Determining the Source Depth of Migrating Problem Gases along Wellbores!

Transcription

1 Determining the Source Depth of Migrating Problem Gases along Wellbores! Karlis Muehlenbachs Dept. Of Earth and Atmospheric Sciences, University of Alberta, AB, Canada SABCS, ptrc, Sep. Nov. 25, '

2 RFF (Washington, DC) did a survey to see what risks experts anticipate from shale gas development! - What routine risks require most attention?! - Provided 264 potential risks! - Choose those that need further government or voluntary industry attention! - What are the accident risks that require most attention?! - Provided 14 accidents that can occur.! - Can choose probability! - Can choose severity! 2

3 Top consensus categories (for routine risks)! Of the 12 agreed upon:!! 7 surface water! 2 groundwater! 2 air quality! 1 habitat disruption!! Industry top priority:! community impacts! 3

4 Top 3 Priorities for Accidents (14 choices)! #1 and #2 is same for all groups:! cement failure and casing failure! #3 for NGOs, Academia, Gov t:! impoundment failure! #3 for Industry:! truck accidents! 4

5 How to identify the source of fugitive gas?! Increasing depth Methane from deep shale gas with isotopic reversals M. Schoell 5

6 Interpreted carbon isotope mud log from the Belloy field, Alberta!

7 Test of Profile Veracity Producing Zones Compare known production gases from nearby wells to the Belloy isotope mud gas depth profile

8 Source depths of SCV gas leaks determined using the Belloy profile scv source depth Depth (m) C1 C2 C3 Problem gas C1 C2 C Carbon Isotope Value Carbon Isotope Value

9 Background data across basin: Correlated gas isotope mud logs!

10 Source depths of SCV flows in the Lindbergh heavy oil field as % from each formation, derived from an isotope mud log.! n=156 FWS SWS BFS BFS Viking Viking sand Grsndrp Clrwt Mcmurray Woodbend % of Leakers The δ 13 C (PDB)

11 Locations of conventional SCV gases! in U of A database n = 3304! 11

12 Location of wells with both known production and SCVF gas! n = 267!

13 Carbon isotope cross plots of SCV vs production gas from same well! Samples on 1:1 line are the only cases where gas in SCV is! production gas! (about 25%)!

14 Likely sources of SCV gas in central, rural Alberta! FWS! 0.12 Med Hat! SWS! BFSC! 0.1 Fraction of SCV Shallow! Milk River! <-60 [-60,-58) [-58,-56) [-56,-54) [-54,-52) [-52,-50) [-50,-48) [-48,-46) [-46,-44) [-44,-42) [-42,-40) [-40,-38) [-38,-36) [-36,-34) [-34,-32) [-32,-30) -30 Ethane carbon isotope value Viking! Deep! Mannville!

15 !!!!!!! Production and SCV gases from the Pembina field of Alberta!

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18 Should we expect better or worse integrity/cementing, sealing in multiply hydraulically fractured wells?! Don Getzlaf! Chief Technology Officer NCS Energy Services! 18

19 Production gases from horizontal, hydraulically fractured wells in the Horn River and Montney! δ 13 C of ethane! higher maturity! Shale gas, isotope reversals & rollover! lower maturity! δ 13 C of ptrc, methane! Nov. '13 19

20 An aside on the origin of shale gas, its rollovers and reversals:! 20

21 Production & SCV gases from horizontal, hydraulically fractured wells, Montney! δ 13 C of ethane! Mixed-multiple! Fraction!! SCV! Production! δ 13 C of methane! Methane, δ 13 C! 21

22 Paired production, SCV and soil gases from a single! horizontal,hydraulically fractured well in the Montney! Example A! Example B! 22

23 Production and 4 SCV gases from horizontal, multiply hydraulically fractured wells from a single pad in the Montney!! 23

24 Other gases migrating to surface from different horizontal, multiply, hydraulically fractured wells in the Montney! 24

25 Production, SCV and soil gases from horizontal, hydraulically fractured wells, Horn River! δ 13 C of ethane! δ 13 C of methane! 25

26 SCV and gas bubbles from a single horizontal, hydraulically fractured well in the HRB!! 26

27 Various, on lease, HRB soil/ground gases compared to production gases!

28 Picking source depths for HRB Soil gases!

29 Conclusions: Source of SCV gases:! In most cases SCV gas is not from production horizon! Usually SCV gas has a shallower source! In some fields, certain formations more prone to gas migration (e.g. SWS)! But a significant fraction of SCVF does come from production horizon.! Some regions more prone to SCVF, but no region is immune from SCVF.!

30 Implications:! Much better cements and sealing techniques need to be developed and employed.! Future regulations and baseline surveys should anticipate that potential contaminants to groundwater from hydraulic fracturing need not originate in the target shales, but rather from shallower and intermediate horizons.! Prevalence of SCVF is a predictor of future problems for CCS in depleted fields. 25% of preexisting wells with SCVF may leak injected CO 2.! Industry & regulators must produce isotope mud gas profiles to improve isotope forensics of fugitive gas. Not just methane, need C 2 + isotopes.!!