WO2007075087A1

WO2007075087A1 - A method and device for stimulation of an underground well

Info

Publication number: WO2007075087A1
Application number: PCT/NO2006/000480
Authority: WO
Inventors: Rune Freyer
Original assignee: Rune Freyer
Priority date: 2005-12-27
Filing date: 2006-12-15
Publication date: 2007-07-05
Also published as: NO325506B1; NO20056208L

Abstract

A method and device for stimulating an underground well (1), in which a fracturing operation is carried out by supplying arenaceous fluid to the well formation (2) through a supply pipe (8) at relatively high pressure, whereby the well formation (2) fractures and sand settles in the fractures, and in which the fluid is brought to flow from the supply pipe (8) into the formation (2) through a first branch tubular (12).

Description

A METHOD AND DEVICE FOR STIMULATION OF AN UNDERGROUND WELL

This invention relates to a method for stimulation of an underground well. More particularly, it concerns the stimulation of an underground well, in which a fracturing operation is carried out in the well formation by supplying arenaceous fluid to the well formation through a supply pipe under a pressure exceeding the fracturing pressure, whereby the well formation fractures and sand settles in the fractures, the pressure fluid being brought to flow from the supply pipe into the formation through a branch pipe. The invention also includes a device for practicing the method.

Insufficient permeability in a well formation is a relatively common problem, which may, to a considerable degree, limit the production from an underground well . The problem may be remedied or reduced by pumping fluid into the formation at a sufficiently high pressure and rate for the formation to fracture. It is normal to supply relatively coarse sand to the well formation together with the fluid. Sand settling in the fractures helps to make it easier for well fluid to flow towards the well . Experience goes to show that the sand, which is supplied to the formation together with the well fluid, may have a tendency to flow back into the well together with the well fluid. Therefore, after some time, the fracturing operation must be repeated.

It is relatively complicated to ensure that the pressure fluid will flow into the formation at the desired depth in the well. Furthermore, the capacity of the pumping equipment available often sets limits to how large a portion of the well may be treated in one turn.

The invention has as its object to remedy or reduce at least one of the drawbacks of the prior art.

The object is achieved in accordance with the invention through the features specified in the description below and in the claims that follow.

In the stimulation of an underground well, in which a fracturing operation is carried out by supplying arenaceous fluid to the formation through a supply pipe under a pressure exceeding the fracturing pressure, the formation fractures and sand settles in the fractures. According to the invention the fluid is brought to flow from the supply pipe and into the formation in a first portion of the well via a first branch tubular.

The supply pipe is typically formed by the production tubing of the well, but may also include other pipes run into the well for the purpose. By sand is meant, in this context, any form of material that a person skilled in the art could use together with pressure fluid in fracturing operations in an underground well .

Advantageously, the first branch tubular is provided with a check valve to prevent sand from flowing back with well fluid through the first branch tubular. Thereby, the well fluid is directed to flow through the sand screen or filter of the well in a manner known per se. The sand screen or filter may be provided with flow control valves or restrictions such as a check valve .

The first branch tubular preferably extends along the supply pipe and typically in a length, which is greater than the diameter .

When a second well portion Is to undergo a fracturing operation, the first branch tubular is blocked up with sand. Thereby, the arenaceous pressure fluid is brought to flow to a second branch tubular .

The second branch tubular may be provided with an overpressure valve, typically in the form of a rupture disc valve, which is arranged to open at a specific pressure.

The first and second well portions may be separated from each other by means of a plug. During treatment the well portions will have a pressure close to the fracturing pressure, so that the differential pressure across the plug will be relatively low. Thus, there may be used a plug which is designed for relatively low pressure and which does not have to close completely to fluid flow either. The plug may, with advantage, be formed as a filter that blocks sand but allows fluid to pass through.

In what follows is described a non-limiting example of a preferred embodiment which is visualized in the accompanying drawings, in which:

Figure 1 shows schematically an underground well, in which there is placed, in the first portion of the well, a supply pipe including a branch tubular according to the invention;

Figure 2 shows schematically the underground well during the pumping of arenaceous pressure fluid into the well formation;

Figure 3 shows schematically the underground well during inflow of well fluid into the supply pipe;

Figure 4 shows schematically the branch tubular in an alternative embodiment;

Figure 5 shows schematically a further second branch tubular arranged in a second portion of the underground well while arenaceous pressure fluid is flowing into the second portion of the well; and

Figure 6 shows the underground well after both portions of the well have been filled with sand.

In the drawings the reference numeral 1 denotes an underground well (a well) in a well formation 2. The well 1 includes a first well portion 4 and a second well portion 6. In figures 1 to 4 only the first well portion 4 is shown.

A supply pipe 8, here in the form of a production tubing, extends from the surface and down into the well 1. The production tubing 8 is provided with a sand screen 10 of the prior art known per se.

A first branch tubular 12 communicates with the production tubing 8 through a through opening 14 in the production tubing wall. The first branch tubular 12 extends a distance along the production tubing 8 and is provided with a check valve 16, for example in the form of an elastic bellows which is manufactured from a rubber-like material, nitrile rubber for example.

When a fracturing operation is to be carried out in the first well portion 4, the production tubing 8 is installed in the well 1 in such a way that the first branch tubular 12 is placed in a suitable position relative to the first well portion 4, see figure 1.

Arenaceous pressure fluid is then pumped down the production tubing 8, through the opening 14, the branch tubular 12 with the check valve 16 and into the formation 2, which then fractures by the formation of a fracture 15, see figure 2, in which an arrow indicates the flow.

When the treatment is finished, the well fluid, which is under pressure, seeks to flow from the well formation 2 and into the production tubing 8 through the branch tubular 12. However, the check valve 16 closes to flow in this direction and, therefore, the well fluid has to enter the production tubing 8 via the sand screen 10, see figure 3, in which an arrow indicates the direction of flow.

Thus, sand is substantially prevented from flowing with the well fluid from the well formation 2 into the production tubing 8.

In an alternative embodiment, see figure 4, the branch tubular is formed by a pipe 17 surrounding the production tubing 8.

If the well 1 includes a second well portion 6, in which there is also to be performed a fracturing operation, the production tubing 8 is provided with a second branch tubular 18 which is formed in a way corresponding to that of the first branch tubular 12. Besides, the branch tubular 18 is provided with a rupture disc valve 20.

The production tubing 8 is provided with a sand screen 10 also in the second well portion 6. A plug 22 is placed in an annulus 24 between the well 1 and the production tubing 8 in the area between the first well portion 4 and the second well portion 6.

When the fracturing operation in the second well portion 4 is to be carried out, the pressure within the production tubing 8 is increased until the rupture disc valve 20 opens. After that, arenaceous pressure fluid flows into the second well portion 6 as indicated by means of an arrow in figure 5.

The first branch tubular 12 is blocked up with sand. By designing the first branch tubular 12 with a suitable design in terms of length and flow properties, the first branch tubular 12 may be brought substantially to resist the through-flow of pressure fluid during the fracturing operation in the second well portion 6.

The first well portion 4 will still have a pressure, which is close to the fracturing pressure, and therefore, the plug 22 will be subjected only to a relatively small pressure difference between its two sides.

Claims

C L A I M S

1. A method for stimulation of an underground well (1), in which a fracturing operation is carried out by supplying arenaceous fluid to the well formation (2) through a supply pipe (8) from the surface, at a pressure exceeding the fracturing pressure, whereby the well formation (2) fractures and sand settles in the fractures, c ha r a c t e r i z e d i n that the fluid is brought to flow in a controlled manner from the supply pipe (8) and into the formation (2) through at least a first branch tubular (12) and a second branch tubular (18) .

2. The method in accordance with claim 1, c h a r a c t e r i z e d i n that the first branch tubular (12) is closed to backflow.

3. The method in accordance with claim 1, c h a r a c t e r i z e d i n that the first branch tubular (12) is blocked up and thereby causes a pressure fluid to flow out from the supply pipe (8) and into the well formation (2) through the second branch tubular (18) .

4. The method in accordance with claim 1, c h a r a c t e r i z e d i n that an overpressure valve (20) in the second branch tubular (18) is opened.

5. The method in accordance with claim 3, c h a r a c t e r i z e d i n that a plug (22) is placed in the underground well (1) between the first branch tubular (12) and the second branch tubular (18) .

6. A device for stimulating an underground well (1), in which a fracturing operation is carried out by the supply of arenaceous fluid to the well formation (2) through a supply pipe (8) from the surface, at a pressure exceeding the fracturing pressure, whereby the well formation (2) fractures and sand settles in the fractures, c h a r a c t e r i z e d i n that at least two branch tubulars (12, 18), which are connected to the supply pipe (8) at different well portions (4, 6) , connect the supply pipe (8) with the well formation (1) .

7. The device in accordance with claim 6, c h a r a c t e r i z e d i n that the branch tubular (12, 18) extends along the supply pipe (8) .

8. The device in accordance with claim 6, c h a r a c t e r i z e d i n that the length of the branch tubular (12, 18) is larger than the diameter of the branch tubular (12, 18).

9. The device in accordance with claim 6, c h a r a c t e r i z e d i n that the branch tubular (12, 18) is provided with a check valve (16) .

10. The device in accordance with the claim 6, c h a r a c t e r i z e d i n that the branch tubular (12, 18) is provided with an overpressure valve (20) .

11. The device in accordance with claim 10, c h a r a c t e r i z e d i n that the overpressure valve (20) is a rupture disc valve.