiated and was lost from ?-? diagenetic facies The porosity was 9.03%,6.79%,9.76%,and 10.99%;the final calculated porosity from the diagenetic facies of ?-IV was 12.17%,11.00%,9.50%,and 6.55%,respectively.(3)Physical property statistics found that the Yan 10 reservoir had the best physical properties,the Chang 2 reservoir was better,and the Chang 6 reservoir was the worst;there was a good positive correlation between porosity and permeability in each study area.The correlation coefficient of the physical properties of the reservoir is 0.3491,the Jiyuan Chang 2 reservoir is 0.7289,and the Wuqi Chang 6 reservoir is 0.9016.It can be found that the Yan 10 reservoir has the strongest heterogeneity,the Chang 6 reservoir is the smallest,and the Chang 2 reservoir is stronger.(4)The NMR mobile fluid saturations of the four diagenetic facies reservoirs are 63.79%,52.09%,54.79%,and 39.28%,respectively.The smaller the pore throat radius of low-permeability sandstone reservoirs,the narrower the distribution range and the denser the physical properties.At the same time,the smaller the pore throat radius ratio,the smaller the separation coefficient,and the stronger the pore throat heterogeneity.The more complex the pore structure of the reservoir,the more limited the percolation capacity,the lower the saturation of mercury inflow,and the lower the saturation of the mobile fluid.Movable fluid saturation found that the Yan 10 reservoir had the largest,83.94%,the Chang 6 reservoir had the smallest 41.10%,and the Chang 2 reservoir was generally 52.01%.(5)The irreducible water saturation of the type ? diagenetic reservoir is 33.48%,the oilwater relative permeability at the intersection is 0.12,the residual oil saturation is 32.64%,and the size of the two-phase co-permeability zone is 33.8%;The irreducible water saturation is 38.93%,the oil-water relative permeability at the intersection is 0.12,the residual oil saturation is 31.99%,and the two-phase co-permeability zone is 29.08%.The irreducible water saturation of the type III diagenetic reservoir is 39.4%.At the intersection the relative oil and water permeability is 0.11,the residual oil saturation is 30.99%,and the two-phase co-permeability zone is 29.61%;the irreducible water saturation of the type IV diagenetic reservoir is 45.41%,and the oil and water relative permeability at the intersection is 0.09.The oil saturation is 31.68%,and the two-phase co-seepage zone is 22.92%.The area of the "seepage triangle zone" formed by the four types of equal seepage points and the co-seepage zone decreases in sequence;the Yan 10 reservoir is the largest and the Chang 2 reservoir is the smallest.(6)The water flooding area of the diagenetic facies reservoirs of type ?-? is getting smaller and smaller,the waterline advancement is slower and slower,and the displacement type is also from uniform network to finger-shaped.The diagenetic facies has the worst final displacement effect and low residual oil saturation,but it has a wide distribution range and a stable production cycle.It has a better percolation capacity than the type IV facies,so it can be used as a reserve for exploration and tapping.(7)From ? to ? diagenetic facies,the quality is from good to poor,the threshold pressure is gradually increased,the amount of mercury entering is decreasing,the movable fluid is decreasing,and the reservoir storage performance is getting worse;meanwhile,the mercury entering space From the pore-throat approach to the pore-type reservoir,the throat with the largest permeability contribution value gradually decreases,the average radius gradually decreases,and the amount of mercury ingress gradually decreases.Poor results in gradual deterioration of reservoir seepage ability.Differences in micro-diagenetic characteristics of reservoirs in the study interval lead to differences in reservoir and percolation capabilities.The Yan 10 reservoir has the highest diagenesis ratio,the best reservoir and permeability,and the highest mobile fluid saturation.The Chang 2 reservoir has the highest saturation.Set performance is better,seepage ability is the worst,and mobile fluid saturation is better;Chang 6 reservoir has the smallest diagenesis ratio,the worst reservoir performance,average seepage capacity,and the smallest mobile fluid saturation.