Quantitative Analysis of Chang 6 Low Permeability and Ultra- Low Permeability Reservoir Space in Banqiao- Heshui Area,Ordos Basin

Based on the casting thin- sections,scanning electron microscopy,X- ray diffraction,rock image granularity analysis and other physical data,the diagenesis and porosity evolution of Chang 6 reservoir was analyzed by adopting the combination of qualitative analysis and quantitative calculation method. The dominating pore type of Chang 6 reservoir was feldspar- dissolved pore,inter- granular pore and lithic- dissolved pore. Using statistical relationship between original porosity and sorting coefficient,the Chang 6 reservoir sandstone original porosity was calculated and the average was 38. 16%. Mechanical compaction and cementation were destructive diagenesis,affected by this effect,the impact of compaction was greatest and its loss- rate of porosity was 72. 9%,this was the main cause of reservoir densification,and the loss- rate of porosity of cementation was 19. 7%. Dissolution of Chang 6was more development,it improved porosity about 20. 9%. In the process of calculation,the error rate was 3. 4%,the main influencing factor of the error rate was sorting coefficient of detrital rock and more stages of diagenesis.