METHOD FOR RESTARTING FLOW IN WAXY CRUDE OIL TRANSPORTING PIPELINE

Abstract

A method (400) for restarting flow in a waxy crude oil transporting pipeline (100), comprising: dividing (402) the gel plug into plurality of smaller gel segments (112, 114, 116) by removing a fraction of gel volume creating plurality of voids (132, 134), introducing (404) a compressible fluid into each of the voids; and applying (406) a pressure at first end (112A) of a first gel segment (112) contiguous to a pumping unit thereby creating a high pressure gradient between first end and second end (112B) of the first gel segment, causing the first gel segment to degrade and move towards a first void (132) thereby compressing the compressible fluid, the movement of the gel segment deforms and breaks the gel segment whereby the broken gel segment migrates towards a next gel segment (114) until all the gel segments are sequentially broken and flow of the waxy crude oil restarts.

Claims

1. A method (400) for restarting flow in a waxy crude oil transporting pipeline (100), the flow of oil in the pipeline (100) being impeded by formation of a gel plug composed of oil, the method (400) comprising: dividing (402) the gel plug into a plurality of smaller gel segments (112, 114, 116) by removing a fraction of gel volume from predetermined locations along the length of the gel plug thereby creating a plurality of voids (132, 134), each of the gel segments (112, 114, 116) having a first end (112A) and a second end (112B); introducing (404) a compressible fluid into each of the voids (132, 134); and applying (406) a pressure (120) at the first end (112A) of a first gel segment (112) contiguous to a pumping unit thereby creating a high pressure gradient between the first end (112A) and the second end (112B) of the first gel segment (112), the high pressure gradient across the first gel segment (112) causes the first gel segment (112) to degrade and move towards a first void (132) thereby compressing the compressible fluid, the movement of the gel segment (112) deforms and breaks the gel segment (112) whereby the broken gel segment (112) migrates towards a next gel segment (114) until all the gel segments are sequentially broken and flow of the waxy crude oil restarts.

2. The method (400) as claimed in claim 1, comprising the step of applying a pressure (120) at the first end (112A) of the first gel segment (112) located contiguous to the inlet (100A) of the pipeline (100) thereby creating a high pressure gradient across the first gel segment (112) sufficient to degrade the first gel segment (112).

3. The method (400) as claimed in claim 1, wherein the compressible gas in the void (132, 134) prevents the further propagation of pressure, allowing a high pressure gradient to establish in the gel segments (112, 114, 116) sequentially.

4. The method (400) as claimed in claim 1, wherein the volume of compressible fluid introduced into the void (132, 134) is equal to the fraction of gel volume removed.

5. The method (400) as claimed in claim 1, wherein the size of the void (132, 134) to be created in between the gel segments (112, 114, 116) is determined in terms of fluid compressibility and yield strength of the gel segment (112, 114, 116).

6. The method (400) as claimed in claim 1, comprising the step of determining (402A) a length of the pipeline (100) blocked with the gel plug.

7. The method (400) as claimed in claim 1, wherein length of a gel segment is less than a threshold value the threshold value dependent on pressure to be applied on the gel segment, internal diameter of the pipeline, and yield strength of the gelled oil.

8. The method (400) as claimed in claim 1, wherein the compressible fluid comprises an uncompressed gas.

9. The method (400) as claimed in claim 8, wherein the uncompressed gas is a combination of one or more compressible inert gases at normal pressure.

10. The method (400) as claimed in claim 8, wherein the uncompressed gas is nitrogen at normal pressure.

11. The method (400) as claimed in claim 1, wherein the fraction of gel volume is removed and the compressible fluid is added to the pipeline (100) by making incisions (152, 154) in the pipeline (100), and subsequently resealing the pipeline (100.

12. The method (400) as claimed in claim 11, wherein the fraction of gel volume is removed by using spades.

13. The method (400) as claimed in claim 11, wherein the fraction of gel volume is removed by siphoning off the waxy crude oil after heating the fraction of gel volume.

Description

BRIEF DESCRIPTION OF THE INVENTION

[0015] Reference will be made to embodiments of the invention, examples of which may be illustrated in accompanying figures. These figures are intended to be illustrative, not limiting. Although the invention is generally described in context of these embodiments, it should be understood that it is not intended to limit the scope of the invention to these particular embodiments.

[0016] FIG. 1 is a schematic representation of a pipeline transporting waxy crude oil, with a gel plug impeding flow of oil.

[0017] FIG. 2 is a schematic representation of a pipeline transporting waxy crude oil, with a gel plug impeding flow of oil.

[0018] FIG. 3 is a schematic representation of an inlet of a pipeline transporting waxy crude oil, with a gel plug impeding flow of oil.

[0019] FIG. 4 is a flowchart illustrating a method for restarting flow in a waxy crude oil transporting pipeline.

DETAILED DESCRIPTION OF THE INVENTION

[0020] The present invention is directed to a method for restarting flow in a waxy crude oil transporting pipeline.

[0021] As shown in FIGS. 1 and 2, waxy crude oil is transported in a pipeline 100 from an inlet 100A to an outlet 100B. The flow of oil in the pipeline 100 is impeded by the formation of a gel plug composed of oil. The (100) may also be blocked due to wax, asphaltene, resin, or any combinations thereof.

[0022] As shown in FIG. 4, the method comprises of step 402 in which the gel plug is divided into a plurality of smaller gel segments 112, 114, 116 by removing a fraction of gel volume from predetermined locations along the length of the gel plug. This creates a plurality of voids 132, 134. Each gel segment has a first end 112A and a second end 112B. The method 400 comprises a further step of introducing a compressible fluid in the voids 132, 134 to replace the fraction of gel volume removed. In an embodiment of the invention, the fraction of gel volume is removed and the compressible fluid is added to the pipeline 100 by making incisions 152, 154 in the pipeline 100. After the incisions 152, 154 have been used to successfully remove the fraction of gel volume and add the compressible fluid, the pipeline 100 is resealed. According to an embodiment of the invention, the volume of compressible fluid introduced in the void is equal to the fraction of the gel volume removed from the pipeline 100. According to a further embodiment of the invention, the fraction of gel volume is removed by using spades or by siphoning off the crude oil in gel form or in liquid form after heating the gel volume.

[0023] The method comprises a further step 406 of applying a pressure at the first end 112A of one of the gel segments 112, which is illustrated in FIG. 3. The pressure 120 applied creates a pressure gradient between the first end 112A and the second end 112B of the gel segment 112. According to an embodiment of the invention, the pressure 120 applied at the first end 112A of the gel segment 112 is contiguous with corresponds with inlet 100A of the pipeline 100. The presence of compressible fluid contiguous to a second end 112B of the gel segment 112 does not allow pressure to propagate downstream without movement of the gel segment 112. Thus, a high pressure gradient is established across the gel segment 112 sufficient to overcome the yield stress requirement of gel segment 112.

[0024] The high pressure gradient created by the pressure 120 applied causes the gel segment 112 to degrade to move towards the void 132. Thus, the compressible fluid in the void 132 is compressed. The movement of the gel segment 112 leads to the further degradation and breaking of the gel segment 112. Thus, the broken gel segment 112 offers a low flow resistance allowing the pressure to develop gradually across the next gel segment 114. A similar pressure gradient now acts on the next gel segment 114 and causes the degradation and breaking of the next gel segment 114. This process continues until all the gel segments are sequentially broken down and flow of the waxy crude oil restarts.

[0025] In an embodiment of the invention, the method 400 comprises a step 402A of determining a length of the pipeline (100) that is blocked with the gel plug. The pipeline 100 blocked with the gel plug is divided into gel segments having length less than a threshold value L. The threshold value L is dependent on the pressure 120 to be applied at the inlet section of the pipeline 100, internal diameter of the pipeline 100, and yield strength of the gelled oil. This is determined by the formula.

L<(D/4*P/τ.sub.y)  (1)

In Equation (1) herein above,

[0026] L=threshold length of the gel segment;

[0027] D=diameter of the pipeline;

[0028] P=Applied pressure;

[0029] τ.sub.y=Yield stress of the gelled oil

[0030] According to an embodiment of the invention, the length of the pipeline 100 in which the compressible fluid is introduced is large enough to create sufficient deformation in the gel segments to cause the gel segments to break. For this, the length of the section of the pipeline from where gel needed to be removed given is by:

ΔL/R>>γ.sub.s/(χ.sub.θΔP)  (2)

[0031] In an embodiment of the invention, equation (2) herein above is represented by:

ΔL/R≥3γ.sub.s/(χ.sub.θΔP)  (3)

In equation (2) and (3) herein above,

[0032] ΔL=length of the pipeline in which compressible fluid is introduced;

[0033] R=radius of the pipeline;

[0034] γ.sub.s=strain in the gel where stress becomes maximum;

[0035] χ.sub.θ=isothermal compressibility of the gas; and

[0036] ΔP=change in pressure in the gas phase after compression.

[0037] In an embodiment of the invention, the compressible fluid used in the method 400 described herein above comprises an uncompressed gas. In a further embodiment, the uncompressed gas is a combination of one or more compressible inert gases at normal pressure. In another embodiment of the invention, the uncompressed gas is nitrogen at normal pressure.

[0038] Advantageously, the sequential breaking of gel segments is achieved by a lower applied pressure. Thus, this invention offers an energy efficient method for restarting flow in a waxy crude oil transporting pipeline.

[0039] While the present invention has been described with respect to certain embodiments, it will be apparent to those skilled in the art that various changes and modifications may be made without departing from the scope of the invention as defined in the following claims.