Abstract: The mineral components of volcanics are complicated and variable. The density of matrix of each type volcanic rock varies widely, so it is difficult for using conventional methods to calculate its porosity. Element capture spectrum (ECS) log can present two measurement results including the percentage of primary rock-forming elements and various oxides of formation, which are closely related to density of rock matrix. According to this, the model for calculating density of matrix of volcanic rocks is established. Integrated with density log, it is used to calculate porosity of volcanic reservoir. Practice shows that the method has good geological application effect in Junggar basin.

Key words: Junggar basin, volcanics, reservoir, porosity, ECS log tool