Characteristics of Microbial Coalbed Gas during Production; Example from Pennsylvanian Coals in Indiana, USA

Abstract

Coalbed gases from 11 wells producing from the Springfield and Seelyville Coal Members (Pennsylvanian) were analyzed for composition and carbon and hydrogen stable isotope ratios in four sampling events to investigate short-term variation trends. Nine wells in the Seelyville Coal Member produce coalbed gases from the virgin seam, whereas two wells in the Springfield Coal Member produce gas from mine voids. Methane dominates gas composition in all wells, and its content ranges from~94% to almost 98%, with ethane typically accounting for less than 0.01%. Carbon dioxide content in most samples is below 1%, whereas N 2 content ranges from less than 2% to 4.8%. Methane δ 13 C values range from −55.3‰ to −61.1‰, and δ 2 H values range from −201‰ to −219‰. Isotopic values of methane and C 1 /(C 2 + C 3 ) ratios indicate a biogenic origin along the CO 2 -reduction pathway, consistent with previous studies in this area. Our results demonstrate that gas properties may change significantly during a period of one year of production history. Compositional trends (e.g., C 1 /(C 2 + C 3 ), CH 4 /CO 2 ratios) are specific for each well and often irregular. These changes result from a combined influence of numerous factors and, therefore, are difficult to predict.

Stable Isotope Systematics of Coalbed Gas during Desorption and Production

“…Admixtures of early and late stage generation microbial methane in coals sometimes comprise a considerable fraction of CBM, as noted by several authors, e.g., Rice [17], Smith and Pallasser [57], Aravena et al [58], Faiz et al [59]; Kotarba and Lewan [38], Pashin [60], Strąpoć et al [44,61], Flores et al [62]. In addition, there is in situ microbial methane production by the conversion of coal to methane by the introduction of microbial nutrients and/or microbial consortia (e.g., Scott [63]; Budwill et al [64]; Gao et al [65]; Ashby et al [66]; Zhang et al [67]; Mastalerz et al [68]).…”

Predicting long term coal seam gas concentrations from multi-component sorption

“…%A Spherical shaped particle is subdivided into 30 equally delr = R/Np; %radius of individual sections, r1, r2, r3,... r31, m MolWt= 16; % MolWt for Methane, g epsp= 0.3258; %porosity may change to two porosity for micro and macro rho= 1.5477*1e6*(1-epsp); % 1.0435 g/m^3 particle density Rgas= 62.363E-3; % Gas Constant value, mmHg K m^3/mol %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% % qAm = 453.8680; % mol/m^3, Langmuir max conc in micropore % EAm= 1.8265073+04; % J/mol Micro % bm=(3.92053995e-6*exp((-EAm/(Rgas*Temp)))); % m3/mol langmuir pressure constant micropore % % qAmo = 0.628392013; % mol/m^3, Langmuir max conc mesopore % EAmo= 85.252602; %J/mol Meso % bmo=(0.4306331*exp((-EAmo/(Rgas*Temp)))); % m3/mol langmuir pressure constant mesopore %new parameters qAm = 5.563499697365191e+02; % mol/m^3, Langmuir max conc in micropore EAm= 1.822936790521974e+04; % J/mol Micro bm=(3.038535432771275e-06*exp((-EAm/(Rgas*Temp)))); % m3/mol langmuir pressure constant micropore qAmo = 2.220556544435218; % mol/m^3, Langmuir max conc mesopore EAmo= 5.582569743563221e+03; %J/mol Meso bmo=(0.057508199598658*exp((-EAmo/(Rgas*Temp)))); % m3/mol langmuir pressure constant mesopore %micro and macro paramters swap to see the match different?? % qAm =0.628392013; % mol/m^3, Langmuir max conc in micropore % EAm= 85.252602; % J/mol Micro % bm=(0.4306331*exp((-EAm/(Rgas*Temp)))); % m3/mol langmuir pressure constant micropore % % qAmo = 453.8680; % mol/m^3, Langmuir max conc mesopore % EAmo= 1.8265073+04; %J/mol Meso % bmo=(3.92053995e-6*exp((-EAmo/(Rgas*Temp)))); % m3/mol langmuir pressure constant mesopore % figure (5),plot(r,Cmi(301,1:Np+1)); % title('CH4 conc in micro all layers vs particle interface') % xlabel('radius "r" cm') % ylabel('CH4 conc mole/m^3') % figure (6),plot(r,Cmo(301,1:Np+1)); % title('CH4 conc in macro all layers vs particle interface') % xlabel('radius "r" cm') % ylabel('CH4 conc mole/m^3') % figure (7),plot(t,N_molads); % title('Normalised CH4 adsorbed vs time') % xlabel('time sec') % ylabel('CH4 amt g') figure (8),plot(t_exp,ads_exp,'. ',t,N_molads); title('CH4 adsorbed per coal mass unit vs time') xlabel('time sec') ylabel('g CH4/g coal expt and model') figure (9),plot(t_exp,ads_exp_abs,'.…”

“…There are many previous works available in prediction of gas production profile using different methods, equations and simulation models [4][5][6]. However, most of the models and theories have limitations in prediction of mixed gas production profile, especially from real coal seams.…”

“…6 attempts to demonstrate that unipore model data was not perfectly matched to the experimental data. On the left, the plot shows normalized experimental data vs. experimental time in sec.…”