Assessment of Organic Petrology Methodology and Characterization of Primary and Secondary Dispersed Organic Matter in Liquid-Rich Shales

L. D. Stasiuk, Amr El-Ezhary, Michelle Asgar-Deen, Volker Dieckmann, Rob Robinson, and Gary Green
Shell Canada, Calgary, AB, Canada. 2 SIEP, Houston, TX, USA

Traditionally, organic petrology (OP) method is defined as an optical-based, reflected white and fluorescent light, microscopic characterization-classification-quantification, and, measurement of % reflectance in oil (%Ro) and VIS of individual primary (kerogen) and secondary (e.g. bitumens, oils, solid hydrocarbons, pyrobitumens) organic matter, referred to as macerals. Combined, primary and secondary organic matter, make up total weight percent of organic carbon in sedimentary rocks, including LRS. Perfecting the sample preparation of fine grained rocks is not achieved in many labs, thus negatively impacting analytical data and interpretations. Ideally LRS samples for OP maceral analyses should be whole rocks, very gently crushed and or sized such that random, parallel, and perpendicular to bedding, and or microfractures are represented, and impregnanted with new, very low viscosity, epoxy, under vacuum conditions. Use of solid, bored, acrylic rods and epoxy are an ideal combination for superior preparation of LRS samples, thus ensuring integrity and retention of all microtextural elements, and organic (e.g. friable ‘solid bitumens’) and mineral (e.g. clays) matter that are otherwise prone to plucking during the grinding and polishing process, resulting in poor quality data, poor interpretations.

Commonly the assessment of microscopic organic matter is inadequate because of lack versatility in classifications, and under recognition of secondary organic matter in LRS. A new, maceral classification for primary and secondary dispersed organic matter in sedimentary rocks will be adopted by the International Committee for Coal and Organic Petrology (I.C.C.P) in 2013, will improve consistency in nomenclature between commercial labs, if explicitly requested by clients. In order to adequately evaluate original kerogen type, organic facies and paleodepositional settings of LRS based on data collected following the I.C.C.P. (proposed 2013 ) classification of DOM, higher levels of macerals classification identification (e.g maceral type, maceral variety, maceral sub-variety; See Table below) needs to be augmented with inorganic microfossil components. Examples will be provided from The WCSB.

Secondary organic matter likely constitutes more of the TOC in LRS than has previously been recognized by OP; that is, there are higher amounts of solid hydrocarbon and pyrobitumens derived from kerogen to bitumen to oil conversion, and, from oil to gas, and oil to condensate cracking. This has implications for assessing original petroleum potential of an LRS, and potential, for linking OM related nano-porosity to individual secondary maceral types using combined OP and FIBSEM type of analyses.

AAPG Search and Discovery Article #90186 © AAPG Geoscience Technology Workshop, Hydrocarbon Charge Considerations in Liquid-Rich Unconventional Petroleum Systems, November 5, 2013, Vancouver, BC, Canada