Pyrolysis experiment and reservoir-forming potential of epimetamorphic rock

Abstract

By taking pyrolysis experiments and analyzing composition and carbon isotopes of pyrolysis products, the hydrocarbon generation potential and products geochemistry of very low-grade epimetamorphic rocks were studied. The carbon isotopes of alkane gases are relatively heavier when the reactant was in an abundant gas generation stage (450–550 °C, e.g., the δ13C1 were °31.4‰ to °22.3‰, carbon isotope series showed δ13C1<δ13C2<δ13C3 or δ13C1<δ13C2, δ13C3<δ13C2, and the common feature being δ13C1<δ13C2 and δ13CCO2<−10.0‰, indicating the biogenic features. These less negative carbon isotope compositions inherit from heavy carbon isotope of organic matters in these rocks. High temperature might result in heavy alkane gases partly reversed and the mechanism has been discussed in this article, but it is still not understood clearly. The reservoir-forming potential of very low-grade epimetamorphic rocks is discussed from the aspect of hydrocarbon generation. Gas generation potential of muddy slate at a depth of 4 115.47 m in Well Zhaoshen 6 reached 86.4 m3/t. It is predicted that the hydrocarbon generation intensity can be 20×108 m3/km2 in areas of eastern Daqing placanticline, where very low grade-epimetamorphic rocks are distributed, capable of forming gas pools of certain scales. Key words: low-grade epimetamorphic rock, pyrolysis experiment, hydrocarbon generation potential, carbon isotopes, reservoir-forming potential