J. Potter, M. Skuce, F.J. Longstaffe, T. Carter, L. Fortner

1. The Abandoned Works Program, SW Ontario: identifying the sources of leaking formation waters and natural gases J. Potter, M. Skuce, F.J. Longstaffe, T. Carter, L. Fortner The University of Western Ontario The Ministry of Natural Resources

3. The Problem:Potentially >22,000 leaking wells in the province that have not been fully recorded • The Abandoned Works Program was set up by the Ministry to confront this problem and establish a remediation program • Plugging a well that has good records can cost ~$10,000 but “problematic” wells have been known to exceed the $250,000 mark before successfully sealed

4. Abandoned Works • Which formation is source of the sulfur water/oil/gas? • Where do plugs need to be set to confine the aquifers? • Which formations are competent for setting of plugs? • Where has casing corrosion likely occurred?

5. The Aim:Identifying fluids from specific horizons • Characterise the geochemical and isotopic compositions of natural gases and waters from SW Ontario reservoirs and aquifers, and use this knowledge to determine the source(s) of gases/waters leaking from abandoned wells. • are there any differences between stratigraphic levels • are any differences geographically related • can we differentiate between these reservoirs and what they may show with regard to origin Analyses being done: Geochemical analysis of waters O and H-isotopes (water) S and O-isotopes (sulphate) C-isotopes (DIC) Sr in water C and H-isotopes (natural gas)

6. Water well records - MOE (from Singer, Cheng, and Scafe 1997)

7. Petroleum Well Records - MNR

10. What can stable isotopes of natural gases tell us? Utilising methane isotope results can provide us with a glimpse of how these gases were formed and subsequently altered Whiticar (1999) now d2H

11. What can stable isotopes of natural gases tell us? • Methane and higher hydrocarbon isotopic compositions can be modified by a number of processes (main processes being): • degree of thermogenic “cooking” • mixing of reservoirs • microbial methanogenesis • microbial oxidation • The d13C and d2H differences between methane (C1) and higher hydrocarbons (C2+) can provide valuable information including • those diagnostic features that we are looking for and.. • how they were formed and subsequently altered due to mixing, fluid infiltration and microbial interaction

12. Carbon- and hydrogen-isotope results of methane – all results incr. microbial influence incr. thermogenic maturity

13. Hydrogen-isotope results of methane and ethane incr. thermogenic maturity incr. microbial influence?

14. Carbon- and hydrogen-isotope results of methane Cambrian ? T008045

15. Carbon- and hydrogen-isotope results of methane Lower Ordovician Black River

16. Carbon- and hydrogen-isotope results of methane Middle Ordovician Trenton

17. Carbon- and hydrogen-isotope results of methane Lower Silurian Whirlpool

18. Carbon- and hydrogen-isotope results of methane Lower Silurian Grimsby

19. Carbon- and hydrogen-isotope results of methane Lower-Mid Silurian Thorold

20. Carbon- and hydrogen-isotope results of methane – Middle Silurian Guelph

21. Carbon- and hydrogen-isotope results of methane Upper Silurian A1 unit

22. Carbon- and hydrogen-isotope results of methane Upper Silurian A2 unit

23. Our first unknown sample! The $250,000 question. microbial CH4 fermentation – terrestrial microbial CH4 CO2 –reduction - mainly marine incr. maturity Lowest d13CCH4 observed so far. Mix of near surface microbial CH4 + thermogenic? d13CCO2 = -20‰

24. Hydrogen-isotope results of methane and ethane d2H results for unknown outside all fields incr. maturity Microbial input?

25. Hydrogen-isotope results for methane vs ethane in the Black River and Trenton pools In most thermogenic gas reservoirs d2HCH4 < d2HC2H6 but here we observe a diagnostic feature where d2HCH4 ~ d2HC2H6

26. SUMMARY OF ISOTOPIC DATA FOR THE NATURAL GASES A series of diagnostic features have so far been identified: • The Cambrian gases are generally the most thermogenically mature • With decreasing age of reservoir, in general, a thermogenic trend to less mature gases is observed • The Ordovician Black River and Trenton natural gas samples have distinct d2H values for CH4 and C2H6 that are easily recognisable - they are = or slightly inversed. • The Silurian Whirlpool and Thorold samples are immature with respect to the Grimsby reservoir of the same age in the same area. • - they also sit slightly off the thermogenic trend • - more data required – geographically controlled?

27. SUMMARY OF ISOTOPIC DATA FOR THE NATURAL GASES A series of diagnostic features have so far been identified: • The large Silurian Guelph sample dataset clearly shows a microbial input in samples from the Lambton area. Samples from Huron are also distinguishable from other reservoirs but do not show quite a shift to low d13CCH4 values • - distinctly high d13CC2H6 and d13CC3H8 values relative to other • reservoirs • The Silurian A1 Salina Group samples in the Lambton area overlap the Guelph samples from this region but can be distinguished by lower d13CC2H6 values. Samples from the Kent area are very different, sitting on the thermogenic trend • The Silurian A2 Salina Group samples in the Lambton and Kent areas do not show the “Lambton anomaly” – a possible time constraint on fluid/microbial interaction in the reservoirs in the Lambton area? • - caution, only 3 samples!

28. Water isotope data Deep aquifers (~500 - 1200m) Shallow aquifers (<250m)

29. FURTHER WORK • Fill in the gaps: • - more samples from the Appalachian side of the Algonquin Arch • - stratigraphic horizons of interest with respect to geographic locality – Lambton looks v. interesting for e.g. • Critically analyse and interpret all these data to confirm observed patterns and ascertain how these reservoirs have been produced/modified and/or show migration/mixing • Continue sampling of abandoned well fluids, as and when required, will provide an ongoing test of this geochemical tool. • create a user-friendly platform to input gas and water isotope analyses and statistically analyse the results of unknowns vsknowns to ultimately identify the unknown reservoir. • SIARS seems to be a good statistical tool at present

30. Acknowledgments As always: LSIS – Kim, Li and Lisa for help on the GC, Picarro, Gasbench and TC/EA Paul and Wendy at GGHatch, UofO for help with sulphur isotope analyses Scott Mundle at UofT for keeping us entertained in the field… even if it is his fault that we have to stand out there for an hour at a time freezing or melting!... Lee thanks for arranging the coldest/hottest/post-tornado blowiest days for heading out into the backwoods!