Study on the Generation Features of Gaseous Hydrocarbon in Different Source Ro cks —— Evidences from DTA coupled with chromatography thermal simulation

Key words: 
• Coal /
• rank /
• source /
• rocks

Abstract: To understand the thermal evolution process and hydrocarbon-forming mech anism of organic matter, the researchers have done lots of hydrocarbon-generatio n experiments on the sediment and rock-containing organic matter. In this paper we have adopted the method DTA coupled with chromatography to simulate the gener ation of gaseous hydrocarbon from the standard coal samples of different ranks a nd oth er source rocks. The method is of the following advantages: (1) rapid temperatur e-rising speed and without influence of pressure; (2) continuous sampling; (3) o nly gaseous hydrocarbon analysed; (4) directly comparing gas-forming state of so urce rock with DTA and weight loss features; (5) less human-induced influence on experiment results. By use of the new analysis method, we have concluded that the low-mature c oal has the strongest exothermic reaction and weight loss in relatively lower th e first temperature of exothemic reaction and weight loss temperature. And the c oal sample with low rank has much stronger hydrocarbon-generating capacity than those with high rank in the course of the themal simulation. The generation amou nt and features of the gaseous hydrocarbon are dependent not only on the abundan ce of organic matter,but also rock types,kerogen types,maturation degree and so on. Source rocks with higher maturation degree belongs to the exhausted rock of the weaker hydrocarbon-generating capacity. Gaseous hydrocarbon produced from th e source rock containing Ⅰ and Ⅱ-type kerogens is generally of the high conten t of heavy components, whereas those formed from the source rock bearing Ⅲ-type kerogen is mainly composed of the light components such as methane and ethane. Carbonate source rocks have weaker hydrocarbon-generating capacity in the proces s of the thermal simulation due to their low content of organic carbon, but the much higher temperature can increase the internal pressure of the inclusion in c arbonate crystals resulting in explosion to release "effective hydrocarbon". Thus, carbonate source rock can usually produce large amounts of gaseous hydroc arbon at the higher temperature stage during thermal simulation.