Gas Generation from Oil-Prone Source Rocks Containing Type-II and -Iis Kerogen as Determined by Laboratory Pyrolysis Experiments

Michael D. Lewan¹, Maciej J. Kotarba², John B. Curtis³, and Dariusz Wieclaw^2
1U. S. Geological Survey, Denver, CO
²AGH-University of Science and Technology, Krakow, Poland
³Colorado School of Mines, Golden, CO

Previous paradigms considered gas generation from oil-prone source rocks to follow oil generation at higher thermal maturities. Experimental pyrolysis studies have shown that although gas generation from a source rock continues beyond oil generation at higher thermal maturities, a significant amount of gas is generated during oil generation. In evaluating this different paradigm, the issue arises whether the mechanisms for gas generation and therefore, its timing are coupled to oil generation. This study addresses the issue by comparing laboratory pyrolysis results on oil and gas generation from oil-prone source rocks of two different organic facies in the Oligocene Menilite Shales of the Polish Carpathians. One of the organic facies contains source rocks with Type-IIS kerogen, which has been shown to generate oil at low thermal maturities. The other organic facies contains source rocks with Type-II kerogen, which generates oil at normal thermal maturities. Both of the samples used to represent these two different organic facies have total organic carbon (TOC) contents of 17 wt % and Rock-Eval hydrogen indices between 600 and 735 mg S2/g TOC. Micro-scale sealed vessel (MSSV) and hydrous pyrolysis are the two laboratory pyrolysis methods used in the study to determine kinetic parameters for oil and gas generation. The resulting kinetic parameters are used in geological heating rates to evaluate the timing of gas generation as it relates to oil generation from both types of oil-prone source rocks.

AAPG Search and Discovery Article #90078©2008 AAPG Annual Convention, San Antonio, Texas