WO2003067026A1

WO2003067026A1 - Gas well packing system

Info

Publication number: WO2003067026A1
Application number: PCT/AU2003/000120
Authority: WO
Inventors: Simon John Mewing
Original assignee: Santos Ltd
Priority date: 2002-02-06
Filing date: 2003-02-06
Publication date: 2003-08-14
Also published as: AUPS034602A0

Abstract

A method of achieving a desired velocity of gas flow through a gas well tubing string, the method including the step of introducing a plurality of void reducing elements into a length of a gas well tubing string.

Description

TITLE "GAS WELL PACKING SYSTEM" FIELD OF THE INVENTION This invention relates to a gas well packing system. In particular, the invention relates to improving production rates for low production gas wells by increasing the velocity of gas flow. BACKGROUND OF THE INVENTION Natural gas has become a popular energy source due to its reduced emissions when utilised as a fuel and lower production costs when compared to oil. Hence, there is an increase demand for natural gas as an alternative fuel for automobiles and electric power units as well as for residential heating.

When a gas well bore is drilled, the tubing string size for the bore is calculated based on near term gas flow rate or historical standard sizes. The tubing string size represents the necessary size for the inherent pressure of the reservoir and the subsequent required velocity.

Natural gas reservoirs contain natural gas as well as other contaminants such as water and intermediate to heavy hydrocarbons. These contaminants often condense into a liquid within the tubing string. However, these contaminants flow to the surface with the gas as a mist or slug when the velocity of gas flow through the tubing string is above a critical level. So long as the velocity of the gas is maintained, the liquids are lifted.

As a gas field matures, the pressure of the reservoir drops and hence the velocity of the gas within the tubing string decreases. This causes the mist flow to change to a churning flow and the lift capacity of the flowing gas decreases substantially. When this state occurs, liquid accumulates at the base of the tubing string creating a backpressure reducing the gas production rate. The gas production rate continues to decrease until the gas production rate is so low that gas well does not produce.

There are a number of solutions to liquid loading of the tubing string including the introduction of a velocity string, a plunger lift and/or swabbing of the tubing string. The above solutions either increase the pressure or increase velocity of the gas. However, all of the above solutions have limits in application and are costly often making the solutions economically unworkable.

OBJECT OF THE INVENTION It is an object of the invention to overcome or alleviate one or more of the above disadvantages or provide the consumer with a useful or commercial choice.

SUMMARY OF THE INVENTION In one form, although not necessarily the broadest or only form, the invention resides in a method of achieving a desired velocity of gas flow through a gas well tubing string, the method including the step of: introducing a plurality of void reducing elements into a length of a gas well tubing string to reduce the void space within the length of gas well tubing string to achieve a desired velocity of the gas flowing through the length of gas well tubing string.

The void reducing elements may be located within the entire length of the gas well tubing string or only a partial length of the gas well tubing string. Normally the void reducing elements are located within at least a lower length of the gas well tubing string.

The void reducing elements may be introduced into the gas well tubing string by dropping them into the gas well tubing string or using a wire line unit. The void reducing elements may be introduced into the gas well tubing string without killing the well.

Alternately, if the gas well has died, the gas well may be unloaded of liquids and then the void reducing elements introduced. The void reducing elements may be constructed from any shape that produces pathways through which gas is able to flow when the void reducing elements are packed into the gas well tubing string without adding excessive pressure drop. Preferably, the void reducing elements have at least one arcuate surface. The void reducing elements may be made from any suitable material that has appropriate temperature and crush resistance properties.

For example, the void reducing elements may be made from Teflon coated steel, high-density polypropylene, high-density polyethylene or chrome based steel alloys. The void reducing elements may be constructed of a lower density than liquids located in the gas well to enable the void reducing elements to float on top of the liquids for easy removal.

Different shaped and/or sized void reducing elements may be used in the gas well tubing string. Different shaped or sized void reducing elements may be used at different sections along the length of gas well tubing to produce different void spaces and hence produce different velocity profiles.

A permeable plug may be located within the gas tubing string to hold the void reducing elements at a predetermined location within the gas well tubing string. A number of plugs may be used to section the gas well tubing string for location of different sized and/or shaped void reducing elements.

In another form, although not necessarily the broadest or only form resides, the invention in a gas well comprising: a gas well tubing string to enable gas to flow from an under ground gas reservoir to a ground surface; and a plurality of void reducing elements located within the a length of the gas well tubing string to increase the velocity of the gas flowing through the length of gas well tubing string.

BRIEF DESCRIPTION OF THE DRAWINGS Embodiments of the invention will be described with reference to the accompanying figures in which:

FIG. 1 is a side view of void reducing elements located within a gas well tubing string;

FIG.2A is a plan view of void reducing elements located with a gas well tubing string;

FIG.2B is plan view of void reducing elements located within a gas well tubing string; FIG.2C is plan view of void reducing elements located within a gas well tubing string;

FIG. 3 is side view of objects located within a gas well tubing string; FIG. 4 is side view of void reducing elements located within a gas well tubing string;

FIG. 5A is a perspective view of a void reducing element;

FIG. 5B is a perspective view of a void reducing element;

FIG. 5C is a perspective view of a void reducing element; FIG. 5D is a perspective view of a void reducing element;

FIG. 5E is a perspective view of a void reducing element; FIG. 5F is a perspective view of a void reducing element. FIG. 5G is a perspective view of a void reducing element; and FIG. 6 is side view of void reducing elements located within a gas well tubing string.

DETAILED DESCRIPTION OF THE PREFFERED EMBOIDMENT

FIG. 1 shows a gas well packing system 10 including a standard 3 1/2-inch diameter gas well tubing string 11 having an internal diameter of 2.9 inches. The gas tubing string is fluid communication with a gas reservoir (not shown).

Void reducing elements 12 have been introduced into a length of the gas well tubing string as shown in FIG. 1. The void reducing elements in this embodiment are 2-inch diameter balls.

The 2-inch diameter balls reduce the void space with the gas well tubing string. Pathways 13 between the balls allow gas to pass through the gas well tubing string. As the pressure from the gas reservoir is relatively constant and the void space through which the gas passes has been decreased, there is a subsequent increase in the velocity of the gas passing through the gas well tubing string. In this embodiment, the increase in the velocity of the gas flow is approximately 40 percent.

The increase in velocity allows liquids to become misted and thus lifted through the gas well tubing string.

FIGS.2A to 2C show a plan view gas well tubing strings having various diameters. Balls of different diameters have been inserted into the different sized gas well tubing strings. A table below indicates the diameters of the gas well tubing strings and balls:

The pathways 13 between adjacent balls and also the gas well tub string allowing the flow of gas are depicted in FIGS 2A to 2C.

It would be appreciated by a person skilled in the art that the diameter of the balls may be varied with respect to the diameter of the gas well tubing string to vary the velocity of the gas flowing through the gas well tubing string. The desired velocity of the gas flow may be dependant upon standard operating conditions. For example, standard operating conditions may include the inherent pressure of the gas reservoir, production requirements, the amount and type of liquid to be lifted or the like operating conditions. These and/or other conditions may be considered when choosing the diameter of the balls with respect to the gas well tubing string.

FIG. 3 shows a gas well tubing string in which balls of different diameters have been introduced into the gas well tubing string. A permeable plug 14 has been placed into the gas well tubing to prevent the balls from falling through the gas well tubing string. In this embodiment, two different balls of 1.5" and 2" diameter have been introduced into a 2 7/8" gas well tubing string. The balls of 2" diameter have been located in a lower part of the gas well tubing string whilst balls of 1.5" diameter have been located in an upper part of the gas well tubing string. The length of tubing in which the 2" diameter balls are located reduce the void space within the lower part of the gas well tuning string by approximately 67 percent whilst the length of tubing in which the 2" diameter balls are located reduce the void space within the upper part of the gas well tubing string by approximately 74 percent. The change in size of the balls and hence the change in void space allows various velocity profiles to be obtained in a gas well tubing string.

FIG. 4 again shows two different void reducing elements 12 utilised in a gas well tubing string. In this embodiment, 2" diameter balls and hollow cylinders have been introduced. The hollow cylinders have an outer diameter of 1 1/2 inches and are 3 inches in length.

The lower part of the tube in which the balls are located causes the gas to flow at a higher velocity than the upper part of the tubing in which the cylinders are located.

FIGS. 5A to 5G shows a variety of different examples of the shapes that may be used for the void reducing elements 12. A person skilled in the art would appreciate that various other shapes may be used and that these shapes are only a mere selection of possible shapes that are available for use.

It is preferable that the shapes of the void reducing elements

12 have arcuate surfaces so that when the void reducing elements are located within the gas well tubing string, pathways 13 are virtually guaranteed of being formed between adjacent void reducing elements and the gas well tubing string.

It would also be appreciated that the shape of the objects will effect a frictional pressure drop of the gas when if flows through a length of the gas well tubing string. Experimentation by a person skilled in the art will enable appropriate selection of the type of void reducing element used to achieve a particular objective.

FIG. 6 again shows two different void reducing elements 12, namely balls and a saddle, utilised within a gas well tubing string 11. In this embodiment, the pathways that are formed within by the balls cause a large increase in gas velocity but also a large pressure drop. The saddle causes only a small pressure drop but the velocity of gas is also decreased.

The void reducing elements are made from a high-density polypropylene, high-density polyethylene or Teflon coated steel. The temperature and crush resiance requirements determine the exact properties of the materials used. Preferably, the void reducing elements float.

The void reducing elements are forced into the gas well tubing string using the wire line unit. A permeable plug is set in the gas well tubing string to hold the void reducing elements in position.

The void reducing elements are able to be removed by blowing them from the gas well tubing string or allowing the void reducing elements to float out of the gas well tubing string.

The advantages of the gas well packing system include installing the void reducing elements without killing the well, the low cost installation and operating costs and no corrosion issues. It would be appreciated that the gas well packing system can be used for velocity strings that have already been installed in gas wells. In this instance, both the original gas well tubing string and/or velocity string can be filled with void reducing elements.

It should be appreciated that various other changes and modifications may be made to the embodiments described without departing from the spirit or scope of the invention.

Claims

CLAIMS:

1. A method of achieving a desired velocity of gas flow through a gas well tubing string, the method including the step of: introducing a plurality of void reducing elements into a length of a gas well tubing string.

2. The method of claim 1 wherein the void reducing elements are located within the entire length of the gas well tubing string.

3. The method of claim 1 wherein the void reducing elements are located within a partial length of the gas well tubing string.

4. The method of claim 3 wherein the void reducing elements are located within at least a lower length of the gas well tubing string.

5. The method of claim 1 wherein the void reducing elements are introduced into the gas well tubing string by dropping them into the gas well tubing string.

6. The method of claim 1 wherein the void reducing elements are introduced into the gas well tubing string using a wire line unit.

7. The method of claim 1 wherein the void reducing elements are introduced into the gas well tubing string without killing the well.

8. The method of claim 1 wherein if the gas well has died, the gas well is unloaded of liquids and then the void reducing elements introduced.

9. The method of claim 1 wherein the void reducing elements provide pathways through which gas is able to flow.

10. The method of claim 1 wherein the void reducing elements have at least one arcuate surface.

11. The method of claim 1 wherein the void reducing elements are made from teflon coated steel, high-density polypropylene, high-density polyethylene or chrome based steel alloys.

12. The method of claim 1 wherein the void reducing elements are constructed of a lower density than liquids located in the gas well.

13. The method of claim 1 wherein different shaped and/or sized void reducing elements are used in the gas well tubing string.

14. The method of claim 1 wherein different shaped and/or sized void reducing elements are used at different sections along the length of gas well tubing.

15. The method of claim 1 wherein a permeable plug is located within the gas tubing string to hold the void reducing elements at a predetermined location within the gas well tubing string.

16. The method of claim 15 wherein a number of permeable plugs are used to section the gas well tubing string for location of different sized and/or shaped void reducing elements.

17. A gas well comprising: a gas well tubing string to enable gas to flow from an under ground gas reservoir to a ground surface; and a plurality of void reducing elements located within the a length of the gas well tubing string to increase the velocity of the gas flowing through the length of gas well tubing string

18. The gas well of claim 17 wherein the void reducing elements are located within the entire length of the gas well tubing string.

19. The gas well of claim 17 wherein the void reducing elements are located within a partial length of the gas well tubing string.

20. The gas well of claim 19 wherein the void reducing elements are located within at least a lower length of the gas well tubing string.

21. The gas well of claim 17 wherein the void reducing elements have at least one arcuate surface.

22. The gas well of claim 17 wherein the void reducing elements are made from teflon coated steel, high-density polypropylene, high-density polyethylene or chrome based steel alloys.

23. The gas well of claim 17 wherein the void reducing elements are constructed of a lower density than liquids located in the gas well.

24. The gas well of claim 17 wherein different shaped and/or sized void reducing elements are used in the gas well tubing string.

25. The gas well of claim 17 wherein different shaped and/or sized void reducing elements are used at different sections along the length of gas well tubing.

26. The gas well of claim 17 wherein a permeable plug is located within the gas tubing string to hold the void reducing elements at a predetermined location within the gas well tubing string.

27. The gas well of claim 26 wherein a number of permeable plugs are used to section the gas well tubing string for location of different sized and/or shaped void reducing elements.