Method of injecting water and gas

Abstract

The invention relates to a method of injecting water and gas, possibly just water, into a petroleum-carrying stratum of a subsoil formation, whereby the water and the gas, possibly just the water, are/is injected by means of an injection well formed in the subsoil formation. The object of the invention is to avoid that water which is to be injected, will require treatment by, among other things, the addition of chemicals inhibiting formation of hydrate from the gas, biological activity in the formation, precipitation of salts and minerals from the water, corrosion of equipment etc. This is realised by the water to be injected, being taken from aquifers in the subsoil formation and carried directly into the injection well through at least one opening which is formed in the wall of the well by said aquifers. Then the water is fed from said opening to the point in the injection well where the water and the gas, possibly just the water, are/is to be injected into said petroleum-carrying stratum. The injection well comprises necessary pumping equipment to be used during the injection.

Description

[0001] The present invention is a continuation of PCT/NO99/00258 having an International filing date of Aug. 18, 1999, which PCT application published as WO 00/11314 and is incorporated herein by reference.

[0002] The invention relates to a method of injecting water and gas, possibly just water, into the petroleum-carrying strata of a subsoil formation.

[0003] People skilled in the art know that it is possible to increase the amount of extractable petroleum of a deposit by injecting water and gas into the petroleum-carrying strata of the subsoil formation. In such cases the injection of water and gas is realised by means of at least one injection well which is formed at a suitable place in the deposit. The injection is done by water and gas being injected either simultaneously or alternately into the subsoil formation. The injection well is normally constructed with a wellhead comprising equipment for the supply of the water and gas to be injected.

[0004] An important condition for allowing injection of water and gas, is that the water and gas have a pressure exceeding the pressure inside said petroleum-carrying strata. An undesirable effect of such elevated pressure is that the gas may form hydrates which will plug the well, so that the injection stops. Such plugs of hydrates, especially near the surface, represent a considerable safety hazard. The formation of hydrates may be avoided through heating of, or by the use of chemicals in, the water to be injected. Other drawbacks by the injection of surface water are that the injection water may cause salt or mineral precipitation in the surface equipment, in the injection well or in the formation, and separation of oxygen which creates corrosion problems. Moreover, the injection water may cause undesired biological activity in the formation. Those are drawbacks which are intensified when injection water from several water sources is used. The last drawbacks may be prevented by thorough treatment of the injection water such as by filtration, removal of oxygen, sulphates etc. The above mentioned heating and treatment of the injection water may result in major additional costs.

[0005] The main object of the present invention is to provide a method of injecting water and gas, possibly just water, whereby is avoided that the water to be injected has to pass said costly treatment. This is achieved by the injection water being recovered from aquifers present in the subsoil formation. The water recovered from the subsoil formation is fed directly into the injection well through at least one opening formed in the wall of the well by said aquifer. Then the water is fed from said opening to the point in the injection well where the water and the gas, possibly just the water, are/is to be injected into the petroleum-carrying strata. Thereby use is made of water from a source of higher temperature and pressure than what has been common with water supplied from the surface. Moreover, such water from the formation will be compatible with the water at the site of injection, which enables prevention/reduction of the above problem of formation of hydrates, precipitation of salts and minerals, separation of oxygen, and biological activity. Other favourable features of the invention will appear from the claims and the following part of the specification.

[0006] Referring to the accompanying figures, embodiments of the invention will be explained in further detail, in which

[0007] FIG. 1 shows a simplified vertical view of an injection well for the injection of water and/or gas; and

[0008] FIG. 2 shows a schematic vertical sectional view of an injection well with pump and injection pipe for water and gas.

[0009] As mentioned, the present method relates to injection of water and gas, possibly just water, into a subsoil formation 1 carrying petroleum. The injection may take place by water and gas being injected simultaneously or alternately, or maybe by just water being injected into the subsoil formation 1. The injection of water and gas, possibly just water, is realised by means of an injection well 4 which is formed in the subsoil formation 1 and extends at least down into a petroleum-carrying stratum 2 thereof. The injection well 4 is preferably formed with a wellhead, and the wellhead comprises, among other things, necessary equipment for supplying the gas to be injected into said petroleum-carrying stratum 2.

[0010] The water to be injected, is recovered from an aquifer 3 of the subsoil formation 1, and the water is fed directly into the injection well 4 through at least one opening 5 formed in the wall of the well by said aquifer 3. The water is then fed to the point in the injection well 4 where the water and the gas, possibly just the water, are/is to be injected into said petroleum-carrying stratum 2 without having been taken to the surface. This may happen, for example by the water being pumped from the opening 5 to the location in the injection well 4 where the water and the gas, possibly just the water, are/is to be injected. A pump 7 is preferably placed close to the opening 5 in the injection well 4. To avoid having to extend the injection well 4 downwards, it is the most favourable that the water is extracted from the aquifer 3 located above said petroleum-carrying stratum 2. The opening 5 may, for example, be formed by perforation of the wall of the well and there could also be arranged a sand filter in connection with the opening 5.

[0011] In FIG. 2 is shown an example of how the injection well may be configured. The injection well 4 also comprises an injection pipe 6 for gas. The injection pipe 6 is passed from the well-head, where the gas is added, and down into the petroleum-carrying stratum 2 where the water and gas, possibly just the water, are/is to be injected. In the area by the opening 5, where the water from the aquifer 3 is admitted into the injection well 4, there is placed an upper packer 8 and a lower packer 9 isolating the aquifer 3 from the surface, or other strata of the formation 1 such as the petroleum-carrying stratum 2. A pump 7 which is positioned in the space between the packers 8, 9, pumps the water into the injection pipe 6 and further out into the petroleum-carrying stratum 2. The pump 7 may be placed in a pipe socket which is formed on the injection pipe 6, and may be operated electrically or hydraulically. At least one check valve 10 is positioned in the injection pipe 6 above the pump 7. At least one additional check valve 11 is positioned at the outlet of the pump 7 into the injection pipe 6.

Claims

1. A method of increasing an amount of extractable petroleum comprising:

injecting water into a petroleum-carrying stratum of a subsoil formation, whereby the water is injected by means of an injection well formed in the subsoil formation and extending to said petroleum-carrying stratum and wherein that the water to be injected is recovered from an aquifer of the subsoil formation, that the water is carried directly into the injection well through at least one opening formed in the wall of the well by said aquifer, and that the water is fed from said opening to the position in the injection well where the water is to be injected into said petroleum-carrying stratum.

2. A method according to

claim 1 wherein water and gas are injected into the petroleum-carrying stratum.

3. A method according to

claim 2 wherein the water and gas are injected simultaneously.

4. A method according to

claim 2 wherein the water and gas are injected alternatively.

5. A method according to

claim 1, wherein the water is recovered from the aquifer located above said petroleum-carrying stratum.

6. A method according to

claim 1, wherein the water is recovered from the aquifer located below said petroleum-carrying stratum.

7. A method according to

claim 5 wherein the injection well is extended to said lower aquifer.

8. A method according to

claim 6 wherein the injection well is extended to said lower aquifer.

9. A method according to

claim 1, wherein the water is pumped from said opening to the position in the injection well where the water is to be injected into said petroleum-carrying stratum.

10. A method according to

claim 9, wherein the water is pumped by means of at least one pump positioned in the injection well near said opening in the wall of the well.

11. A method according to

claim 2, wherein the gas is supplied at the upper end of the injection well.

12. A method according to

claim 9, wherein the water and the gas are supplied simultaneously, possibly alternately, into said petroleum-carrying stratum.

13. A method according to

claim 1 wherein the water is prevented from entering the aquifer or flowing to the surface, by the provision of at least one check valve between the aquifer and the entrance of an injection pipe provided in the injection well and at least one check valve in the injection pipe, said check valve being provided downstream of a packer in the annulus between the injection pipe and the wall of the well.

14. A method according to

claim 2 wherein the water and gas are prevented from entering the aquifer or flowing to the surface, by the provision of at least one check valve between the aquifer and the entrance of an injection pipe provided in the injection well and at least one check valve in the injection pipe, said check valve being provided downstream of a packer in the annulus between the injection pipe and the wall of the well.