Circulating flow method for conveying thick oil through horizontal circular pipe at normal temperature

Abstract

The invention discloses a circular flow method for normal-temperature conveying of thick oil through a horizontal circular pipe, and relates to normal-temperature conveying of the thick oil in a wide flow ratio by using dimethyl silicone oil and poly-alpha olefin oil as fluid for isolating the thick oil. The dimethyl silicone oil and the poly-alpha olefin oil are used as circulation media, the difference between the apparent viscosity of the circulation media and the thick oil at 25 DEG C and 5 s <-1 > is 50-300 times, the kinematic viscosity of the circulation media and the thick oil at the temperature of-20 DEG C is 500-3000 cSt, the pipeline temperature is the normal temperature of 25 + / -5 DEG C, and the wide flow ratio is that the volume flow ratio range of the thick oil and the circulation media is 0.5-4.0. According to the circulation flowing method for conveying the thick oil at the normal temperature through the horizontal circular pipe, stable circulation flowing can be formed in the hydrophilic circular pipe and the lipophilic circular pipe with the horizontal smooth inner wall through a simple device, the thick oil is prevented from adhering to the wall, and the flowing method which is low in energy consumption, not prone to instability and easy to separate subsequently is provided for long-distance pipeline conveying of the thick oil at the natural environment temperature.

Description

Technical Field

[0001] This invention belongs to the field of heavy oil pipeline transportation technology, specifically relating to a method for forming a stable circulating flow pattern at room temperature with heavy oil by using dimethyl silicone oil and polyalphaolefin oil as low viscosity isolation fluids. Background Technology

[0002] Heavy oil is a type of heavy, high-viscosity crude oil. Due to its high viscosity and poor fluidity at both room and low temperatures, its asphaltenes and gums easily adhere to solid surfaces, unlike conventional crude oil. This makes pipeline transportation difficult, and onshore transport is typically done by tanker trucks. In deserts, hazardous operating areas, and during extreme cold or heat, pipeline transportation still has advantages. When ambient temperatures are low, methods such as electric heating / steam viscosity reduction, emulsification viscosity reduction, blending with thinner oil, viscosity reducers, and catalytic cracking viscosity reduction are used to achieve viscosity reduction and drag reduction in heavy oil transportation. Among these, heating and blending with thinner oil are relatively mature methods, suitable for short-distance and long-distance heavy oil transportation, respectively, but they suffer from high energy consumption and high blending costs.

[0003] Currently, heating and diluting methods require heating and insulation measures. Patent CN100435932C discloses a method and supporting equipment for transporting dehydrated extra-heavy oil via pipeline, using heat tracing and insulation at 75~80℃ to reduce viscosity during transport. Patent CN103450929B discloses a method for rapid oil-water separation of SAGD produced fluid and long-distance transport of extra-heavy oil by adding light hydrocarbons at 50~100℃, with a reasonable viscosity value of 300~500 mPa·s for the mixed oil. According to the Karamay Civilization Network, the longest onshore heavy oil pipeline in Xinjiang Fengcheng, which was put into operation in 2012, is 102.26 kilometers long. It uses diesel to reduce the viscosity of extra-heavy oil, and the heating of the first station of the mixed oil pipeline is controlled at about 95℃, while the temperature of the last station is controlled above 50℃.

[0004] Low-viscosity ring flow technology for transporting heavy oil is a multiphase flow technique using a ring-shaped flow. The low-viscosity lubricant isolates the heavy oil from the pipe wall, preventing adhesion and allowing for drag reduction at room temperature, significantly lowering energy consumption. Currently, the ring flow method utilizes the immiscibility of oil and water, using a water-based low-viscosity fluid as the ring medium. However, the operating conditions for the water-based low-viscosity fluid to form a ring flow with heavy oil are demanding; unstable flow patterns can cause heavy oil to adhere to the pipe wall, increasing transport resistance. Many patents disclose improved methods to achieve stable water ring flow. For example, foreign patent US8298997B2 uses polycyclic aromatic hydrocarbon sulfonates added to the water ring to stabilize the flow of heavy crude oil in wellbore and pipeline water ring flow transport, and patent US005988198A... In China, foam is used to suppress the floating and adhesion of asphalt in water ring transport. Domestic patent CN202546272U is a water ring generator for drag reduction in heavy oil pipelines in mines. Patent CN210637321U is a stabilizing device for oil-water annular flow. Patent CN109252838A discloses a foam ring generator that uses foam to suppress the floating of oil in the water ring. Patent CN207438003U discloses a heavy oil dilution drag reduction and stratification transport device that combines dilution and water ring technology to solve the problems of uneven mixing and stratification in heavy oil dilution transport and the eccentricity of the water ring in heavy oil water ring transport. Patent CN108870081B discloses a low-viscosity ring heavy oil transport stabilizing device, which is a spiral groove inner wall design of the pipe, set according to the actual spacing to avoid direct contact between heavy oil and the inner wall of the pipe.

[0005] Besides the narrow range of parameters for the formation of the circulation pattern, water-based low-viscosity ring transport of heavy oil also has the following two limiting factors: it cannot operate below the freezing point and cannot operate in cold seasons such as winter; and during long-distance transport, water emulsifies with heavy oil, which increases the energy consumption for demulsification and dehydration after arrival at the station.

[0006] Therefore, although the energy-saving properties of circulating pipelines for transporting heavy oil are very attractive, enabling the transportation of heavy oil at room temperature and reducing energy consumption, it is still necessary to expand the stable flow pattern region of the circulating flow. Under a wider temperature range, a wider flow ratio, and different transportation requirements, a stable flow pattern must be maintained to smoothly achieve the transportation of heavy oil at room temperature.

[0007] The purpose of this invention is to obtain a method for heavy oil circulation with a wide flow ratio under ambient temperature conditions (even below zero) without heating, thereby solving the problems of unstable flow pattern and high energy consumption in the aforementioned water-based liquid circulation method and heating method for transporting heavy oil. Summary of the Invention

[0008] To achieve the above objectives, this invention uses dimethyl silicone oil and polyalphaolefin as non-aqueous circulating media to provide a circulating flow method for transporting heavy oil in horizontal pipelines at room temperature with a wide flow ratio.

[0009] The following is a detailed description of the technical solution of the present invention.

[0010] The flow is horizontal, meaning that the axial direction of the circular pipe and the fluid flow inside the pipe are in a horizontal direction parallel to the ground.

[0011] The pipe cross-section is circular, and the inner wall of the pipe can be either hydrophilic or oleophilic. This includes glass pipes with hydrophilic inner walls, plastic pipes with hydrophobic inner walls, as well as engineering circular pipes such as stainless steel pipes and steel pipes with epoxy resin coating on the inner wall that meet the strength requirements of the actual conveying distance and pressure. Hydrophilic inner walls are preferred.

[0012] The outside of the pipeline is not heated, and the pipeline body and circulation are at ambient temperature, including the laboratory ambient temperature of 25±5℃ and the ambient temperature at a depth of 0.5~1.0 meters below the ground of about -20~30℃.

[0013] After the circulating medium and heavy oil are injected into one end of the pipeline by a pump, they are transported from one end of the pipeline to the other end through a circulating flow pattern.

[0014] The preferred heavy oil is dehydrated and degassed heavy oil.

[0015] During the circulation process, the circulation medium acts as an isolation fluid, with the heavy oil being encapsulated and flowing axially through the oil core. The flow resistance of the low-viscosity circulation medium is the main resistance to pipeline transportation. However, the circulation pattern does not mean that there are no small radial fluctuations or changes in the laminar flow curve.

[0016] Stable circulation flow is characterized by the fact that the heavy oil is continuously enveloped by the circulating medium and flows continuously without contacting the pipe wall and causing adhesion.

[0017] The stability of the circulating flow pattern is judged based on the amount of heavy oil adhering to the inner wall of the pipe. In the visualized pipeline, the flow can be observed and recorded. If there is no heavy oil adhering to the inner wall of the pipe during or after the flow, it is a stable circulating flow. However, in actual engineering long-distance pipelines, the stability of the flow pattern is judged based on the pressure drop stability to determine whether the circulating flow is stable, or based on the amount of heavy oil adhering to the inner wall of the pipe after the transportation is completed.

[0018] The circulating medium is selected from millions of low-viscosity substances based on the physical properties of heavy oil and the specific conditions for the formation of flow patterns.

[0019] The criteria for selecting the circulating medium are that it can easily form a circulating flow with heavy oil, can be formed with simple equipment, the circulating flow pattern can be maintained stably during flow and short-term stop-transport, and the flow ratio range is wide.

[0020] The circulating medium must have certain freezing point, viscosity, viscosity index, density, solubility parameters, gravitational viscosity ratio, flash point and boiling point, and must meet the specific chemical and physical property requirements of C1, P1~P4.

[0021] The circulating medium must be C1 in chemical properties, non-flammable and non-explosive at room temperature, have a flash point greater than 200℃, and not react with heavy oil and the inner wall of the circular pipe at the operating temperature.

[0022] The physical properties of the circulating medium must be P1, meaning that after long-distance flow, the heavy oil and the circulating medium should not be physically mixed and should be easily separated at room temperature.

[0023] The circulating medium must have physical properties of P2, low volatility, boiling point greater than 100℃, remain liquid at -40~200℃, be able to flow and operate at room temperature, and will not adhere to or clog pipes when transported alone.

[0024] The circulating medium must have a physical property of P3, a viscosity not exceeding 3000 cSt at a low temperature of -20℃, and be suitable for long-distance pumping.

[0025] The physical properties of the circulating medium must be P4. The density of the circulating medium selected based on the heavy oil type must be close to that of the heavy oil, with a low gravitational viscosity ratio, so that the flow pattern can be easily maintained after the formation of the multiphase circulating flow.

[0026] Based on the above requirements, this invention selects dimethyl silicone oil and polyalphaolefin oil with certain viscosity and density as circulating media.

[0027] Dimethyl silicone oil and polyalphaolefin oil products of different densities and viscosities can be purchased from the market.

[0028] The selected dimethyl silicone oil and polyalphaolefin oil circulating medium have a lower gravitational viscosity ratio and density difference compared to the flow system composed of water and heavy oil, effectively preventing the oil core from floating.

[0029] The selected dimethyl silicone oil and polyalphaolefin oil viscosity were compared with those of heavy oil at 25°C and 5 seconds. -1 The apparent viscosity differs by 50 to 300 times, meeting the requirements for stable circulation pattern and pumping efficiency.

[0030] Specifically, the dimethyl silicone oil and polyalphaolefin oil circulating medium included in this invention have a kinematic viscosity of 80~500 cSt at 25°C, a pour point below -40°C, and a kinematic viscosity of no more than 2000 cSt at -20°C.

[0031] The selected dimethyl silicone oil was subjected to a beaker stirring and layering test. After thorough mixing, it automatically separated from the heavy oil within 24 hours of standing and could be separated by a room temperature liquid separation method.

[0032] The selected dimethyl silicone oil and heavy oil were tested for flow. Under the same flow conditions, they did not mix and formed a stable circulation. After being collected at the flow tailpipe, they could automatically separate into layers at room temperature within 24 hours.

[0033] The selected polyalphaolefin oil was tested in flow experiments and found that it did not mix with heavy oil and dimethyl silicone oil under flow conditions and could form a stable circulation.

[0034] Before the circulation flow, the ratio of heavy oil to circulation medium flow rate is calculated based on the flow requirements, delivery distance, inner diameter of the circular pipe, pump power, and viscosity of heavy oil and circulation medium.

[0035] The process of forming a circulating flow is described in steps S1 to S2, which are the initial steps in the formation of the circulating flow.

[0036] Step S1: At the horizontal circular pipe confluence, first inject the circulating medium into the side port, such as... Figure 1 As shown.

[0037] Preferably, a substance with a density difference of no more than 0.06 g·cm³ from heavy oil is first injected into the lower injection port. -3 The heavier circulating medium 1.

[0038] Preferably, the upper injection port injects a substance with a density difference of no more than 0.08 g·cm³ from the heavy oil. -3 2. A lighter circulating medium.

[0039] When the densities are similar, circulation medium 1 can also be injected simultaneously as circulation medium 2.

[0040] Step S2: The circulating media 1 and 2 are in laminar flow. After stabilizing for a certain distance, heavy oil 3 is injected into the main pipe port.

[0041] The circulating flow method of the present invention ensures that the heavy oil and the circulating medium do not mix and are easily separated at room temperature.

[0042] Compared to water-based low-viscosity liquid circulation, the circulation flow method of the present invention has a wider range of stable circulation flow patterns and a volumetric flow rate ratio of heavy oil to circulation medium of 0.5 to 4.0.

[0043] It should be noted that in actual engineering conditions that are more complex, more preliminary tests and more factors should be considered. Heavy oil is difficult to flow at room temperature and easily adheres to the pipe wall. Depending on the viscosity and flowability of the heavy oil, the pump's operating mode and requirements, the heavy oil is injected at room temperature or after heating at the injection port. After entering the pipe, it is cooled to ambient temperature by the circulating medium. For example, ordinary heavy oil can be pumped in at room temperature, while extra-heavy oil, super-heavy oil, and natural asphalt are injected at temperatures depending on their viscosity and pump parameters. After being heated to flowability, they are then pumped into an industrial confluencer with a similar function.

[0044] The heavy oil circulation method of the present invention differs from the existing water-based circulation method in that the circulation media above and below the heavy oil are non-water-based, which can theoretically operate at sub-zero temperatures. The circulation system has a lower gravitational viscosity ratio and a wide range of controllable circulation flow patterns, flow rates, velocity ranges, and temperature ranges. It can form a stable circulation pattern without the need for special flow stabilization equipment or other additives, thus isolating the heavy oil from contact with the pipe wall to complete the transportation.

[0045] The heavy oil circulation flow method of the present invention differs from existing blending technologies for diesel, condensate, distillate, and crude oil, as well as emulsification viscosity reduction methods for transporting heavy oil, in that it uses dimethyl silicone oil and polyalphaolefin oil as circulation media instead of additives. The heavy oil does not undergo physical changes, and the boundary between the circulation media and the heavy oil is clear and stable in the radial direction of the multiphase flow, whereas there is no obvious macroscopic boundary in the fluid of blending or emulsification viscosity reduction technologies.

[0046] The heavy oil recirculation flow method of the present invention differs from existing blending technologies for diesel, condensate, distillate, and crude oil, as well as emulsification viscosity reduction methods for transporting heavy oil, in that the recirculation medium, dimethyl silicone oil, is non-hydrocarbon and immiscible with heavy oil. Even after stirring and standing for no more than 24 hours, the two can still automatically separate into layers. Upon arrival at the station, no fractionation is required; the layers can be separated and recycled after standing at room temperature. The operation is simple.

[0047] The heavy oil circulation method of the present invention differs from existing viscosity reduction technologies using diesel, condensate oil, and distillate oil blending in that 80~500cSt dimethyl silicone oil and polyalphaolefin oil have the characteristics of stable chemical properties, flash point greater than 200℃, non-flammability, and low volatility at operating temperature.

[0048] The heavy oil circulation method of the present invention differs from the existing diesel blending viscosity reduction technology in that it is transported at room temperature. The viscosity of the circulating medium at room temperature is comparable to that of the super-heavy oil mixture with 20% coking diesel at 70~80℃. Therefore, the pipeline does not need to be heated and can operate at room temperature. Detailed Implementation

[0049] The following detailed description, with reference to specific embodiments, further illustrates the method for transporting heavy oil in a horizontal circular pipe at room temperature using circulating flow, as described in this invention. It should be understood that the specific embodiments described herein are for illustrative purposes only and are not intended to limit the scope of the invention.

[0050] The example is a laboratory-scale flow experiment in a pipe. The pipe used is a PVC plastic flexible tube and a quartz glass rigid tube. The flow is transparent and visible. A high-speed camera on the side of the pipe is used to record the flow during and after the process. The pipe wall is checked for thick oil adhesion to determine the stability of the flow pattern.

[0051] The flow ratio design and the selection of the circulating medium type are carried out according to steps E1 to E5.

[0052] Step E1: Based on the operating temperature and flow rate requirements of the environment to be transported, test the density and apparent viscosity of the heavy oil, and calculate the gravity viscosity ratio of the circulating flow pattern.

[0053] Step E2: Based on the apparent viscosity and density of the heavy oil to be transported, select a circulating medium with a certain density, viscosity, and pour point, so that the operating temperature and the designed pipeline distance meet the allowable power requirements of the pump for the circulating medium, such as dimethyl silicone oil or polyalphaolefin oil of a certain viscosity grade.

[0054] Step E3: Perform a stirring and stratification test on the heavy oil and the selected circulating medium. The beaker test should meet the requirements of being immiscible without stirring for 24 hours at ambient temperature, and automatically stratifying within 24 hours after stirring.

[0055] Step E4: At the inlet of the laboratory dendritic confluence, inject circulating media with a density slightly lower and a density slightly higher than that of heavy oil into the upper and injection ports, respectively. Alternatively, inject the same circulating media with a density close to that of heavy oil. After the flow stabilizes, inject heavy oil into the coaxial inlet.

[0056] Step E5: Start the flow experiment according to the designed flow ratio of heavy oil to circulating medium. The average flow velocity is the same, so that the circulating medium maintains laminar flow along the pipe wall, and the heavy oil flows in laminar flow or plunger flow in the center of the pipe.

[0057] To verify the effectiveness of the technical solution of the present invention, specific embodiments 1 to 4 are provided.

[0058] Example 1

[0059] Inside a horizontal quartz glass tube at room temperature, heavy oil is at 25°C for 5 seconds. -1 The apparent viscosity is 2.5 × 10⁻⁶. 4 mPa·s, the circulating medium 1 has a viscosity of 500 cSt and a density of approximately 0.93 g·cm³. -3 Dimethyl silicone oil, with circulating medium 2 having a viscosity of 80 cSt and a density of approximately 0.81 g·cm³. -3 Polyalphaolefin oil, with a heavy oil to circulating medium volumetric flow rate ratio of approximately 1.0, such as... Figure 2-1 .

[0060] Example 2

[0061] Inside a horizontal quartz glass tube at room temperature, heavy oil is at 25°C for 5 seconds. -1 The apparent viscosity is 2.5 × 10⁻⁶. 4 mPa·s, circulation medium 1 has a density of 500 cSt and a density of approximately 0.93 g·cm³. -3 Dimethyl silicone oil, with circulating medium 2 having a viscosity of 100 cSt and a density of approximately 0.80 g·cm³. -3 Polyalphaolefin oil, with a heavy oil to circulating medium volumetric flow rate ratio of approximately 1.5 to 4.0, such as... Figure 2-2 2-3.

[0062] Example 3

[0063] In a horizontal plastic pipe at room temperature, heavy oil is at 25°C for 5 seconds. -1 Apparent viscosity 2.5 × 10 4 mPa·s, the circulating medium 1 has a viscosity of 500 cSt and a density of approximately 0.93 g·cm³.-3 Dimethyl silicone oil, with circulating medium 2 having a viscosity of 80 cSt and a density of approximately 0.81 g·cm³. -3 Polyalphaolefin oil, with a heavy oil to circulating medium volumetric flow rate ratio of approximately 0.5~1.0, such as... Figure 3-1 3-2.

[0064] Example 4

[0065] In a horizontal plastic pipe at room temperature, heavy oil is at 25°C for 5 seconds. -1 Apparent viscosity 2.5 × 10 4 mPa·s, the circulating medium 1 has a viscosity of 500 cSt and a density of approximately 0.93 g·cm³. -3 Dimethyl silicone oil, with circulating medium 2 having a viscosity of 100 cSt and a density of approximately 0.80 g·cm³. -3 Polyalphaolefin oil, with a heavy oil to circulating medium volumetric flow rate ratio of approximately 2.0~3.0, such as... Figure 3-3 3-4. Attached Figure Description

[0066] Figure 1 The diagram shows a non-heavy oil mixed with non-water circulating media (1 and 2) and degassed, dehydrated heavy oil (3) forming a circulating flow inside a horizontal circular tube with a hydrophilic or oleophilic inner wall at ambient temperature. The left side is a radial AA cross-section of the circular tube, and the right side is a three-dimensional side view of the confluencer and the circular tube.

[0067] Figure 2 Corresponding to Examples 1 and 2, at a room temperature of 25±5℃, the circulating medium and heavy oil circulate in a horizontal circular tube of quartz glass, with the flow direction from right to left.

[0068] Figure 3 For examples 3 and 4, at room temperature 25±5℃, the circulating medium and heavy oil circulate in a horizontal plastic tube, with the flow direction from right to left.

Claims

1. A horizontal circular pipe cold heavy oil transportation loop flow forming method, characterized in that, The pipeline working temperature is stable circular flow of non-water-based medium and thick oil in a hydrophilic or oleophilic horizontal pipe without heating and insulation.

2. The pipe operating temperature of the loop according to claim 1, wherein The stable circular flow is at a natural environment temperature lower than 30℃ and higher than -20℃ without heating and insulation.

3. The pipe operating temperature of the loop according to claim 2, wherein The stable circular flow is at room temperature 25±5℃ without heating and insulation.

4. The non-aqueous based loop fluid medium of claim 1, wherein, The non-water-based liquid is non-flammable and non-explosive, resistant to shearing, easy to pump, and does not chemically react with thick oil and the inner wall of the pipe.

5. The looped flow medium of claim 4, wherein, The liquid in claims 2 and 3 is liquid at the pipeline working temperature, has low volatility, a boiling point higher than 200℃, a flash point greater than 200℃, and a freezing point lower than -40℃.

6. The looped flow medium of claim 5, wherein, The kinematic viscosity at -20℃ is not more than 3000cSt.

7. The looped flow medium according to claims 4 to 6, characterized in that The non-water-based liquid is immiscible with thick oil and has a relative density of 0.8-0.

98.

8. The looped flow medium of claim 7, wherein, After mixing with the to-be-thickened oil in a beaker with stirring, the two are automatically layered after standing for no more than 24 hours, and the apparent viscosity difference is 50~300 times that of the thickened oil at 25°C, 5s -1 Dimethyl silicone oil with an apparent viscosity difference of 50~300 times.

9. The looped flow medium of claim 7, wherein, The apparent viscosity of the thickened oil 25°C, 5 s -1 Polyalphaolefin oil with a difference in apparent viscosity of 50-300 times.

10. The injection process of the heavy oil horizontal circular pipe loop method according to claim 1, characterized in that, The order of injection is first injecting the circular flow medium in claims 8 and / or 9 through the side port, and then injecting thick oil through the main pipe port.

11. The injection process in claim 10, wherein the volume flow rate ratio of the circular flow medium to the thick oil is 0.5-4.0.

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