Title:
Pipes, systems, and methods for transporting hydrocarbons
Kind Code:
A1


Abstract:
There is disclosed a method of transporting a produced fluid through a pipe while limiting deposits at a desired pipe inner-wall location comprising providing a pipe having an inner surface roughness Ra less than 2.5 micrometers at said desired pipe inner-wall location, forcing the produced fluid through the pipe, wherein the produced fluid has a wall shear stress of at least 1 dyne per centimeter squared at said desired pipe inner-wall location.



Inventors:
Balkanyi, Szabolcs Roland (Houston, TX, US)
Broze, James George (Houston, TX, US)
Esparza, Jose Oscar (Katy, TX, US)
Hatton, Gregory John (Houston, TX, US)
Mehta, Ajay Praful (Houston, TX, US)
Nimmons, Johnny Frank (Brookshire, TX, US)
Tsai, Chien Kuei (Katy, TX, US)
Wicks III, Moye (Houston, TX, US)
Zabaras, George John (Houston, TX, US)
Application Number:
11/328686
Publication Date:
08/24/2006
Filing Date:
01/10/2006
Primary Class:
Other Classes:
73/815, 138/177, 165/95, 73/54.41
International Classes:
C10G45/00
View Patent Images:



Primary Examiner:
RIVELL, JOHN A
Attorney, Agent or Firm:
SHELL OIL COMPANY (HOUSTON, TX, US)
Claims:
1. A system for producing and transporting crude oil, comprising: a well for producing the crude oil; a processing facility for processing the crude oil; and a pipeline for traversing at least a portion of the distance between the well and the processing facility, wherein at least a portion of the pipeline travels through an atmosphere having a temperature less than 20 C, wherein the pipeline comprises a surface roughness on its interior surface less than 0.025 mm.

2. The system of claim 1, wherein the atmosphere has a temperature less than 15 C.

3. The system of claim 1, wherein the atmosphere has a temperature less than 10 C.

4. The system of claim 1, wherein the surface roughness is between 0.025 mm and 0.0025 mm.

5. The system of claim 1, wherein the surface roughness is between 0.025 mm and 0.01 mm.

6. The system of claim 1, wherein the surface roughness is between 0.01 mm and 0.0025 mm.

7. A method of producing and transporting crude oil, comprising: extracting crude oil from a well; placing the crude oil in a pipeline to transport the crude oil away from the well; wherein at least a portion of the pipeline travels through an atmosphere having an ambient temperature less than 20 C; and wherein the pipeline has a surface roughness less than 0.025 mm on an interior surface.

8. The method of claim 7, wherein the atmosphere has a temperature less than 15 C.

9. The method of claim 7, wherein the atmosphere has a temperature less than 10 C.

10. The method of claim 7, wherein the surface roughness is between 0.025 mm and 0.0025 mm.

11. The method of claim 7, wherein the surface roughness is between 0.025 mm and 0.01 mm.

12. The method of claim 7, wherein the surface roughness is between 0.01 mm and 0.0025 mm.

13. A method of transporting a produced fluid through a pipe while limiting deposits at a desired pipe inner-wall location comprising: providing a pipe having an inner surface roughness Ra less than 2.5 micrometers at said desired pipe inner-wall location; and forcing the produced fluid through the pipe, wherein the produced fluid has a wall shear stress of at least 1 dyne per centimeter squared at said desired pipe inner-wall location.

14. The method of claim 13, wherein the inner surface roughness Ra is less than 1 micrometer at said desired pipe inner-wall location; and wherein the wall shear stress is at least 20 dyne per centimeter squared at said desired pipe inner-wall location.

15. The method of claim 13, wherein the inner surface roughness Ra is less than 1.5 micrometers at said desired pipe inner-wall location; and wherein the wall shear stress is at least 100 dyne per centimeter squared at said desired pipe inner-wall location.

16. The method of claim 13, wherein the wall shear stress is at least 400 dyne per centimeter squared at said desired pipe inner-wall location.

17. The method of claim 13, wherein the pipe comprises an inner surface roughness angle root-mean-square of less than 5 degrees at said desired pipe inner-wall location.

18. The method of claim 13, wherein the pipe comprises an inner surface roughness angle root-mean-square of less than 6 degrees at said desired pipe inner-wall location, and wherein the wall shear stress is at least 20 dyne per centimeter squared at said desired pipe inner-wall location.

19. The method of claim 13, wherein the pipe comprises an inner surface roughness angle root-mean-square of less than 7 degrees at said desired pipe inner-wall location, and wherein the wall shear stress is at least 100 dyne per centimeter squared at said desired pipe inner-wall location.

20. The method of claim 13, wherein the pipe comprises an inner surface roughness angle root-mean-square of less than 9 degrees at said desired pipe inner-wall location, and wherein the wall shear stress is at least 400 dyne per centimeter squared at said desired pipe inner-wall location.

21. A method of calculating optimal shear stress in a pipeline system comprising: providing a pipe having an inner surface roughness Ra of less than 5 micrometers; forcing an produced fluid through the pipe at operating temperature; increasing the pipe's inner wall shear stress value until no wax deposits are formed on the inner wall.

Description:

RELATED APPLICATIONS

This application claims priority to U.S. Provisional Application 60/643,320 filed on Jan. 12, 2005, having attorney docket number TH1043. This application claims priority to U.S. Provisional Application 60/715,250 filed on Sep. 8, 2005, having attorney docket number TH2733. U.S. Provisional Application 60/715,250 and 60/643,320 are herein incorporated by reference in their entirety.

FIELD OF INVENTION

There is disclosed pipes, systems, and methods for transporting produced fluids from one or more wells, more particularly, there is disclosed deposit-growth retarding pipes, systems, and methods for transporting well production streams.

BACKGROUND

As produced fluid is transported through pipes in an environment that cools the fluid, for example to temperatures less than 5° C., for certain types of produced fluids, deposits may form on pipeline walls. Some of these deposits may be, for example, wax deposits as the wax solidifies due to the cold temperatures or gas hydrates. Such wall deposits serve to reduce the efficiency of the pipeline because they block part of the pipeline opening, and reduce the flow rate of the produced fluid and/or increase the pressure in the pipeline. Numerous solutions to the problem of pipeline deposits have been proposed. One solution is a heated pipeline, which serves to keep the oil flowing through the pipeline above the temperature at which solids would form. Patents have been issued to Shell Oil Company in the area of electrically heated pipelines, which solve this problem.

Another solution to the problem of deposits on a pipeline wall is to insulate the pipeline to keep the crude oil at an elevated temperature.

It is desired to avoid the problem of deposition on a pipeline wall.

In the cases that deposits are not avoided, it is desired that the deposits be easily removed by a pig.

In the cases that use pigs to remove deposits, it is desired that the pigged stream be a slurry of pigged deposits and produced fluid.

SUMMARY OF THE INVENTION

One aspect of invention provides a method of transporting a produced fluid through a pipe while limiting deposits at a desired pipe inner-wall location comprising providing a pipe having an inner surface roughness Ra less than 2.5 micrometers at said desired pipe inner-wall location, forcing the produced fluid through the pipe, wherein the produced fluid has a wall shear stress of at least 1 dyne per centimeter squared at said desired pipe inner-wall location.

Advantages of the invention include one or more of the following:

transport of produced fluids with significantly reduced deposits;

transport of produced fluids without deposits;

a reduced force required for pigging; and

generation of a fluid slurry when pigging.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view of a platform and a satellite subsea well connected by a subsea pipeline.

FIG. 2 is a side cross-sectional view of a pipeline.

FIG. 3 is an end cross-sectional view of the pipeline of FIG. 2.

FIG. 4 is a side cross-sectional view of a pipeline.

FIG. 5 is an end cross-sectional view of the pipeline of FIG. 4.

FIG. 6 is a side cross-sectional view of a pipeline.

FIG. 7 is a side cross-sectional view of a pipeline.

FIG. 8 is a view of a smooth pipe with a deposit.

FIG. 9 is a view of a standard-roughness pipe with a deposit.

FIG. 10 is a plot of surface roughness Ra for four different pipes.

FIG. 11 is a plot of Rti distribution for four different pipes.

FIG. 12 is a plot of the angle distribution for four different pipes.

FIG. 13 is a deposition map as a function of roughness and wall shear stress.

FIG. 14 is a plot of pressure drop across a pig.

DETAILED DESCRIPTION

In one embodiment, there is disclosed a pipe adapted to transport crude oil, the crude oil having a temperature less than 65 C in at least a portion of the pipe, wherein the pipe comprises a surface roughness less than 0.025 mm. In some embodiments, the crude oil has a temperature less than 55 C. In some embodiments, the crude oil has a temperature less than 38 C. In some embodiments, the surface roughness is between 0.025 mm and 0.0025 mm. In some embodiments, the surface roughness is between 0.025 mm and 0.01 mm. In some embodiments, the surface roughness is between 0.01 mm and 0.0025 mm.

In one embodiment, there is disclosed a system for producing and transporting crude oil, comprising a well for producing the crude oil; a processing facility for processing the crude oil; and a pipeline for traversing at least a portion of the distance between the well and the processing facility, wherein at least a portion of the pipeline travels through an atmosphere having a temperature less than 20 C, wherein the pipeline comprises a surface roughness on its interior surface less than 0.025 mm. In some embodiments, the atmosphere has a temperature less than 15 C. In some embodiments, the atmosphere has a temperature less than 10 C. In some embodiments, the surface roughness is between 0.025 mm and 0.0025 mm. In some embodiments, the surface roughness is between 0.025 mm and 0.01 mm. In some embodiments, the surface roughness is between 0.01 mm and 0.0025 mm.

In one embodiment, there is disclosed a method of producing and transporting crude oil, comprising extracting crude oil from a well; placing the crude oil in a pipeline to transport the crude oil away from the well; wherein at least a portion of the pipeline travels through an atmosphere having an ambient temperature less than 20 C; and wherein the pipeline has a surface roughness less than 0.025 mm on an interior surface. In some embodiments, the atmosphere has a temperature less than 15 C. In some embodiments, the atmosphere has a temperature less than 10 C. In some embodiments, the surface roughness is between 0.025 mm and 0.0025 mm. In some embodiments, the surface roughness is between 0.025 mm and 0.01 mm. In some embodiments, the surface roughness is between 0.01 mm and 0.0025 mm.

In one embodiment, there is disclosed a system for producing and transporting crude oil, comprising a well means; a processing means; and a pipeline for connecting the well means with the processing means; at least a portion of the pipeline traveling through an atmosphere having an ambient temperature less than 20 C; and a means for reducing the surface roughness on an interior surface of the pipeline. In some embodiments, the atmosphere has a temperature less than 15 C. In some embodiments, the atmosphere has a temperature less than 10 C. In some embodiments, the means for retarding comprises a surface roughness less than 0.025 mm. In some embodiments, the surface roughness is between 0.025 mm and 0.01 mm. In some embodiments, the surface roughness is between 0.01 mm and 0.0025 mm.

In one embodiment, there is disclosed a method of transporting a produced fluid through a pipe while limiting deposits at a desired pipe inner-wall location comprising providing a pipe having an inner surface roughness Ra less than 0.5 micrometers at said desired pipe inner-wall location, forcing the produced fluid through the pipe, wherein the produced fluid has a wall shear stress of at least 1 dyne per centimeter squared at said desired pipe inner-wall location.

In one embodiment, there is disclosed a method of transporting a produced fluid through a pipe while limiting deposits at a desired pipe inner-wall location comprising providing a pipe having an inner surface roughness Ra less than 1 micrometer at said desired pipe inner-wall location, forcing the produced fluid through the pipe, wherein the produced fluid has a wall shear stress of at least 20 dyne per centimeter squared at said desired pipe inner-wall location.

In one embodiment, there is disclosed a method of transporting a produced fluid through a pipe while limiting deposits at a desired pipe inner-wall location comprising providing a pipe having an inner surface roughness Ra less than 1.5 micrometers at said desired pipe inner-wall location, forcing the produced fluid through the pipe, wherein the produced fluid has a wall shear stress of at least 100 dyne per centimeter squared at said desired pipe inner-wall location.

In one embodiment, there is disclosed a method of transporting a produced fluid through a pipe while limiting deposits at a desired pipe inner-wall location comprising providing a pipe having an inner surface roughness Ra less than 2.5 micrometers at said desired pipe inner-wall location, forcing the produced fluid through the pipe, wherein the produced fluid has a wall shear stress of at least 400 dyne per centimeter squared at said desired pipe inner-wall location.

In one embodiment, there is disclosed a method of transporting a produced fluid through a pipe while limiting deposits at a desired pipe inner-wall location comprising providing a pipe having an inner surface roughness angle root-mean-square of less than 5 degrees at said desired pipe inner-wall location, forcing the produced fluid through the pipe, wherein the produced fluid has a wall shear stress of at least 1 dyne per centimeter squared at said desired pipe inner-wall location.

In one embodiment, there is disclosed a method of transporting a produced fluid through a pipe while limiting deposits at a desired pipe inner-wall location comprising providing a pipe having an inner surface roughness angle root-mean-square of less than 6 degrees at said desired pipe inner-wall location, forcing the produced fluid through the pipe, wherein the produced fluid has a wall shear stress of at least 20 dyne per centimeter squared at said desired pipe inner-wall location.

In one embodiment, there is disclosed a method of transporting a produced fluid through a pipe while limiting deposits at a desired pipe inner-wall location comprising providing a pipe having an inner surface roughness angle root-mean-square of less than 7 degrees at said desired pipe inner-wall location, forcing the produced fluid through the pipe, wherein the produced fluid has a wall shear stress of at least 100 dyne per centimeter squared at said desired pipe inner-wall location.

In one embodiment, there is disclosed a method of transporting a produced fluid through a pipe while limiting deposits at a desired pipe inner-wall location comprising providing a pipe having an inner surface roughness angle root-mean-square of less than 9 degrees at said desired pipe inner-wall location, forcing the produced fluid through the pipe, wherein the produced fluid has a wall shear stress of at least 400 dyne per centimeter squared at said desired pipe inner-wall location.

In one embodiment, there is disclosed a method of calculating optimal shear stress in a pipeline system comprising providing a pipe having an inner surface roughness Ra of less than 5 micrometers, forcing an produced fluid through the pipe at operating temperature, and increasing the pipe's inner wall shear stress value until no wax deposits are formed on the inner wall.

In one embodiment, there is disclosed a method of transporting a produced fluid through a pipe and forming deposits that require less force to pig and that produce a slurry when pigged comprising providing a pipe having an inner surface roughness Ra less than 3 micrometers, forcing the produced fluid through the pipe, wherein the produced fluid has a wall shear stress of at least 1 dyne per centimeter squared in at least a portion of the pipe, and providing a non-metallic, over-sized, compliant pig. In some embodiments, the pig comprises a bypass pig, wherein the pigging results in a diluted slurry of the fluid and the deposits.

In one embodiment there is disclosed a method to prevent deposits on the inner wall of a pipe, tubing, pipeline, flowline, and/or well tubing (hereafter referred to as pipeline or pipe) during production and transportation of produced fluids, for example in pipelines used in deep water, where the problem of deposition is common due to the low ambient temperature of the environment surrounding the pipeline.

As produced fluids are transported, solids may precipitate and deposit on the pipeline wall. For example, paraffinic constituents of crude oils can precipitate when the crude oils are cooled below a critical temperature (hereafter referred to as wax appearance temperature). Solid paraffin (sometimes designated as wax) that is transported to the pipeline wall or wax forming at the pipe wall may stick to the wall and over time the wax may reduce the pipe cross sectional area that is available for flow. The temperature at which wax comes out of solution varies from one crude or condensate to the next, with some crudes or condensates dropping out of solution some paraffinic components at temperatures as high as 55° C. One solution to keep wax from forming on a pipeline wall is to keep the temperature in the transport pipeline above the wax appearance temperature to keep the wax from depositing on the pipe wall or even creating a wax plug.

In one embodiment, there is disclosed an alternative solution to keep deposits from forming on a pipeline wall whereby solids are allowed to drop out of the production fluids but discouraged from adhering to the pipe wall and forming plugs. If solids are allowed to drop out but prevented from adhering to the pipe wall, the bulk fluid may continue to flow as a slurry with suspended solids. This can be accomplished by making the inside walls of the transport pipes smoother than the walls of pipe normally used in subsea flowlines and pipelines either mechanically, with coatings, and/or with electro-polishing, and by controlling the transport rate so as to provide a critical wall shear stress within the pipeline. In general, significantly eliminating the pipe roughness of the inner wall of the pipe will decrease the force required to remove a deposit and in some cases decrease the rate of deposit buildup in the pipe. In some embodiments, the force required to remove wax, asphaltenes, and/or inorganic deposits like hydrates, salts, and/or scale, may be decreased by using a smooth pipe wall.

Lowering the wax deposition rate in pipelines may also lessen the needed frequency of pigging (i.e. mechanical scraping). Flow rate capacity may be maintained closer to the deposit-free capacity as a result of the decreased flow obstructions and/or blockages created by deposits.

Referring now to FIG. 1, in one embodiment, there is illustrated remote satellite well 12, which is connected to platform 14 with subsea pipeline 10. Subsea pipeline 10 includes seafloor section 19 and riser section 18. Seafloor section 19 may be up to 30 or more kilometers long. Pipeline 10 may be composed of 12 meter joints of pipe welded together. It is common to form individual 48 meter segments of pipe, called quads (4 joints), which have been welded together as they are placed subsea to form pipeline 10. Seafloor section 19, which may be a kilometer or more below surface 28 of the ocean, terminates at sled 20. There is also illustrated an export pipeline 26 to transport oil or other products from platform 14 to the shore. Platform 14 may include surface facilities 16, as are known in the art. The pipe traditionally used in subsea pipeline 10 and export pipeline 26 is referred to hereafter as “traditional pipe.” That is, traditional pipe is the standard pipe with respect to roughness currently used for pipeline 10 and pipeline 26.

Referring to FIGS. 2 and 3, seafloor section 19 of the pipeline is illustrated. Seafloor section includes a passage 102 and a wall 104 that encloses the passage 102. Wall 104 includes surface roughness 104a typical of traditional pipe. Produced fluids may be enclosed within wall 104 and passed through passage 102.

Referring to FIGS. 4 and 5, produced fluids have been passed through passage 102 of traditional pipe, where seafloor section 19 is exposed to a cold temperature environment, so that deposit 106 has been deposited on surface roughness 104a. As deposit 106 is deposited, passage 102 is constricted. In general, the larger the surface roughness 104a, the greater the strength of adhesion of the deposit 106 to the pipe wall.

In some embodiments, referring to FIG. 6, sea floor section 19 is illustrated which includes passage 202 enclosed by walls 204. Walls 204 have surface roughness 204a, which is significantly smoother than surface roughness 104a of traditional pipe.

Still referring to FIG. 6, as produced fluids are passed through passage 202 at a rate for which the wall shear stress exceeds a critical value, few or no deposits are deposited on surface roughness 204a. In general, a combination of smoother surface roughness 204a and a wall shear stress above the critical value, leads to few or no deposition of deposits. For a very smooth pipe surface, the critical wall shear stress required to prevent deposits is low to moderate; as the pipe surface roughness increases, the critical wall shear stress required to prevent deposits increases. In pipes with roughness equal to that of traditional pipe, the wall shear stress required to prevent deposits may be above that provided by normal operating rates.

In one embodiment, it is not required to use a pig to clean wax deposits from wall 204, because at the provided wall shear stress little or no wax deposits on surface roughness 204a as compared to surface roughness 104a of traditional pipe.

In one embodiment, it is not required to use a pig to clean wax deposits from wall 204 as often as it is required to clean wax deposits 106, because at the provided wall shear stress little or no wax deposits on surface roughness 204a as compared to surface roughness 104a of traditional pipe.

FIG. 8 is a magnified view of a perfectly smooth surface. The streamlines of the flow are parallel to the surface. When the flow passes around a deposit, the drag on the deposit is in the direction of the flow and parallel to the contact surface between the deposit and the wall. This flow-wall configuration applies the largest shear stress at the deposit-wall interface and consequently is the most efficient configuration for preventing or removing deposits.

FIG. 9 is a magnified view of surface roughness 104a of traditional pipe. With such a rough surface, the flow streamlines do not follow the surface and vortices are produced as shown on the left side of FIG. 9, where the flow over a “peak” of a rough surface generates vortices in the downstream valley. These vortices may apply a weak and incoherent drag on deposits. This drag is generally not parallel to the deposit-wall contact. Because of this, deposits are apt to build in the valleys. Once deposits fill a valley, the deposit may be anchored to the wall over the entire valley surface area and may become more difficult to remove. Consequently, surface roughness and flow rate play a large role in determining when and where deposits form and when and where they are removed.

Surface roughness is quantified in several ways. In ASME B46.1-2002, herein incorporated by reference, “Surface Texture (Surface Roughness, Waviness and Lay),” Ra is defined as the arithmetic average of the absolute values of the profile height deviations over the evaluation length and measured from the mean line. Ra is the most commonly used roughness parameter in surface finish measurement. Another measure of the surface roughness is the root-mean-square of the angle (relative to horizontal) distribution, αrms, along the surface. Another measure of the surface roughness, Rti, is the local vertical distance to each point i from the lowest valley in the sample interval. Another measure of the surface roughness is the root-mean-square of the Rti for a single sample length, Rtirms.

FIG. 10 shows the wall profiles for four pipes. The horizontal axis (x) shows distance (in centimeters (cm)) along the plane of the mean surface, and the vertical axis (z) shows deviation in height (in micrometers) from the mean surface. Above the x-axis from 0.0 inch to 0.29 cm is shown the height relative to the surface mean for Pipe A, a commercial stainless steel traditional pipe with a roughness typical of pipes used in subsea pipelines and flowlines. To the right of the data for Pipe A in FIG. 10 are data for smoother pipes. Above the x-axis from 0.29 cm to 0.65 cm is shown z for Pipe B, a commercial stainless steel tube. Above the x-axis from 0.65 cm to 0.98 cm is shown z for Pipe C, a commercial stainless steel tube with a smaller roughness, marketed to have a roughness Ra of 0.25 micrometers or less. Above the x-axis from 0.98 cm to 1.3 cm is shown z for Pipe D, a commercial stainless steel tube with an even smaller roughness, marketed to have a roughness Ra of 0.125 micrometers or less. The difference in variation in z between Pipe A, the traditional pipe, and Pipes B-D is very great.

FIG. 11 shows the Rti distributions for the four pipes shown in FIG. 10. FIG. 12 shows the angle (α) distributions for the said four pipes shown in FIG. 10. The Ra values and root-mean-square angle of the distributions and the root-mean-square Rti for the said four pipes are listed in Table 1, below. Pipe A, the traditional pipe, has roughness measures that are quite different from those of Pipes B-D, the smooth pipes.

TABLE 1
Values of Surface Roughness Parameters
PipeRoot-Mean-SquareRoot-Mean-Square
descriptionRaAngleRti
Pipe A>60>13>175
Pipe B256150
Pipe C2.5425
Pipe D<2.5<2<8

Traditional pipe, the current standard for pipeline 10 and pipeline 26, may have an absolute surface roughness Rt of about 50, or 75 micrometers or higher and an αrms of about 13 degrees or more as purchased from a supplier. Rt, similar to Rti defined earlier, is the longest vertical distance from peak to valley over a measured length.

In some embodiments of this invention with moderate to high wall shear stress, suitable smooth pipeline 10 or pipeline 26 has a surface roughness 204a Ra of less than about 25 micrometers Ra, or less than one-half the surface roughness Ra of standard steel pipe 104a.

In some embodiments of this invention with moderate to high wall shear stress, suitable pipeline 10 or pipeline 26 has a surface roughness 204a αrms of less than about 9 degrees, or less than two-thirds of the surface roughness αrms of standard steel pipe 104a.

In some embodiments of this invention with moderate to high wall shear stress, suitable smooth pipeline 10 or pipeline 26 has a surface roughness 204a Ra of less than about 15 micrometers Ra, or less than one-fourth the surface roughness Ra of standard steel pipe 104a.

In some embodiments of this invention with moderate to high wall shear stress, suitable pipeline 10 or pipeline 26 has a surface roughness 204a αrms of less than about 7 degrees, or less than about one-half of the surface roughness αrms of standard steel pipe 104a.

In some embodiments of this invention with moderate to high wall shear stress, suitable smooth pipeline 10 or pipeline 26 has a surface roughness 204a Ra of less than about 10 micrometers Ra, or less than one-sixth the surface roughness Ra of standard steel pipe 104a.

In some embodiments of this invention with moderate to high wall shear stress, suitable pipeline 10 or pipeline 26 has a surface roughness 204a αrms of less than about 6 degrees, or less than one-half of the surface roughness αrms of standard steel pipe 104a.

In some embodiments of this invention with small to high wall shear stress, suitable pipeline 10 or pipeline 26 has a surface roughness 204a Ra of less than about 5 micrometers, or less than one-tenth the surface roughness Ra of standard steel pipe 104a.

In some embodiments of this invention with small to high wall shear stress, suitable pipeline 10 or pipeline 26 has a surface roughness 204a αrms of less than about 5 degrees, or less than about one-third of the surface roughness αrms of standard steel pipe 104a.

In some embodiments, surface roughness 204a and/or surface roughness 104a may be coated with a suitable coating to reduce the surface roughness value.

Referring now to FIG. 7, pipeline 19 is illustrated which includes passage 302 enclosed by walls 304. Walls 304 define passage 302 having a diameter of 2R 306, or a radius of R. A portion of passage 302 has a length L 308 from point 310 to point 312. Pressure is P1 at point 310, and pressure is P2 at point 312. The pressure drop along length L 308 from point 310 to point 312. is (P1−P2). The cross-sectional area of passage 302 is πR2. The force across the fluid in passage 302 from point 310 to point 312 is (P1−P2)(πR2). This force is equal in magnitude and opposite in direction to the total resistance at the wall in passage 302 from point 310 to point 312. The total resistance at the wall is the wall shear stress T times the wall-fluid interface area in passage 302 from point 310 to point 312, which area is 2πRL. Equation 1 shows that the force due to the wall shear stress equals the force required to move a fluid through passage 302:
(P1−P2)(πR2)=(τ)(2πRL) (1)
Solving for τ from equation 1 yields:
(τ)=((P1−P2)(R))/(2L) (2)

In some embodiments, produced fluids passing through pipeline 10 or pipeline 26 have a wall shear stress at wall 204 of at least about 1 dyne per centimeter squared.

In some embodiments, produced fluids passing through pipeline 10 or pipeline 26 have a wall shear stress at wall 204 of at least about 20 dyne per centimeter squared.

In some embodiments, produced fluids passing through pipeline 10 or pipeline 26 have a wall shear stress at wall 204 of at least about 100 dyne per centimeter squared.

In some embodiments, produced fluids passing through pipeline 10 or pipeline 26 have a wall shear stress at wall 204 of at least about 400 dyne per centimeter squared.

In some embodiments, in order to calculate the optimal flow rate for crude oil or condensate flowing through pipeline 19, a pipeline having a surface roughness less than about 200 microinches is selected and tested with the crude oil that will be pumped through it in a test facility, where the crude oil is cooled in a temperature range at which the crude will be transported through pipeline 10 or pipeline 26. The flow rate and/or the wall shear stress is then increased until there is either no deposition, or the equipment is not able to produce a higher flow rate. If the equipment is not able to produce a higher flow rate, a smoother pipe may be selected such as a pipe having a surface roughness less than about 100 microinch, then the flow rate and/or the wall shear stress may be increased until such time there is no wax deposition or the equipment can not pump any faster, and smoother pipes may be tested, such as a pipe having a surface roughness less than about 15 micrometers, until such time as a smooth pipe is found which produces little or no wax deposition under the operating conditions.

Different fluid systems have different deposition tendencies and require different combinations of roughness and wall-shear-stress to avoid deposits. Nonetheless, the roughness necessary to prevent deposits for produced fluid streams with wall shear stress corresponding to the upper limit of practical production rates is much smaller than the roughness of traditional pipe. For streams with smaller wall shear stress, the roughness necessary to prevent deposits is even smaller.

Those of skill in the art will appreciate that many modifications and variations are possible in terms of the disclosed embodiments, configurations, materials and methods without departing from their spirit and scope. Accordingly, the scope of the claims appended hereafter and their functional equivalents should not be limited by particular embodiments described and illustrated herein, as these are merely exemplary in nature.

EXAMPLE

A flow loop for deposition testing was used. Test sections with different inner-wall roughness were installed. Deposition tests were conducted with a 6-day period with temperature-controlled pumping of a waxy crude oil from a deepwater field in the Gulf of Mexico. Summary results are shown in FIG. 13. In FIG. 13, “White” diamonds denote a PASS in a deposition test (i.e., zero or insignificant deposition), “Gray” triangles denote a MARGINAL result, and “Black” diamonds denote a FAIL (i.e., significant and quantifiable deposition). The x value is the Ra and the y value, wall shear stress, is calculated from fluid properties, flow rates, and pipe diameter. As FIG. 13 indicates, the said smooth Pipes B-D used in the test section of the flow loop showed significant reduction in deposition compared to smooth Pipe A (test FAIL). It should be noted that Pipe B is considerably smoother than Pipe A, traditional pipe. As FIG. 13 further indicates, the said smooth Pipe D used in the test section of the flow loop has no or insignificant amount of deposit (test PASS). The data of FIG. 13 demonstrate the reduction in deposition in pipe with smaller Ra roughness and higher wall shear stress.

Other tests were conducted in the flow loop for deposition testing in which deposits were formed in a pipe much smoother than a traditional pipe but not smooth enough to prevent deposits from forming. The pipes were then pigged, and data were collected on the pigging and resulting pigged stream. Some of these data are shown in FIG. 14. The force (directly related to test section differential pressure, dP) required to pig the deposit from the “Polished Pipe” wall was significantly smaller than that used for pigging deposits formed in a similar test with the “Standard Pipe.” Furthermore, the pigged stream of the smooth pipe produced a slurry, whereas the pigged stream of the Traditional Pipe produced a viscous agglomeration of wax and occluded oil.