USGS Research Origin of Stray Gas in Groundwater

Transcription

1 Origin of combustible gases in water-supply wells in north-central Pennsylvania -- isotopic data from 2005 during a time when there was no Marcellus development or hydraulic fracturing activity Kinga M. Révész, 1 Kevin J. Breen, 1 Alfred J. Baldassare, 2 and Robert C. Burruss 1 1. U.S. Geological Survey, 2. E C H E L O N Applied Geoscience Consulting Presented at Stray Gas Incidence & Response Forum, Ground Water Protection Council, July 2012, Cleveland, Ohio U.S. Department of the Interior U.S. Geological Survey

2 USGS Research Origin of Stray Gas in Groundwater Carbon and hydrogen isotopic evidence for the origin of combustible gases in water-supply wells in north-central Pennsylvania Revesz, and Others, 2010, Applied Geochemistry, v. 25, p and as an erratum, 2012, Applied Geochemistry v. 27, p

3 Outline of the talk I. About the site, where the problem occurred. II. Sample collections. III. About basic isotope principles. IV. Results and data interpretation. V. New drilling or fracturing in the area.

4 Methane (CH 4 ) concentrations in well water Uplands-- Fractured BEDROCK AQUIFER -- Lock Haven Formation of Devonian age Valley-- GLACIAL OUTWASH AQUIFER of Quaternary age Révész et al., 2012

5 Possible Origins of Methane in the Area (end members) Oriskany gas - thermogenic, local gas. Pipe Line gas thermogenic. Microbial from possible landfill, or natural decay of organic matter. Devonian gas (shallow) - thermogenic. Mixture of all above.

6 Sample collection and analyses Collections: End member Gases: Oriskany, Pipe Line, Storage gas. Groundwater, containing natural gas and possible background wells from the same aquifer. Analysis: 13 C of CH 4 and C 2 H 6 ; 2 H of CH 4 ; 14 C of CH 4 of some samples, Dissolved gas concentration, 2 H and 18 O of water, 13 C of DIC, Alkalinity.

7 Stable Isotope of elements and the Delta notation delta notation δ 13 C = R sample R R reference reference Where R = 13 C/ 12 C, R reference = VPDB (Vienna PeeDee Belemnite) δ 2 H = R sample R R reference reference Where R = 2 H/ 1 H, R reference = VSMOW (Vienna South Mean Ocean Water) 2 H alternative name is D (deuterium). δ 2 H = δd Carbon element, for example, has two stable isotopes, 13 C and 12 C, reflecting the number of neutrons in the atom. During compound production or reactions, the ratio of 13 C/ 12 C changes, because the two isotopically different atoms react at different rates. Therefore, isotope ratio measurements of an element can give information about the production of the compound, and the possible secondary reaction of the compound.

8 Microbial Methane production 1. Near-surface environment, marsh etc. CH 4 production by fermentation pathway: CH 3 COOH = CH 4 + CO 2 Isotope change: Intra-molecular fractionation: CH 3 = δ 13 C in CH 3 depleted in 13 C; the C is enriched in COOH. Product: CH 4 = is depleted in 13 C; CO 2 = is enriched in 13 C. (DIC) Concentration change: CH 3 COOH decreasing CH 4 and CO 2 increasing (DIC) 2. Drift gas -old, covered by glacial drift deposit. CH 4 production by CO 2 reduction pathway : CO 2 + 4H 2 = CH 4 + 2H 2 O Isotope change: CH 4 = is depleted in 13 C; CO 2 = is enriched in 13 C (DIC); Concentration change: CH 4 increasing, CO 2 decreasing (DIC) 3. Minimal C 2 and C 3 production, they are very depleted in 13 C. Presented by K.M. Révész at Stray Gas Incidence & Response Forum, Ground Water

9 Thermogenic Methane production formed by thermal break down. 1. Higher hydrocarbons (C 2 ; C 3 ; etc.) are present 2. δ 13 C of CH 4 is closer to the isotope of substrate it is produced from (more enriched than microbial). 3. C 2 and C 3 are more enriched in 13 C than those in microbial natural gas, if there is any.

10 Methane oxidation independent from production pathways 2CH 4 + 4O 2 = 2CO 2 +4H 2 O Concentration change: CH 4 decreasing, CO 2 (DIC) increasing. 13 C isotope change: CH 4 becomes enriched in 13 C; CO 2 (DIC) becomes depleted in 13 C.

11 Révész, and Others, 2012 in Applied Geochemistry Whiticar, 1999: Thermogenic Gas: δ 13 C=-50 to -20 ; δd= -275to -100 Microbial Gas:δ13C=-110 to -50 ; δd= -400 to -150 C and H stable isotopes of CH 4 Oriskany gas wells Storage gas obs. wells Storage gas Inj. wells Rock wells (GW) Outwash wells (GW)

12 The importance of the δ 13 C of ethane Révész, and Others, 2012 in Applied Geochemistry

13 Identifying secondary reaction; oxidation of methane 2CH 4 + 4O 2 = 2CO 2 +4H 2 O δ 13 C isotope change: CH 4 becomes enriched ; CO 2 (DIC) becomes depleted in 13 C delta 2 H vsmow of CH 4 in per mill delta 13 C VPDB of CH 4 in per mill Concentration change: CH 4 decreasing, CO 2 (DIC) increasing. d13c of DIC in per mill VPDB delta 13 C CH4 in per mill VPDB

14 Bernard graph Oxidation and mixing curves Modified from Révész et al., 2012

15 Methane Signatures in GW Wells Thermogenic with >0.1 percent ethane Microbial Methane Signatures in Groundwater from Wells Révész et al., 2012

16 New potential sources

17 δ 13 C of ethane, partial isotope reversal effect δ 13 C of ethane could help further differentiate among thermogenic origin of combustible gases. Fred Baldassare and others, GWPC, Atlanta, GA, September 2011

18 Modified from Révész, et al., δ 13 C of CH 4 and C 2 H 6 in end member gas wells

19 Essential data to identify stray gas origins 1. Identify possible gas sources. 2. Create a baseline gas signature library. Determine concentrations and δ 13 C - δ 2 H of CH 4 ; and δ 13 C of higher hydrocarbons across the area from various source units. 3. Carry out site specific monitoring of natural gas in groundwater before (baseline), during and after drilling. (Concentrations and δ 13 C - δ 2 H of CH 4 ; and δ 13 C of higher hydrocarbons). Determine the source(s) of stray gas in domesticsupply wells and identify gases from major and minor gas production zones across the area. 4. Monitor longer-term changes in methane presence/concentration as area develops (well density), and as the wells age (leakage from casing/grout seals) during and following gas production (decades).

20 The Royal Society Science Policy Center, Royal Academy of Engineering More likely causes of possible environmental contamination include faulty wells, and leaks and spills associated with surface operations. Neither cause is unique to shale gas. Both are common to all oil and gas wells and extractive activities (RSSPC, RAE). Combined gas (Révész et al 2010) and water (Osborn and McIntosh 2010) analyses can be carried out to understand the origin of gases in aquifers (RSSPC, RAE).

21 References Baldassare, A. J., Laughrey, C.D., McCaffrey, M, and Harper, J.A., Ground Water Protection Council Annual Forum, Atlanta, GA, September Accessed as presentation 19s at Bernard, B.B., Brook, J.M. and Sackett, W.M., 1976, Earth Planet. Sci. Lett. 31, Coleman, D. D., American Gas Association, Operating Section Proc., pp Osborn, S. G. and McIntosh, J. C.,2010, Appl. Geochem., 25, Révész, K. M., Breen, K. J., Baldassare, A. J., and Burruss, R. C., 2010, and as an Erratum, 2012 in Applied Geochemistry Vol. 27, p Schoell, M., 1980., Geochim. Cosmochim. Acta 44, The Royal Society Science Policy Center, The Royal Academy of Engineering, June 2012, ;