Research on Evolution of Burial Diagenesis of Tight Reservior of the Upper Paleozoic in Daniudi Gas Field

Key words: 
• Ordos Basin /
• Daniudi gas field /
• tight sandstone /
• diagenetic evolution /
• fluid charging

Abstract: Based on casting thin sections, scanning electron microscope, clay mineral X-ray diffraction, cathodeluminescence, fluid inclusion and laser-raman spectrum, the paper reveals the process of evolution of burial diagenesis of tight reservoir of the Upper Paleozoic in Daniudi Gas Field from aspects including burial history, temperature, pressure, diagenetic feature of reservoir, diagenesis fluid and porosity evolution of reservior. The research shows the process of burial diagenesis can be divided to four stages. They are rapid burial stage (a) in which the effect of decreasing of primary porosity was remarkable(compaction rates ranged from 30% to 97.5%), complexly diagenetic stage(b) in which there were two phases of gas charging (B.P. 200 Ma and B.P 180 Ma); definition stage for reservoir characteristic (c) when there was one phase of gas charging (B.P. 140 Ma) and reservoir tended towards stability and tight and stage of being weak-reworked for reservoir (d) when amplitude of tectonic uplift was about one kilometer and tension fissure weakly developed. Porosity of most reservoir decreased to 10%, and became tight. With several times of gas charging, the reservoir appeared to present the diagenetic and accumulational model of being tight when gas charging. Hydrpcarbon-changing happened before reservoir's being tight. Microfractures may be the key factor for improving reservoir's permeability.