1. NMR Measurement and Viscosity Evaluation of Live Bitumen Elton Yang, George J. Hirasaki Chemical Engineering Dept. Rice University April 26, 2011

2. Introduction & Objective  The well log T 2 measurements on the live bitumen appear to be significantly longer than the laboratory NMR measurements of dead bitumen sample. This is likely due to the dissolved gas in heavy oil.  Saturate the bitumen sample with three reservoir gases (CO 2, CH 4, C 2 H 6 ) at different pressure levels in laboratory. Make NMR and viscosity measurements on recombined live heavy oils.  Correlate the T 2, viscosity, and gas content of live bitumen and resolve the differences between the NMR log and laboratory data.

3. Samples and Equipments  Sample: Bitumen Sample #10-19  Three gases (CO 2, CH 4 and C 2 H 6 ) used in this work are provided by Matheson Tri-Gas with product grade of Ultra High Purity.  2 MHz Maran Spectrometer (Oxford Instrument).  A 40 mm probe with minimum TE = 0.2 msec was employed for all the NMR measurements on bitumen.  Brookfield Viscometer LVDV-III+ (Brookfield Company) for dead oil at different temperatures.  Capillary viscometer for live bitumen at room temperature.

4. T 2 Distribution of Bitumen #10-19 at Different T & Corrected T 2 with Specified M 0 and Lognormal Distribution Model** ** Yang and Hirasaki, JMR, 2008

5. Correlation Between Corrected T 2 and Viscosity/Temperature Ratio for Three Different Heavy Oils  T 2 values are corrected by using lognormal distribution model and specified M 0  Corrected T 2 and viscosity/temperature ratio of three dead oil samples closely follow linear relationship on log-log scale.  Data from Brookfield oil deviates from the data of two bitumen samples.

6. Measurements on Live Heavy Oils  The pressure vessel was manufactured by TEMCO and was customized to fit the 40 mm probe. The minimum echo spacing = 0.2 msec.  Pressurized gas was injected into the vessel from top. The gas pressure inside the vessel was monitored during the entire process. NMR measurements were performed periodically.  Convection was generated by rocking the pressure vessel to boost the gas dissolving rate. After equilibrated at the highest pressure, the gas-bitumen system was depressurized to different lower pressure levels.  Viscosity of live bitumen was measured and correlations between T 2, viscosity, pressure and gas solubility were established. Generation of Convection

7. Changes of T 2 and Pressure of C 2 H 6 Dissolved Bitumen During Pressurization Stage  Bi-modal for the peak of bitumen with C 2 H 6 as C 2 H 6 gradually transfers into bitumen.  Bitumen and gas reached equilibrium after 308 hours.

8. Depressurization of C 2 H 6 to Lower Pressures

9. T 2 of C 2 H 6 Saturated Bitumen at Different Pressures  The dissolving of C 2 H 6 in Bitumen significantly changes oil T 2.  The T 2 of C 2 H 6 saturated bitumen decreases as equilibrated pressure decreases.  The bitumen peak is broad and has fast relaxing components shorter than TE even at the highest saturation pressure.  T 2 from regular interpretation > T 2 from lognormal distribution model with specified M 0. The difference decreases as saturation pressure increases.

10. Corrected Initial Pressures at Different Pressure Levels for Solubility Calculation Pressurization Stage Depressurization Stage (Example: C 2 H 6 -Bitumen)  System would be either heated by pressurization or cooled by depressurization temporarily, and then return to the temperature of air bath (30 o C).  Significant pressure change resulting from the temperature fluctuation would display incorrect P 0 for the solubility calculations.  Extrapolation is employed to remove the temperature effect on the initial pressure reading.

11. Summary for Live Bitumen with Different Gases  T 2 vs P of each reservoir gase is found to be closely linear on semi-log scale and extrapolated near the value of dead oil T 2.  Solubility of CH 4 and C 2 H 6 in the bitumen follow the Henry’s law well.  The calculated solubility of CO 2 in bitumen is overestimated.

12. Correction for Deviation of CO 2 Solubility in Bitumen L-L-V Three-Phase-Equilibrium could have formed inside the pressure vessel

13. Correlation Between T 2 and Viscosity/Temperature Ratio for Bitumen and Brookfield Oil  Regardless of the gas type used for saturation, the live oil T 2 correlates with viscosity/temperature ratio on log-log scale.  The changes of T 2 and viscosity/temperature ratio caused by gas saturations in oil follows the same trend of those caused by temperature variations on the dead oil. Bitumen Brookfield Oil

14. Comparing with Previous T 2 vs Viscosity Data ** Hirasaki, Lo and Zhang, Magnetic Resonance Imaging, 2003 Relaxation time and viscosity/temperature ratio are normalized with respect to 2 MHz as shown below**:

15.  The live bitumen T 2 is significantly larger than T 2 of dead bitumen, even at the lowest pressure level in this work (~100 psia).  The relationship between live bitumen T 2 and equilibrium pressure / solubility is linear on semi-log scale for all three reservoir gases.  Regardless of the gas type used for saturation, the live bitumen T 2 correlates with viscosity/temperature ratio on log-log scale.  More importantly, the changes of T 2 and viscosity/temperature ratio caused by solution gas follows the same trend of those caused by temperature variations on the dead oil. Conclusion

16. Appendix A  The method for computing solubility from pressure data is described as follows: (1) Pressurization stage: (2) Depressurization stage: s g,i is the solubility at current pressure level. s g,i-1 is the solubility at previous pressure level right before the depressurization. V g is the volume of vapor phase inside the pressure vessel. V oil is the volume of oil sample inside the pressure vessel. Assuming the swelling effect of oil in this work is negligible, both V g and V oil are constant. P 0 and P eq are system pressure at beginning and pressure at equilibrium after each pressurization/depressurization, respectively. z 0 and z eq are compressibility at beginning and compressibility at equilibrium after each pressurization/depressurization, respectively.

17. Back-up Slides

18. Approach to Compensation for T 2 Information Loss  Determine initial magnetization M 0 from FID.  Supplement M 0 into the regular CPMG data and assume lognormal distribution for bitumen. M o from FID Collected data in CPMG

19. Changes of T 2 and Pressure of CO 2 Dissolved Bitumen During Pressurization Stage

20. Depressurization of CO 2 to Lower Pressures

21. T 2 &T 1 of CO 2 Saturated Bitumen at Different Pressures  The dissolving of CO 2 in Bitumen significantly changes oil T 2.  T 2 from regular interpretation > T 2 from lognormal distribution model with specified M 0. The difference decreases as saturation pressure increases.  The change of T 1 with pressure is much less significant, comparing to the corresponding T 2.  The change of bitumen viscosity has much more effect on the T 2 response rather than T 1.

22. Changes of T 2 and Pressure of CH 4 -Bitumen at Different Pressure Levels Pressurization Stage Depressurization Stage

23. T 2 of CH 4 Saturated Bitumen at Different Pressures  The change of bitumen T 2 resulting from the saturation of CH 4 is obviously less significant than that observed in the case of CO 2 or C 2 H 6  The T 2 of C 2 H 6 saturated bitumen decreases as equilibrated pressure decreases.  The minor peaks between 100 msec and 1 sec are from CH 4 in the vapor phase. As pressure decreases, the gas peak moves to the smaller values and peak area shrinks.  T 2 from regular interpretation > T 2 from lognormal distribution model with specified M 0. The difference decreases as saturation pressure increases.

24. Re-adjustment of z factor of CO 2 to Correct the Calculated Solubility to Follow Henry’s Law  Adjustment of z 0 at the initial pressure gives the re-evaluated value of z factor (z 0 *) to be 0.96, which is very unlikely for the compressibility factor of CO 2 at 745 psia.  Adjustment on of z e at the equilibrium pressure shows that, the corrected value of z factor (z e *) needs to move down to 0.55 at 709 psia.  The calculated mole fraction of CO 2 in vapor phase is 0.54, and the mole fraction in CO 2 -rich liquid phase is 0.46. Correspondingly, the volume fraction of CO 2 in either vapor phase or CO 2 -rich liquid phase is calculated to be 0.82 and 0.18, respectively.