Vertical zoning of oil and gas formation: historico-genetic aspects

Abstract

Considerable variations in depth zoning of dispersed organic matter (DOM) catagenesis are caused by various physical and geological factors. The evolution of a sedimentary basin (SB) implies successive changes in organization levels of this system. In the process of evolution the system structure is determined by the interaction of its subsystems. Any parameter of an SB (physical properties of rocks, degree of OM catagenesis, temperature, formation pressure, phase ratio of hydrocarbons) is governed by the processes running in the system. Variations of these parameters in space and time characterize the structure of the changing system. The intensity of lithification of terrigenous rocks, OM catagenesis, and HC generation in time is approximated by a curvilinear relation, which becomes asympthotic at a particular stage. In other words, these processes drastically decay 150 ± 50 Myr after the main sedimentation had completed. For an SB system with a natural set of main subsystems (mineral, water, organic, hydrocarbon), the age is less important (at least throughout the Phanerozoic) than the duration of the process. Analysis is given to the formation of vertical HC zoning, which includes all the processes observable within an SB. The relationship of events and qualitative temporal and spatial changes during these processes is considered.