Adventures in Programmed Pyrolysis I

Abstract

Programmed pyrolysis has been used to evaluate source rocks for 50 years. The “standard” method was developed and has been used to assess the potential for generation of conventional petroleum accumulations. It has now been applied to unconventional reservoirs. Recently, alternative pyrolysis programs have been suggested to improve identification of moveable and immovable hydrocarbons in unconventional systems. We have investigated two of these alternate methods, one using multiple steps in heating rate (IFP Shale Play Method) and the other a single ramp (Extended Slow Heating, Sanie et al 2015) and compared the results to the standard method. This discussion will focus on a comparison of the standard and multi ramp methods. Twenty core and outcrop samples containing primarily Type II kerogen were analyzed pre and post solvent extraction using both SRA and RE6 instruments. Aliquots of each sample were retained for eventual mineral and elemental analyses.

The pyrograms for the standard method consist of two peaks: S1 volatile hydrocarbons distilled from the sample at 300°C, and the S2 peak theoretically the hydrocarbons derived from the conversion of kerogen between 300°C and 650°C. The multi-ramp method produces three peaks, Sh0 the most volatile compounds distillable at 200°C, Sh1 compounds which distill between 200° and 350°C, and Sh2 theoretically attributed to kerogen breakdown. Total pyrolysis yields for both methods were equivalent. The average difference between Tmax values of the kerogen peak, pre and post extraction is 1.9°C for both methods.

Solvent extraction removes the S1 peak, but also reduces the size of the S2 peak in most samples. The S2 peak pre extraction contained some soluble compounds which may or may not be moveable within a reservoir. The multi-ramp method is designed to better separate potentially moveable hydrocarbons from those generated by kerogen conversion. Multi-ramp analysis of extracted samples removed the Sh0 and most of the Sh1 hydrocarbons. However, some samples showed evidence of kerogen conversion at temperatures below ~350°C. This observation indicates that not all the Sh1 signal can be attributed to hydrocarbons that were previously generated by the kerogen and have the potential to be moveable. Some of these are being generated in the laboratory. The reasons some sample show low temperature generation and some do not are twofold: kerogen thermal maturity and organic matter type, as will be presented in detail.

AAPG Datapages/Search and Discovery Article #90323 ©2018 AAPG Annual Convention and Exhibition, Salt Lake City, Utah, May 20-23, 2018