Lower-Middle Ordovician Cave-Reservoir Characters and Dominant Factors in Southern Tahe Oil Field

It is discussed characteristic and dominant factors of lower-middle Ordovician cave-reservoir in southern Tahe oilfield by analyzing data such as core, well drilling, logging, and seismic systematically, and by applying reservoir identifying, wells comparing, section of seismic analyzing, and ancient physiognomy recovering technology in this article. Three cave layers effected by the early hercynian karstification have been discovered in the study area. In single well section, the cave layer with strong heterogeneity corresponds with the Karst cycle with six combinations. The cave layers dominated by the early hercynian unconformity concentrate under0-200metre of the unconformity surface. The nearer to the unconformity surface, the more caves are filled. With effecting of fracture, the caves layers, especially larger cave, are often discovered in fractures concentrated zone. With effecting of ancient physiognomy, the caves layers are often in gentle carbonate slope. The unconformity, regional fractures and ancient physiognomy are the dominant factors of lower-middle Ordovician cave-reservoir in southern Tahe oil field.