Abstract:

Characteristics of pores evolution of Carboniferous volcanic reservoirs in Dixi area, Kelameili Gas Field, are difficult to predict as the result of obviously complex diagenesis. On the basis of core observation and description, combined with the analysis of cast thin section, scanning electron microscopy, cathodoluminescence, electron microprobe, X-ray diffraction and inclusion, the diagenesis and pore evolution of volcanic reservoirs in the study area were studied. Considering the influence factors and sign of diagenesis, the diagenesis stage would be divided into four periods: condensation stage, post-magmatic hydrothermal stage, weathering and leaching stage and buried stage. Original pores and cracks were mainly formed in condensation stage and decreases drastically under the alteration and infilling of minerals in the post-magmatic hydrothermal stage, when pore porosity down to the lowest value. Weathering fragmentation, dissolution and leaching caused the formation of secondary fract ures and dissolved pores, which improves the volcanic reservoir properties. The destruction of the original pores and the formation of secondary dissolved pores are both occurred in burial diagenesis stage. Mechanical compaction affects the preservation of original pores, while infilling of minerals make the disappearance of the original pores in whole or in part, which plays a negative role to volcanic reservoirs. Benefiting from variety of secondary pores and cracks produced from the dissolution and tectonic fragmentation, the volcanic rock develops into high-quality reservoirs.

Key words:  glutenite reservoir , steep slope zone , physical property evolution , formation water , Dongying Sag