GB2185196A - Method for distributing corrosion inhibitor with foam - Google Patents

Abstract

A liquid corrosion inhibitor is deposited in a pipeline system by flowing a foam formed from a gaseous fluid and a carrier liquid including the liquid corrosion inhibitor, through the pipeline. <IMAGE>

Description

SPECIFICATION Method for distributing corrosion inhibitor with foam The invention relates to methods of distributing corrosion inhibitors, and particularly to methods for distributing corrosion inhibitors in horizontal gas pipeline systems.

Gaseous hydrocarbons are typically transported by pumping them through horizontally oriented pipeline systems.

Many of these systems, particularly those utilized to convey wet corrosive gases have significant problems of internal corrosion of the pipeline.

These problems are even further exacerbated with subsea pipeline systems, where it is difficult and very expensive to inspect and repair the pipeline if a leak develops.

One commonly used technique for combating this problem is to treat the inside of the pipeline with a liquid corrosion inhibitor.

The conventional technique for distributing corrosion inhibitor within a horizontal pipeline is by the use of pipeline pigs.

A typical pipeline pig is constructed in the form of a hollow inflatable urethane ball. The ball is inflated with glycol and/or water to a size that will just fit through the pipeline system.

A first pipeline pig is placed in the pipeline through the use of pig launching equipment, and then a volume of liquid corrosion inhibitor is placed in the pipeline followed by a second pig. This pair of pipeline pigs with the volume of liquid corrosion inhibitor contained therebetween is then pumped through the pipeline so that the liquid corrosion inhibitor will contact the internal surfaces of the pipeline.

The pipeline pigs must then be removed from the pipeline through the use of pig recovering equipment associated with a terminal end of the pipeline.

As will be understood by those skilled in the art, the equipment utilized for launching and recovering pipeline pigs is both complex and expensive.

Also, even in a system which is equipped with suitable pig launching and recovering equipment, it is not possible to adequately treat lateral pipelines branching from a main pipeline.

Furthermore, many existing pipeline systems are not equipped with pig launching and recovering equipment, and thus there is no satisfactory existing means for treating any portion of those pipelines with a corrosion inhibitor.

A couple of techniques are commonly used to place corrosion inhibitor in a vertical pipeline such as a production tubing of a well.

In the first of these techniques, the liquid corrosion inhibitor is atomized with nitrogen gas and then is pumped down into the well and into the subterranean formation as a mist.

Subsequently, the liquid corrosion inhibitor produces back out of the formation into the production tubing and thus coats the production tubing for a relatively long period of time.

In the second of these techniques, the corrosion inhibitor is mixed with a carrier fluid such as produced water or diesel fuel in a ratio of approximately ten parts carrier fluid to one part corrosion inhibitor. This mixture is pumped through the production tubing to coat the tubing.

These two techniques are not generally useful, however, for horizontal pipeline systems Viewed from a first aspect the invention provides a method of distributing a liquid corrosion inhibitor in a pipeline, said method comprising the steps of: (a) forming a foam including a liquid corrosion inhibitor; (b) flowing said foam into said pipeline; and (c) depositing said liquid corrosion inhibitor from said foam on an inner surface of said pipeline.

The present invention provides an improved method for treating horizontal pipelines with a liquid corrosion inhibitor. The requirement for pipeline pigs and the associated pig launching and pig recovering equipment may be avoided, and additionally, in accordance with the invention lateral pipelines can be adequately treated with corrosion inhibitor.

Advantageously the foam is formed from a gaseous fluid and a carrier liquid including the liquid corrosion inhibitor. This foam may then be injected into a pipeline system and displaced through the pipeline system including any lateral pipeline portions thereof. The foam distributes the liquid corrosion inhibitor throughout the pipeline system and the liquid corrosion inhibitor is deposited on substantially an entire inner surface of the various portions of the pipeline. An embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings, wherein: Figure 1 is a schematic illustration of an offshore petroleum production facility including numerous horizontal subsea pipelines for conveying gaseous hydrocarbons.

Figure 2 is a schematic illustration of the manner in which a foam including corrosion inhibitors is formed and injected into the pipeline system of Fig. 1.

Figure 3 is a cross-section view of a pipeline filled with the corrosion inhibitor carrying foam.

Referring now to the drawings, and particularly to Fig. 1, a typical offshore petroleum production facility in which the methods of an embodiment of the present invention could be utilized is shown.

Fig. 1 represents schematically an actual offshore production facility located in the Arabian Gulf and participated in by the applicants hereof in connection with which use of the methods of an embodiment of the present invention is envisaged.

Fig. 1 illustrates three offshore platforms 10, 12 and 14 located in a body of water 16.

Platforms 12 and 14 are production platforms which are associated with one or more subsea petroleum producing wells located therebelow as will be understood by those skilled in the art.

The petroleum producing wells associated with the platforms 12 and 14 are being produced through the use of gas lift production techniques.

When using gas lift techniques to produce petroleum products from a well, gas (typically gaseous hydrocarbons) is injected into the production tubing at various depths within the well through the use of injection valves having a supply of gaseous hydrocarbon connected thereto.

In the production system illustrated in Fig.

1, the petroleum products produced from the wells associated with production platforms 12 and 14 are conveyed through other pipelines (not shown) to a production facility 18 located on platform 10.

At the production facility 18, the produced hydrocarbons are treated in various ways, including treatments to separate liquid hydrocarbons from gaseous hydrocarbons produced from the wells. It is desired to reinject these gaseous hydrocarbons into the wells associated with production platforms 12 and 14 through the gas lift valves previously mentioned in order to aid in further production from those wells.

Gaseous hydrocarbons separated at the production facility 18 are directed through a pipeline 20 to a compressor station 22 located on the platform 10.

At the compressor station 22, the gaseous hydrocarbons are pressurized and introduced into a main pipeline 24 which runs to the production platform 12 where the main pipeline 24 is connected to gas lift supply lines for directing the gaseous hydrocarbons to the gas lift valves located down in the wells.

That portion of main pipeline 24 indicated in dash lines can generally be described as a substantially horizontally oriented subsea main pipeline portion 26.

A substantially horizontal lateral pipeline 28 having a subsea portion 30 is connected to main pipeline 24 at a branch connection 32.

As is schematically represented in Fig. 2, the lateral pipeline 28 will usually be of a smaller diameter than the main pipeline 24, although that is not necessarily always the case.

Fig. 2 schematically illustrates the compressor station 22 of Fig. 1 and a portion of the main pipeline 24, the lateral pipeline 28, and the connecting pipeline 20 between production facility 18 and compressor station 22.

During normal operation of the system seen in Fig. 1, the gaseous hydrocarbon products separated in production facility 18 flow through the connecting pipeline 20 to a compressor 34 which pressurizes the gaseous hydrocarbons -and pumps them into the main pipeline 24.

The compressor station 22 seen in Fig. 2 is also schematically illustrated as including the equipment necessary to generate and inject a foam containing liquid corrosion inhibitors into the main pipeline portion 24.

A supply of a carrier fluid including the liquid corrosion inhibitor is contained in vessel 36 from which it can be pumped through a conduit 38 to foam generator 40.

The carrier fluid including the liquid corrosion inhibitor can be any liquid which is foamable. If the particular liquid corrosion inhibitor chosen is itself foamable, then the carrier liquid could in fact be the pure corrosion inhibitor without any additions.

Typically, however, the carrier liquid will be an aqueous fluid. That is, the carrier fluid will typically be comprised primarily of water with a certain portion of liquid corrosion inhibitor mixed therewith. Also, typically, a surfactant will be added to the aqueous carrier fluid to aid in the foaming of that fluid.

One example of a liquid corrosion inhibitor which would typically be utilized for treating a pipeline system like that described with regard to Fig. 1 is that sold under the trade name NOWCO ODC-587. The particular corrosion inhibitor utilized, however, may vary in accordance with the present invention, and those skilled in the art will be familiar with many liquid corrosion inhibitors which would be satisfactory candidates for use in the methods in accordance with the present invention.

A gaseous fluid is supplied to foam generator 40 through a conduit 42. The gaseous fluid and the carrier liquid supplied through conduits 42 and 38 to foam generator 40 are combined in foam generator 40 to generate a foam and are then directed through conduit 44 to the pipeline 20 connected to the inlet of compressor 34.

As will be understood by those skilled in the art, the foam generator 40 may in fact be a simple T-connection between the conduits 38 and 42 which directs the flows from conduits 38 and 42 against each other so as to turbulently mix them thus creating a foam from the carrier liquid.

It is generally contemplated that the foams utilized in the illustrated method would be created in a manner similar to that in which foamed fluids are presently formed for use in foam fracturing treatments of wells. The general design of such foams is discussed in a paper entitled "The Design Of Stable Foam Fracturing Treatments" by Holditch and Plummer, presented at the Southwest Petroleum Short Course 23rd Annual Meeting held in April, 1976, in Lubbock, Texas. The references cited in that paper include most of the standard references utilized in the design of foam as used in well fracturing operations.

The foam is pumped by the compressor 34 into the main pipeline 24 and the lateral pipeline 28.

In Figs. 2 and 3, the foam is designated by the numeral 46.

Preferably, the gaseous fluid directed through conduit 42 to foam generator 40 for creating the foam is the gaseous hydrocarbon material from pipeline 20.

An alternative source of gaseous fluid for use in creation of the foam can be provided from gas cylinder 48 which typically will be a cylinder of pressurized nitrogen gas.

A plurality of valves 50, 52, 54 and 56 are illustrated in Fig. 2 for controlling the flow of either gaseous hydrocarbons from production facility 18 or nitrogen gas from gas cylinder 48 to the foam generator 40.

If it is desired to utilize gaseous hydrocarbons to generate the foam, the valves 52 and 54 are closed and the valves 50 and 56 are opened so that the gaseous hydrocarbon will be directed from pipeline 20 through a connecting conduit 58 to the conduit 42 and to the foam generator 40.

If it is desired to use nitrogen gas to generate the foam, the valves 54 and 56 are closed and the valves 50 and 52 are opened to directly transmit the nitrogen gas from gas cylinder 48 to the foam generator 40.

After a sufficient volume of foam has been generated and injected into the main pipeline system 24 and lateral pipeline 28, the valves 50 and 52 are closed and the valves 54 and 56 are opened to inject gaseous hydrocarbons into the pipeline 24 behind the foam to thus displace the foam throughout the pipeline system.

As illustrated in Fig. 3, the foam 46 com pletely fills the pipeline and thus distributes liquid corrosion inhibitor contained in the foam on substantially the entire inner cylindrical surface 58 of the pipelines such as main pipeline 24.

After the foam 46 has been placed throughout the pipeline system, it may be desired to inject a fluid designed to aid in breaking the foam so that the corrosion inhibitor will be left in place coating the inner surfaces 58 of the pipeline system. It will be understood that it is generally not desired to pump large volumes of the foam onto the production platforms 12 and 14 and into the petroleum producing wells.

Instead, the foam 46 should be left in the pipeline system for a sufficient time for the foam 46 to break so that the liquid corrosion inhibitor will be deposited primarily within the pipeline system 24,28.

By the use of the illustrated method, a liquid corrosion inhibitor can easily be placed in any horizontal pipeline system, including those having branch pipelines, without the use of pipeline pigs and the associated complex pig launching and pig recovery equipment.

While certain preferred embodiments of the invention have been illustrated and described changes e.g. in the sequence and execution of the various steps may be made by those skilled in the art and such changes together with any other modifications which retain one or more of the advantages envisaged are intended to be encompassed by the present disclosure even if features forming the subject of the claims presently appended hereto are omitted.

Claims (13)

1. A method of distributing a liquid corrosion inhibitor in a pipeline, said method comprising the steps of: (a) forming a foam including a liquid corrosion inhibitor; (b) flowing said foam into said pipeline; and (c) depositing said liquid corrosion inhibitor from said foam on an inner surface of said pipeline.

2. A method as claimed in claim 1 wherein said foam includes surfactant.

3. A method as claimed in claim 1 or 2 further comprising the step of breaking said foam while said foam is in said pipeline.

4. A method as claimed in any of claims 1 to 3 wherein said pipeline forms part of a gas pipeline system for conveying gaseous hydrocarbons.

5. A method as claimed in claim 4 wherein gaseous fluid used in forming said foam comprises gaseous hydrocarbons from said gas pipeline system.

6. A method as claimed in claim 4 wherein gaseous fluid used in forming said foam is a second gaseous fluid other than said gaseous hydrocarbons from said gas pipeline system.

7. A method as claimed in claim 6 wherein said second gaseous fluid is nitrogen.

8. A method as claimed in any preceding claim wherein the pipeline forms part of a pipeline system including a substantially horizontal main pipeline portion and a substantially horizontal lateral pipeline portion connected to said main pipeline portion at a branch connection, and wherein said method comprises forming the foam from a gaseous fluid and a carrier liquid including said liquid corrosion inhibitor, injecting said foam into said pipeline system including said substantially horizontal main pipeline portion and said substantially horizontal lateral pipeline portion thereof, and thereby distributing said liquid corrosion inhibitor in said pipeline system, so that the liquid corrosion inhibitor is distributed on substantially an entire inner surface of said substantially horizontal main pipeline portion and said substantially horizontal lateral portion.

9. A method as claimed in claim 8 wherein said carrier liquid is an aqueous carrier liquid.

10. A method as claimed in claim 4 or 5 and in claim 8 or 9 wherein said foam is displaced through said substantially horizontal main pipeline portion, through said branch connection, and through said substantially horizontal lateral pipeline portion of said pipeline system, by said gaseous hydrocarbons.

11. A method as claimed in claim 8, 9 or 10 wherein a substantial portion of said foam is held in said main pipeline portion and said lateral pipeline portion until said foam breaks.

12. A method as claimed in any preceding claim wherein said foam is displaced through said pipeline or pipelines without the aid of pipeline pigs.

13. A method of distributing a liquid corrosion inhibitor substantially as herein described with reference to the accompanying drawings.