Abstract

Present-day temperature and vitrinite reflectance (R o ) profiles are considered key factors for calibration in numerical basin modeling; therefore, it is important to understand how such profiles are generated. Basin modeling typically considers factors such as rock consolidation, depth-variation of petrophysical characteristics, changes in heat flow, and paleoclimate; however, our basin evaluations have shown that other processes that influence temperature and R o (vitrinite reflectance) profiles commonly are inadequately studied. Modeling within the Urengoy field of the West Siberian basin has allowed numerical estimates of some of these nonstandard processes. First, a substantial increase in temperature (up to 5-10 degrees C) is expected from changes in heat conductivity due to the formation of significant free gas, gas-condensate, and condensate. Second, climate variations creating numerous periods of formation and degradation of permafrost zones for the last 3.4 m.y. could decrease the modern rock temperatures by 10-17 degrees C in the upper 1.5 km of the sedimentary section and up to 10 degrees C at its base. Due to the short duration of these two processes, their effect on organic matter maturation is minimal; nevertheless, their roles in the formation of present-day temperature profiles necessitate their inclusion in basin modeling. Third, modeling results demonstrated that change in heat conductivity of rocks with dispersed organic matter can increase temperature of sedimentary rocks by 3-5 degrees C and rock maturity by not more than 0.02% (R o ). Finally, the sharp increase in vitrinite reflectance (% R o ) with depth, typical for the deep sedimentary units of the Urengoy field and many other continental rift basins, is possible to explain from hydrothermal activity. The influence of these processes on subsurface temperatures and maturation of organic matter can vary significantly depending on lithology, organic matter content, and the location of the modeled section relative to the ancient rift system. The results of this study can help one estimate the relative influence of these parameters.

You do not currently have access to this article.