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Maria Mastalerz Indiana Geological Survey, IU Dariusz Strapoc Arndt Schimmelmann Department of Geological Sciences, IU, Bloomington Origin of Coalbed Gas.

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Presentation on theme: "Maria Mastalerz Indiana Geological Survey, IU Dariusz Strapoc Arndt Schimmelmann Department of Geological Sciences, IU, Bloomington Origin of Coalbed Gas."— Presentation transcript:

1 Maria Mastalerz Indiana Geological Survey, IU Dariusz Strapoc Arndt Schimmelmann Department of Geological Sciences, IU, Bloomington Origin of Coalbed Gas in Indiana: Insights from Isotopic Ratios

2 INTRODUCTION What is coalbed gas? Natural gas formed and stored in coals Natural gas formed and stored in coals (mainly adsorbed on micropores <2nm) (mainly adsorbed on micropores <2nm) Consists mainly of CH 4 + some C 2, C 3, C 4, CO 2, N 2 Consists mainly of CH 4 + some C 2, C 3, C 4, CO 2, N 2 Generated by: Generated by: 1) thermal cracking of OM from coal, if Ro > 55% - the treshold value (thermogenic gases – C 1 -C 4 hydrocarbons) 2) microbial activity (biogenic methane)

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4 INTRODUCTION Microbially generated methane Microbial consortia (consuming the organic matter from coal, mainly long chain aliphatics): acetogens, acetotrophs, with CO 2 reducing methanogens as a terminal step Microbial consortia (consuming the organic matter from coal, mainly long chain aliphatics): acetogens, acetotrophs, with CO 2 reducing methanogens as a terminal step CO 2 + 4H 2 = CH 4 + 2H 2 O Content of biogenic CH 4 can be up to 100% in shallow coals gas and with Ro<55% (<200m) Content of biogenic CH 4 can be up to 100% in shallow coals gas and with Ro<55% (<200m) In deeper and/or more mature coals it is mixed with thermogenic gas and their ratio can be assessed using molecular and isotopic analyses of the gases In deeper and/or more mature coals it is mixed with thermogenic gas and their ratio can be assessed using molecular and isotopic analyses of the gases

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7 OBJECTIVES OF THIS STUDY OBJECTIVES OF THIS STUDY CBM Origin Establish method of representative coalbed gas sampling from desorption canisters Establish method of representative coalbed gas sampling from desorption canisters Generate compositional and isotopic data of coalbed gases (C1-C4 hydrocarbons, CO 2 ) in Indiana Generate compositional and isotopic data of coalbed gases (C1-C4 hydrocarbons, CO 2 ) in Indiana Evaluate thermogenic and biogenic contribution to the total gas Evaluate thermogenic and biogenic contribution to the total gas Determine controls on gas distribution Determine controls on gas distribution

8 >2.8m 3 /t >3.4m 3 /t Gas content of Indiana coals

9 Recently desorbed Gas content (raw basis) Variations in measured gas content

10 Degree of saturation Degree of saturation %

11 Modified from Meissner, 1984 Coal maturity (Ro) and maximum thermogenic gas potential of coal vs coalbed gas content in Illinois Basin coals Illinois Basin Indiana coals KY In addition to thermogenic gas, Indiana coals have another source of gas (biogenic methane ??) [m 3 /t] RESULTS Maximum Thermogenic gas potential Coal Rank subbituminous high volatile bituminous C high volatile bituminous B high volatile bituminous A medium volatile bituminous

12 Study area SE Illinois Basin SE Illinois Basin Core samples of Pennsylvanian coals: Core samples of Pennsylvanian coals: Herrin Herrin Springfield (V) Houchin Creek (IVa) Houchin Creek (IVa) Survant (IV) Survant (IV) Seelyville (III) Seelyville (III) Range of vitrinite reflectance % (high volatile bituminous C coals) Range of vitrinite reflectance % (high volatile bituminous C coals) fault zone 100km

13 Sampling coalbed gas sampling from desorption canisters with N 2 purging of tubing coalbed gas sampling from desorption canisters with N 2 purging of tubing

14 Off-line H,C-isotopic analyses of CH 4 (oxidation of CH 4 in quartz tube with CuO at 800C; cryogenic separation of CO 2 and H 2 0; reduction of H 2 O to H 2 in Uranium oven at 850C; dual inlet on Finnigan MAT 252 or Delta Plus) Off-line H,C-isotopic analyses of CH 4 (oxidation of CH 4 in quartz tube with CuO at 800C; cryogenic separation of CO 2 and H 2 0; reduction of H 2 O to H 2 in Uranium oven at 850C; dual inlet on Finnigan MAT 252 or Delta Plus) Continuous flow molecular and C-isotopic analyses of C1- C4, CO 2 using on-line GCC/MS (syringe injection module with variable sample size 0.05ul to 50ul; GC; oxidative reactor Cu, Ni, Pl at 850C; MS Finnigan MAT 252 or Delta Plus) Continuous flow molecular and C-isotopic analyses of C1- C4, CO 2 using on-line GCC/MS (syringe injection module with variable sample size 0.05ul to 50ul; GC; oxidative reactor Cu, Ni, Pl at 850C; MS Finnigan MAT 252 or Delta Plus) Analytical procedures

15 RESULTS: Molecular composition of coalbed gases from the Illinois Basin * N 2 not included 150m 300m Depth R o [%] Coal maturity (vitrinite reflectance)

16 Thermogenic field Biogenic field - CO 2 Reduction Biogenic field – acetate fermentation Mixing zone CBM origin – genetic classifications: C vs H isotopes in CH 4 CO 2 reduction reaction used by methanogenic bacteria: CO 2 + 4H 2 = CH 4 + 2H 2 O

17 Thermogenic field Microbial field CBM origin: C1/[C2+C3] gas wetness indicator vs C-isotopes in CH 4 Transition zone Mixed

18 Thermogenic gases Microbial CO 2 -reduction Laboratory pyrolysis gases CBM origin: C-isotopes in CH 4 and CO 2

19 Pr Et Bu Me Estimation of biogenic CH 4 content: Compound-specific C-isotopic data method developed by Chung et al Extrapolated pure T-genic methane Assumed pure biogenic CH % biogenic CH4

20 Estimation of biogenic CH 4 content: Compound-specific C-isotopic data Danville 96% Seelyville 59% Springfield, IN 57% Springfield, KY -12% (~0) Extrapolated pure T-genic methane Assumed pure biogenic -70 Herrin, IL 89% Pr Et Bu Me

21 Examples of gas variations Sullivan County, Indiana

22 Biogenic vs thermogenic CH 4 content Biogenic gas content – varies within coalbed (controls unknown, pore size distribution ~permability?, nutrients availability?), important contribution to total CBM (62% on average) ~constant Seelyville coal Sullivan County Thermogenic gas content - almost constant, low and corresponding to Ro

23 Gas play concepts in Indiana Indiana – biogenic methane prevailing R o at treshold of thermogenic gas generation ( %) R o at treshold of thermogenic gas generation ( %) <50% thermogenic gas content <50% thermogenic gas content coal rarely reached T>80C (upper limit of bacterial activity), therefore… coal rarely reached T>80C (upper limit of bacterial activity), therefore… bacteria can be synsedimantary or bacteria can be synsedimantary or …transported with fresh water after erosional uplift and/or …transported with fresh water after erosional uplift and/or …transported with water from melting ice sheets after last ice age into the coal after relaxation of the cleats and fractures, or …transported with water from melting ice sheets after last ice age into the coal after relaxation of the cleats and fractures, or …transported with modern meteoric waters …transported with modern meteoric waters Illinois Indiana Kentucky Max range of ice

24 Gas play concepts in Indiana Indiana – thermogenic gas present in low quantities gas present in low quantities tectonic and volcanic activity (higher geothermal gradient) in the Western Kentucky fault zone tectonic and volcanic activity (higher geothermal gradient) in the Western Kentucky fault zone Ro up to 0.8% corresponding to ~140C (thermogenic gas generation treshold ~0.55%) Ro up to 0.8% corresponding to ~140C (thermogenic gas generation treshold ~0.55%) no secondary biogenic methane generation no secondary biogenic methane generation thus after erosional uplift ice melt or meteoritic water hadnt transported methanogens to the coalbed environment (ice didnt cover this area – higher elevation) thus after erosional uplift ice melt or meteoritic water hadnt transported methanogens to the coalbed environment (ice didnt cover this area – higher elevation) fault zone Illinois Indiana Kentucky Max range of ice

25 CONCLUSIONS C isotopic data of CO 2 and C 1 - C 4 hydrocarbons plus H isotopic data of C 1 provide powerful tools for assessing the coalbed gas origin, evolution and alteration; C isotopic data of CO 2 and C 1 - C 4 hydrocarbons plus H isotopic data of C 1 provide powerful tools for assessing the coalbed gas origin, evolution and alteration; Biogenic gas is the dominant component in CBM in Indiana (62% on average), whereas thermogenic gas occurs in lower but variable quantities; Biogenic gas is the dominant component in CBM in Indiana (62% on average), whereas thermogenic gas occurs in lower but variable quantities; The highest volumes of gas are expected in areas where there is a substantial amount of thermogenic gas and also there were (are?) favorable conditions for biogenic gas generation The highest volumes of gas are expected in areas where there is a substantial amount of thermogenic gas and also there were (are?) favorable conditions for biogenic gas generation CBM in Indiana – renewable resource?? meteoric prod water

26 Gas is beautiful!

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