Differentiating recalcitrant carbon residues in spent oil shale and source rocks

Transcription

1 Differentiating recalcitrant carbon residues in spent oil shale and source rocks Justin E. Birdwell 1, Tim E. Ruble 2, Christopher D. Laughrey 3, David R. Roper 2 & Greg Walker 2 1 U.S. Geological Survey, Denver, CO 2 Weatherford International Ltd., Houston, TX 3 Weatherford International Ltd., Golden, CO U.S. Department of the Interior U.S. Geological Survey

2 Acknowledgements Augusta Warden and Michael Lewan (USGS CERSC Organic Geochemistry Lab) Larry Cox and Kevin Thorn (NMR work, USGS/NRP Water Resources Lab) Donovan Sam and David Chin (Fischer Assay work, Weatherford Labs) Herman Lemmens (FIB-SEM work, FEI)

3 Objectives Track changes in organic pyrolysis products (bitumen, oil, gas) and byproducts (char, pyrobitumen) Compare pyrolysis methods (Fischer Assay and In-Situ Simulator) Examine new techniques for characterizing recalcitrant organic residues Joachim Esche 2008

4 Why do we care about pyrobitumen? Gas storage potential (Organic Porosity) Natural gas CO 2 storage following in situ retorting Understanding maturation chemistry Simplified overall reaction Kerogen (+heat & time) Oil + Gas + Pyrobitumen Interconnected organic network may provide mechanism for unconventional gas recovery May be the origin of late-stage methane generation during metagenesis

5 Standard Methods Organic Petrology Standard qualitative evaluation but subjective and dependent upon experienced petrologist Rock-Eval & Source-Rock Analyzer Useful complement for Fischer Assay, but typical temperature programs are too low to pyrolyze recalcitrant carbon residues FTIR and 1D-NMR Moiety distributions, but not what s contributing Bulk analysis Can t separate recalcitrant residues

6 Project: Marcellus Depth = 10,000 Number of measurements Sample: EW XXXXXX Solid bitumen reflectance 546nm Ordered R o random Values Minimum R o (%) 1.68 Maximum R o (%) 2.41 Number of points 25 Std Deviation Mean R o value (%) 1.93 vitrinite pyrobitumen Comments: Solid bitumen (pyrobitumen) is the only type of organic matter present. The rock is rich in carbonate and pyrobitumen fills porosity, occurring usually as thin film. At places it forms interconnected network. Pyrobitumen is non-fluorescent. Because of unavailability of vitrinite, reflectance of pyrobitumen was measured and based on 25 measurements, the average R o of solid bitumen is 1.93%. This value translates into vitrinite reflectance equivalent (using Landis & Castano equation) of 2.15%. These reflectance values indicate that the organic matter is post-mature and at the dry gas window Visual kerogen analysis (mineral matter free basis) Well Sample ID Alginite, % Amorphous OM, % Other Liptinite % Vit., % Inert., % Liptinite Fluoresc. % Solid Bit, % Oil prone, % Gas prone, % Pollen/ Spores TAI* Well #1 XXXXXX nd * after Staplin, 1969

7 Other Methods High Temperature Programmed Pyrolysis (HT-PPy) Going to higher temperatures (800 C) to degrade and detect pyrobitumen X-ray Diffraction Presence of graphitic material? Illite crystallinity (Kübler Index) Multidimensional NMR Examine molecular and nanoscale structural characteristics (aromatic cluster size) not discussed here

8 Other Methods Scanning Electron Microscopy (SEM) Prepare samples using Argon Ion Milling to examine carbonaceous residues

9 Other Methods Focused Ion Beam-SEM FIB is used to ablate thin (10nm) slices from a sample which is then analyzed by SEM Hundreds of slices are then combined to create a 3-D SEM image Can distinguish organic materials based upon morphology and elemental composition L. HOLZER, et al., Journal of Microscopy Vol. 216, Pt 1 October 2004, pp

10 Generation of Spent shale Pyrolysis experiments In Situ Simulator 360 C, 6h to 12d, no water, autogenous atmosphere (p > 500 psig) Fischer Assay 360 C, 3-18h approx. atmospheric pressure All materials are collected for mass balance (>95% recovery) All oil shale samples ground and sieved to -8/+35 mesh

11 Low Temp. Fischer Assay FA 360C, 1C/min, 18 hr FA 360C, 12C/min, 18 hr FA 360C, 12C/min, 3 hr Fischer Assay 500C Post-pyrolysis product distribution Raw shale 0% 20% 40% 60% 80% 100% Weight % (original rock basis) Mineral Bitumen Kerogen + Char Total Oil Water Gas+Loss

12 In Situ Simulator Post-pyrolysis product distribution 12d/360C 5d/360C 3d/360C 24h/360C 6h/360C Can t differentiate between char, pyrobitumen and residual kerogen based on insoluble fraction Raw shale 0% 20% 40% 60% 80% Weight % (original rock basis) 100% Mineral Bitumen Kerogen + Char Total Oil Total Gas

13 Source Rock Analyzer Pyrolysis instrument that uses an FID detector and IR cell to measure: Residual Oil Content S 1 Remaining Hydrocarbon Generation Potential S 2 Carbon dioxide S 3 Organic richness TOC Thermal Maturity Tmax Pyrobitumen Content S py

14 SRA vs. Fischer Assay 250 SR Analyzer Pyrolysis (S2) Yields (mg HC/g R) y = x R 2 = Fischer Assay Yields (wt.% oil)

15 High Temperature Programmed Pyrolysis Pyrogram Temperature Haynesville Shale S 1 (Oil) S 2 (Kerogen) 1.56% Ro High Temperature Pyrobitumen Peak (S py ) Area Counts Time Weatherford Labs SRA is a direct method to quantify pyrobitumens

16 Fischer Assay & In Situ Simulator HT-PPy Response (µv) Temperature ( C) S1 S2b S2a Spy Time (min) Raw shale FA 360 C, 18 hr (1 C/min) FA 360 C, 18 hr (12 C/min) ISS 360 C, 288 hr

17 In Situ Simulator HT-PPy Detector response hr 6 hr 24 hr 72 hr 120 hr 288 hr Oven Temperature (oc) S1 S2a S2b Spy Time (min)

18 In Situ Simulator Maturity Trends Bulk Analysis HT-PPy Analysis Weight % Original Rock mg HC/g Rock Time (hrs) Time (hrs) TOC Bitumen Kerogen+Char Oil Gas S1 S2 Spy The Flame Ionization Detector only responds to molecules with a carbon-hydrogen bond may explain Spy trend?

19 High maturity source rocks Thermal alteration of kerogen involves hydrogen disproportionation reactions Kerogen loses hydrogen to form gasoline, wet gas and dry gas in succession Hydrogen depleted kerogen condenses & aromatizes eventually forming graphite Similar reactions would occur in pyrobitumens Hunt, J.M. (1996) Petroleum Geochemistry and Geology

20 CP/MAS 13 C-NMR Aromatic Aliphatic 75% 25% Carbonate not observed in CP experiments (~4% inorganic carbon in all samples) 41% 48% 59% 52% Raw shale FA 3h FA 18h TOC = 18.6% TOC = 15.9% TOC = 10.9% 56% 44% Chemagnetics CMX C frequency = 50.3 MHz MAS = 5 khz ± 100 Hz ~1500 transients (15 min experiment) 59% 41% FA 18h* FA 500C TOC = 10.5% TOC = 6.4% Chemical Shift (ppm) -50

21 CP/MAS 13 C-NMR Aromatic Aliphatic 75% 25% 41% 59% Raw TOC = 18.6% Carbonate not observed in CP experiments (~4% inorganic carbon in all samples) Chemagnetics CMX C frequency = 50.3 MHz MAS = 5 khz ± 100 Hz ~1500 transients (15 min experiment) 48% 56% 59% 64% 52% 44% 41% 36% ISS 6h ISS 24h ISS 3d ISS 5d ISS 12d TOC = 13.8% TOC = 13.1% TOC = 11.7% TOC = 10.9% TOC =10.8% Chemical shift (ppm) -50

22 X-ray diffraction (XRD) Graphitic Pyrobitumen Ø Ø Ø Whole Pattern Fitting Reitveld Refinement Method Quantitative phase analysis using calculated full patterns as a method of refining crystal structures using neutron powder diffraction data. Minimize the sum of the weighted squared differences between observed and calculated intensities. Bennett #1 Well 2550m Marcellus Shale 3 wt.% Graphite Ro = 2.54% Semi-Anthracite Zone

23 Changes in density with maturity Type II Kerogen 0.19 g/cc Density (g/cc) 1.25 Pyrobitumen Bitumen Kerogen 1 Pyrobitumen 0.37 g/cc H/C Ratio Rogers et al. (1974) AAPG Bull, v. 58. p Okiongbo et al. (2005) Energy & Fuels, v. 19, p

24 Organic Porosity in Pyrobitumen During maturation the density change in pyrobitumen is almost double that observed for kerogen Akin to dolomitization, this should translate into an equivalent increase in organic porosity for pyrobitumen compared to kerogen Depending upon abundance, the organic porosity developed in the pyrobitumen network may be the dominant source of hydrocarbon storage for in-situ retort & in unconventional shale gas systems

25 Summary Pyrobitumen (S py peak) identified in spent shale NMR data indicates high aromaticity graphitic pyrobitumen? Combination of analytical needed to fully assess recalcitrant residues More to come Raw (left) and spent (ISS-12d, right) oils shale micrographs (500 magnification, 300 µm field of view) (courtesy of Mark Pawlewicz) Image provided by Herman Lemmens (FEI) & Christopher Laughrey (WFT Labs)