Overpressure retardation of organic-matter maturation: a kinetic model andits application

A kinetic model, T-P-Ro, has been developed to address the issue that overp ressure increases the activation energies during organic-matter maturation and that the retardation of organic-matter maturation by overpressure is du e to the fact that organic-matter is hindered from progressive molecular or dering. Under overpressured conditions, the mean effective stress (i.e. mea n stress minus pore pressure) is much lower and the pore pressure is usuall y higher than under hydrostatic pressure conditions. As a result, the progr essive molecular ordering of the vitrinite, such as the aromatization, is r etarded, and the vitrinite reflectance can hardly be increased. The reflect ance values predicted by TP-Ro model as it has been applied to the Well LD3 011 at Yinggehai Basin in South China Sea, are similar to the measured ones . The kinetic model predicts that overpressure can cause the oil window flo or and the peak oil generation to shift to greater burial depth. In the cas e of Yinggehai Basin, the local geological conditions are prone to generate light hydrocarbons and natural gas (instead of oil), hence they constitute the predominant products in this high temperature (heating rate) basin. (C ) 2001 Elsevier Science Ltd. All rights reserved.