Abstract:

Using comprehensive lithological, mineralogical, and geochemical methods, this paper studies the diagenetic
interaction system after oil injection into the sandstone reservoir of Triassic Yanchang formation in southeastern Ordos basin. Wedemonstrate that the change of diagenetic environment after oil emplacement in certain degree affected the diagenetic evolution of the reservoir. In the arkose reservoir of this area, organic acid and carbon dioxide appeared in a large amount after oil injection and the pH value decreased, which promoted dissolution as the rock matrix of feldspar particles, resulted in the development of secondary pores, and enhanced the property of reservoir. However, due to low oil saturation, the change of diagenetic environment restrained illite growth slightly. To certain extent, the pore“ bridging” cement of illite reduced the property of reservoir.Meanwhile, the oil emplacement resulted in dissolution of carbonate cement formed in the early diagenetic stage. While the diagenetic temperature was higher than 100℃, the thermal evolution of organic matter would produce higher carbon dioxide partial pressure, which buffered pH value, precipitated a large amount of iron carbonate cements, and compacted the reservoir sediments.

Key words: oil emplacement, southeastern Ordos basin, Yangchang Formation, diagenetic interaction system, diagenetic evolution