Characteristics of oil and gas generation, expelling and retention of coaly source rock

Abstract

To understand the effectiveness of hydrocarbon generation, expelling and retention capacities of coaly source rocks, carbonaceous mudstones and mudstones in coal layers and interlayers of different sedimentary environments and ages were selected to carry out the simulation experiments with a semi-open system operated at high tempera-ture and high pressure, and a corresponding model of evolution was established. With different depositional environments, the type Ⅱ2 coaly source rocks expelled oil in the oil generation window with gas generated. Therefore, they worked as source rocks for both of oil and gas. However, for the coaly source rocks of type Ⅲ kerogen, the generated oil was mainly retained during the oil generation window and basically did not expel. As a result, this type of source rock was regarded as source rocks of gas only. The conversion rate of hydrocarbon generation was mainly controlled by the type of organic matter, while the ability to expel hydrocarbons was controlled by lithology and organic matter abundance. For each unit mass of rock, coal rocks has much higher conversion rates than the carbonaceous mudstones and mudstones in their interlayers. In the full evolution stage of coal rock, both low-rank and high-rank coals had strong ability for hydrocarbon gas generation and oil-and-gas retention, which showed a good potential for coal bearing methane development.

Keywords

• hydrocarbon generation
• hydrocarbon expelling
• hydrocarbon retention
• simulation experiment
• source rock
• coaly strata