Name: Measurement of the Rheology of Crude Oil in Equilibrium with CO2 at Reservoir Conditions (Video) | JoVE Journal
Uploaded: 2017-06-06T16:00:00.000+00:00
Duration: 10 min 38 s
Description: Learn to measure crude oil rheology in equilibrium with CO2 at reservoir conditions using a double-gap geometry pressure cell system. This method reveals how dissolved carbon dioxide affects viscosity and flow behavior.

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5 minutes

The authors gratefully acknowledge funding from the Qatar Carbonates and Carbon Storage Research Centre (QCCSRC), provided jointly by Qatar Petroleum, Shell, and Qatar Science and Technology Park. The authors thank Frans van den Berg (Shell Global Solutions, Amsterdam, Netherlands) for providing the crude oil sample.

Note: Since the experiment operates at high temperature and pressure, safety is paramount. The system is protected against over-pressure by the software limit on the syringe pump controller and bursting discs at the mixer and between the gear pump and the rheometer (see Figure 1 and Figure 2). Furthermore, before each experiment, it is recommended to perform a regular leak check. It is also recommended to perform the friction check of the pressure cell geometry to make sure the rheometer is functioning well9,10.
1. Preparing the Crude Oil Sample
NOTE: Use the Zuata crude oil sample as received. The following table shows the basic physical properties of the Zuata crude oil.
<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>Characteristics</td>
			<td>Value</td>
		</tr>
		<tr>
			<td>API Gravity</td>
			<td>9.28</td>
		</tr>
		<tr>
			<td>Barrel Factor (bbl/t)</td>
			<td>6.27</td>
		</tr>
		<tr>
			<td>Total Sulphur (% wt)</td>
			<td>3.35</td>
		</tr>
		<tr>
			<td>Reid Vapor Pressure (kPa)</td>
			<td>1</td>
		</tr>
		<tr>
			<td>Pour Point (&#176;C)</td>
			<td>24</td>
		</tr>
		<tr>
			<td>Existing H2S Content (ppm)</td>
			<td>-</td>
		</tr>
		<tr>
			<td>Potential H2S Content (ppm)</td>
			<td>115</td>
		</tr>
		<tr>
			<td>Potential HCl Content (ppm)</td>
			<td>-</td>
		</tr>
		<tr>
			<td>Calc. Gross Cal. Value (kJ/kg)</td>
			<td>41,855</td>
		</tr>
	</tbody>
</table>
Table 1: The physical properties of the Zuata crude oil.
<ol>
	<li>Add 128.57 g of toluene to 300 g of Zuata crude oil to prepare the dilution with 70 wt% Zuata crude oil and 30 wt% toluene. Rock the mixture at room temperature for 3 h.</li>
</ol>
2. Loading the Crude Oil Sample into the Mixer
<ol>
	<li>Disconnect the mixer from the system, and open it up. Place a stirrer at the bottom of the mixer. Load 200 mL of crude oil sample into the mixer. After tightening all the screws, connect the mixer back to the system.</li>
</ol>
3. Priming the Entire System with the Crude Oil Sample
<ol>
	<li>Prime the system with the coaxial cylinder geometry pressure cell. 
	NOTE: Please refer Figure 1 to locate the valve.
	<ol>
		<li>Close the rheometer pressure cell by tightening the pressure head9. Mount the rotation cup on the rheometer spindle. Adjust it to the measuring position9.</li>
		<li>Close valves A, D, E, F, G, and H. Open valve C.</li>
		<li>Open the nitrogen cylinder. Introduce the compressed gas into the mixer by opening valves H and E. When the gas reaches the mixer, close valve H and the gas cylinder.</li>
		<li>Open valve A. The compressed gas will push the crude oil sample into the circulation loop through the suction tube. When the crude oil sample is dripping down from valve C in Figure 1, the entire system is primed by the crude oil sample.</li>
		<li>Open valve F to release the remaining gas. Close valve C and open valve D. Turn on the gear pump to circulate the fluid for a while. Depending on the viscosity of the crude oil sample, this could take 1 to 5 h. 
		NOTE: The pressure of the compressed nitrogen introduced into the mixer depends on the viscosity of the crude oil sample. If the viscosity of the crude oil sample is beyond 5 Pa&#8729;s, the pressure of compressed gas may be larger than 15 bar.</li>
	</ol>
	</li>
	<li>Prime the system with the double gap geometry pressure cell. 
	NOTE: Please refer Figure 2 to locate the valve.
	<ol>
		<li>Remove the pressure head and the measuring cylinder of the pressure cell.</li>
		<li>Close valves A, D, E, F, G, H and I. Open valve C.</li>
		<li>Open the nitrogen cylinder. Introduce the compressed gas into the mixer by opening valves H and E. When the gas reaches the mixer, close valve H and the gas cylinder.</li>
		<li>Open valve A. The compressed gas will push the crude oil sample into the circulation loop through the suction tube. When the crude oil sample just immerse the inner part of the double gap geometry, open valve F to release the pressure in the mixer.</li>
		<li>Turn on the gear pump. Carefully adjust the gear pump rotation speed. Make sure that the inlet flow rate to the pressure cell, which is determined by the gear pump, is less than or equal to the outlet flow rate from the pressure cell, which is determined by gravity. When a reasonable rotation speed of the gear pump is found and the crude oil sample is dripping down from valve C, the entire system is primed by the oil. Then turn off the gear pump.</li>
		<li>Mount the measuring cylinder and pressure head on the pressure cell10. Close valve C and open valve D. Turn on the gear pump to circulate the fluid. 
		NOTE: If the crude oil sample has a viscosity similar to water, the compressed gas with pressure of 3 to 4 bar is enough.</li>
	</ol>
	</li>
</ol>
4. Evacuating the Remaining Volume in the System
<ol>
	<li>Close valves A and D in Figure 1 or Figure 2. Connect the vacuum pump to valve F. Turn on the vacuum pump for 15 min.</li>
	<li>Close valve F and then turn off the vacuum pump.</li>
</ol>
5. Introducing CO2 into the Mixer
<ol>
	<li>With coaxial cylinder geometry pressure cell
	<ol>
		<li>Open valve G and the CO2 cylinder in Figure 1. Open valve D in Figure 1.</li>
		<li>After the CO2 fills up the remaining space in the system, close valve G and the CO2 cylinder to prevent CO2 from back flowing to the cylinder.</li>
	</ol>
	</li>
	<li>With double gap geometry pressure cell
	<ol>
		<li>Open valve G and the CO2 cylinder in Figure 2. Open valve D and I in Figure 2.</li>
		<li>After the CO2 fills up the remaining space in the system, close valve G and the CO2 cylinder to prevent CO2 from back flowing to the cylinder.</li>
	</ol>
	</li>
</ol>
6. Setting the Temperature and Pressure
<ol>
	<li>Input the desired temperature value to the mixer and rheometer. Input the desired temperature value to the heating system of the pipeline network. Input the desired pressure value to the syringe pump.</li>
	<li>Wait for the temperature and pressure to stabilize.</li>
</ol>
7. Turning on the Stirrer and Gear Pump
<ol>
	<li>Open the valves in the downstream and upstream of the gear pump.</li>
</ol>
8. Monitoring the Volume in the Mixer and the Mixture Viscosity
<ol>
	<li>Record the volume reading in syringe pump for every 6 h.</li>
	<li>After every 6 h, turn off the stirrer and gear pump. Measure the viscosity of the mixture through the rheometer. The viscosity measurement starts with a 5 min settling time, and then measure viscosity at constant shear rate of 10 s-1.</li>
	<li>When the volume and viscosity values show considerable differences (&#62; 4%) between two consequent measurements, turn on the gear pump and stirrer again to continue the mixing. When both the volume and viscosity measurements show no change in the values (&#8804; 4%), the equilibrium between the CO2 and crude oil sample is confirmed.</li>
	<li>Turn off the gear pump and stirrer for the rheology measurement. 
	NOTE: The mixing period could last for 1 to 2 days, depending on the viscosity of the crude oil sample.</li>
</ol>
9. Performing the Rheology Measurement
<ol>
	<li>With coaxial cylinder geometry pressure cell9
	<ol>
		<li>Close valves A and D in Figure 1 for the rheology measurement. Pre-shear the mixture at shear rate of 10 s-1 for 0.5 min. Rest the mixture for 1 min.</li>
		<li>Measure the mixture viscosity at shear rate from 500 s-1 to 10 s-1. At each shear rate, the shear rate adjusting time is 0.2 min. The measurement duration at each shear rate step is logarithmically increased from 0.5 min to 1 min, excluding the shear rate adjusting time.</li>
	</ol>
	</li>
	<li>With double gap geometry pressure cell10
	<ol>
		<li>Close valves A and D in Figure 2 for the rheology measurement. Pre-shear the mixture at shear rate of 10 s-1 for 0.5 min. Rest the mixture for 1 min.</li>
		<li>Measure the mixture viscosity at shear rate from 250 s-1 to 10 s-1. At each shear rate, the shear rate adjusting time is 0.2 min. The measurement duration at each shear rate step is logarithmically increased from 0.5 min to 1 min, excluding the shear rate adjusting time.</li>
	</ol>
	</li>
</ol>
10. Increasing the Pressure to the Next Desired Value
<ol>
	<li>With the coaxial cylinder geometry pressure cell
	<ol>
		<li>Close valve E in Figure 1.</li>
		<li>Introduce more CO2 into the syringe pump by opening valve G and the CO2 cylinder. Close valve G and the CO2 cylinder. Open valve E to add more CO2 to the mixer.</li>
		<li>If the pressure is less than the desired value, repeat to introduce more CO2.</li>
		<li>Input the new pressure set point into the syringe pump. Wait for the pressure to stabilize.</li>
	</ol>
	</li>
	<li>With the double gap geometry pressure cell
	<ol>
		<li>Close valves E and I in Figure 2.</li>
		<li>Introduce more CO2 into the syringe pump by opening valve G and the CO2 cylinder. Close valve G and the CO2 cylinder. Open valves E and I to add more CO2 to the mixer.</li>
		<li>If the pressure is less than the desired value, repeat step to introduce more CO2.</li>
		<li>Input the new pressure set point into the syringe pump. Wait for the pressure to stabilize. 
		NOTE: Repeat steps 7 to 10 for the rheology measurement at higher pressures.</li>
	</ol>
	</li>
</ol>

<ol><li>Hasan, S. W., Ghannam, M. T., Esmail, N. <a target="_blank" href="https://www.researchgate.net/publication/244068484_Heavy_crude_oil_viscosity_reduction_and_rheology_for_pipeline_transportation">Heavy crude oil viscosity reduction and rheology for pipeline transportation.</a> Fuel. 89 (5), 1095-1100 (2010).</li>
<li>Henaut, I., Barre, L., Argillier, J. F., Brucy, F., Bouchard, R. Rheological and Structural Properties of Heavy Crude Oils in Relation With Their Asphaltenes Content. SPE International Symposium on Oilfield Chemistry. , 13-16 (2013).</li>
<li>Ghannam, M. T., Hasan, S. W., Abu-Jdayil, B., Esmail, N. <a target="_blank" href="http://www.sciencedirect.com/science/article/pii/S0920410511003020">Rheological properties of heavy & light crude oil mixtures for improving flowability.</a> J. Petrol. Sci. Eng. 81, 122-128 (2012).</li>
<li>Martínez-Palou, R., et al. <a target="_blank" href="http://www.sciencedirect.com/science/article/pii/S0920410510002640">Transportation of heavy and extra-heavy crude oil by pipeline: A review.</a> J. Petrol. Sci. Eng. 75 (3-4), 274-282 (2011).</li>
<li>Behzadfar, E., Hatzikiriakos, S. G. <a target="_blank" href="https://www.tib.eu/en/search/id/elsevier%3Adoi~10.1016%252Fj.fuel.2013.08.024/Rheology-of-bitumen-Effects-of-temperature-pressure/">Rheology of bitumen: Effects of temperature, pressure, CO2 concentration and shear rate.</a> Fuel. 116 (0), 578-587 (2014).</li>
<li>Royer, J. R., Gay, Y. J., Desimone, J. M., Khan, S. A. <a target="_blank" href="http://onlinelibrary.wiley.com/doi/10.1002/1099-0488(20001201)38:23%3C3168::AID-POLB170%3E3.0.CO;2-E/full">High-pressure rheology of polystyrene melts plasticized with CO2: Experimental measurement and predictive scaling relationships.</a> J. Polym. Sci., Part B: Polym. Phys. 38 (23), 3168-3180 (2000).</li>
<li>Gerhardt, L. J., Manke, C. W., Gulari, E. <a target="_blank" href="https://www.researchgate.net/publication/230434504_Rheology_of_polydimethylsiloxane_swollen_with_supercritical_carbon_dioxide">Rheology of polydimethylsiloxane swollen with supercritical carbon dioxide.</a> J. Polym. Sci., Part B: Polym. Phys. 35 (3), 523-534 (1997).</li>
<li>Lee, M., Park, C. B., Tzoganakis, C. <a target="_blank" href="http://onlinelibrary.wiley.com/doi/10.1002/pen.11400/abstract">Measurements and modeling of PS/supercritical CO2 solution viscosities.</a> Polym. Eng. Sci. 39 (1), 99-109 (1999).</li>
<li>CC29/Pr Pressure Cell Operation. Anton Paar. , Available from:
 <a target="_blank" href="http://www.anton-paar.com/us-en/products/details/pressure-cell/">http://www.anton-paar.com/us-en/products/details/pressure-cell/</a> (2014).</li>
<li>DG35.12/Pr Pressure Cell Operation. Anton Paar. , Available from:
 <a target="_blank" href="http://www.anton-paar.com/us-en/products/details/pressure-cell/">http://www.anton-paar.com/us-en/products/details/pressure-cell/</a> (2014).</li>
<li>Seifried, C., Hu, R., Headen, T., Crawshaw, J., Boek, E. IOR 2015-18th European Symposium on Improved Oil Recovery. Eage. , (2015).</li>
<li>Priyanto, S., Mansoori, G. A., Suwono, A. <a target="_blank" href="https://www.researchgate.net/publication/222516046_Measurement_of_Property_Relationships_of_Nano-Structure_Micelles_and_Coacervates_of_Asphaltene_in_a_Pure_Solvent">Measurement of property relationships of nano-structure micelles and coacervates of asphaltene in a pure solvent.</a> Chem. Eng. Sci. 56 (24), 6933-6939 (2001).</li>
<li>Zhao, Y., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Effect+of+compressed+CO2+on+the+properties+of+lecithin+reverse+micelles%5BTitle%5D)+AND+%22Langmuir%22%5BJournal%5D)">Effect of compressed CO2 on the properties of lecithin reverse micelles.</a> Langmuir. 24 (17), 9328-9333 (2008).</li>
<li>Hu, R., Trusler, J. P. M., Crawshaw, J. P. <a target="_blank" href="http://pubs.acs.org/doi/abs/10.1021/acs.energyfuels.6b02359?src=recsys">The effect of CO2 dissolution on the rheology of a heavy oil/water emulsion.</a> Energy Fuels. , (2016).</li>
<li>Hu, R., Crawshaw, J. P., Trusler, J. P. M., Boek, E. S. <a target="_blank" href="http://pubs.acs.org/doi/abs/10.1021/acs.energyfuels.6b01858">Rheology and Phase Behavior of Carbon Dioxide and Crude Oil Mixtures.</a> Energy Fuels. , (2016).</li>
<li>Zhang, Y. P., Hyndman, C. L., Maini, B. B. <a target="_blank" href="https://www.researchgate.net/publication/254541066_Measurement_of_Gas_Diffusivity_In_Heavy_Oils">Measurement of gas diffusivity in heavy oils.</a> J. Petrol. Sci. Eng. 25 (1-2), 37-47 (2000).</li>
<li>Kariznovi, M., Nourozieh, H., Abedi, J. <a target="_blank" href="https://www.researchgate.net/publication/251724773_Experimental_apparatus_for_phase_behavior_study_of_solvent-bitumen_systems_A_critical_review_and_design_of_a_new_apparatus">Experimental apparatus for phase behavior study of solvent-bitumen systems: A critical review and design of a new apparatus.</a> Fuel. 90 (2), 536-546 (2011).</li>
<li>Tang, J., Quinlan, P. J., Tam, K. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Stimuli-responsive+Pickering+emulsions%3A+recent+advances+and+potential+applications%5BTitle%5D)+AND+%22Soft+Matter%22%5BJournal%5D)">Stimuli-responsive Pickering emulsions: recent advances and potential applications.</a> Soft Matter. 11 (18), 3512-3529 (2015).</li>
<li>Aveyard, R., Binks, B. P., Clint, J. H. <a target="_blank" href="https://www.researchgate.net/publication/223835132_Emulsions_Stabilised_Solely_by_Colloidal_Particles">Emulsions stabilised solely by colloidal particles.</a> Adv. Colloid Interface Sci. 100, 503-546 (2003).</li>
<li>Kawashima, Y., Hino, T., Takeuchi, H., Niwa, T., Horibe, K. <a target="_blank" href="https://www.researchgate.net/publication/223530868_Rheological_study_of_WOW_emulsions_by_a_cone-and-plate_viscometer_negative_thixotropy_and_shear-induced_phase_inversion">Rheological Study of W/O/W Emulsion by a Cone-and-Plate Viscometer - Negative Thixotropy and Shear-Induced Phase Inversion.</a> Int. J. Pharm. 72 (1), 65-77 (1991).</li>
<li>Perazzo, A., Preziosi, V., Guido, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Phase+inversion+emulsification%3A+Current+understanding+and+applications%5BTitle%5D)+AND+%22Adv.+Colloid+Interface+Sci%22%5BJournal%5D)">Phase inversion emulsification: Current understanding and applications.</a> Adv. Colloid Interface Sci. 222, 581-599 (2015).</li>
<li>Yeo, L. Y., Matar, O. K., de Ortiz, E. S. P., Hewitt, G. F. <a target="_blank" href="https://www.researchgate.net/publication/282679283_Phase_inversion_and_associated_phenomena">Phase Inversion and Associated Phenomena.</a> Multiphase Sci Technol. 12 (1), (2000).</li>
<li>Liu, L., Matar, O. K., de Ortiz, E. S. P., Hewitt, G. F. <a target="_blank" href="http://www.academia.edu/19853329/Experimental_investigation_of_phase_inversion_in_a_stirred_vessel_using_LIF">Experimental investigation of phase inversion in a stirred vessel using LIF.</a> Chem. Eng. Sci. 60 (1), 85-94 (2005).</li>
</ol>

The authors have nothing to disclose.

Two steps are critical in the operation. The first one is priming the entire system by the crude oil sample. By filling up the system with the crude oil sample, the gear pump can be well lubricated by the oil sample, and any blockages in the circulation loop can be easily identified. Thus the gear pump can be prevented from damage. The second critical step is periodically monitoring the mixture viscosity to confirm the equilibrium between the CO2 and crude oil. Given that it takes a considerable amount of time to reach the equilibrium between CO2 and viscous heavy crude oil16, performing the rheology measurement too early will underestimate the effect of CO2 addition on the oil viscosity. Therefore, only when the viscosity measured reaches a constant value (less than 4% change), can the mixture be considered in equilibrium with CO2.
The current measurement system only allows the rheology measurement of the CO2 saturated mixture. To measure under-saturated mixtures, an upstream vessel could be introduced to the CO2 stream. The CO2 will be introduced to the upstream vessel first and then isolated from the source, so that the amount of CO2 can be controlled by the volume and pressure in the upstream vessel. The total pressure of the system in this case would be controlled by an inert gas, such as helium. Kariznovi et al. provides a good review on the apparatus used to measure the physical properties of CO2 and heavy crude oil mixture17. Modifications can refer to the systems that reviewed in their paper.
It should be mentioned that the system described here can measure the rheology of any gas-liquid mixtures; therefore its application is not limited to crude oils. For example, it can be used to measure the CO2 effect on the rheology of Pickering emulsions18,19 and gas-induced plasticization6. By introducing the electrical conductivity measurement device into the rheometer pressure cell, the effect of gas dissolution on the shear-induced phase inversion of emulsions could also be studied20,21,22,23.

In most of the literature on the physical properties of CO2 and crude oil mixtures, viscosity is measured using a viscometer, meaning that the measurement is made at a constant shear rate or shear stress. In these studies, the viscosity of CO2 and crude oil mixture is investigated in a simple way: the focus of interest is the relations between the viscosity and other parameters, such as temperature, pressure and CO2 concentration. The key assumption made in these studies, yet rarely mentioned explicitly, is that the CO2 and crude oil mixture behaves as a Newtonian fluid. However, it is well known that some crude oils, especially heavy crude, can show non-Newtonian behavior under certain conditions1,2,3,4. Therefore, to fully understand the CO2 effect, the viscosity of CO2 and crude oil mixture should be studied as a function of shear rate or stress.
To our knowledge, only the study by Behzadfar et al. reports the viscosity of a heavy crude oil with CO2 addition at different shear rates using a rheometer5. In the measurement by Behzadfar et al., the mixing between CO2 and crude oil is achieved by the rotation of the inner cylinder of the coaxial cylinder geometry, a very slow process. In addition, the effect of the CO2 dissolution on the rheology of polymer melts has been reported in the literature, which could shed light on the study of heavy crude oil and CO2 mixtures. Royer et al. measure the viscosity of three commercial polymer melts at various pressures, temperatures and CO2 concentrations, using a high-pressure extrusion slit die rheometer6. They then analyze the data through the free volume theory. Other similar studies can be found in Gerhardt et al.7 and Lee et al.8. Our method, where mixing is performed in an external mixer and the rheology measurement in a coaxial cylinder geometry, allows a more thorough measurement of the rheology of CO2 and crude oil mixture.
The circulation system that we developed contains four units: a syringe pump, mixer, gear pump and rheometer, as shown in Figure 1 and Figure 2. A stirring bar is placed at the bottom of the mixer and magnetically coupled with a rotating magnet set. Stirring is used to enhance the mixing between CO2 and crude oil in the mixer, speeding up the approach to equilibrium between the phases. The CO2 saturated oil phase is withdrawn from close to the bottom of the mixer using a dip tube and circulated through the measurement system.
The viscosity is measured by a high-pressure cell mounted on a rheometer. There are two types of pressure cells. One is with a coaxial cylinder geometry, which is designed for the measurement of viscous fluid; and the other is with a double gap geometry for low viscosity application.
<img alt="Fluid dynamics diagram with pump, rheometer, mixer for pressure control study." class="xfigimg" src="/files/ftp_upload/55749/55749fig1.jpg" data-altupdatedat="1788250015000" data-alt="Figure 1"> 
Figure 1: The scheme of the circulation system with coaxial cylinder geometry pressure cell. The blue line represents CO2 flow, and the black line represents the crude oil mixtures. Reprinted with permission from Hu et al.14. Copyright 2016 American Chemical Society. <a href="http://cloudflare.jove.com/files/ftp_upload/55749/55749fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="High-pressure rheometer system diagram with syringe pump, gear pump; measures material flow." class="xfigimg" src="/files/ftp_upload/55749/55749fig2.jpg" data-altupdatedat="1788250015000" data-alt="Figure 2"> 
Figure 2: The scheme of the circulation system with double gap geometry pressure cell. The blue line represents CO2 flow, and the black line represents the crude oil mixtures. <a href="http://cloudflare.jove.com/files/ftp_upload/55749/55749fig2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Cylindrical viscometer diagram with sapphire bearings for fluid viscosity measurement research." class="xfigimg" src="/files/ftp_upload/55749/55749fig3.jpg" data-altupdatedat="1788250015000" data-alt="Figure 3"> 
Figure 3: The coaxial cylinder geometry pressure cell. <a href="http://cloudflare.jove.com/files/ftp_upload/55749/55749fig3large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
The coaxial cylinder geometry pressure cell (Figure 3) has a 0.5 mm gap between the inner and outer cylinder, leading to a sample volume of 18 mL. The inner cylinder is magnetically coupled with a rotational cup, which is attached to the rheometer spindle. There are two sapphire bearings at the top and bottom of the inner cylinder, which are directly in contact with the rotation axis of the inner cylinder. Since the sapphire bearings are exposed to the sample by design, the bearing friction may vary according to the lubrication properties of the sample.
<img alt="Rheometer setup diagram, double gap geometry; rotation cup, measuring cylinder labeled." class="xfigimg" src="/files/ftp_upload/55749/55749fig4.jpg" data-altupdatedat="1788250015000" data-alt="Figure 4"> 
Figure 4: The double gap geometry pressure cell. <a href="http://cloudflare.jove.com/files/ftp_upload/55749/55749fig4large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
On the other hand, the double gap pressure cell comprises a cylindrical rotor in a double gap geometry, as illustrated by Figure 4. The measuring cylinder is mounted on the pressure head through two ball bearings and magnetically coupled with the rotation cup, which is connected to the rheometer spindle. The ball bearings are located inside the pressure head and not in contact with the sample, which is injected into the measurement gap and overflows into a recess in the stator from which it is returned to the mixing vessel.
In a typical experiment, the crude oil sample is first loaded into the mixer. After priming the entire system with the crude oil, the remaining volume in the system is evacuated using a vacuum pump. The CO2 is then introduced into the mixer through the syringe pump and the system brought to the desired temperature and pressure. The system pressure is controlled through the CO2 phase by the syringe pump. When the pressure stabilized, the stirrer is turned on to mix the CO2 and crude oil inside the mixer. Then the gear pump is turned on to withdraw the oil phase from the mixer, fill the rheometer and recycle the fluid back to the mixer. Therefore, the mixing between CO2 and crude oil is done by simultaneously stirring in the mixer and circulating in the loop. The equilibrium status is monitored by periodic measurement of both the volume in the syringe pump and the mixture viscosity. When there is no change (≤4%) in both the volume and viscosity, the equilibrium is confirmed. At that stage the gear pump and stirrer are turned off, suspending the flow through the measurement cell and the rheology measurement is carried out.

<table><tbody><tr><td>Heavy Crude Oil</td><td>Shell</td><td>N/A</td><td>Produced from the Zuata oil flied. Used without further treatment</td></tr><tr><td>Toluene</td><td>Sigma-Aldrich</td><td>244511-2L</td><td>Anhydrous, 99.8%. Used without further treatment</td></tr><tr><td>CO&lt;sub&gt;2&lt;/sub&gt;</td><td>BOC</td><td>111304-F</td><td>CP Grade. Used without further treatment</td></tr><tr><td>&lt;strong&gt;Name&lt;/strong&gt;</td><td>&lt;strong&gt;Company&lt;/strong&gt;</td><td>&lt;strong&gt;Catalog Number&lt;/strong&gt;</td><td>&lt;strong&gt;Comments&lt;/strong&gt;</td></tr><tr><td>Syringe Pump</td><td>Teledyne ISCO</td><td>65D</td><td></td></tr><tr><td>Mixer</td><td>Parr Instruments</td><td>4651</td><td>Vessel volume 250 mL. Mounted on a series 4923EE bench-top heater</td></tr><tr><td>Gear Pump 1</td><td>Polymer Systems Inc.</td><td>CIP-12/1.5</td><td>Used with CC29/Pr pressure cell for high viscosity fluids.</td></tr><tr><td>Gear Pump 2</td><td>Micropump</td><td>GAH X21</td><td>Used with DG35.12/Pr pressure cell for low viscosity fluids.</td></tr><tr><td>Rheometer</td><td>Anton Paar</td><td>MCR301</td><td></td></tr><tr><td>Pressure cell 1</td><td>Anton Paar</td><td>CC29/Pr</td><td>With flow-through configuration. Used for high viscosity fluids. Coaxial cylinder geometry</td></tr><tr><td>Pressure cell 2</td><td>Anton Paar</td><td>DG35.12/Pr</td><td>With flow-through configuration. Used for low viscosity fluids. Double gap geometry</td></tr></tbody></table>

measurement of the rheology of crude oil in equilibrium with co2 at reservoir conditions

Measurement of the Rheology of Crude Oil in Equilibrium with CO2 at Reservoir Conditions

A rheometer system to measure the rheology of crude oil in equilibrium with carbon dioxide (CO2) at high temperatures and pressures is described. The system comprises a high-pressure rheometer which is connected to a circulation loop. The rheometer has a rotational flow-through measurement cell with two alternative geometries: coaxial cylinder and double gap. The circulation loop contains a mixer, to bring the crude oil sample into equilibrium with CO2, and a gear pump that transports the mixture from the mixer to the rheometer and recycles it back to the mixer. The CO2 and crude oil are brought to equilibrium by stirring and circulation and the rheology of the saturated mixture is measured by the rheometer. The system is used to measure the rheological properties of Zuata crude oil (and its toluene dilution) in equilibrium with CO2 at elevated pressures up to 220 bar and a temperature of 50 &#176;C. The results show that CO2 addition changes the oil rheology significantly, initially reducing the viscosity as the CO2 pressure is increased and then increasing the viscosity above a threshold pressure. The non-Newtonian response of the crude is also seen to change with the addition of CO2.

A method for measuring the rheology of crude oil in equilibrium with carbon dioxide at reservoir conditions is presented.

A rheometer system to measure the rheology of crude oil in equilibrium with carbon dioxide (CO2) at high temperatures and pressures is described. The ...

The overall goal of this experiment is to study the effects of carbon dioxide dissolution on the rheology of crude oils. When CO2's injected into an oil reservoir, it dissolves into the crude oil. This can strongly affect the oil rheology, a crucial parameter in predicting flow in the reservoir.The main advantage of this technique is the thorough measurement of the rheology of a gas-liquid mixture at restful conditions. Answering the fundamental question:whether the mixture is Newtonian or non-Newtonian. To begin preparing the double-gap geometry pressure cell system, disconnect and open the high-pressure mixer.Load a stir bar in 200 milliliters of low-viscosity oil into the mixer. Close the vessel with screws, and reconnect the mixer. Remove the pressure head and measuring cylinder from the pressure cell.Ensure that the valves to the gas tanks are closed. Close the oil and gas valves connected to the mixer, the gas valve to the pressure cell, and the gas relief valve. Open the relief valve on the recycle path of the circulation loop.Then, open the mixer to nitrogen gas. Once the gas reaches the mixer, close the nitrogen valve and cylinder. Open the oil valve downstream of the mixer and monitor the double-gap geometry.Once the inner part of the double-gap geometry is just barely immersed in oil, open the gas relief valve to depressurize the system. Start the gear pump and adjust the rotation speed, so that the oil flow rate into the pressure cell is less than or equal to the gravity-driven flow rate out of the pressure cell. When the inlet flow rate is acceptable and oil is dripping from the relief valve outlet, stop the gear pump.Close the relief valve, then open the valve on the recycle path of the circulation loop. Start the gear pump and allow the oil to circulate through the system. Mount the measuring cylinder in the pressure head on the pressure cell.Mount the rotation cup on the spindle and set it to the measuring position. Then, turn off the gear pump and close the oil valves. Connect the vacuum pump to the gas relief valve and evacuate the system for 15 minutes.Then, close the valve and turn off the vacuum pump. Open the carbon dioxide gas flow, the valve on the recycle path of the circulation, and the gas valve to the pressure cell. Once the system is pressurized, close the carbon dioxide valve and cylinder to prevent backflow.Set the mixer, pressure cell, and system heater to the desired temperatures. Set the syringe pump to the desired pressure. Once the temperature and pressure have stabilized, open the oil ball valves.Start the stir motor and gear pump. Every six hours, record the volume in the syringe pump. Turn off the stir motor and gear pump, and allow the oil to settle for five minutes.Then, measure the viscosity at a constant shear rate of 10 inverse seconds. If the volume of viscosity differ from the previous measurement by more than 4%restart the stir motor and gear pump and continue mixing for another six hours. Once the change in volume and viscosity over a six-hour period is 4%or less, close the oil ball valves.Pre-shear the equilibrated oil mixture at a shear rate of ten inverse seconds for 30 seconds. Allow the mixture to rest for one minute and then measure the viscosity at shear rates, stepping from 250 inverse seconds to 10 inverse seconds. Close the gas valves to the mixer and the pressure cell.Allow carbon dioxide to flow into the gas system. Then, close the carbon dioxide valve and cylinder and introduce the carbon dioxide into the mixer and pressure cell. Continue adding carbon dioxide in this way to achieve the next pressure step.Set the new pressure set point on the syringe pump and wait for the pressure to stabilize. Re-equilibrate the oil mixture before performing the next measurement. To begin preparing the coaxial cylinder geometry pressure cell system, load the high-pressure mixer with 200 milliliters of viscous oil.Next, tighten the pressure head of the coaxial cylinder geometry pressure cell to close the cell. Mount the rotation cup on the spindle and set it to the measuring position. Ensure that the valves to the gas cylinders are closed.Close the oil valves, the gas valve to the mixer, and the gas relief valve. Open the relief valve on the recycle path of the circulation. Prime the mixer with the loaded viscous oil using compressed nitrogen gas and then close the nitrogen gas valve and cylinder.Open the oil valve downstream of the mixer and monitor the relief outlet. When oil begins dripping from the outlet tube, open the gas relief valve to depressurize the system. Close the relief valve and open the valve on the recycle path of the circulation.Start the gear pump and allow the oil to circulate for one to five hours, depending on the viscosity. Then, turn off the gear pump, close the oil valves, and evacuate the system for 15 minutes via the gas relief valve. Open the carbon dioxide flow and the valve on the recycle path of the circulation.Once the system is filled with carbon dioxide, close off the gas flow. Set the system temperature and pressure and wait for them to stabilize. Open the oil valve downstream of the mixer and start the stir motor and gear pump.Take volume and viscosity measurements every six hours until the viscous oil and carbon dioxide gas are in equilibrium. Then, close the oil ball valve. Pre-shear the oil mixture at 10 inverse seconds for 30 seconds and then rest the mixture for one minute.Measure the viscosity at shear rates, stepping from 500 inverse seconds to 10 inverse seconds. Close the valve between the mixer and the gas system. Introduce carbon dioxide into the gas lines and then transfer the carbon dioxide into the mixer.Increase the pressure set point and re-equilibrate the system as previously described. Zuata crude oil, saturated with carbon dioxide at 50 degrees Celsius, was subjected to shear strain at shear rates ranging from 500 inverse seconds to 10 inverse seconds at various carbon dioxide pressures. The viscosity decreased with increasing pressure up to 100 bar.At which point the viscosity slowly increased with increasing pressure. A preparation of Zuata crude oil, diluted with toluene, was evaluated under similar conditions, at shear rates ranging from 250 inverse seconds to 10 inverse seconds. The viscosity decreased with increasing carbon dioxide pressure up to 70 bar.At which point the viscosity increased with increasing pressure. The crude oil displayed Newtonian behavior at pressures exceeding 40 bar, indicating that the dissolved carbon dioxide disrupted an associative network of macromolecules in the oil. The diluted crude oil displayed shear thinning between 30 and 60 bar of carbon dioxide, suggesting that the dissolved carbon dioxide facilitated the formation of an associative network within a narrow range of pressures.With this system, we no longer assume that the mixture behaves as a Newtonian fluid, but consider shear rate as another variable. Using this system, we have measured the viscosity of the crude oil in equilibrium with CO2 under restful conditions. The result shows that the CO2 addition has a significant effect on the rheology of crude oil.The rheological properties of a liquid containing dissolved gas are vital for applications from enhanced oral recovery to polymer processing. And the measurement system reported here can be used to characterize such fluids, even if they're non-Newtonian. Precautions, such as wearing PVC, should always be taken while performing the procedure.Before the procedure, it is recommended to perform air check for rheometer to ensure that rheometer is functioning well.

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