--> --> Abstract: On the Cracking of Oil to Gas in Source Rocks and Reservoirs, by Volker Dieckmann, Olaf Podlaha, Matthias Keym, Andy Bell, and Joseph Westrich; #90124 (2011)

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Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA

On the Cracking of Oil to Gas in Source Rocks and Reservoirs

Volker Dieckmann1; Olaf Podlaha1; Matthias Keym1; Andy Bell1; Joseph Westrich1

(1) R&D, Shell SIEP, Rijswijk, Netherlands.

The cracking of oil to Gas cracking (OTGC) is a key process for the formation of gas in deep, hot source rocks, gas shales and reservoirs. The ability to predict the timing of OTGC and the composition of the formed gas phase is of particular interest as the complex transformation process itself controls the compositional characteristics of the residual fluids in time and space. Of particular interest is if OTGC has taken place in organic rich source rocks sources rock or in TOC lean formations such as reservoirs and/or silts. In our study we will attempt to show that the properties of asphaltenes, aromatic and saturated hydrocarbons in reservoir oils and source rock bitumen as well as the different cracking reaction network have a key control on Oil to Gas Cracking characteristics.

Our results are somewhat in contraction to previous studies as neither interactions with residual kerogen nor with the rock matrix at high temperatures significantly influence the cracking behaviour of oil in different environments. We will show that OTGC measured for TOC lean reservoirs started at much higher temperatures than for the source rock. Interestingly, such behavior persists when the residual source rock kerogen, which should act as a catalyst, is no longer present during the cracking process. The difference is in the range of around 30oC and can also be reproduced when extrapolated to geological conditions. This difference is also supported by field evidence and results from a case study will be shown to illustrate the impact on subsurface gas risk and distribution.