Hydrocarbon evolution during pyrolysis of source rocks of Yacheng coal formation from the Yanan depression in the South China Sea

Closed-system pyrolysis experiments were conducted on coal and carbonaceous mudstone samples using gold tubes pressured to investigate the gas generation potential and evolution. The results indicate that the total gas potential of coal is 5times that of carbonaceous mudstone, and the total oil concentration is 2.5times that of carbonaceous mudstone. Methane continuously increased with increasing temperature of pyrolysis. The increase ratio of heavy hydrocarbon gas is the largest at low temperature. The gas evolution of both samples is controlled by activation energy. Coal can be divided into four stages, namely kerogen degradation, kerogen cracking, oil cracking, and C-2 cracking stage. Carbonaceous mudstone can be divided into kerogen cracking and oil cracking. The temperature of turning point for coal is higher than carbonaceous mudstone.