Gases in Reservoirs: A Balance between Generation and Migration, Part I: Compositional Modelling
Jean-Luc Rudkiewicz, Sylvie Wolf, Francoise Behar, Mireille
Vandenbroucke, and Johannes Wendebourg
New developments in compositional cracking and generation as well as migration modeling allow a discussion about the origin of gases in reservoirs.
Experimental closed system pyrolysis allows to describe compositional primary cracking of kerogen and secondary cracking of oil using a comprehensive kinetic scheme. In addition, experiments give us some indications as to the relative amount of gas that is generated. Kerogens of Type II or III show early gas generation, coinciding with oil generation. However for Type III kerogen, the most important gas generation is late gas generation. In contrast, gas generated from Type II kerogen comes mainly from secondary cracked oil.
Whether or not oil generated in a source rock might migrate to a reservoir or crack to gas depends on geological time and temperature conditions and on its transport properties. An improved version of IFP's 2-D basin model has been developed to account for compositional generation, cracking during migration. In addition, the generated or migrating hydrocarbons may split into a gas and an oil phase. The model allows to distinguish between the generation of dry gas, condensate, light or heavy oil. Under geologic times and temperature evolution, oils seem to exhibit a higher thermal stability than previously assumed, resulting in a larger oil window and thus deeper gas window.
AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California