Caprock Evaluation of Natural Gas Reservoir within the Eastern Depression, Liaohe Rift

Key words: 
• caprook evaluation /
• eastern depression /
• caprock /
• exploration

Abstract: The Eastern depression is one of the three depressions of Liaohe Rift and located in the lower Liaohe plain in Liaoning Province. This paper indicates by means of the analysis of caprock types, effect of compaction on seal ability of caprocks and the seal ability of volcanic caprocks that local caprocks are very developed, of which the best caprock is the volcanic rock, although the depression lacks the regional caprock. The variation of shale caprocks in different beds is great. The mudstone caprock was formed in the periods of saltatory and tight compactions in the middle-deep horizons, but the volcanic caprock complemented the lack of mudstone caprock in shallow horizons. Based on the relationship between mudstone caprock and reservoir, it is known that there is a poor caprock but good reservoir in shallow horizons, but it is contrary in deep horizons. In view of mudstone caprock, the medium-large gas reservoirs should be formed in middle-deep horizons, and small gas reservoirs should be formed in shallow horizons. However, in the depression well-developed volcanic caprocks increased the probability of formation of large gas reservoirs in shallow horizons, which broke the regularity of vertical distribution of natural gas on the condition of mudstone caprock. According to the distribution of breakthrough pressure of mudstone caprock in different horizons and depths as well as the distribution of volcanic rocks, the exploration potential of gas reservoirs in deep horizons was proposed.