Dielectric Properties of Oil Shale

Transcription

1 Dielectric Properties of Oil Shale Lawrence Livermore National Laboratory 26th Oil Shale Symposium, Golden CO, October 16-18, 26 Jeffery Roberts. Jerry Sweeney. Philip Harben. Steve Carlson UCRL-ABS This work was performed under the auspices of the U.S. Department of Energy by the University of California, Lawrence Livermore National Laboratory under Contract No. W-745-Eng-48. A171-1

2 Acknowledgements Anadarko Petroleum Corporation for Wyoming samples Bureau of Land Management for Anvil Points samples Paul Daggett A171-2

3 A171-3

4 Can RF energy be effectively utilized for in-situ heating of oil shales? Is there a dielectric loss mechanism in the kerogen between 1 MHz and 1 GHz? Can RF energy significantly penetrate and be deposited within the oil shales? What is the effect of fluids (and ions) on the dielectric properties of the oil shales? What is the effect of temperature on the dielectric properties of the oil shales? - measured complex dielectric constant on two sample suites from 1 MHz GHz - measured complex dielectric constant at various water and brine saturations - measured complex dielectric constant on dry samples up to ~ 15 C A171-4

5 Measurements Were Conducted Using an HP4291A Impedance/Material Analyzer and High Temperature Probe Anadarko samples (1): SW Wyoming, Green River, /-.75 g/cc, / gal/ton* Anvil Points samples (8): W Colorado, Green River, /-.57 g/cc, / gal/ton* J. Smith, Theoretical Relationship Between Density and Oil Yield for Oil Shales, U.S. Bureau of Mines Pub. 7248, A171-5

6 The complex dielectric constant was measured between 1 MHz and 1.8 GHz on all samples Complex dielectric constant ε = ε - jε Power dissipated P ~ ε f E 2 ε is the dielectric constant ε is the loss factor Skin depth D p ~ ε 1/2 /(ε f) (Penetration depth For E to fall to 1/e) ε Teflon (1&3 GHz) Water (1 GHz) Water (3 GHz) ε A171-6

7 Measurement variability within a sample was tested P- face parallel to bedding T - face perpendicular to bedding OS1 to OS3 - Anvil Points samples OS4 to OS7 - Anadarko samples 5 OS1 P1 dry vs. position of measurement.1 OS1 P1 dry vs. position of measurement Real relative permittivity position a position b position c position d position e position f position g position h Imaginary relative permittivity position a position b position c position d position e position f position g position h T (not shown) more variable than P, both relatively small A171-7

8 Dry, room temperature results for Anadarko samples 1 Anadarko shale dry P orientation Anadarko shale dry P orientation.4 Real relative permittivity os4 p2 os5 p2 os6 p2 os7 p1 Imaginary relative permittivity os4 p2 os5 p2 os6 p2 os7 p1 No kerogen-related loss mechanism in frequency band A171-8

9 Complex dielectric constant at different de-ionized water saturations 12 OS1 P3 vs. DI saturation 6 OS1 P3 vs. DI saturation Real relative permittivity Sw = % Sw = 36% Sw = 82% Sw = 81% Sw = 86% Imaginary relative permittivity Sw = % Sw = 36% Sw = 82% Sw = 81% Sw = 86% 2-1 The loss factor is highly dependent on water saturation A171-9

10 Large skin depths are measured in dry samples 5 Anadarko shale dry P orientation 1 Anvil points shale dry P orientation 4 os4 p2 os5 p2 os6 p2 os7 p1 8 os1 p1 os1 p2 os1 p3 os1 p4 Skin depth, m 3 2 Skin depth, m Heating rates are low in dry samples at lower frequencies. A171-1

11 Saturation controls skin depth with de-ionized water 2 Anadarko shale vs. DI saturation 5 OS1 P3 vs. DI saturation 15 os5 t1 Sw = % os5 t1 Sw = 89% os5 p2 Sw = % os5 p2 Sw = 8% 4 Sw 36% Sw 82% Sw 81% Sw 86% Skin depth, m 1 Skin depth, m For skin depths of 1 meters, f < 2 MHz A171-11

12 Saline water further reduces the skin depth 15 Anadarko shale brine saturation os7 t1 Sw = 74% os6 p2 Sw = 91% os7 p1 Sw = 8% os7 p2 Sw = 81% Skin depth, m 1 5 A171-12

13 Anadarko dry sample measured at elevated temps 8 OS4 T4, dry vs. temperature.6 OS4 T1, dry vs. temperature Real relative permittivity C 45 C 65 C 85 C 1 C Imaginary relative permittivity C 45 C 65 C 85 C 1 C No temperature dependent loss mechanism was identified up to 1 C A171-13

14 Anvil Points dry sample measured at elevated temp 5.4 OS1 P1, dry vs. temperature OS1 P1, dry vs. temperature Real relative permittivity C 123 C 146 C Imaginary relative permittivity C 123 C 146 C 4 No temperature dependent loss mechanism was identified up to 146 C A171-14

15 At higher temperatures there will be a kerogen related change in the loss factor Lower frequencies have a much larger loss factor above 4 C During a slow heating process the loss factor changes will occur at lower temperatures Near kerogen decomposition temperatures, an RF heating frequency should be utilized that avoids a runaway loss factor Jesch, R.L. and R.H. McLaughlin, Dielectric Measurements of Oil Shale as Functions of Temperature and Frequency, IEEE Trans. Geoscience and Remote Sensing, Vol. GE-22, No. 2, March 1984 A171-15

16 In-situ RF heating will be a complex dynamic process Below 1 C, fluids control dielectric heating Skin depth is controlled by saturation and brine concentration Heating rate is controlled by skin depth Above 1 C, fluid migration will dynamically change skin depth and heating rate Skin depth will increase Heating rate will decrease At kerogen decomposition temperatures, skin depth and heating rate will dynamically change Skin depth will decrease Heating rate will increase A171-16

17 In-situ RF heating experiments are essential to determine the regime of applicability (if any) Since pore fluids will control the early-phase heating process and limit RF penetration into the formation, early diffusive heating may be preferable on an economic basis If significant drying of the formation near the borehole occurs, RF heating will penetrate deeper into the formation and preferentially deposit energy there hence it may be preferable to diffusive heaters As kerogen breakdown temperatures are reached, previous studies indicate that the loss factor will significantly increase, reducing RF penetration. It is not clear if RF heating has any advantage over diffusive heating in this regime A171-17