1. Introduction

Pipelines are the foundation of our liquid energy supply. Crude oil has traditionally been collected by pipelines from inland production areas. Crude oil also arrives in the U.S. by marine tankers, often moving for the final leg of that trip from a U.S. port to a refinery by pipeline, too. The United States consumes millions of gallons of crude oil every day. This is especially important because frequently pipelines permit the movement of large quantities of crude oil and product to these areas with little or no disruption to communities everywhere. Pipelines also move crude oil produced far offshore in coastal waters. Currently hydrocarbons remain the leading energy source. While the amount of conventional light crude oil becomes less, and less available, more and more heavy crude oil and off-shore crude oil are needed. High viscosity of these oils becomes a critical issue. Not only the heavy crude oil has a high viscosity, the off- shore crude oil also has very high viscosity because the deep-water temperature is very low, around 1.5-1.6 °C. The high viscosity makes the pressure required to pump crude oil via pipeline very high and creates much difficulties in oil extraction, too. The importance of this issue, reducing the crude oil viscosity, called the attention more than 30 years ago. However, the current dominate methods remain heating and dilution of crude oil with gasoline or diesel. The heating method is slow and energy consuming and raises concerns about its environmental impact, too. Moreover, for the off-shore crude oil, it is very difficult to utilize the heating or dilution methods. Based on the concepts of Electrorheology (ER), a new micro-nanotechnology to reduce the viscosity of crude oils by a strong electric field was proposed [1-4]. Comparing to the heating method, this technology consumes much less energy and is very fast and, therefore, much more efficient. Afterwards, the technology has developed very fast [5-8] and verified by experimental test and computer simulation [9-13]. In this paper, we will report our finding that the AOT technology (Apply Oil Technology) significantly reduces the viscosity of Saudi Aramco crude oil and increase the flow rate.

1. Dr. Tao`s Viscosity Theory

Crude oil is a mixture of many different molecules. Gasoline, kerosene, and diesel, the liquid made of small hydrocarbon molecules, have very low viscosity. If we treat the rest large molecules, paraffin particles, and asphalt particles etc. as suspended particles in such low viscosity base liquid made of gasoline, kerosene, and diesel, crude oil is a liquid suspension. These suspended particles are typically of nanoscale. The theory about liquid suspensions thus provides the physics basis for our new method to reduce viscosity of crude oil. Einstein first studied a dilute liquid suspension of non-interacting uniform spheres in a base liquid of viscosity and found the effective viscosity as follows [14-16],

        (1)

where the small parameter is the volume faction of the suspended particles. Following Einstein`s work, Krieger-Dougherty introduced the intrinsic viscosity for particles of different shapes and generalized it for all volume fractions [17],

(2)

Where is the maximum value fraction allowed for packing the suspended particles. When is unchanged, the most widely used method to reduce viscosity is to reduce , such as raising the temperature. On the other hand, Equation (2) suggests that there is another method: if we change the rheology of the suspension to increase the value of and lower intrinsic viscosity , we will reduce the viscosity . The physics is clear: the effective viscosity depends on how much freedom the suspended particles have in the suspension. A and low mean high freedom for the suspended particles, which leads to lower dissipation of energy and lower viscosity [18]. The following three mechanisms contribute to the viscosity reduction [18,19]:

1. Aggregate the nanoscale particles into short chains with their shapes streamlined along the flow direction

2. Increase the polydispersity to increase .

3. Increase the average size of suspended particles.

Our technology is illustrated in (Figure 1).

The crude oil flows from left to right along a pipe. Initially the nanoscale particles are randomly distributed and the viscosity is high (left side of the tube). When the oil passes a strong local electric field (two parallel metal meshes), the suspended particles are polarized by the electric field. The induced dipolar interaction forces the nanoscale particles to aggregate into micrometer-size short chains once they passed the electric field. They have high polydispersity and large size. In addition, the most important is that they are of streamline shape with low along the flow direction as the electric field is parallel to the flow direction.

It is also important to note that after formation of short-chains along the field direction, similar to the flow of nematic liquid crystal with its molecular alignment parallel to the flow direction which breaks the rotational symmetry, making the viscosity of crude oil anisotropic. Along the field direction, the viscosity is significantly reduced, while the viscosity along the directions perpendicular to the field is actually increased [20]. This fact is very important and very useful as it does not only improve the flow along the field direction, but suppresses the turbulence inside the pipeline.

2. Application of Dr. Tao`s Viscosity Theory to Reducing Viscosity

It is clear from the above background that aggregating the nanoscale particles into short chains with their shapes streamlined along the flow direction will reduce the effective viscosity while remains the same. At the same time, it is important to note that after formation of short-chains along the field direction, its molecular alignment parallel to the flow direction which breaks the rotational symmetry, making the viscosity of crude oil anisotropic. Along the field direction, the viscosity is significantly reduced, while the viscosity along the directions perpendicular to the field is actually increased. For most suspensions, this aggregation can be realized with either electric or magnetic fields. We assume that the particles have an electric dielectric constantdifferent from the dielectric constant of the base liquid.

In an electric field, the particles are thus polarized along the field direction. The dipole moment is estimated by , where is the local electric field, which should be close to the external field in dilute cases. The dipolar interaction between the two induces electric dipoles is , where r is the distance between these two dipoles and is the angle between the joining line and the electric field. If this interaction is stronger than the thermal Brownian motion, that is , these two dipoles will aggregate together to align in the field direction. , where n is the particle number density, is the Boltzmann constant and is the absolute temperature. We derive the following critical field

(3)

If the applied electric field is weaker than, the thermal Brownian motion prevents particles from aggregating together. So the applied electric field must be not lower than. The required pulse duration time is,

(4)

If the duration of electric field is too shorter than, the particles do not have enough time to aggregate together [2]. Once the e field is turned off, the hysterisis time is[2].

Our lab device is outlined in (Figure 2a), which is placed in an environment chamber (Figure 2b).

The chamber provides the desirable and stable temperature for our test. The crude oil sample is loaded in cylindrical container at the top (Figure 2a), which serves as the reservoir. Underneath the reservoir, there are three meshes, serving as electrodes. The electrodes are connected to a low-amperage high-voltage power supply. Using a gravity feed, the crude oil flows through the three electrodes into a long capillary tube. A beaker on a microbalance collects the crude oil below the capillary tube. The microbalance is connected to a computer, which automatically records the oil mass in the beaker as a function of time with LabVIEW software. Using this configuration, we can accurately determine the untreated flow rate. When the power supply is turned on, a strong electric field is produced in the flow direction of crude oil, forcing the suspended particles inside to aggregate into streamlined short chains anisotropically along the flow direction (Figure 1).

In this way, the effective viscosity of crude oil along the flow direction is reduced, while no heating, drag reducing agents, or diluents are used. Because the Reynolds number is low, the crude oil flow inside the capillary tube is laminar. The capillary tube serves as a viscometer. From the flow rate, we can mathematically and precisely determine the viscosity. In this experimental setup, the pressure gradient due to the gravity remains constant. Therefore, the flow rate increases as the viscosity is reduced. Usually, we measure the flow rate without the electric field applied first and obtain the viscosity of the untreated oil. Following the baseline test, we turn on the electric field, measure the new flow rate, and obtain the viscosity of the electric-field treated crude oil. By adjusting the electric field strength, we can reach the optimal state to reduce the crude oil viscosity. The viscosity reduction and resultant flow rate improvements should significantly improve tariff revenue when this technology is employed commercially. Nuclear method is widely used in soft condensed matter study [21-24]. We also run small angle neutron scattering test at NIST for crude oil samples.

2. Results

We conducted the tests at three different temperatures, 270C, 480C and 660C for these three samples to meet various conditions for oil pipelines in Saudi. The results show that the AOT technology can significantly reduce the viscosity of all these three samples effectively.

1. Test Results for NAPD Crude Oil Sample

At 270C, with an electric field of 6176V/cm, the flow rate of the NAPD sample was increased 108.4%. The viscosity was reduced by 52.03% (Figure 3).

The typical test results are shown in (Figure 3). The crude oil was tested inside the Environment Chamber (Figure 2b) for temperature stability. Initially, there was no electric field applied and the oil was allowed to flow through the capillary tube. The slope of the curve was the flow rate. Afterwards, the electric field was applied; the curve’s slope jumps, indicating that the oil flow rate is increased significantly. The viscosity is reduced effectively. From the flow rates, we calculated the viscosities. The test results are summarized in the following (Table 1) and plotted in (Figure 4).

2. Test Results for KHU Crude Oil Sample

The AOT technology can significantly reduce the viscosity of KHU crude oil and increase the flow rate, to shows the typical test results (Figure 5).

It is clear that after an electric field is applied, the curve slope jumps up, indicating that the viscosity is reduced significantly. From the flow rates, we calculated the viscosities. The test results are summarized in (Table 2) and plotted in (Figure 6).

3. Test Results for HAW Crude Oil Sample

HAW is a very light crude oil. Its original viscosity is quite small. However, the AOT technology can also significantly reduce the viscosity of HAW crude oil and increase the flow rate. The test results are summarized in (Table 3) and plotted in (Figure 7)

The applied electric field for all these tests is listed in all the three Tables. The electric current used during the tests was about 200 µA, indicating that the water content inside the crude oil is moderate. In summary, the AOT viscosity reduction technology significantly reduces the viscosity of NAPD, KHU, and HAW crude oil samples.

3. Conclusion

The test results fully confirm the theoretical analysis. On the other hand, in comparison with the theoretical prediction, there is still some room for improvement. This implies that in our electric field treatment, some particles are not aggregated into short chains. If we need to reduce the viscosity further, it is required to find an optimal range of electric field strength and optimal application time to make almost all particles inside the crude oil to aggregate into short chains. Or with mew technology, we can make the electric field even stronger for better effect [25,26].

Naturally, there is a question: How long can such reduced viscosity last after the electric-field treatment? Since the viscosity reduction is the result of aggregated short chains along the flow direction, the viscosity will return to the original value once the aggregated chains are completely dissembled. To answer the above question, we conducted a number of tests. It shows a low viscosity after the short chains are tilted along the flow direction. We have found that the reduced viscosity keeps more than 12 hours. The above results are understandable. The aggregated short chains make the suspension as a viscoelastic fluid. It is well known that to dissemble such viscoelastic chains is very slow. On the other hand, if we deliberately shake the crude oil violently, the chains will be broken and the viscosity will return to the original value quickly.

Figure 1: As the crude oil flow passes a strong local electric field from left to right, the suspended particles (brown dots) aggregate along the field direction after the mesh which applied high voltage, and the viscosity along the flow direction is reduced. 

Figure 2: Device to test the crude oil samples (2a): The gravity feed crude oil flows through the three electrodes into a long capillary tube which is used to measure the viscosity (2b): the environment chamber. 

Figure 3: At 27⁰C, with an electric field of 6176V/cm, the flow rate of the NAPD sample was increased 108.4%. The viscosity was reduced by 52.03%.

Figure 4: The AOT test results for NAPD crude oil sample.

Figure 5: At 66⁰C, with an electric field of 6040V/cm, the flow rate of the KHU sample was increased 36.5%. The viscosity was reduced by 26.8%.

Figure 6: The AOT test results for KHU crude oil sample.

Figure 7: The AOT test results for HAW crude oil sample

Table 1: Test Results for NAPD Crude Oil Sample.

Table 2: Test Results for KHU Crude Oil Sample.

Table 3: Test Results for HAW Crude Oil Sample.

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