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New and Revised Vitrinite Reflectance Data

for the Bowser and Sustut Basins, British Columbia

GSC Open File 4669

 

 

C.A. Evenchick1, L.D. Stasiuk2, K.G. Osadetz2, and F. Ferri3

1Geological Survey of Canada

Natural Resources Canada

101 - 605 Robson Street

Vancouver, BC V6B 5J3

 

2Geological Survey of Canada

Natural Resources Canada

3303 – 33 Street NW

Calgary, AB T2L 2A7

 

3Ministry of Energy and Mines

Resource Development and Geoscience Branch

Government of British Columbia

6th Fl., 1810 Blanshard Street

PO Box 9323 Stn Prov Govt

Victoria, BC V8W 9N3

 

 

Abstract

This CD contains over 500 analyses of thermal maturity in the form of vitrinite reflectance and vitrinite reflectance calculated from bitumen, for large parts of the Bowser and Sustut basins (north-central British Columbia).  Strata are Middle Jurassic to Late Cretaceous age.  The data are expressed in HTML, Excel, and comma delimited formats.  The eastern limit of data coverage is 127°W, the western limit is 130°W, the northern limit is 58°N, and the southern limit is 54°S.

 

Introduction

This report presents new and revised vitrinite reflectance and vitrinite reflectance calculated from bitumen as an interim data release in a project to evaluate the level of thermal maturity in the Bowser and Sustut basins (see also Evenchick et al., 2002). The 286 new analyses are from samples from the Ritchie wells, parts of the northern two-thirds of the basins with sparse data coverage, a vertical profile in one region previously recognized as low maturity, and the southern third of the basin.  These are the first data reported for the southern basin.  The 226 revised analyses are from samples previously reported (Evenchick et al., 2002).  Interpretation and integration with previously reported data will be provided in future reports.

Since the rate of reaction and per cent reflectance in oil (%Ro) of huminite and vitrinite (hereafter vitrinite is used) increases with increasing temperature, these data provide an indirect geo-thermometer for evaluating thermal conditions in a sedimentary basin. Multiple reaction first order Arrenhius-based kinetics control the reaction rate in vitrinites, and thus the approximate exponential increase in huminite reflectance with increasing temperature. Because of this relationship vitrinite reflectance has been widely used to calibrate thermal history and time-temperature models for stratigraphic successions within sedimentary basins, particularly for evaluating the stage of thermal maturation with respect to oil and gas generation and preservation (Fig. 1). Reflectance studies of vitrinite have been less commonly used to evaluate the thermal history of high temperature plutonic and volcanic events in terms of absolute temperature, although many have reported on the very rapid increase in vitrinite reflectance within country rock shale beds and coal seams with increasing proximity to country rock-intrusion contact.

Several thermal maturity based studies have been published on the correlation between solid bitumen reflectance, vitrinite reflectance, and Rock Eval Tmax values (e.g. Riediger, 1993; Landis and Castano, 1995; Potter, 1999) in petroleum-enriched sedimentary basins. These correlations have been made using either the reflectance of indigenous (Potter, 1999), migra- (Jacob, 1989) or primary (this study) bitumen. Optical indices of indigenous or primary solid bitumens provide reliable data for evaluating thermal maturity when translated in vitrinite reflectance equivalent values.


 

Hydrocarbon fluid inclusions (including crude oils) are present in many of the samples examined from the Bowser and Sustut basins. The majority of data related to these inclusions will be forthcoming in the next phase of the project. Here we present some findings from samples from the Ritchie wells drilled in the central Bowser Basin. Fluorescence properties (e.g. color, emission maxima) of hydrocarbon fluid inclusions and crude oils are a signature of the gross chemical composition (i.e. aromatic and saturate hydrocarbons; NSO-bearing asphaltenes and resins) as well as the density (°API) of the included oil and thus are useful for assessing oil quality/thermal maturity, and for exploratory purposes for discerning petroleum migration pathways (see Stasiuk and Snowdon, 1997). In general, the lightest and most thermally mature oils have shortest wavelength ‘blue region’ fluorescence, and the heaviest, least mature oils have longer wavelength ‘red region’ fluorescence. As a result of these relationships, fluorescence studies of oil inclusions and crude oils can provide valuable information regarding regional distribution of oil types, quality, and potentially their migration within a petroleum system.

 

Methods

Reflectance

Whole rock outcrop samples were prepared for organic petrographic analysis by mounting in epoxy, then grinding with carborundum and diamond grit and polishing on cloth and silk using an alumina-water slurry. Samples were analyzed using both incident white light and fluorescent light microscopy. Per cent reflectance in oil (%Ro) analyses were performed using Zeiss and Leitz MPM II reflected light microscopes equipped with both white and ultra-violet light sources. Glass (1.025, 1.82 %Ro) and diamond (5.26 %Ro) standards were used to calibrate the photometer system. Thermal maturation of the sedimentary rocks and the contained organic matter has been assessed using per cent random reflectance in oil (%RoR) of wood-derived vitrinite (Organic Type 2, Table 1) and of primary solid bitumen and primary pyrobitumen (Organic Type 4, Table 1) macerals. Vitrinite reflectance equivalent (Organic Type 3, Table 1) was calculated from primary bitumen and pyrobitumen (Organic Type 4) using the relationship of Jacob, 1989, where %RoV = 0.618 x %Robitumen + 0.40 values. Evenchick et al. (2002) previously expressed the thermal maturity of surface samples from Bowser and Sustut basins using primarily %Romax of vitrinite and calculated %Romax (from bitumen), of which some data was converted from %RoR measurements. Here, however, vitrinite %Ro and vitrinite calculated %Ro are expressed as %RoR since this is the conventional standard for expressing thermal maturity in petroleum exploration and related burial-thermal history studies.

Two other types of bitumen and pyrobitumen (Organic Type 60 and 21) were also measured, which are interpreted as representing solid carbon residues derived from migrated petroleum and thus are not indicative of thermal maturity. At locations where there is a pronounced difference between vitrinite or calculated vitrinite and the reflectance or thermal maturity of the migrated bitumens, this likely indicates migration of petroleum after maximum burial of the host strata, during an uplift phase.

 

Table 1. Key for Organic Types

CODE

ORGANIC TYPE

02

VITRINITE

03

VITRINITE EQUIVALENT (04)

04

PRIMARY SOLID BITUMEN - PYROBITUMEN

15

HYDROCARBON FLUID INCLUSION A

16

HYDROCARBON FLUID INCLUSION B

17

HYDROCARBON FLUID INCLUSION C

21

PYROBITUMEN(PB)_ISOTROPIC

60

MIGRABITUMEN ISOTROPIC

 

Fluorescence

Visible light region fluorescence of hydrocarbon fluid inclusions was conducted with a Zeiss Axioplan II microscope using water immersion objectives (total magnifications up to X2500) and ultra-violet, blue and green light excitation. Fluorescence microspectrometry (between 400 and 700 nm) was conducted with a Zeiss UMSP incident light microscope (03 photomultiplier, a continuous filter monochromator b  with 1/2 band width of 14 nm at 540 nm) and Zeiss UMP pc-base controller system. An epiplan-neofluor water immersion 40x objective (total magnification x640), HBO 100 ultraviolet source, and an ultraviolet G 365 nm excitation filter (395 nm beam splitter; 420 nm barrier filter) were used during analysis. Background fluorescence was subtracted and the spectra were normalized to the wavelength of maximum energy emission. Photochemical alteration of the “well-sealed” hcfi did not occur during spectral scanning. Two spectral parameters have been used to characterize the fluorescence properties: (i) Lambda max (Lmax = wavelength of maximum emission intensity in nm) and; (ii) R/G quotient (Q = Intensity650nm/Intensity500nm).

 

 

 


Acknowledgements

 

This project was funded by the Natural Resources Canada, Earth Science Sector, Geological Survey of Canada, Northern Resource Development Program. Maria Tomica of Ramtrec Research Projects and Dr. Judith Potter of JP Petrographics, Calgary, assisted in petrographic analyses. Kim Dunn and Ryan Diamond of GSC Calgary are thanked for providing excellent technical assistance.

 

References

 

Evenchick, C.A., Hayes, M.C., Buddell, K.A., and Osadetz, K.G.

2002    Vitrinite and bitumen reflectance data and preliminary organic maturity model for the northern two thirds of the Bowser and Sustut basins, north-central British Columbia. Geological Survey of Canada Open File 4343.

 

Potter, J.

1999:   A genetic approach to the characterization of microbitumens; implications for thermal maturity determinations. Sixteenth Annual Meeting of the Society for Organic Petrology, Abstracts and Program 16, p. 11-13.

 

Jacob, H.

1989:   Classification, structure, genesis and practical importance of natural solid bitumen (“migrabitumen”). International Journal Coal Geology, v. 11, p. 65-69.

 

Landis, C.R. and Castano, J.R.

1995:   Maturation and bulk chemical properties of a suite of solid hydrocarbons. Organic Geochemistry, v. 22, p. 137-150.

 

Riediger, C. L.

1993:   Solid bitumen reflectance and Rock-Eval Tmax as maturation indices: an example from the “Nordegg Member”, western Canada sedimentary basin. International Journal Coal Geology, v. 22, p. 295-315.

 

Stasiuk, L.D. and Snowdon, L.R.

1997:   Fluorescence microscopy of synthetic and natural hydrocarbon fluid inclusions: crude oil chemistry, density and application to petroleum migration. Applied Organic Geochemistry, v.12, p. 229-241.



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