CO2 Sequestration Potential of Charqueadas Coal Field in Brazil Vyacheslav Romanov National Energy Technology Laboratory Pittsburgh, October 23-24, 2012 The technical effort was performed in support of the National Energy Technology Laboratory s on-going research in carbon Sequestration, partly under the RES contract DE-FE000-4000.
Team The project was sponsored by the U.S. DOE within framework of Carbon Sequestration research program and MOU with Pontificia Universidade Catolica Do Rio Grande Do Sul (PUCRS). NETL (federal) Vyacheslav N. Romanov Robert P. Warzinski NETL-URS Dustin Crandall Igor V. Haljasmaa James J. Fazio NETL-University of Pittsburgh (RUA) Tae-Bong Hur PUCRS (Brazil) Cristian S. Santarosa PETROBRAS-CEPAC (Brazil) Roberto Heemann J. Marcello M. Ketzer 2
Background The core samples used in the study were obtained as part of a joint initiative between PETROBRAS and CEPAC in 2010, to evaluate the potential for unconventional gas production and CO 2 storage in the Charqueadas coal seams. The pilot site was chosen in Porto Batista, Charqueadas coal field, about 60 km west of Porto Alegre. There are six coal seams in this area, named SB, MB, I1F, I1Fa, I2B, I3F (from top to bottom), but only three of them, MB, I1F, and I2B were considered d as targets t for CBM production and CO 2 injection owing mainly to their thickness and rank. The overall goal of this work is complementary to the joint initiative of PETROBRAS and CEPAC. 3
Project Objectives Although coal is not the primary source of energy in Brazil there is growing interest to evaluate the potential of coal from the south of the country for various activities. The I2B coal seam in the Charqueadas coal field has been evaluated as a target for enhanced coal bed methane production and CO 2 sequestration. 4
Scope of Work The samples were low rank coals (high volatile bituminous and sub-bituminous) obtained from the I2B seam as Ø3 cores (left). Such properties as sorption capacity, internal structure of the samples, porosity and permeability were of primary interest in this characterization study. Some samples were sub-cored to Ø1.5 (below); the others were crushed to pass a 100-mesh screen for powder sorption isotherm tests. 5
Sample Characterization Sample Depth Moisture Volatile Ash content Fixed Canister (m) (%) matter (%) (%) carbon (%) C-13 339.0 4.06 18.98 49.67 27.46 C-14 339.5 4.40 18.59 58.08 19.11 C-25 346.3 4.64 22.73 46.66 26.19 C-28 347.6 4.27 18.90 51.82 25.19 C-29 348.2 4.73 23.46 43.32 28.70 Proximate analysis was carried out according to Brazilian standards (ABNT DBR) corresponding to the ASTM certified methods (D3172-07a and D7582-10e1). Micro-CT image of a sub sample of C-14 Even though this C-14 sample was observed to be uniform in the medical CT scans, this higher resolution scan reveals that there is a large amount of variability in the core. The microfractures most likely provide pathways for CO 2 to enter the coal matrix, while the shale increases the overall resilience of the core to external stressing. 6
Porosity and Permeability Measurements (A)TEMCO helium porosimeter, HP-401 (B) AutoLab-1500 (NER, Inc.) with installed core holder (zoom-in) Medical CT Scanner Universal Systems HD350-E 4th generation; 140 kv and 400 ma, resolution 0.25 mm X 1 mm. Sub-cores of coal were exposed to CO 2 over three week periods within TEMCO composite core holder 401 and a Buna-N sleeve 7
Composite core-holder (CT) Sub-cores of coal were exposed to CO 2 over three week periods within the TEMCO composite core holder 401 (Core Lab Instruments, t Tulsa, OK). A coal sample was placed within a Buna-N sleeve and enclosed within the composite core holder. After centering the core holder in the medical CT scanner gantry chucks, high pressure ISCO model 260D pumps were used to apply axial and radial confining gpressures to the coal core. 8
Mechanical Properties Dilation Density ρ = A CTN High + B CTN Low + C Young s modulus (assumed ν = 0.3) Dual-energy scanning enables accurate estimates of density from CT scanning by obtaining CT number (CTN) above and below the threshold of Compton scattering. High-energy scans were performed at 140 kev and low-energy scans were performed at 80 kev. Aluminum, graphite and fused quartz were scanned throughout the experiments to determine A, B and C, and to ensure that the CTN did not vary throughout the testing. 9
RESULTS (mechanical properties) C-13 (D = 38 mm, L = 47.4 mm) had 1.6 % porosity and about 140 nd permeability C-25 (D = 37.87 mm, L = 60.55 mm) had 4.3 (initial) to 3.4 (final) % porosity and about 340-730 nd permeability C-29 had permeability below detection limit 0.50 Young g's Modu ulus, GP Pa 045 0.45 0.40 0.35 0.30 0.25 0.20 0.15 0.10 0.05 0.00 Increasing P Decreasing P 0 5 10 15 Confining Pressure, MPa C-25 core sample (CT): E does not reach a stable value, even with a confining pressure of 11.1 MPa. This suggests that micro-cracks will be open within the in-situ coal. 10
CT scanning prior to CO 2 18 1.8 C-14 (C) (D) 1.7 C-25 Density y, g/cc 1.6 1.5 1.4 1.3 1.2 1.1 0 10 20 30 40 50 60 Length along core, mm (C) 11 False color montages from medical CT scanner. Higher density material is shown as bright yellows while dark purple and orange are lower density. Each slice is 2 mm thick and has a pixel resolution of 0.25 mm by 0.25 mm.
CT scanning prior to CO 2 (C-14) 18 1.8 1.7 C-14 C-25 Density y, g/cc 1.6 1.5 1.4 1.3 1.2 1.1 0 10 20 30 40 50 60 Length along core, mm (C-25) C-14 was used as a representative sample from the upper section of I2B and C-25 as a representative sample from the lower section of I2B. Brighter regions correspond to high-density zones and darker regions indicate lower-density areas. Upper seam is shown to be fairly uniform in material structure, while numerous mineralized fractures are apparent in lower seam. 12
RESULTS (sorption in cores) ity (g/cc) Aver rage Dens 1.51 1.5 1.49 ity (g/cc) rage Dens 1.38 1.37 1.36 1.48 MPa 1.35 1.48 2.86 MPa 4.24 MPa 1.47 2/6/11 2/11/11 2/16/11 2/21/11 2/26/11 3/3/11 Scan Date Ave 1.48 MPa 2.86 MPa 4.24 MPa 1.34 3/13/11 3/18/11 3/23/11 3/28/11 4/2/11 4/7/11 Scan Date C-14 CT-derived density measurements C-25 CT-derived density measurements The scans show that the majority of this CO 2 uptake was occurring within the third of the sample closest to CO 2 inlet port. The rate of CO 2 sorption into the sample slowed when the pore pressure increased to 2.86 and 4.24 MPa. During the entire experiment the confining pressure was held 1.48 MPa greater than the pore pressure. The dual-energy values used to derive these densities were calibrated to standards of known density before and after the CO 2 exposure of the core and showed little change. 13
Manometric sorption isotherms Adsorbed amount (Gibbs definition) n Gibbs = n total ρ g V o ; V o = V a + V i ; V a = n abs /ρ a ; Absolute adsorption Langmuir model n abs = n Gibbs (ρ a /(ρ a ρ g )) (assumed ρ a = 1.18 g/cm 3 ) V = V L (P/(P L + P)) The Langmuir model was used in order to provide engineering parameters by fitting the absolute adsorption plots. 14
RESULTS (sorption on powder) Absolute sorption n, mmol/g 1.2 1 0.8 0.6 0.4 0.2 0 C-25 rption, mmol/g Absolute so 12 1.2 12 1.2 1 0.8 0.6 0.4 0.2 0 C-13 Moist at 35 ⁰C Moist at 55 ⁰C Dry at 55 ⁰C 0 1 2 3 4 5 Moist at 35 ⁰C Moist at 55 ⁰C Dry at 55 ⁰C 0 1 2 3 4 5 Pressure, MPa Pressure, MPa Absolute sorption n, mmol/g Absolute so orption, mmol/g 1 0.8 0.6 0.4 0.2 0 C-14 1 0.9 C-28 0.8 0.7 06 0.6 0.5 0.4 0.3 0.2 Moist at 35 ⁰C 0.1 Moist at 55 ⁰C Dry at 55 ⁰C 0 0 1 2 3 4 5 Pressure, MPa Moist at 35 ⁰C Moist at 55 ⁰C Dry at 55 ⁰C 0 1 2 3 4 5 Pressure, MPa Absolute sorption n, mmol/g 1 0.9 C-29 0.8 0.7 06 0.6 0.5 0.4 0.3 0.2 Moist at 35 ⁰C 0.1 Moist at 55 ⁰C Dry at 55 ⁰C 0 0 1 2 3 4 5 Pressure, MPa 15
Summary Currently, the I2B coal seam in the Charqueadas coal field is NOT recommended for CO 2 sequestration but further research is justified. Positive findings: It was observed that the lower layers of the I2B coal seam have a significant potential for carbon sequestration but only in a powder or fractured form. The upper seam has permeability too low to justify a direct injection of carbon dioxide. id However, it may serve as a good secondary seal. Further research of how the coal properties p at this micro- scale can be related to the properties observed on the macroscale will provide insight into how well the Charqueadas I2B coal seam will release methane or adsorb CO 2 for geologic storage. 16