Studying Advances in Effect of Pressure on Organic Matters Maturation

Key words: 
• fluid pressure /
• organic maturation /
• pyrolysis experiments /
• kinetic models

Abstract: Most experiments are using gold bags to investigate the effect of pressure on maturation of organic matters, and no significant differences have been found in the majority of the results. However, the results from high-pressure fixed volume autoclave hydrous experiments usually showed pressure retardation on organic matters maturation. Although fixed volume autoclave hydrous pyrolysis may partly simulate the geological conditions under which hydrocarbons are being generated, the WYMN-3 HTHP instrument developed by Lanzhou Institute of Geology, Chinese Academy of Sciences or formation pore space pyrolysis built in Wuxi Research Institute of Petroleum Geology are better to investigate the organic matter maturation in overpressure basins because they also take into account of the lithostatic pressure. And high water pressure enhances the activation energy via increasing the pV work; it also reduces the entropy(ΔS) to decrease the pre-exponential factor(A). At present, using PreRo^TM and T-P-R_o models would be better for overpressure basins, but both only take account of excess fluid pressure, rather than absolute fluid pressure. So a kinetic model incorporated absolute fluid pressure is needed in further studies. Given that it is hard to compare the results obtained from different experimental methods or instruments, it is quite necessary to establish a set of standard experimental rules to fully understand the pressure effect on organic matter maturation. In addition, the exploration and development of shale gas with high maturity levels provide valuable geological data for studying the effect of pressure on hydrocarbon generation at overmature stages, but this requires the accurate determination of thermal maturity levels of marine shales in which the vitrinite macerals are usually absent or rare.