A METHOD AND A DEVICE FOR COUNTERACTING THAT A VALVE'S FUNCTIONALITY IS REDUCED

This invention relates to a method for counteracting reduction in a valve's functionality. More particularly, it relates to a method for counteracting reduction in the functionality of a valve during the cementing of a pipe in a borehole in the ground, the method being characterized by the valve being encased, at least partially, in a material which is degradable, or permeable to at least drilling fluid or protective fluid. The invention also includes a device for practising the method.

Insufficient permeability of a well formation is a relatively common problem, which can limit, to a considerable degree, the production from an underground well. A normal way of preparing a petroleum well includes cementing a casing in the well by filling the annulus with concrete and then perforating both the pipe wall, concrete and, in part, also the well formation, for example by means of an explosive charge. After such perforation the formation is often fractured by high-pressure pumping and pumping of gravel into the fracture, so that the permeability is increased. The formation can also be cracked open and dissolved by means of acid.

It is relatively complicated to ensure that a fracturing is distributed in the desired manner in the formation. Often,

complex fracture patterns form around the borehole, so that the flow of the well fluid from the well formation into the borehole is lacking in hydraulic permeation and the productivity of the zone is restrained.

In some cases it may be advantageous to install one or more valve devices, hereinafter called valves, in the casing to avoid the perforating operation. A valve can be constituted by, for example, a rupture disc valve, a sliding sleeve valve, a pipe portion which is partly sealed during use, or other form of valve of an embodiment known per se.

Thereby, the well formation can be opened by pumping fluid into the formation under sufficiently high pressure and rate via the valves for the concrete and formation to crack open. It is usual to introduce relatively coarse sand into the well formation together with the fluid. Sand settling in the fractures contributes to facilitating the flow of reservoir fluid towards the well.

It is well known that the functionality of valves of this kind is reduced, to a substantial degree, during cementing operations.

The invention has for 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 which are specified in the description below and in the claims that follow.

A method in accordance with the invention for counteracting reduction in the functionality of a valve during the cementing of a pipe in a borehole in the ground is characterized by the valve being encased, at least partially, in a material which is degradable, or permeable to at least

reservoir fluid or protective fluid.

By a degradable material is meant, in this connection, a material which can be brought to rupture by means of, for example, pressure, alternatively that it is dissolved, for example by means of acid, or is eroded away.

In a preferred embodiment the valve is encased at least from the outside or from the inside of the pipe in, typically, a metallic material before the pipe is lowered into the borehole. Most advantageously, the space between the valve and the material is filled with a protective fluid.

The protective fluid can be formed by drilling mud or other non-curing material.

In an alternative method the valve is encased in a porous material with open cells, for example a foamed rubber material. Preferably, the cells are filled with a protective fluid before the pipe together with the valve is moved into the borehole, the protective fluid remaining, in the main, in the porous material during the filling of concrete.

After the valve has been opened for fracturing, the material will be displaced away from the valve and eroded away by the material flowing through the valve.

Alternatively, the porous material may remain in position and work as a flow path for reservoir fluid, while sand is prevented at the same time from flowing from the formation into the pipe.

The degradable or permeable material can be removed during the stimulation operation by erosion from abrasive liquids or by pumping in acid or other dissolving liquid.

As an alternative the cell structure of the porous material

may be closed and prefilled with protective fluid.

The protective material may comprise various layers of solid and porous materials, the materials possibly being different in strength, porosity and permeability.

Known procedures for cementing include removal of curable material from the inside of the pipe, mainly by means of liquid circulation. Still, it may be necessary to encase the valve in a porous material also on the inside of the pipe to avoid function faults caused by imperfect concrete cleaning.

The invention provides a relatively simple solution to a long-known problem.

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

Figure 1 shows schematically a casing disposed in a borehole, the valves being encased in accordance with the invention;

Figure 2 shows schematically the casing of figure 1, but after an annulus between the casing and the formation has been filled with concrete; and

Figure 3 shows schematically the same as figure 2, but after the valve has been opened, as fracturing fluid is flowing out of the valves.

In the drawings the reference numeral 1 indicates a casing which is provided with a pipe portion 2 and a sliding sleeve valve 4 of an embodiment known per se. The casing 1 is placed in a borehole 6 in a formation 8.

The pipe portion 2 is arranged to be sealed by fracturing

particles after injection thereof, in order thereby to work as a partially sealing valve.

The outlet 10 of the pipe portion 2 is provided with a porous body 12, the cells of the porous body 12 being filled with protective fluid. A rupture disc valve 14 is arranged in the pipe portion 2.

The sliding sleeve valve 4 includes a movable sealing sleeve 16 covering, in its closing position, outlet openings 18 in the pipe wall of the casing 1. It is emphasized that the drawings are schematic and illustrate mechanical components which will be known to a skilled person. Necessary details that must be present for the sliding sleeve valve 4 to work are not shown.

A sealing material 20 in the form of a relatively thin aluminium sheet encases the sliding sleeve valve 4. The space between the casing 1, sleeve 16 and sealing material 20 is filled with protective fluid. The outlet openings 18 are filled with a porous and permeable material 22.

After the casing 1 with valves 2, 4, together with the porous body 12 and the sealing material 20 forming the encasing material 12, 20, has been placed in the borehole 6, concrete 24 is pumped down in a manner known per se via the casing 1 and up an annulus 26 between the borehole 6 and casing 1.

The concrete 24 is prevented from filling the pipe portion 2 as the pipe portion 2 has already been filled with fluid and the rupture disc valve 14 is intact. The concrete cannot enter the outlet openings 18 either, because of the porous material 22. Because of the porous body 12 and the sealing material 20 the concrete is prevented from entering the outlet 10 of the pipe portion 2 and the sliding sleeve valve 4 from the annulus 26.

When the concrete 24 has cured, see figure 2, the sliding sleeve valve 4 can be opened while, at the same time, fracturing fluid 28 flows from the casing 1 via the pipe portion 2 and outlet openings 18 under sufficiently high pressure for the concrete 24 and formation to be fractured by fractures 30 forming, see figure 3.

In a further embodiment, not shown, the pipe portion 2 is provided with a separate pipe outlet, not shown, which is opened only after the fracturing has been carried out. The aim is to provide a flow path for formation fluid, in which the flow resistance is relatively low.