Basic Energy Sciences researchers unravel the record of fluid flow in oil and gas-bearing rock
Researchers R. L. Ripperdan, L. R. Riciputi, and D. R. Cole of Oak Ridge National Laboratory and R. D. Elmore, S. Banerjee, and M. H. Engel of the University of Oklahoma have challenged the traditional assumptions about how to identify the source and to date the flow of waters across hundreds of kilometers through basins of sedimentary rock. In their research to understand oil and gas migration and concentration in the Belden Formation of western Colorado, Ripperdan and co-workers questioned the standard assumption regarding the relationship between the rock's magnetic properties and the origin and timing of episodic flow in reservoirs. The answer to this question is of great significance because some of the flow processes concentrate oil and gas within reservoirs.
The magnetic properties of rocks can be used to date the flow of fluids because magnetic polarity is frozen when a common magnetic mineral, magnetite, is formed. The standard assumption is that magnetite precipitates from hot water generally associated with mountain building. Ripperdan and co-workers tested this assumption by analyzing the temperatures of the fluids recorded in the oxygen isotopes of the magnetites from the Belden formation rocks. Based on oxygen-isotope analyses, Ripperdan and co-workers find that the temperature of the original water from which the magnetite was formed was much colder than that associated with mountain building. This lower temperature is associated with rain or ocean water. These results are consistent with other evidence that the magnetites precipitated at the same time as oil and gas were formed, which is much earlier than mountain building that took place during the Rocky Mountain uplift. In addition, their findings require that the traditional association of timing recorded by rock magnetic properties with mountain-building events be reinterpreted.
