Diagenetic history of Ordovician and Devonian oil ... - Geology Ontario

STUDY AREA
The study area is located in the extreme southwest corner of Ontario (Figure 2).
Ordovician oil and gas pools are found throughout southern Ontario, but the majority of
currently producing pools are located here. Many of the earlier discovered pools, such as
Hepworth and Acton, are no longer in production. From southwest to northeast the wells
examined include those located in the following pools: Malden, Colchester, Hillman,
Goldsmith-Wheatley, Renwick, Dover and Lambton. Each pool typically has one or two
cores available with the exception of the Hillman pool which has four cores. In order to
observe the pre-fracturing characteristics and compare pre- and post-fracturing diagenesis a
core (OGS-82-2 Harwich 25-DECR in Kent County) located away from the oil pools was
also examined.
METHODOLOGY
A list of the wells used in the study and core descriptions are presented in
Appendix 1. Approximately 350 thin sections were produced and stained with potassium
ferricyanide to indicate relative iron content and Alizaran Red-S to distinguish between
calcite and dolomite. The microscopic examination includes transmitted light and
cathodoluminescence. Geochemical analyses include major and trace elements (Ca, Mg,
Fe, Mn and Sr) of limestone and dolomite examined with microprobe and stable isotopes
(C and O) of limestone and dolomite.
Thirty-two samples of dolomite and sixteen of limestone were drilled with a
modified dental drill for bulk analyses of stable carbon and oxygen isotopes. The analyses
were performed at the University of Waterloo on a VGMM903 mass spectrometer.