What are we going to talk about?

Transcription

1 What are we going to talk about?

2 Hydraulic Fracturing: How to assess its impact on groundwater: Lessons from Alberta, Canada Karlis Muehlenbachs Department of Earth and Atmospheric Sciences University of Alberta Edmonton, Alberta, Canada

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5 Method proven to be extremely $$$ effective for production

6 Vancouver Sun Why???

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9 Breaking news! On USA Federal lands:

10 #9 Escaped fracturing fluids, Innisfail, AB Jan

11 About 18 incidents have been reported in BC.

12 #8 Domestic wells in the area of investigation overlie the Pavillion gas field which consists of 169 production wells which extract gas from the lower Wind River Formation and underlying Fort Union Formation. Hydraulic fracturing in gas production wells occurred as shallow as 372 meters below ground surface with associated surface casing as shallow as 110 meters below ground surface. Domestic and stock wells in the area are screened as deep as 244 meters below ground surface. With the exception of two production wells, surface casing of gas production wells do not extend below the maximum depth of domestic wells in the area of investigation.

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14 An aside: Not all fracturing is deep! Fracturing allowed 50 m Many thousands of shallow CBM wells beneath water well already fracked in AB

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16 #5 (Also oil field brines) #4

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18 #3 Man induced, magnitude 4 earth quake, Ohio, Dec 31,

19 #2 Methane carbon isotope value

20 #1 Burning water: Industry induced Or natural background?

21 Anthropogenic gas seeps Well Head, Dimock, PA Gas well, leaking , Turner Valley, Alberta

22 Natural gas seeps NW Alberta, Canada Eternal flame, Chimaera Turkey

23 Yes, but, what happens if the job is not done right? How frequently are instances of poor cementing and casing problems encountered?

24 Wells are encased in a variety of casings to capture gas migrating up well bores. How often are there errors in 1)setting the surface casings 2) cementing etc.?

25 Well completions at Pavillion, WY.; revisit #9 Shallowest Frac Only two gas wells have SC deeper than deepest water wells! Aquifer USEPA, 2011

26 Problems and poor cementing are common and lead to gas migration and sustained casing pressure Data from off shore Gulf of Mexico, USA From Schlumberger, Oilfield review

27 Soil Gas Watson & Bachu

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29 Innisfail!

30 Natural fractures may be up to 1100m long But note, induced fractures may be up to 600m long, and impact may be take 6 to 10 years to show up.

31 So, how can we identify the source of fugitive gas in aquifers, soils and surface casings? Isotope ratios of problem gases captured at surface indicate source depths!

32 Biogenic gas Shallow CBM Thermogenic gas Increasing depth Methane from deep shale gas M. Schoell

33 Determining source of migrating gas: Start with Mudlog (NE Alberta) methane C1 C2 ethane C3 nc4 propane normal butane 300 Depth δ 13 C

34 Determining source of migrating gas: Interpret the Mudlog, identify formations 100 C1 C2 C3 200 nc4 300 Depth Mannville δ 13 C

35 Determining source of migrating gas: Find best match C1 nc4 C2 C3 C1 C2 C3 Methane nc4 Ethane SCV Water Well Depth Propane n-butane Mannville Source of Migrating SCV gas δ 13 C

36 Determining source of migrating gas: Same with gas from water well C1 C1 C2 C3 nc4 C2 C3 nc4 Methane Ethane SCV Water Well Propane Depth 400 n-butane Mannville Source of gas in water well δ 13 C

37 Locations of SCV gases in U of A database n = 3304

38 Source of leaking gases In most cases SCV, soil and water gases are not from production horizon 75% of SCVF gases have a shallower source (well integrity issues) In some fields, certain formations more prone to gas migration! Isotope fingerprinting works best if lots of background data available. BWWT?

39 Gases in selected water wells in central Alberta U of A Database 0-10 δ 13 C ethane Biogenic gases? Thermogenic gases - Impacted by gas drilling Are all these gases really naturally occurring in domestic water? δ13 C methane

40 Gases in selected water wells in central Alberta C ethane δ When we consider the possible sources of gas migration, there are many more water wells that may have been impacted by gas well drilling. gases in selected water wells in central Alberta Alberta thermogenic gases Alberta coals commercial biogenic gases from Medicine Hat δ13 C methane 7/26/2011, BT, U od A

41 Locations of water well complaints in U of A database. Oil Sands Scollard Formation Horseshoe Canyon Fm. Belly River Group Mannville Group Luscar Group Kootenay Group

42 Locations of water well complaints in U of A database. Mixed, biogenic and deep thermogenic gas Shallow, biogenic gas Mixed, biogenic gas, possibly with CBM Oil Sands Water well gases from both the Mannville as well as overlying shales. Thermogenic gas Scollard Formation Horseshoe Canyon Fm. Belly River Group Mannville Group Luscar Group Kootenay Group Mixed gases, biogenic with CBM, some legacy thermogenic gas

43 Conclusions and suggestions to Industry and regulators: To protect and identify specific sources of gas contamination in groundwater we need to mandate baseline isotopic fingerprinting of methane, ethane and propane for: Pre-development water wells Post-fracing surface casing vents of new wells Retest SC of preexisting wells near new frac jobs. Production gases Detailed gas isotope stratigraphy (mudgas isotope log) *The above requirements are not onerous, CAPP has similar recommendations.

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